Molecular and Cell Pathology PDF

06/03/2023 Pathology: the study of the disease Pathology derives from Greek “pathos logo” which refers to the study of suffering, of the disease. In this context we can distinguish etiology -it refers to the causes of the disease (a disease can have more than one causes...

06/03/2023 Pathology: the study of the disease Pathology derives from Greek “pathos logo” which refers to the study of suffering, of the disease. In this context we can distinguish etiology -it refers to the causes of the disease (a disease can have more than one causes)- and pathogenesis -there is the genesis of the pathological causes, it refers to all the mechanisms (molecular and cellular) that lead to the manifestation of the disease. This includes also all the repair mechanisms, how the immune system and tissues in general respond to an injury; everything that happens since the cause till the manifestation of the diseases, with signs (what the doctor can see like the yellow tone of skin or red stains/dots, …) and symptoms (what the patient feels). A patient with a thoracic trauma has a reduction in lung expansion (can’t breathe well), which means that there is a reduction of air in the alveoli that causes a reduction of blood oxygenation. Polipnea: increase in respiratory frequency Cyanosis/asthenia: clinical signs, bluish color of mycoses, nails, and the patient is very tired Tachycardia: heart tries to pump more blood in the periphery. The succession of events leads to disease manifestation (the doctor can measure cardiac frequency, respiratory frequency, …) General pathology is a branch of life sciences, which studies basic mechanisms responsible for disease development. Basic mechanisms are all the general mechanisms that are at the bases of disease development (molecular, cellular, systemic processes that constitute a paradigm of disease development). - cell death, tumors development, inflammation (acute and chronic) Disease is an alteration (reduction, increase or lack) of cellular function which can involve groups of cells from tissues or organs. Alteration of homeostatic equilibrium → homeostasis is an equilibrium condition of organisms/cells to maintain an equilibrium condition in presence of external changes, alteration of the normal equilibrium and cell’s normal function. Health - for WHO- is a state of complete physical, mental and social well-being and not merely the absence of diseases or infirmity. Cell as unit of health and unit for disease development: Inherited or acquired alterations of specific molecules can result in damage to an organelle, alterations of cell functions and possibly cell death. Lysosomes: they are vesicles which are usually membrane-bound and they have a very acidic content (they are full of hydrolases like proteases, lipases, glycosidases, …). Enzymes in the lysosomes are synthesized in the endoplasmic reticulum (proteins). Lysosomes, due to the enzymes, are able to digest lots of materials: external material which comes inside the cells from endosomes (endocytosis) included inside the cell will fuse with a lysosome and the endosomal content will be degraded. (heterophagy, form outside) In particular cells called phagocytes, there are vesical forms called phagosomes that will form from phagocytosis. During this process, phagocytes will eat/incorporate external material (like microbes, pisces of apoptotic cells) in the phagosome and inside the cell it will fuse with the lysosome and will lead to the formation of a phagolysosome and the phagosome content will be degraded. (heterophagy, form outside) Autophagy (altered in many diseases) is a process in which cells will degrade their own proteins or organelles, especially denatured proteins or senescent organelles. All these materials will be incorporated in vesicles called autophagosomes which will fuse with lysosomes and the content will be degraded by all the enzymes present in the lysosomes. All the materials degraded will be used to produce new molecules or will be eliminated outside the cell (exocytosis). Proteasome: under certain pathological conditions, such as exposure to UV, heat, presence of reactive oxygen species (ROS) proteins can be denatured or become senescent (during aging process). These proteins will be conjugated with monomers of ubiquitin and then go into the proteasome and will be degraded in peptide fragments. This process is very important for antigen presentation: the peptide fragments are presented in the context of MHC class 1. When this process is not working well in some disease, proteic material will accumulate inside the endoplasmic reticulum. Altered proteins, misfolded proteins will accumulate inside the endoplasmic reticulum (metabolic alterations, genetic mutations, viral infections) which become large and cells can also die. Proteasomes are important organelles inside the cells. Mitochondria: have a complex structure; They are important for ATP generation (energy metabolism), Krebs cycle. They are also involved during pathological conditions (cell death necrosis or apoptosis) like ischemia or presence of toxins. Etiology: causes of disease can be classified in many ways. Congenital, which means that are present at birth and the causes can start before or in concomitance with birth. They can be genetic (like trisomy 21), due to pregnancy or due to delivery. Hereditary, when the causes are transmitted from the parents (hemophilia, anemias,) Acquired (after birth) due to: - chemical: exogenous compounds (either natural or deriving from human activities - like dioxin, benzene/solvents, colorants, insecticides, cigarette smoke) or endogenous molecules (metabolic/catabolic products -bilirubin, lactic acid-; Reactive oxygen and nitrogen species; modified molecules -oxidized lipoproteins, glycated proteins, excess of glucose) - physical: temperature, radiations, pressure, noise, electrical - biological: direct or indirect damage deriving from pathogen overgrowth - deficiencies or excesses: oxygen deficiency; vitamin deficiency; iron deficiency/excess; nutrients deficiency/excess; cholesterol accumulation (insoluble, needs to be transport by lipoproteins) - immunological like SLA, autoimmune diseases, allergies (hyperactivity in presence of an allergene) - iatrogenic: like drugs, diseases caused by human being Steps in the evolution of a disease: the first step is etiology, the cause of the disease (genetic abnormalities, trauma, …), then there is the pathogenesis which is all the succession of events in which there are cellular and tissues dysfunctions/abnormalities at molecular, functional and morphological level that lead to clinical manifestation of the disease (signs and symptoms) but it’s not always immediate. Pathogenesis is the mechanisms of development and progression of diseases, which account for the cellular and molecular changes that give rise to the specific functional and structural abnormalities that characterize any particular disease. A bacterial agent will cause inflammation, produced by infected tissues and immune system, that is acute at the beginning, which usually lasts a few days. Then it can evolve into complete resolution (return to normal state), chronic inflammation (lead to tissue injury) and sometimes it can also lead to an amplification of tissue damage and death of the organism. 1. Cell pathology 1.1 Degenerative alterations, cell injury There are different causes of cell injury: - hypoxia and ischemia, most frequent cause - physical agents: trauma, extremes of temperature, electrical shock, sudden changes in atmospheric pressure, radiations - chemical agents: toxins, insecticides, air pollution, CO, asbestosis, ethanol, cigarette smoke, drugs - infectious agents - immunological reactions - genetic abnormalities - nutritional imbalances - aging Cell injury can be reversible or irreversible (leading to cell death). A cell, under pathological condition, will change morphology and functions until a certain point. If the cause is removed the cell can recover and can return to the normal state; if the cause will persist or change intensity the cell injury is irreversible and leads to cell death. Cells become larger, the cell membrane will become abnormal/irregular due to cell swelling (blebs), some structures called myelin figures are present (membrane damage). There is an increase in fat deposition/lipid accumulation inside the cell due to the lack of oxygen and energy: the cell can’t transport lipids outside (need of lipoproteins and energy to produce them) so lipids will accumulate inside the cell (fatty changes). The nucleus is intact but there is chromatin clumping, especially with acid pH. If the cause is eliminated, the cell can slowly return to normal. If the cause persists, there is the progression of the injury and the cell will die (by necrosis). A necrotic cell’s membrane is discontinuous, the cellular content will leak outside the cell. Organelles membranes are destroyed too, if a lysosomal membrane is destroyed the enzymes will be released and digest the cell’s cytoskeleton (that maintains the cellular shape) so the cell will lose its morphology. There isn’t the nucleus (it’s digested). Hypoxia is low supply of oxygen and ischemia is low supply of blood to tissues/cells (this happens because there is occlusion). Lack of oxygen in the mitochondria will lead to reduced oxidative phosphorylation, leading to a reduced production of ATP. Reduction of energy (ATP) will cause alteration in Na/K pump (eliminate Na and enter K in the cell) if it’s not working because of lack of energy the Na will accumulate inside the cell and there will be water accumulation in the cell that will become larger. Cells need energy so anaerobic glycolysis will start, that leads to production of lactic acid which will lower the pH (chromatin aggregation). Lipoproteins aren’t synthesis so there will be lipid deposition. During cell injury there is reduction of ATP that will lead to plasma membrane damage because usually the membrane undergoes turnover, it continuously changes the molecular composition of the membranes (requires energy). During cell damage there is also an increased production of ROS but also intracellular Calcium. Ca is released inside the cytoplasm from organelles or enter from outside the cell. This has many damaging consequences, fundamental events that amplify cellular damage. Ca excesses have bad consequences, it can activates many types of enzymes like ATPases that reduces ATP (amplifies the damage); it activates phospholipase that destroys phospholipids (membrane component); many types of proteases are activated (cytoskeletal disruption) and activation of endonuclease that destroys nuclear material. 09/03/2023 Heart pumps blood to the periphery (to tissues). If in the periphery there is high pressure (higher resistance) the heart has to push stronger. Because of this, cells will adapt and become larger (same principle as muscles when trained→increased volume due to the mechanical stress). In other circumstances there is injury (not just adaptation) - for example during ischemia (reduction of blood flow) - and eventually cell death. Types of Cell death: Necrosis: there is destruction of cellular membranes -plasma and organelles’ membranes- with the release of enzymes from lysosomes which lead to the lysis and digestion of cellular molecules (proteins). Causes are the same as cell injury: if the alterations in a cell are reversible teh cell can go back to normal state but if cell injury causes have high intensity or duration cell may undergo death via necrosis. There are nuclear alteration: - KARYORRHEXIS (nuclear fragmentation) - PYKNOSIS (nucleus is compact, hyperchromic -darker- and smaller) - KARYOLYSIS (lack of chromatin and nucleus -lysis of chromatin and nucleus) The cytoplasmic changes: - Increased eosinophilia (cytoplasm is stained red by the eosin in the H&E staining and the nucleus is blue) due to increased binding of eosin to denatured cytoplasmic proteins and loss of binding of hematoxylin to ribonucleic acid in the cytoplasm - cell may have a glassy, homogeneous appearance, mostly because of the loss of lighter staining glycogen particles→loss of glycogen because the cell will use it to produce energy - discontinuities in plasma and organelle membranes - marked dilatation of mitochondria associated with the appearance of large amorphous intramitochondrial density  - disruption of lysosomes→clear sign of cell injury lead to cell death - intracytoplasmic myelin figures due to the damage of membranes (pieces of membranes that fold into each other) When enzymes have digested cytoplasmic organelles, the cytoplasm becomes vacuolated (appears “moth-eaten”). Membrane changes: membrane blebs, myelin figures and disruptions of cellular membranes. Necrotic cells are phagocytosed -internalized and ate- by local inflammatory cells (granulocytes, monocytes -precursor of macrophages- can migrate from blood to necrotic tissue) There are different types of Necrosis (always pathological): - Coagulative: protein coagulation; underlying (global) tissue architecture is preserved for at least several days after death of cells in the tissue; denaturation of structural proteins and enzymes; happens in myocardial infarction and in infarcts in all solid organs → infarctions are a pathological conditions in which a blood vessel is obstructed and there is ischemia in the tissue. - Caseous: dry aspect -amorphous aspect (very frequent in tuberculosis - infectious disease), called caseous because of the macroscopic aspect, it looks like cheese - yellow-white cheesy aspect. - Liquefactive: due to very prominent cell lysis - tissues will undergo liquefaction and have a liquid/viscous aspect; dead cells are completely digested, the tissue is transformed into a viscous liquid; it’s an enzymatic digestion; it happens in cerebral infarct and after focal bacterial (and some fungi) infections with pus formation and abscess. - Fibrinoid: deposition of fibrinoid material (fibrin); it occurs in immune reactions in which complexes of antigens and antibodies (immune complexes, circulating) are deposited in the walls of blood vessels; may occur in severe (malignant) hypertension. The staining is more pink. Apoptosis: programmed cell death. Apoptosis is a pathway of cell death in which cells activate enzymes that degrade the cells’ own nuclear DNA and proteins (nuclear and cytoplasmic) - cellular suicide. Causes: - Physiological conditions: embriogenesis (structures not useful anymore); turnover of proliferative tissues (epithelial/intestinal/bone marrow -during immune response) tissues continuously undergoes turnover); involution of hormone-dependent tissues (like endometrium -menstruation period); decline of leukocyte numbers at the end of immune and inflammatory responses; elimination of self-reactive lymphocytes. - Pathologic conditions: DNA damage (radiation and cytotoxic drugs - taken by patients with cancer), viruses (hepatitis A/B/C, AIDS), accumulation of misfolded proteins. It requires energy (is an active process -necrosis is a passive process) because it requires formation and activation/expression of new protein. If apoptotic cells are low in number they are phagocytosed by local and resident macrophages, no need for an inflammatory reaction usually (physiological apoptosis).  Apoptsosi activates enzymes inducing DNA and cell fragmentation leading to the formation of apoptotic bodies, which are phagocytosed by macrophages. Formation and activation of new proteins - It’s not an inflammatory reaction! Phagocytosed by local macrophages if small, no need for inflammatory reaction if apoptosis is very limited (except for viruses infections). Compared to necrotic cells, apoptotic cells are smaller in size, cytoplasm is denser and the organelles are more packed. The membrane has blebs (like in necrosis), in the nucleus there is chromatin condensation. Next there is cellular fragmentation, typical for apoptosis. Cells will be transformed in smaller fractions called apoptotic bodies. These apoptotic bodies contain several organelles, cytoplasm and so on. The apoptotic bodies will be phagocytosed by local phagocytes which will then be digested due to the fusion with a lysosome and die inside the phagocyte. There are two pathways leading to apoptosis: mitochondrial pathway (intrinsic)→pathological conditions leading to intrinsic pathway activation are reduction of growth factor withdrawal (reduction), DNA damage (by radiation, free radical and toxin - ROS) and protein misfolding. Different molecules are involved, some of them are called sensors (BH3) that will activate the effectors molecule (Bcl-2 family) and these proteins will enter the mitochondria and damage it leading to the release of cytochrome c and other pro apoptotic proteins. They go into the cytoplasm where they lead to the activation of caspase that will lead to endonuclease activation with nuclear fragmentation which is useful for the formation of apoptotic bodies and there is the breakdown of the cytoskeleton which will promote the formation of apoptotic bodies. death receptor pathway (extrinsic)→due to the presence on the cell membrane of particular receptors called death receptors (→they induce death - Fas and TNF receptors). The activation of these receptors will bind inside the cytoplasm adaptor proteins which will activate caspase. Both pathways converge on caspase activation.→ caspase is a sort of end point comparison between necrosis and apoptosis (slide 43) Necroptosis: has features of both necrosis and apoptosis→it is triggered by TNF receptors (like apoptosis), cell disruption is more similar to necrosis because of the activation of particular kinases called RIP (receptor-interacting proteins) kinases. This activation leads to the dissolution of the cell more like necrosis. This type of cell death is not very well understood yet, it can occur during ischemia, infection and condition with a lot of TNF (tumor necrosis factor) production. Pyroptosis: Apoptosis with fever, occurs during some infections. It’s associated with activation of a cytosolic which can induce fever. danger-sensing The activation inside the cell of a large complex molecule called inflammasome which activates inflammation and some caspases which are important to produce active form of some cytokines (interleukin 1) that induce inflammation manifested by fever. NETosis: production of structures released from neutrophils called neutrophil extracellular traps (NETs). - studied in vitro or in vivo  Neutrophils are fundamental in inflammation and infections (phagocytosis) and during NETosis is like a final sacrifies of these cells (a kind of suicide). During NETosis, neutrophils will diploid the nuclear material outside the cell together with the material of the cytoplasm, forming a trap and keeping bacteria there (and not infecting other cells) and killing them inside the nets. These nets are full of enzymes. There is a lot of nuclear material and structures. There are neutrophil enzymes (like elastase). Important enzymes are PEDs, activated in order to activate the phenomen. Autophagy is altered in many pathological processes. It means self-eating, referring to lysosomal digestion of intracellular material. A reduction of autophagy with accumulation of senescent material. It occurs during starvation, the cell will try to survive eating its own organelles. It occurs during infections, ischemic injury and some pathology of the muscles (myopathy) During autophagy, all these degradation of internal material/organelles performed by lysosomes fused with the autophagic vacuole. All the vacuole content will be degraded by the lysosomal content. 13/03/2023 Oxidative injury: a particular type of injury, there is damage produced by molecules deriving from oxygen. These molecules are called ROS electron structures of common reactive oxygen species (ROS). Superoxide anion with an umpire electron and negative charged; Hydrogen peroxide Hydroxyl radical, with an impaired electron Oxidative damage is very common in our body in many types of pathological conditions. It verifies during acute (or chronic) inflammation, it’s a way to kill bacteria. ROS are produced by neutrophils and macrophages. The reperfusion injury can occur after blood vessels occlusion. In many patients the vessel will open (occlusion will disappear due to therapy or if the clot will disintegrate) and then there is reperfusion. Reperfusion injury is due the reactivation of the blood vessels will produce ROS. Ionizing radiation can produce ROS and exposure to some chemicals (metals like nickel, arsenic, … because they can interfere with ROS production and promote their production) in the environment can favor the production of ROS. Carbon tetrachloride will lead to a damage similar to the oxidative one. ROS production is at the basis of aging and tumors and other pathological conditions. ROS will lead to cellular injury and then lead to death (coagulative necrosis, pyroptosis or apoptosis). ROS production: ROS are produced by NADPH oxidase (membrane of the phagosome), xanthine oxidase (cytoplasm), aldehyde oxidase (h2o2), … and during mitochondrial oxidative phosphorylation (respiration). Under physiological conditions there is ROS production. O₂ is converted to superoxide (O₂⁻) by oxidative enzymes in the endoplasmic reticulum (ER), mitochondria, plasma membrane, peroxisomes and cytosol. Superoxide can be generated during infections and phagocytosis (NADPH oxidase), mitochondrial respiration and by some enzymes (such as xanthine oxidase) under certain conditions. It’s a very reactive radical, rapidly neutralized in the body (can damage normal tissues) in particular during mitochondrial respiration. It is transformed/neutralized by SOD (superoxide dismutase). There are three different types of SOD: 1 cytoplasm, 2 mitochondrial and 3 extracellular. Ros production is due to the Haber-Weiss reaction which generates hydroxyl radicals from hydrogen peroxide and superoxide. Slow reaction catalyzed by iron. there are two steps: 1) first step involves the reduction of ferric ion (3+) to ferrous ion (2+) 2) The second step, called Fenton reaction: ferrous ion in presence of H2O2 will lead to the production of hydroxyl radicals (and other reactants too). Superoxide is transformed by SOD in H2O2 (less reactive) H2O2 is neutralized in water and O2 by catalase and glutathione peroxidase. May be converted to OCl (destroy microbes and cells) Superoxide dismutase (SOD) catalyzes the conversion of superoxide in hydrogen peroxide and molecular oxygen. Catalase (peroxisomes) catalyzes the degradation of hydrogen peroxide in water and oxygen. Glutathione peroxidase catalyzes the conversion of reduced glutathione (GSH) in oxidized glutathione (GSSG) neutralizing hydroxyl radical and hydrogen peroxide. Cell injury induced by ROS: Three types are the main mechanisms. a) lipid peroxidation: ROS can attach lipid and lead to membrane damage; cascade of free radical chain reaction. Unsaturated fatty acids are attached (unstable due to C=C), Hydroxyl radical will steal an H to become water (the more vulnerable one) forming a lipid radical turning into lipid peroxide in presence of oxygen. b) protein modifications: pathological protein modification which can lead to protein misfolding or even protein breakdown. c) DNA damage: if ROS binds the DNA they’ll lead to mutations (substitution of some bases at the basis of tumor formation→changing in phenotype). Ionizing radiation: X or 𝛄 rays. They can induce direct or indirect damage to the cells. Direct damage means that radiation can directly damage the DNA structure (one or both filaments, if it’s on one cell may repair the damage but if it’s on both there is cell death due to the disruption of the DNA double filaments). Indirect damage produced by ROS because ionizing radiation will lead to water ionization (water radiolysis, water is transformed in different molecules -hydroxyl radical and hydrogen peroxide which can damage lipids, proteins and DNA). Endoplasmic reticulum stress can lead to adaptation reactions in which there is a mild ER stress - accumulation of misfolded proteins. Cells will adapt through different mechanisms and resist this stress. The severe ER stress may lead to the activation of the caspases and induction of apoptosis (as terminal unfolded protein response) The causes or intracellular accumulation of misfolded proteins are genetic mutations, aging, neurodegenerative diseases, viral infections, ischemia/hypoxia. 1.2 adaptive alterations of cell size and number Hypotrophy: reduction of cell volume in a tissue or in an organ due to an acquired cause. Cells are smaller due to loss of substance. If this condition is very severe there is atrophy. It’s associated with autophagy of organelles in order to produce energy. It can be: - physiological atrophy (due to involution): fetal period some tissues/structures undergo atrophy because they are not needed anymore; infancy (umbilical vessels), adolescence (lymphoid tissue) or adult (loss of hormone stimulation in menopause or uterus after pregnancy) - pathological atrophy due to loss of nutrition, growth factors or oxygen (ischemic condition). It can be: - generalized due to malnutrition, senile (aging) or hormonal condition (- endocrine, anterior hypopituitarism produces growth hormones) - localized with hypoxia (ischemic condition, associated with cell death), due to local pressure exerted by tumors, neuropathic due to denervation of tissues and muscle, idiopathic pathological with unknown causes or limb immobilization (disuse) - following a trauma, patient with a broken limb it will be immobilized and may undergo atrophy. Hypertrophy: increased in size of a cell, tissue or organ of specialized cells. It often occurs with hyperplasia increase of the number of cells in certain conditions (pure only after mechanical stimulation). Classical hypertrophy of the smooth muscle in case of obstruction of emptying viscera - meaning that there are different conditions. Stenosis or hypertrophy of the esophagus (or gut -hypertrophy above the tumor for example); hypertrophy of the prostate gland (below the urinary bladder) will lead to hypertrophy of urinary bladder (has to push harder). In people with hypertension there is hypertrophy of arteries. It has an effect in the cardiac muscle: patient with hypertension have also hypertrophy of the left ventricle (high hypertension/resistance in the periphery so the left ventricle has to push harder - enlargement of left ventricle wall which is an adaptation reaction) but it’s due also to Aortic stenosis (aorta become obstructed). Right ventricle can undergo hypertrophy due to dysfunction (occlusion) of pulmonary arteries (pulmonary hypertension. The skeletal muscle hypertrophy is due to mechanical stimulus. Hypertrophy (associated with hyperplasia) induced by hormone stimulation during pregnancy with an increase in the number of cells (with the increasing of the volume) Hyperplasia: increase of the volume/dimension of an organ or tissues due to the increase of the number of its specialized cells. - the uterus during pregnancy (physiological condition) increases its number of cells. It must be distinguished from edema (increased volume of tissue due to water content), phlogosis (inflammation with leukocytes), amyloidosis (accumulation of protein material) and tumors (increased number of tumor cells in a tissue but not specialized cells). Under persistent stimulus of chemical nature (hormones of growth factors) there is an increased organ functionality and an increased number of the cells. This can happen also during pathological conditions like hyperthyroidism (the thyroid gland will undergo hyperplasia), another physiological condition is when the mammary gland during pregnancy and puberty will undergo hyperplasia, while a pathological condition called gynecomastia which occurs only in males and there is an increase of the mammary gland. Also endometrium undergoes hyperplasia during menstrual cycle. Consequence is the increase of organ functionality. 16/03/2023 1.3 alterations of cell differentiation Metaplasia is a reversible change, so if the cause is eliminated the tissue will go back to a normal state. One adult cell type (either epithelial or mesenchymal) is replaced by another adult cell type. It’s the consequence of a chronic stimulation of the tissue, a chronic inflammation can lead to metaplasia -this process lasts for weeks/months- or chronic tissue irritation (of chemicals) can lead to metaplasia; also the exposures to some chemicals can favor metaplasia -epithelial tissue exposed to cigarette smoke. It’s a replacement starting from local stem cells due to reprogramming of them (there isn't transdifferentiation). This transformation has some advantages (the new cell type is more robust) but the new adult cell type may lose some functions (and the tissues too) and may favor the development of tumors (it can have a pre-neoplastic condition if this condition is not removed). - Epithelial metaplasia often consists in the transformation of a cylinder columnar epithelium (monolayer of cells) in a stratified squamous epithelium (has more layers, cells are flat). This happens in many conditions: in smokers (in bronchi cells lose the cilia -the functionality is reduced even though cell are more robust -cancer with squamous cells) or when there are small stones in the gallbladder or in the pancreatic duct which can inflame/irritate chronically the tissue and favor the formation of metaplasia. There can also be the transformation of squamous epithelium to a cylindrical one which occurs classically in the esophagus (lower), to a more intestinal-like columnar epithelium. It occurs because of gastritis or reflux of gastric acid from the stomach into the esophagus; it's a chronic acidic chemical irritation and cells become similar to intestinal cells used to acids (with glandular organization), cancer may develop - adenocarcinoma, they secrete something like pituitary adenoma-. Sometimes there is also metaplasia in which there is pancreatic acinar tissue at the gastroesophageal junction. - Connective metaplasia (mesenchymal cells) for scar formation and wound repair. Fibroblast may become myoblast in a scar formation, which is a cell with contraction capacity and if the scar occurs at bone level we need lots of osteoclast to produce bone. At skin level fibroblasts during a wound will transform in a cell with contraction capacity (fibro myoblast). Dispalsia includes many types of abnormalities. There is the loss of uniformity and sometimes even loss of tissue architecture. It includes all cytological and histological abnormalities regarding cell differentiation, proliferation and organogenesis (can happen in newborns) It can occur in all tissue types. Cells have different shape/abnormal morphology (cellular pleomorphism, classical Displasia characteristic), they have abnormal nuclei (they are hyperchromatic) and cells proliferate more in abnormal locations. In advanced stages there is architectural anarchy (the tissue architecture is lost). It’s a very severe condition, considered carcinoma in situ, a kind of tumor that didn't invade the tissue. At the level of bone marrow (which produces erythrocytes, platelets -from megakaryocytes- and leukocytes) may occur myelodysplasia -with hyperplasia (occurs in old people usually) and not all cell lines are equally involved, some cell lines are more damaged - lost of platelets (megakaryocytes) production may be very critical. Neoplasm (tumors), neoplasia means new growth. It is a mass of cells (dimension depends on tumor type and site of tumor) which originate from one single cell. It’s not a normal cell, the original tumor cell has to have genetic alteration (one or more alterations) which is transmitted to daughter cells. The cell must be a proliferative cell in order to transmit the alteration to other cells. If the cells are similar there is no loss of function (can keep some functions), if it’s very different from the normal cell they usually proliferate a lot, change the function, change the morphology. - better cells similar to the normal ones. The function can be kept (benign tumors) loss or gain (if the tumor cells produce hormones). The growth depends on the type of tumor and can be variable, progressive -malignant tumors, growth-. is autonomous -tumor cells can induce angiogenesis which means formation of new blood vessels, in order to block tumors are used to block angiogenesis or use antibody against antigen that promote angiogenesis; in some cases they produce growth factor needed for their own growth and proliferation -and have atypical growth. Tumors can be benign which are usually localized (do not invade the surrounding tissues, they stay well localized) and have a capsule. They can be removed by surgery and usually they don't affect the patients’ survival. In some conditions they can be very dangerous like the one in the brain (meningioma) which grows inside the skull/bone and may lead to hemorrhage (because they bleed) which press against other tissues and can affect patients’ survival. They can be removed with surgery (not so easy) but can reform. Malignant tumors are not localized anymore, they normally invade and destroy the surrounding structure/tissues. These tumors lack a capsule. They can migrate to distal organs/tissues (not only local) and metastasis is the main cause of death (stomach tumors may have metastasis in lungs). They are also called cancers (crab) because they can infiltrate the tissues and are very obstinate. Patients’ survival could be at risk. Tumor-dependent injury: There is a deficit of function (or excess) like at lung level there will be difficulty in breathing due to the presence of the tumor, oxygen deficit. In case of adenoma there is an increase of function (excess of hormones, hyperpituitarism). There is mechanical damage because tumor mass can press blood vessels, lymphatic vessels, other tissues. There is metabolic dysfunction which leads to weight loss (cachexia) and accumulation of lactic acids and sometimes production of cytokine (associated with skeleton muscles loss, atrophy) And metastasis, which means invasion at distant sites, are dangerous because they can infiltrate other organs. - at advantage stages they contribute to cachexia. Tumors have 2 basic components: parenchyma formed by neoplastic cells (the transformed one) and stroma which is the supportive part (non-neoplastic) usually made of connective tissues, blood and lymphatic vessels and inflammatory cells- because tumors are often associated with chronic inflammation (there are leukocyte). [smuuus] Polyp: benign tumor, small on mucosal surface (intestine, nose) may cause some obstruction/inflammation and sometimes it may transform into an invasive cancer. Papilloma: is a benign tumor of the epithelium, it has a cauliflower-like aspect; wart (verruche) is papillomas at skin level. They can be due to infection (HPV). The main types of cancer leading to overall cancer mortality each year are: lung; stomach; colorectal; liver and breast More frequent among men: lung, stomach, liver, colorectal, esophagus and prostate. Most frequent among women: breast, lung, stomach, colorectal, cervical. Some lifestyle conditions and agents were incriminated as potential causes of cancer like obesity/diet (women in particular), smoking, alcohol consumption (toxic molecule), reproductive history (estrogen stimulation, women in menopause) and infectious agents (HPV). There are many risk factors that can be avoided: tobacco use, being overweight/low physical activity, alcohol use, HPV -cervical cancer, can be avoided through vaccination-, occupational carcinogens -work environment/exposure can favor the formation of some types of tumors-, low fruit and vegetables intake, urban pollution, smoke of solid fuels, exposures to UV-lights (tumors at skin level, melanoma), some types of gas (radon gas, a gas that derives from uranium transformation in some caves), some medical treatments (radiation -chemotherapy- or drugs like hormones or immunosuppressive) can help the formation of some types of tumors -they can lead to DNA changes. About 30% of all cancer deaths can be prevented with lifestyle. 20/03/2023 Occupational carcinogens: - Arsenic (and derived compound) can induce lung and skin carcinomas; it can be present in medications, alloys (metal mixtures used for industries), herbicides and fungicides; - Asbestos promote different types of tumors, especially lung, esophageal, gastric, colon carcinoma and mesothelioma (cancer that occurs in pleura, membrane that cover the lung), present in old buildings (used because very resistant to fire, heat and friction) and now it has been removed; - Benzene promotes acute myeloid leukemia, it is used a lot as a solvent (also in hospitals for coloration of tissues to make diagnosis), in painting, printing, rubber, dry cleaning, adhesives, …; - Cadmium can promote prostate cancer, it is used for yellow pigment, found in batteries, alloy and for the army’s material; - Chromium can promote lung carcinoma, found in preservatives, paints, pigments; - Nickel can promote lung and oropharyngeal carcinomas; it is found in alloys with other metals and in ceramics, in batteries and it can also be produced in arc welding (saldatura) - it’s a by-product; - Radon can promote lung carcinoma, found normally in the environment, radioactive gas, it can release 𝛂 particles and it is found also in the soil and underground mines - second cause of lung tumor, present in the environment and not just occupational; - Vinyl chloride causes hepatic angiosarcoma (liver tumors), these polymers are used for plastic - frequent in industry usage. Chronic inflammatory conditions promote cancer. Chronic inflammation is bad because it lasts months or more and can promote some types of cancers. - Asbestosis and silicosis can be occupational diseases and are associated with chronic inflammation (in concat silica particles, asbestos fibers -etiologic agents) and promote mesothelioma and lung carcinoma; - Inflammatory bowel diseases (IBDs) are associated with colorectal carcinoma; - Pancreatitis can be due to alcoholism (or germline mutations) and can promote pancreatic carcinomas; - Barrett esophagus, reflux esophagitis due to the present gastric acid can promote with esophageal carcinoma; - Gastritis/ulcers due to the presence of Helicobacter pylori and are associated with gastric adenocarcinoma; - (chronic) Hepatitis induced by HBV or HCV may promote hepatocellular carcinoma; - Chronic cervicitis induced by HPV is associated with cervical carcinoma. Chemical carcinogens: many molecules present in our environment can represent agents promoting carcinogenesis.  - polycyclic and heterocyclic aromatic hydrocarbons came from incomplete combustion of different materials (breast, scrotal, lung, digestive tract cancers), present in cigarettes smoke, grilled/smoked meat or fish; - aromatic amines and azo colorants (textile and clothing industry; leather), cause liver and bladder cancers, bases of amiline (organic compound that is at the basis) used in many industries, very bright and cheap colorants in textile industry (indigo, used for jeans) –found also in paracetamol but in this case it doesn’t induce cancer (not toxic); - N-nitrosamines (-N=O nitro group bonded to an amine, derive from nitrates/nitrites and a secondary amine), promote stomach and esophagus cancers; they are found in some types of foods (food preservatives in processed meat); - Aflatoxins promotes liver cancer, are a family of toxins produced by fungi (aspergillus) present in warm and humid regions, the most most famous is B1; found in different type of food; a prolonged exposure to humid region will promote their production (under aspergillus infections). It can be present in corn, peanut, millet rice, sesame seeds, nuts, wheat can be contaminated (also some spices) almond, pistachio -if not well preserved. Low levels have low risk. The most widely used system for classifying carcinogens comes from the IARC. There are 4 groups of carcinogens: 1. contains about 100 agents, contains the names of molecules for sure carcinogens for humans like benzine, asbestos, processed meat, smoke, UV radiation, some viruses (HPV, HBV); 2. A are probable carcinogens to humans (red meat, these molecules are usually upgraded to group 1 after scientific demonstrations) B possible carcinogens 3. unclassifiable as carcinogens in humans now 4. probably not carcinogenic to human These molecules need laboratory demonstration in order to be sure that they are carcinogens. – in 2016 processed meat was included in group 1 (2A red meat) as result of a study (promoted by IARC) Processed meat consumption (50g/die) can promote colon and stomach cancer. The risk increases by 18%. Red meat can promote colon, pancreatic and prostate carcinomas (100g/die). The risk increases by 17%. - alkylating agents - used as anticancer drugs used for a type of lymphoma -hodgkin, increase the risk of developing leukemias in patients who take this drug. Molecular targets of carcinogens: -why these molecules may promote cancers These molecules may promote cancer because they can bind directly to DNA/RNA/proteins in a covalent manner leading to the formation of adducts. - DNA binding may induce an alteration which in proliferating cells can be transmitted to daughter cells. Direct alteration of DNA can occur after binding with carcinogens. This genetic alteration of the DNA can be transmitted to daughter cells. The most reactive are purine bases. Not all kinds of gene alterations, some particular genes need to be altered especially genes involved in cell proliferation of survival. Can provoke transmissible genetic alterations to proto-oncogenes (silent oncogenes) or alter regulatory genes.  - RNA or binding of particular protein (histone or regulatory proteins) inside the nucleus may cause epigenetic changes and some this can promote tumor formation. The epigenetic changes need to affect the activity of genes involved in cell proliferation, differentiation, … because tumor cells usually proliferate more than normal cells (they are transformed cells). -specific genes need to be affected Hallmarks of cancer cells: There is often self-sufficiency in growth signals, tumor cells can produce the growth factors necessary for their own growth. PDGF -platelets derived growth factors- produced by tumor cells, TGF 𝛂 -transforming growth factor- factor that tumor cells can produce themself. They produce and respond to the molecules that produce (they have the specific receptor). They also have insensitivity to growth-inhibitory signals, there are many types of genes that suppress the growth of cells like rb genes, usually inactive in tumor cells -it's a tumor suppressor, or tp53 which encodes p53 which is inactive in many types of tumor. There are genes which control cell growth and proliferation which are inactivated in tumors, so cells are insensitive to growth inhibitory signals. Cells grow even with an alteration in the DNA. There is altered cellular metabolism, they have to proliferate. There is a metabolic reprogramming in tumor cells (also happening in T-cells) called Warburg effect: if the cell is starving it can use autophagy in normal conditions (quiescent normal cells) meanwhile a tumor cell need lot of energy in order to proliferate and to produce proteins, DNA, membrane (to divide) to be able to produce another cell, the cells will do a metabolic reprogramming to be able to produce all the essential tools to produce a new cell, it will shift to anaerobic glycolysis which means that glucose and glutamine usage are increased because this allows the production of molecules needed for lipogenesis, proteins, lipids, nucleic acids synthesis; there is the production of lactic acid, a sign of the metabolic shift. -there is a shift to aerobic glycolysis in order to the formation of molecules needed for protein, lipids and nucleic acids synthesis. Tumor cells don't undergo apoptosis, they are potentially immortal. These cell lines are studied and using cell lines started years ago. They can undergo other mutations and may change their phenotype. There is limitless proliferation potential and immortality. Solid tumors may promote the formation of new blood vessels used to feed the tumor mass (sustained angiogenesis). There is invasion and metastasis as hallmarks of malignant tumors and evasion of immune surveillance. Some immune system cells may recognise and kill tumor cells (killer cells and T-cells). A normal immune system should recognize and kill tumor cells, if it’s not able to do it, or tumor cells are transformed and can’t be recognised, the tumor will form. -may be due to an immunosuppressed patient, someone whose immune system is not working well or if tumor cells escape the immune surveillance. Many kinds of tumors contain lymphocytes which promote tumor formation -particular phenotypes of lymphocytes called regulatory lymphocytes blocking the immune response so the tumor cells are not killed. DIFFERENCES BETWEEN BENIGN AND MALIGNANT TUMORS: Growth velocity: benign tumors may have normal mitosis so they proliferate normally, there is a slow mitosis percentage so not so many cells are proliferating and mitosis looks normal, well differentiated cells -normal nucleoli (mitosis is a bit higher than a normal cell). Malignant cells have high mitosis percentage (they proliferate at higher rate) with abnormal mitosis and larger nucleoli -larger, hyperchromic nucleoli. Differentiation: benign tumor cells are similar to normal cells, they keep normal functions, they are well differentiated. In the case of malignant cells there is a very low grade of differentiation (these cells are not well differentiated), leading to loss of functions, transformed cells compared to normal cells are different (with loss of normal function). Diffusion: benign tumors do not invade surrounding tissues, they do not give metastasis, they are normally encapsulated -so they remain in situ inside this capsule. While malignant cells do not have a capsule normally, they perform local invasion (they can infiltrate locally the tissue) and they can perform metastasis (formation of new tumors non contiguous with the original tumor site). 23/03/2023 Tumor growth - The biology of tumor development: Tumor development process starts from a normal cell. In the presence of a carcinogen (carcinogen-induced change), there is the initiating mutation -there is a mutation at the DNA level leading to the formation of the final tumor mass. Then there is the acquisition of cancer hallmarks (the characteristics of tumor cells) and then there is tumor growth with accumulation of other genetic mutations -additional mutations normally occur during tumor development. - clones are populations of proliferation cells which are all the same. Additional mutations will lead to the formation of cells with different characteristics/different genetic alterations. Inside the tumor there are different cell populations (with different mutations), there are many variants of tumor cells because of these additional mutations. At the end, the tumor mass is a heterogeneous mass of cells. This is an advantage for the tumor mass (a disadvantage from a therapeutic point of view because it is possible that the therapy won’t kill all the cells in the tumor mass and give birth to a new tumor mass). This is also a disadvantage for the organism in terms of tumor evolution because some of these cells may be more metastatic/migratory giving birth to other tumors. - Tumor mass is heterogeneous, inside the tumor mass there are different types of tumor cells variants. Malignant tumors may perform local invasion with progressive infiltration (invasion) and destruction of surrounding tissues Then there is metastasis which means the formation of a new tumor mass which is physically discontinuous with the primary tumors (this can be in the same organ or in other organs). Metastasis is a complex process. First of all, tumor cells have to detach from the original tumor site. This process is very important because normal ells in the tissues are in a state of adherence, in order to migrate a cell must detach from other cells and in the case of epithelial cells very important is the inhibition of function of a molecule called i-cadherins (important to keep the cells together, intercellular glues) adhesion molecule that keep together the cells. These adhesion interactions have to be broken for tumor cells to migrate. Adhesion interactions mediated by cadherins need to be blocked, also the tumor cells should detach from the extracellular matrix and this is made through secretion of proteases such as matrix- metalloproteinases released by tumor cells in order to break the bound with extracellular matrix or other proteases like collagenases or plasminogen activator. There are enzymes which promote tumor cell detachment from the extracellular matrix and then migrate.- These proteases will also degrade the extracellular matrix, creating a way to migrate. Through the action of these enzymes, growth factors and chemotactic factors are also released from the extracellular matrix (they are normally attached to the proteins of the extracellular matrix) which help tumor cells to migrate. Cells migrate in different directions, they can spread inside the body in different ways: they can spread within body cavities (pleura cavity, peritoneal cavity -abdomen); they can be spreading via lymphatic vessels (lymphatic spread -tumor of epithelial origin like breast cancer gives metastasis through lymphatic vessels) or through blood vessels, having an hematogenous spread (in general, sarcomas spread through blood vessels). It was observed that some tumors give preferential metastasis in particular organs, for instance melanoma (skin tumor) gives preferential metastasis in the brain; tumors from the prostate can give metastasis to the bones (vertebras); thyroid tumor give metastasis to the bone too. After the migration /dissemination process, tumor cells will stop somewhere, attach and destroy the blood vessels wall and migrate into the target tissue. Cells will adhere and there is the phase called implantation. After the implantation there is tumor growth and the formation of the second tumor mass at distance. Very affected are filter organs (lungs and liver) because tumor cells arriving to the blood can implant into the lung (affected by tumors from all the body -liver only peritoneal tumors in particular from vena porta). Paraneoplastic syndromes can be the very first manifestation of the tumors. - Chasing syndrome due to occlusion of a hormone called ACDH, leading to the production of cortisol. THis hormone can be produced in abdominal manner in lung tumors and some pancreatic tumors (ASDH or ASDH-like molecules); - Hypercalcemia, increased calcium in the blood like in some lung tumors, breast carcinomas and some rhinal carcinomas can lead to this condition because they produce molecules which resemble parathyroid hormones (PTH). This hormone (or related molecules) will mobilize calcium from bones (opposite of calcitonin) - abnormal production. 1.4 alterations of genetic information Cancer genes: There are two types of cancer genes involved in tumor induction and tumor growth. There are genes that positively regulate proliferation which means that these genes normally promote proliferation processes at different levels. These genes are called protooncogenes and are more active in tumors through different mechanisms. If these genes are mutated they become oncogenes (genes that promote the oncological process). The second gene category are genes that normally negatively regulate proliferation, meaning that the normal function is to block proliferation called oncosuppressor genes. These genes are inactivated in tumors (they don’t work well). Genetic alteration in cancer can be amplifications, mutations (K-ras, proto oncogenes or TP53, a suppressor gene), gene rearrangements, deletions or chromosomal translocations. Oncogenes: there are 4 category: 1. Genes which encode for Growth factors like sis gene -which encode for PDGF𝜷 platelet derived growth factor- it can be overexpressed in some types or tumors; 2. Genes encoding for Growth factors receptors like erb-genes which encode for EGF receptors molecules (epidermal growth factors), these genes can undergo different alteration such as overexpression or amplification -signal transduction pathways are altered; 3. Genes encoding for Proteins involved in signal transduction like ras -a GTP-binding protein which can undergo a point mutation which can lead to the formation of a very aggressive tumor (important in cell proliferation and migration. -activate the transcription in the nucleus, signal transduction pathways. These molecules are activated starting from growth factors leading to the activation of the transcription factors. 4. Genes encoding for Nuclear regulatory (transcription factors) proteins which are usually transcription factors, molecules which induce activation and transcription like myc, usually these genes undergo transactions. There are different myc proteins with different types of genetic alteration depending on the type of tumor (translocation, amplification). 1st category: molecules of growth factors can be produced by tumor cells for their own growth. The cells are in a presence of an excess of molecules of growth factors. The number of growth factors receptors are normal, the growth factor concentration is increased. There are stimulatory signals from the membrane. 2nd category: amplification leading to an excess of growth factors receptors. The number of growth factors molecules is normal. Due to the increased number of growth factor receptors the cells are more sensitive to these molecules, they immediately capture all molecules of growth factors. There is a strong activating signal going into the nucleus and inducing cell proliferation. 3rd category: involves molecules which bring the signal from the membrane to the nucleus, the cells have normal growth factor receptors and the growth factors are in a normal concentration, but cells with continuously activated transducer (signal transduction) molecules don’t need growth factors. The new structure is active, leading to activating signals to the nucleus leading to cell proliferation and migration. 4th category: these cells have a mutant transcription activator gene which will lead to the production of transcription factors which will continuously activate transcription and proliferation. Oncosuppressor: these genes are inactivated in tumor cells through different mechanisms (mutations, deletions, …). An important oncosuppressor gene in humans is TP53, encoding for p53 protein). In the presence of a mutagenic agent, leading to DNA alteration, will lead to the binding of p53 (phospho protein) to the DNA and leads to cell cycle arrest -block of proliferation. There is a DNA alteration which has a DNA damage that should not be transferred to daughter cells. This will have 2 possible consequences: cells will have the time to repair the damage, if the DNA is repaired p53 protein will detach from the DNA and will allow cell cycle progression, but if the DNA damage cannot be repaired p53 triggers apoptosis (cell death). -p53 is called genome guardian. With mutated TP53 (so p53 is mutated/damaged too, the protein is not working), in the presence of mutagenic agents the cell will lose p53 function. In the case of a DNA damage cells will continue to proliferate and transmit the DNA damage/mutations to daughter cells and eventually the genetic alteration transmitted to daughter cells may lead to transform cells (tumor cells). p53 has a short half life (20 minutes) so if it’s not working the concentration is high because cells try to compensate for the malfunction producing more proteins. p53 can be activated during hypoxia, DNA damage (genetic alteration of TP53), nutrient deprivation, oxidative stress, shortening of telomeres. p53 is activated by different conditions and block cell cycle (blocking a potential tumor formation). p53 activation can also lead to other effects, like apoptosis, DNA repair, angiogenesis, autophagy (nutrient deprivation), cell senescence, normal cell migration and many types of metabolic changes. ROS formation can lead to DNA damage, favoring mutations, like ionizing mutations. Viruses which promote tumor formations: 1. Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) which can induce diseases which resemble multiple sclerosis (myelopathy) leading to a tropical spastic paraparesis because it occurs in tropical countries, south of japan. This infection can lead to T-leukemia. Virus infects T-cells stimulating abdominal proliferation, increasing the number of T-cells and leading to polyclonal T-cell proliferation increasing the vulnerability of cells to mutations, cells that proliferate more are more prone to be transformed. The virus leads to abnormal proliferation which may easily undergo mutations and become transformed cells. 2. Epstein-Barr virus (EBV) leads to a common infection in humans (mononucleosis), and can last for months in humans. can lead to autoimmune diseases. It’s at the basis of the formation of different types of tumors. The process is similar in Burkitt lymphoma, it affects B-cells (lymphocytes) which produce normally antibodies (receptor is CD21) and EBV triggers proliferations, leads to a polyclonal proliferation (no DNA damage) which can favor the fixation of mutations which can be transmitted to daughter cells (indirect tumor transformation). 27/07/2023 Immune system Immune system is a system formed by molecules, cells and organs. It's a homeostatic (equilibrium state maintained in the presence of external changes) system which evolved to first recognize foreign molecules and agents and then eliminate these agents that are potentially dangerous for the organism. Immune system intervenes in many potentially damaging situations in our body, it evolved to protect the body against infections (microbes). It can also contribute to the induction of cancer, during tumors the immune system doesn't work well locally (it is suppressed). Some cells in our body are able to recognize cells that are transformed but they don’t work in the tumor mass. The dysregulation of the immune system may lead to the formation of cancer. Inside the tumor mass there are lymphocytes called regulatory T-cells with a suppressor effect. The immune system and its downregulation contribute to the formation of malignant tumors. Primary organs of the immune system are the organs in which the immune system cells are born in bone marrow and thymus in which T-cells need to be educated to recognize the antigens and learn to be tolerant to self-antigens. Antigens are foreign or not molecules and the system has to kill only the foreign ones. Regarding self antigen it has to be tolerant/quiescent or else autoimmune diseases will develop. T-lymphocytes differentiate in the thymus and after maturation they are able to discriminate between self and foreign antigens. The secondary organs are: lymph nodes (drain lymph from the tissues, from extracellular spaces), spleen (responsabile for the recognition of blood antigens), adenoids, tonsils, peyer’s patches (intestinal level, kind of flat lymph nodes), appendix and also mucosas and skin are full of immune system cells. Bone marrow: All WBC are formed (leukocytes, immune system cells) in the bone marrow - granulocytes lymphocyte, monocyte, eosinophil, basophil and neutrophil, and also red blood cells and platelets (coming from megakaryocytes) -not cells, they lack the nucleus. Thymus: is divided in small lobes, each of which have an external area called cortex and a more internal area called medulla. In the thymus T-cells mature and differentiate. Lymph nodes: these structures are roundish, they have a capsule in the external part, crossed by lymphatic vessels which are called afferent lymphatic vessels because they bring the lymph from the tissues to the lymph node, they have an area called hilum in which start the efferent lymphatic vessels and there are also blood vessels (arteries and veins). Lymph nodes are organized with a cortical area more external and a more center area called medulla. The cortical area has blue areas in which there are B-cells in which from follicles. Surrounding these follicles there are many T-cells placed (parafollicular). Inside the follicles there are areas in which B-cells grow and proliferate. There is a particular vessel inside the lymph node called high endothelial venule (HEV) which is fundamental for lymphocytes recirculation between blood and secondary immune system organs. Lymphocytes enter into the lymph node at the level of HEV. The recirculation process is very important for immune surveillance. T-cells continuously recirculate from the blood migrating to the lymph nodes searching for antigens, if there aren't any antigens they get out through efferent lymphatic vessels which communicate with the blood vessels through the thoracic duct. Peyer’s patches have a similar structure with lymph nodes but are flat. Spleen is divided in red and white pulp which looks whitish due to the presence of immune system cells like lymphocytes B-cells, T-cells surround B-cells. Mucosas are full of immune system cells, and the gut has peyer's patches (on the intestinal surface). Inside the mucosa there is the MALT (mucosa-associated lymphoid tissue) which can be divided in GALT (gut associated lymphoid tissues) which includes lymphocytes and peyer’s patches -useful for intervene and neutralize toxins, microbes. Also respiratory mucosas have GALT because we inhale air with a lot of microorganisms. BALT (bronchus associated lymphoid tissues) is present at the bronchi level, a bronchial lymphoid tissue. Skin associated lymphoid tissues (SALT): skin is divided into three layers and there are different types of immune system cells. Langerhans cells (dendritic cells), lymphocytes and other types of dendritic cells. Leukocyte production occurs in the bone marrow starting from hematopoietic stem cells. There are 2 precursors: myeloid and lymphoid stem cells. Myeloid stem cells is the precursor of myeloid cells which include the 3 types of granulocytes monocytes progenitor (common progenitor of neutrophils and dendritic cell), neutrophils, basophils and mast cells have a common precursor (very dark granules, which contain histamine) Erythrocyte progenitors and megakaryocyte (give birth to platelets/thrombocytes) Lymphoid stem cells give birth to lymphocytes: T-cells, B-cells and NK-cells (natural killer) from a common precursor (lymphoid stem cell). If not activated they are naive and are small, they become larger when activated with more cytoplasm. Monocytes have a bean-like nucleus (non polymorphic), round cells that become macrophages when migrating. Neutrophils have polymorphic nuclei as eosinophil and basophil. - mm³=1 ml [tabella 11] Macrophage differentiation: during fetal development hematopoietic stem cells are produced in the yolk sac (blood supply to the fetus during development). These precursors arrive from the blood and migrate to different tissues and populate them. They have different names depending on the tissues. In the spleen these macrophages are called sinusoidal macrophages, in the lung alveolar macrophages,in the liver Kupffer cells and in the brain microglial cells. During adult life macrophages derive from blood monocytes, produced in the bone marrow which migrate to the tissues -especially during inflammatory conditions. Monocytes migrate, become macrophages which become large cells and are able to phagocytes (also neutrophils are phagocytes). Professional phagocytes in our body are neutrophils and macrophages Neutrophils are originated in the bone marrow (HSC) while macrophages can be produced during early development from the yolk sac and liver and during adulthood from bone marrow. Neutrophils’ lifespan is 1-2 days while macrophage's lifespan is longer (years, inflammatory only days/weeks). They are both phagocytes but neutrophils are rapid cells (rapidly migrate, ingest microbes, rapidly release enzymes, rapidly produce ROS during inflammation), these are very reactive cells while macrophages’ reactions are slower but also prolonged (they are efficient cells), they can produce ROS in a less prominent way, less enzymes secreted but the production of cytokines is higher (important protein during inflammatory reactions -macrophages+leukocytes). Dendritic cells during fetal life are born from hematopoietic stem cells from embryonic precursors coming from liver and yolk sac. These cells go into the blood and migrate into the tissues and become dendritic cells; this was demonstrated for Langerhan cells in the epidermis layer of the skin. During adult life they are produced in the bone marrow from a precursor (common to monocytes) and from the blood precursors of dendritic cells migrate into the tissues and differentiate into different types of dendritic cells. Monocytes can also be precursors to dendritic cells, especially during inflammatory reactions. These cells are dendritic cells due to the presence of dendrites/ramifications (in the tissues) with which they present antigens to T-cells. Maturation of lymphocytes: B-cells are produced in the bone marrow (they were discovered in birds in the Bursa of Fabricius) and leave the bone marrow as mature cells (they maturate inside the bone marrow); T-cells are produced in the bone marrow but they need an additional maturation step in the thymus where they mature and differentiate. Both B-cells and T-cells recirculate from the blood into the peripheral lymphoid organs (and mucosal tissues and skin) and from all these tissues cells go back into the recirculation through lymphatic vessels. Afferent lymphatic vessels are originated/formed at tissue level and they drain the fluid from the tissues to the lymph nodes -stations on the lymph drainage. Afferent lymphatic vessels bring the lymph to the lymph node. From the draining lymph node the lymph goes from lymph nodes to other and at the end is collected in larger vessels which all converge on the thoracic duct (start at T12) and this duct will bring the lymph into the blood circulation. Lymphocytes are able to recognize a particular type of antigen (molecule) and their recirculation is important because of this way. Each lymphocyte recognizes its specific antigen. -neutrophils enter the tissues only during inflammation for example. Immune system cells can arrive to the lymph node also by afferent lymphatic vessels. Dendritic cells can migrate from the tissues to the lymph nodes via afferent lymphatic vessels. This is important because dendritic cells can bring antigens from tissues to lymph nodes, foreign antigens arrive to the lymph nodes from the tissues. Lymph nodes are important because in them immune response starts (also in the spleen), antigen are recognised by T-cells in the lymph node (it enlarges when drains the lymph and generates the immune response). The different stages of lymphocytes activation (B-cells and T-cells), can be present in different activation stages. Naive lymphocytes are smaller, round, with low level of cytoplasm (only thin ring) and during an infection (in the presence of an infectious agent) these cells will recognise the antigens and will become activated lymphocytes which become larger cells, they proliferate and become effector cells. Effector cells in the case of T-cells produce many types of molecules including cytokines and chemokines. Naive B-cells -produce antibodies (immunoglobulin) when activated- and have antibodies on their surfaces like receptors for microbes. Naive B-cells do not secrete antibodies. After antigen recognition they will become activated, proliferate and differentiate into effector cells called plasma cells (which are larger with a lot of cytoplasm) able to release a lot of anti bodies outside the cells. Some of those cells will die (apoptosis) and some of them will continue to live as memory lymphocytes cells (smaller, similar to naive cells) recirculating in the body so with a second infection of the same agents they can rapidly activate and can rapidly mount an immune response. Naive and memory cells can recirculate continuously in our bodies, activated cells (which are bigger) normally don’t recirculate from blood to lymph nodes but they are more prone to migrate to tissues in which there is an inflammation - these cells are able to fifth infection, produce antibodies, cytokines. 30/03/2023 Immunity molecules: general categories of molecules responsible for immune system functions. There are many types of membrane receptors, some of them are very specific (antigen receptors, T-cell receptors -TCR) and other are non specific that can be for proteins (cytokines receptors or receptors involved in phagocytosis FC, specific for FC portion of immunoglobulins) Soluble systems formed by many molecules called polymolecular soluble systems (are soluble in blood/plasma) like coagulation system, complements system, chinins -small molecules, polypeptides, important for immunity and inflammation, … Cytokines are soluble proteins which can be produced by immune system cells, endothelial cells, fibroblast, and so on and are fundamental molecules for immune system function under normal conditions and during inflammation processes. They need cytokines receptors (membrane receptors) fondamental for the immune system -activate intracellular pathways and induce particular function/changes in the immune system cells. Chemokines are a group of cytokines with chemotactic activity, they can attract other cells (including immune system) into particular areas of immune system organs under normal conditions (germinal centers in the lymph node; HEV release particular cytokines and chemokines which attract naive T-cells into secondary lymphoid organs -CCN19 and CNN21), during inflammations are important because they attract immune system cells in the site of inflammation (they have a fundamental role for the immune system in general). Growth factors are important for cell proliferation, for B-cells and T-cells and are also important in bone marrow to produce precursors. Immunoglobulins (antibodies), molecules can be bound on B-cells membrane when are naive B-cells (not activated) but can also be produced in a soluble from by activated B-cells (plasma cells) and they can travel at distance through the blood circulation. There are many types of inflammation mediators like prostaglandins, ROS (produced neutrophils for example and other immune system cells). The immune system evolved to defend/protect the organism against different types of infections/microbes, however not only microbes can activate the immune system but also other molecules are able to do it like molecules involved in allergies, which activate the immune system cells (molecules that we breathe or that came from food). Immune response is a very complex process and consists of coordinate and cooperative response of immune system cells in the presence of an infective agent. This occurs because immunity is divided into 2 categories with specific characteristics (molecules and immune system cells). These 2 types of immunity coordinate their actions - the innate immunity will be the first to intervene and then the other one intervene too- and also cooperate -adaptive immunity cells cannot perform phagocytosis but can activate innate immunity cells in order to activate phagocytosis. Innate immunity is the first one to intervene (during the first hours) and defend our bodies against infections. The components include epithelial barriers, phagocytes -neutrophils and monocytes/macrophages, dendritic cells (present the antigens), complement system, NK cells, Innate Lymphoid Cells and present the antigens to adaptive immune cells (cooperations). After 10- 12 hours adaptive immunity start to be activate and need days in order to be activated (innate is quicker), lymphocytes are the main components B-cells activated by microbes (antigen is soluble) and release antibodies in the extracellular space; T-cells are activated recognising an antigen presented by another cell and fight infections. a. Innate immunity (or natural, native) is responsible for the initial response against microbes. It first recognizes the dangerous agent and then eliminates it. Its mechanisms are used by the adaptive immunity cells. Adaptive immune cells can activate innate immunity increasing the phagocytosis. Innate immunity cells can stimulate the adaptive immunity producing particular cytokines inducing a specific adaptive response, like interleukin 4 or 12 which are important to generate particular immune responses by T-cells (4 toward allergic response). In general it’s less specific -it has limited specificity- , it is rapid and efficient. It recognizes structures, which are general characteristics to microbes and not to mammal cells like mannose residues from oligosaccharides -recognised by mannose receptors; residues starting with N-formylmethionine residues present in the structure of bacterial proteins, which are very chemotactic for innate immune cells: they attract immune system cells binding specific receptors involved in chemotaxis (FMLP receptors); LPS of Gram- bacteria (recognized by TLR receptors) -they are specific for structures of particular category of microbes. They can also recognise structures critical to microbe survival (dsRNA, by TLR). PAMPs -pathogen associated molecular patterns- using different TLR innate immunity cells can recognise different molecular patterns present in microbes (Toll- like receptors). The fundamental receptors are TL-receptors which recognise different PAMPs of microbes; Formyl peptide receptors recognize the formylated part from the microbe's proteins, mannose receptors which recognise the mannose receptors and scavenger receptors -bind microbes, they can bind also apoptotic cells, oxidase lipoproteins (so are involved in atherosclerosis). The distribution of the receptors is non clonal: all cells from the same lineage can express identical receptors. -in contrast for receptors of adaptive immunity which are clonal for T-cell receptors. They are able to discriminate between self and non-self, they are tolerant in the presence of self molecules and do not attack normal cells/molecules. Innate immunity components are: physical and chemical barriers like epithelial barriers - they consist of layers of epithelial cells which lay between the external environment and the human body (respiratory epithelium barrier between the air we breathe and the lungs, gut mucosa, skin) but are also chemical barriers because they produce peptides with antibacterial activity which are defensins produced by skin cells and neutrophils (in their granules) and at the level of intestinal mucosas there are cryptocides which are peptides with antimicrobial activity. phagocytes -neutrophils, monocytes/macrophages- can perform phagocytosis so they recognize microbes and ingesting microbes, internalizing it and after the internalization it is destroyed. Neutrophils halflife is increased during inflammatory response due to the presence of cytokines, they have a segmented nucleus (3-5 lobes) and they contain a lot of intra cytoplasmic granules (of different types of granules, granulocytes, fondamental for their functions). They are the most represented cells in the blood and are ready to intervene against infections and are very reactive cells -quiet in normal conditions, activated only when it’s needed- they age rapidly and they become more prone to be pro inflammatory (phenotype) that’s why they are killed and continuously produced ex-novo.  They have 4 types granules inside the cytoplasm -which are released gradually during infection (primary granules content is released lastly due to its high content of enzymes which can damage tissues): 1. primary (azurophil) granules, they have myeloperoxidase (MPO) an important enzyme to kill microbes (used like a marker for neutrophils); there are a lot of proteases (elastases and cathepsin) so they can also degrade extracellular matrix - during some types of inflammation they can produce collateral damages because of these enzymes- and lysozyme a molecule important to kill microbes; 2. secondary (specific) granules with collagenase, gelatinase, lysozyme and also adhesion molecules such as integrins and fMLP-R, important in the proinflammatory function of neutrophils; when a neutrophil become activated these granules will fuse with the cell membrane and release the content outside the cells increasing the function of fMLP receptors (chemotactic receptor) and molecules important for neutrophil migration 3. tertiary (gelatinase) granules which contains integrase, gelatinase, lysozyme 4. secretory vesicles which can contain integrase, fMLP-R, CR1, alkaline phosphatase. NK cells and ILCs complement system Cytokines are important because immune system cells will function during inflammation especially due to cytokines. They activate the innate immunity cells (and are adaptive immunity). How it recognise microbes: There are G-protein coupled receptors (GPCR) which pass the membrane 7 times and they are coupled with G-protein which is a trimeric protein (3 chains -𝛂, 𝛃 and 𝛄), there are many type of GPCR receptors and they transduce the signal very rapidly, for example N-formylmethionine residue receptors. Also receptors for chemokine. Both chemokines receptors and fMLP receptors are involved in immune cell chemotaxis -directed movement given by a gradient of chemotactic factor. Mannose receptors can bind mannose and fucose residues (of glycoproteins and glycolipids); “Scavenger” receptors; TLRs – Toll-like receptors; FCR – Receptor for the FC portion of Ig (opsonized microbes) and CR – complement receptors (opsonized microbes). Ig and complement molecules can bind the surface of the microbes in a process called opsonization, recognizing microbes indirectly -so if microbes were covered by Ig or components of the complements systems and are opsonized microbes. PAMPs (pathogen-associated molecular patterns) are sequences/residues of the pathogens that can be recognized by Innate immunity cells. They can be from Nucleic acids from Viruses (ssRNA or dsRNA, CpG) or bacterial (CpG) by TLR; some proteins coming from the bacteria structure can be recognize such as Pilin -fibrose proteins found in Pilus that allows movement and adhesion- or Flagellin -present in the Flagellum, a protrusion that allows movement- and are recognize by some TLR; some kinds of lipids like Lipoteichoic acid (Gram+) and LPS  (Gram-) by particular TLR; some types of carbohydrates from fungi and bacteria like mannan and glucans. Innate immunity cells are also sensing Damage-Associated Molecular Patterns (DAMPs), molecules which are like alarm signals (alarmins) during inflammation. These molecules are a sign of inflammation and tissue damage -released by damaged cells. Typical examples are stress-induced proteins like HSPs (heat shock proteins) which are a family of proteins which are produced and released by cells under stressful conditions (like exposure to heat or UV radiation, a trauma/wound production) and there are many types of HSPs. Crystals can also activate innate immunity cells, like uric acid crystal -monosodium urate- lead to the release of inflammation mediators, which deposit in the tissue in the disease called Gout - deposition of these crystals at the level of articulation. Another classical DAMPs is a protein normally present inside the cells HMGB1 -nuclear protein that binds to DNA, important in the architecture organization of the chromatin and during cellular damage this protein is released outside the cells which it’s chemotactic for innate immunity cells and induces a strong activation. 03/04/2023 Receptors for PAMPs are also called pattern recognition receptors (PRR) of the innate immunity able to recognize PAMPs and DAMPs. PRR can be present in almost all cellular compartments. They can be expressed on plasma membranes (mannose receptors, TLR). They can be present inside the cytosol (soluble form) like NLR, RLR and CDC - in the cytosol there are soluble pattern recognition receptors able to recognize PAMPs. PRR can be present on the endosomal membrane (endosomal vesicles), especially a particular type of TLR. Innate immunity cells have many of these PRR, they are full of these receptors in order to be able to defend the body against infections (first line of defense). They are redundant in order to ensure the response and give high efficiency of response - microbe can be recognized by different receptors, not just one. These PRR can be cell associated (inside or on the cell surface) or can be soluble. Cell-associated PRR: 1. Toll-like receptors (TLRs) discovered in drosophila, express on the endosomal or plasma membrane of different cells such as phagocytes or dendritic cells and belong to the innate immunity. They can be expressed by other immune cells such as leukocytes, and also other cells of the body such as some neurons (during inflammatory conditions). There are 9 types of TLR (1, 2, 5, 4 -for LPS-, 6 -peptidoglycans- are on the plasma membrane, some are expressed on endosomal membrane in peculiar 3 -dsDNA-, 7 and 9 -will bind ssDNA and CpG DNA). They can bind different types of PAMPs. 2. NOD-like receptor: are present in the cytosol of phagocytes (and other cells); NOD1 and NOD2 are the most common, inflammasomes (different types) are groups of molecules binding together forming big complexes stimulating inflammatory responses. They can bind bacterial peptidoglycans and also some DAMPs (crystals). 3. RIG-like receptors (RLRs) are cytosolic in phagocytes (but also other cells). RIG-1 and MDA-5 are two examples and are sensors of viral replication (they bind viral RNA)  4. Cytosolic DNA sensors (CDCs) are present in the cytosol and they can bind bacterial and viral DNA (sensors). 5. C-type lectin-like receptors (CLRs) lectin is a protein able to bind carbohydrates and are present on the plasma membrane or phagocytes and are mannose receptors (recognised mannose and fructose) and dectin (recognise glucan, a component of fungi’s wall) of bacterial structures. 6. Scavenger receptors can be present on the plasma membrane of phagocytes (CD36) and recognise microbial diacylglycerides. However they can bind other molecules (glycated proteins/molecules -AGE, product after glycation- are present in people with diabetes and activate a lot of cells, lipids/fatty acids/phospholipids/collagen) rich on macrophages' surfaces -key cells during atherosclerosis because they eat lots of lipids (phone cells). Also amyloid 𝛃 during alzheimer 7. N-formyl met-leu-phe receptors (sequence typical for bacteria), these receptors recognize di- or tri-peptides. These peptides are released by bacteria and are very chemotactic for phagocytes. These receptors transduce rapidly (important for cell movements) and are G-protein coupled receptors, trimeric G-proteins. -important in cell movement. Similar peptides are released by damaged cellular structures (mitochondrial components). Soluble: molecules soluble in the plasma 1. Pentraxins are a group of plasmatic molecules (C-reactive protein -CRP is also a marker for inflammation) and they can bind different microbial molecules like phosphoryl choline and phosphatidyl ethanolamine. They have many types of role 2. Collectins -like Mannose-binding lectin- are soluble molecules and they can bind carbohydrates rich in mannose and fructose. They have a particular structure similar to the other molecules (3 and 4). 3. Ficolins are on plasma and can bind Ficolin, they can bind to lipoteichoic acid, a component of Gram+ bacteria, and can also bind N-acetylglucosamine. 4. Complement molecules can bind some microbial structures and - especially for components which are also opsonins, are typical of molecules which are able to bind covalently to glycoproteins on the target cell surface. Important molecules able to perform opsonization are C3b and C4b. TLR signaling: TLRs are present on plasma or endosomal membrane (anchored on a membrane, not soluble). They can transduce a particular strong signal transduction in the cells. They can activate different modules inside the cytosol. They can activate some adaptor protein and tyrosine kinase and finally the signaling cascade activates transcription factors in the nucleus in particular NF-kB and IRFs - These 2 transcription factors are important. NF-kB activates genes encoding for cytokines (TNF, IL-1 and IL-2 -innatw immunity, cytokines which are proinflammatory), chemokines -for monocytes, neutrophils,...-, expression of adhesion molecules important for leukocyte migration during inflammation and molecules called costimulatory molecules (important for adaptive immunity cells, CD80 and CD86). These genes are involved in acute inflammation, cell migration and stimulation of adaptive immunity (collaboration). IRFs will induce expression of type 1 interferons (𝛂 and 𝛃) and these molecules are important because they will induce an antiviral state that means that they'll block viral replication. TLR signaling is strong and proinflammatory, important during infections. Phagocytosis and killing microbes: Phagocytosis is a function characteristic of innate immunity cells called phagocytes (professional phagocytes like neutrophils and monocytes macrophages). During phagocytosis microbes are recognized in different ways before being phagocytosed. The first step is microbe recognition and microbe binding -bind the Ig bound to the microbe (the Ig recognise the microbe) and in this way microbes are opsonized (they are covered by other molecules recognized by the immune system cell -opsonins) -indirect recognition of the microbe by FC receptors. Then other receptors involved are mannose, scavenger and integrins (TLR do not mediate phagocytosis, they recognise microbes). There is redundancy of phagocytes receptors (recognise the same structure) because it gives robustness to the immune system -if there is a mutation in a receptor phagocytes have other receptors to perform phagocytosis. The second step of phagocytosis is the formation of a kind of zip around the microbe in order to internalize the complex between microbe and receptors. Then there is the formation of the phagosome (a intracellular vesicle which contains the microbe) and then the phagosome will fuse with lysosome and this fusion will lead to the killing of microbes (lysosomes are full of enzymes that will degrade the microbe). Opsonins are important for the phagocytosis process, to increase the efficiency of phagocytosis. They are soluble molecules that bind to microbic surfaces and enhance the phagocytosis capacity of phagocytes (they are IgGs, components of the compliments system - C3b and C4b- and some plasmatic proteins like fibrinogens, fibronectin, CRP). Effector functions of antibodies: a phagocyte has a receptor for the FC portion which does not bind free Ig, otherwise phagocytosis will be continuously stimulated. There is an inefficient phagocytosis mediated by other receptors but microbes are not opsonized. Free microbes are recognized by antibodies (opsonized) and these Ig bind the FC receptors enhancing the capacity of phagocytosis, an efficient phagocytosis. Activated monocytes will become macrophages which will become larger when activated. Natural killer cells are lymphocytes but are included in innate immunity because of their function. They can kill target cells. They are very efficient in recognizing cells infected by viruses; they have granules in the cytoplasm which contain cytotoxic molecules which can kill the target cell. They are efficient also in recognizing tumor cells because tumor cells and virus infected cells do not express the MHC complex and this lack is sensed by NK cells which will kill these cells (cells that lost MHC-I expression usually expressed in all cells of the body). They also have FC receptors on their surface so they can recognize Ig which are bound on infected cells. These infected cells which express on their surface virus derived antigens which are recognized by immune globulins. They can also recognize some structures and when they become activated (by macrophages, other mechanism) they release an important cytokine called Interferon type 𝛄, important to activate phagocytes and the activation of phagocytes consist also of increase phagocytosis - can directly activate phagocytes.  Innate Lymphocytes cells:-tiny round cells- there are different types based on their function and they resemble some populations of helper T-cells. ILC 1 produces interferon 𝛄 like T-helper type 1 cells, ILC 2 produces cytokinesis involved in allergies like T-helper type 1 cells and ILC 3 produces cytokinesis like IL-17 (T- helper 17) and IL-22, important in the function of international barrier. These cells were discovered recently. Complement system is formed by many types of molecules and can be activated through different pathways. It’s very important. There are main pathways: classical, alternative or lectin. Its final goal is the formation of a MAC -membrane attack complex- which will damage the membrane of the microbes or infected cells and will lead to the lysis of microbes or infected cells. The Complement system is an important system to fight infections. It also promotes inflammation (amplifies inflammation), some of the complement system molecules are strongly proinflammatory. Some of the complement system molecules -like C3b and C4b- are very good opsonins, they enhance phagocytosis’ efficiency -promote phagocytosis. - cytokines - may lead to the differentiation of some T-cells. b. Adaptive immunity intervenes later in an immune response against microbes. It becomes activated after days (depends on type of infection). B-cell and T-cell are fundamental cells for adaptive immunity. -It is mediated by lymphocytes. T-lymphocytes are more heterogeneous. The majority of them have a receptor called TCR (T-cell receptor) which can have 𝛂-𝛃 chain or 𝛄-𝛅 chain. The majority have 𝛂-𝛃 chains. They all have CD3 on their surfaces -marker of T-cells. - T helper cells are CD4+ cells, they are the majority in blood, lymph nodes and spleen; - cytotoxic T-cells, CD8+ cells do not have CD4 (and vice versa) -lower number; - Regulatory T-cells have suppressive functions and their number is low (rare cells), they have a suppress effect on the immune response; - NKT-cells have mixed characteristics between NK-cells and T-cells, all 𝛂-𝛃 chains; some specific receptors of NK-cells like CD56. - 𝛄 𝛅 T-cells, rare but important cells with 𝛄 𝛅 chains, have some characteristic of innate immunity although they are adaptive immunity (as NK-cells). They  have a fundamental role in cancer and during infections because they can recruit neutrophils. B-lymphocytes can be present in the blood but also in lymph nodes and spleen. Based on their location they are called follicular B-cells (inside the follicles) and marginal zone B-cells -perifollicular area. They produce antibodies. 06/04/2023 It’s also called specific or acquired - more specific compared to innate immunity. It is able to stimulate innate immunity. For instance some T-cells can produce interferon 𝛄 which activates macrophages (also vice versa, innate immunity can stimulate adaptive immunity -cooperation during an immune response). It cannot perform phagocytosis, it uses effector mechanisms of innate immunity stimulating it. Interferon 𝛄 stimulates phagocytes and increases phagocytosis capacity. Antigen is any kind of molecule recognized by antibodies or by T-cell receptors. Antibodies can exist in a soluble form or can be exposed on the surface of B-cells if they were not yet activated by the antigen -on the surface they resemble the function of TCRs (soluble antibodies can recognize antigens too). Adaptive immunity is more evolved, sophisticated and it’s very specific for types of antigens and microbes. It can distinguish between microbes also of the same class. Lymphocytes have a repertoire of antigens and receptors which consist of a very large number of antigens that can be recognised by the adaptive immunity -high diversity of antigens that can be recognized by adaptive immunity. It has memory, after an immune response against a specific antigen and microbes some adaptive immunity cells specific for that antigens will remain in the body and in the case of a second infection with the same antigen will react with major efficacy (remember the previous activation, recirculate in the body continuously ready to give a second immune response). It is specialized and there are 2 types of adaptive immunity: cellular/cell mediated and humoral. This specialization is due to the fact that adaptive immunity reacts against antigens/microbes anywhere - inside or outside the cells, soluble in the blood (targets are antigens)