Inmunología PDF

IMMUNOLOGY.pdf _laia_pinyol_ Immunology 1º Grado en Biomedicina Facultad de Ciencias de la Salud y del Deporte Universidad Alfonso X El Sabio Reservados todos los derechos. No se permite la explotación económica ni la tr...

IMMUNOLOGY.pdf _laia_pinyol_ Immunology 1º Grado en Biomedicina Facultad de Ciencias de la Salud y del Deporte Universidad Alfonso X El Sabio Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME IMMUNOLOGY 1. INTRODUCTION 1.1. Pathogens Microorganisms that produce a pathology, classified by the immune system by size and niche. SIZE: Virus < Bacteria < Fungus < Parasites (Helminths, protozoa, arthropods) NICHE: site where the pathogen infects. Phagocitable extracellular, intraphagosomals, cytoplasmic intracellular, and non-phagocitable extracellular 1.2. Immune system response INNATE ADAPTIVE Exists at birth, before the pathogen arrives It gets ready when the pathogen arrives and it adapts to it Quick / immediate response (1 day max) Slow (week) Low specificity, recognises Pathogen High specificity, recognises the antigen (Ag), Associated Molecular Pattern which are a particular component of the pathogen Clonal expansion, cells proliferate profusely Immunological memory 1.3. Immunopathology Due to excess (hypersensibilities and allergies) Due to defects (immunodeficiencies) Due to tolerance failure (autoimmune disorders) 1.4. Applications to biomedicine Immune system resembling therapies: vaccines and immunological therapies Immune system blockage therapies in determined diseases: immune system exacerbated illnesses, allergies and transplants. 2. PATHOGEN MICROORGANISMS 2.1. The microorganisms: commensals and pathogens Pathogens: Microorganisms that cause illness or disease a. Harmless b. Commensals / Microbiome. Colonize (birth, contact, tooth eruption) and live inside an organism without causing harm or disease. We can find them in the skin, respiratory, digestive, or genitourinary mucosa. 1 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Commensal Opportunistic - Beneficial: microbiological barriers, secrete - Detrimental antibiotic substances, help digestion… - May invade tissues - Cannot invade tissues - Depressed immune system c. Pathogens Opportunistic Strict Illness due to an immunodeficiency Virulence factors Atypical clinal symptoms Specific clinical presentations Staphylococcus epidermis, Candida… Staphylococcus aureus, Salmonella… Transmission routes: Feces-hand-mouth, Aerosols, Blood, Sexual, Maternal-fetal 2.2. Bacteria Components External membrane (Gram-) Bacteria wall → peptidoglycans Plasmatic membrane DNA → 1 circular chromosome VIRULENCE FACTORS: Non-essential components that make bacteria pathogenic 1. Capsula: evades 2. Pili / Flagellum: cell adhesion and tissue invasion 3. Toxins 4. Hydrolytic enzymes PAMP/Antigens Capsule Peptide-glycan (bacterial wall) Lipopolysaccharides (external Pili/flagellum membrane) DNA sequences: rich in GC Toxins 2.3. Virus Components Lipidic envelope Proteinic capsid DNA/RNA single or double-stranded VIRULENCE FACTORS: Non-essential components that make viruses more pathogenic. Viruses are not self-sufficient, they need the cellular metabolism to proliferate. 1. Proteins on the capsid: invasion 2. Antigenic variation: Influenza virus 3. Integration into cellular DNA 2 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Life cycle 1. Cell penetration 2. Decapsidation and DNA release 3. DNA replication and protein synthesis 4. Integration into cellular DNA (ONLY lysogenic cycle) 5. Encapsidation 6. Exit: envelope or lysis PAMP/Antigens Proteins in the lipidic envelope Capsid proteins DNA with fewer methylations, GC-rich sequences Virus proteins: retrotranscriptase, integrase 2.4. Helminths Components They can be protozoa (bacteria-like response), arthropods, or helminths (intestinal worms, specific response). Anasakis, Taenia, Ascaris… Different life forms → only one is pathogenic Trigger alternating and incompatible immune response VIRULENCE FACTORS: Non-essential components that make parasites more pathogenic 1. Cysts: forms of resistance and evasion 2. Antigenic variation 3. Hydrolytic enzymes PAMP/Antigens: Molecules of protozoa and helminths (surface glucans) Immune system against bacteria, viruses, and helminths Detects components, like PAMP or antigens, and initiates an immune response 3. INNATE IMMUNE SYSTEM Molecules, cells, tissues, and organs that we already possess at birth. First line of defense: Immediate: exists at birth, without prior exposure to the pathogen Fast Low specificity: recognizes molecular patterns associated with pathogens: PAMP. No immune memory No clonal expansion 3.1. Objectives 1. Eliminate the pathogen or control the infection 2. First response: prevent, control, and remove 3. Warn and orientate the Adaptative Immune System, necessary for activation 3 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME 3.2. Components Tissues: Barriers Avoid the invasion and proliferation of microorganisms. Physical, chemical, and microbiological. Skin The biggest organ in our body PASSIVE ROLE: Several continuous cell layers Desquamation of the surface layers/epidermis Acidity and waterproofness: fatty acids from sebaceous glands Commensal microorganisms: compete with pathogens ACTIVE ROLE: Dermis: - Mast cells: Inflammatory signals (histamines) - Macrophages: recognize pathogens, induce inflammatory signals, phagocytose… - Dendritic cells Epidermis: - Keratinocytes: recognize pathogens by their PAMP, and give inflammatory signals. They also secret peptide antibiotics. - Intraepithelial T cells: recognize common pathogens, and induce cytotoxicity… - Dendritic cells: phagocytes that recognize PAMP, and warn and orientate the adaptative IS migrating and presenting the antigen. - Conventional - Plasmacytoids. Specific role Mucosal barriers Epithelial tissue internally lines the areas of contact with the outside: eyes, ears, airways, digestive pathways, and genito-urinary pathways. Formed by: - Epithelial layer: goblet and paneth cells - Lamina propria of connective tissue: mast and dendritic cells, macrophages 4 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME PASSIVE. - Epithelium continuity - Desquamation of the epithelial surface - Mucus (goblet cells) - Commensals ACTIVE. - Epithelial cells. Recognize pathogens only by basolateral zone, “when it goes through”, and produce inflammatory cytokines. - DC, MAC and Mast cells. Perform their function below the epithelial layer - Paneth cells and commensals. Secret antimicrobial peptides. Molecules: Pattern Recognition Receptors (PRR) Immune system receptor proteins that recognize molecules of pathogens (PAMP). 1. Cellular PRR a. Inflammatory role b. Plasma and endosomal membrane, cytoplasm c. Membrane and endosomal PRR: Phagocytes (DC, MAC, Monocytes, Neutrophils), skin keratinocytes, mucosal epithelial cells, mast cells d. Cytoplasmic PRR: all cell types! 2. Soluble PRR a. Opsonization role (opsonins: soluble proteins recognize and attach to pathogens) b. Blood, secreted by the liver c. Acute Phase Proteins, Mannose Binding Lectins d. PRR-PAMP recognition induces opsonization for phagocytosis PRR also recognize cell injuries: Danger Associated Molecular Patterns. For example, excess cell or tissue damage appears as danger signals, and PRR-DAMP induces inflammation. Pathogen Associated Molecular Patterns. Components of the pathogen with specific features: - Essential for pathogen survival - Same PAMP present in many pathogens → few, not diverse, not specific… - Each type of pathogen has several PAMP - Our cells have several PRR that bind to PAMP (Toll-like Receptors: TLR 1-9) The complement system Set of blood proteins that act in coordination, secreted by the liver. Activated when they recognize the pathogen Cascade, one member activates the other Zymogens: inactive precursors are broken in two, and activate It has many roles: 1. Opsonization (3b) 2. Inflammation (a fragments) 3. Lysis (C9) 5 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Cytokines Intercommunicate immune cells, “messenger molecules”, giving migration (different cell types), activation (NK cells), or inhibition (T lymphocytes) signals. Cells Phagocytic Cells Recognize pathogens and induce inflammation Phagocytosis of the pathogens Destroy the pathogen Monocytes and macrophages Monocytes circulate through blood, and get converted to macrophages when they extravasate to tissues. FUNCTIONS Secrete cytokines. Guide Adaptive IS and activate NK Present antigens. Repair tissue. Phagocytose apoptotic cells, and secrete growth factors. TYPES (tissue): Kupffer cells → Liver Microglia → Nervous tissue Osteoclasts → Bone tissue Alveolar macrophages → Lung Macrophages develop into different profiles depending on what they encounter: a. PAMP, inflammatory cytokines → classical: phagocytosis and inflammation b. Apoptotic cells, helminths, tumors → alternative: inflammation inhibition, tissue repair Neutrophils Granulocytes and polymorphonuclear leukocytes, in blood. They extravasate to tissue when there is inflammation. Although their half-life is only 24h, they are very abundant (70% leukocytes). OTHER DESTRUCTION WAYS - Degranulation: delivery of granule contents which create an antimicrobial media - Release of NETs: Neutrophils’ Extracellular Traps made of chromatin and enzymes 6 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Dendritic cells Formed in the bone marrow, we can find them in the skin. They migrate to the adaptive immune system’ (lymphoid) organs to present the antigen and warn and guide the response. a. Conventional DC (majority) b. Plasmacytoid DC (minority). Play a specific role against intracellular pathogens Antiviral Cells Natural killer cells We can find them in the lymph nodes and circulating in blood Kill infected / tumoral cells → liberate granules with perforins Collaborate with macrophages, using cytokines and IFN-γ Plasmacytoid DC Boost the action of natural killer cells, liberating cytokines (IFN-α) when activated by PAMP. 3.3. Mechanisms Inflammation Process of attraction and migration of immune system cells and proteins to infectious sites. Cells’ PRR recognize PAMP and release inflammatory cytokines (TNF-α, IL-1). Mast cells secrete histamines (increases vessels’ permeability), and the complement systems are activated, releasing inflammatory fragments (C3a, C5a). Stages 1. Blood vessel wall activation (endothelial cells). Permeability induction, expression of chemotactic and adhesion signals. 2. Chemotaxis. Attraction of leukocytes by chemical signals 3. Migration through the vascular endothelium a. Rolling by weak adhesion. Adhesion molecules, “sticky fingers”: selectins b. Firm adhesion to the endothelium. Adhesion molecules: integrins c. Diapedesis or extravasation through the vascular endothelium: integrins Integrin blockade is an anti-adhesion therapy in Multiple Sclerosis, an auto-immune disease. DC, intraepithelial T cells, and MAC arrive to the tissue before inflammation, while NK cells, neutrophils, and monocytes arrive after inflammation. Clinical consequences depending on the type of inflammation - Acute local: sticks to the infection site Heat, redness, tumor/swelling, pain, loss of function Pneumonia, pulmonary edema - Acute systemic → septic shock: inflammatory cytokines are overproduced, reaching all tissues. Septic shock: Low heart rate, lower blood pressure (clots), metabolic disorders. It is treated with anti-inflammatory drugs and antibiotics. 7 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Brain → fever Liver → Secrete substances (soluble PRR; Acute Phase Proteins), biomarkers Bone marrow → generate more immune system cells - Chronic: different pathogen types, slow but extended inflammation, several spikes of acute inf. Phagocytosis Process of ingestion and clearance of extracellular pathogens. 1. Adhesion. Occurs through receptors on the cell surface (PRR) which can bind to pathogens and activate the cytoskeleton to coat them. a. Plasma membrane PRR b. Opsonin receptors: soluble PRR, Complement, antibodies c. Scavenger, C-type lectin… 2. Ingestion. The receptors must engage the cytoskeleton to coat and engulf the pathogen. Phagosome generation 3. Elimination of the pathogen. The phagosomes fuse with lysosomes, generating phagolysosomes, where the pathogen is killed: a. Oxygen-independent (vary between phagocytes) i. Degradative enzymes ii. Antimicrobial peptides b. Oxygen-dependent: respiratory burst i. Reactive oxygen species: ROS ii. Reactive nitrogen species: RNS Defects in this process cause Chronic granulomatous disease, where granulomas and abscesses, that contain phagocytes surrounding the pathogen, are formed. Neutrophils are particularly affected and it increases the susceptibility to bacterial and fungal infections. NK cell cytotoxicity Process of elimination of infected or tumor cells 1. Detection of infected cells. Using NK receptors (activators and inhibitors of cell death), the altered cells express molecules that bind to activating Receptors. 2. Destruction. Delivery of granule content: a. Perforins. Form a pore in the membrane of the infected cell b. Granzymes. Enter the cell and initiate the apoptosis cascade: programmed cell death. 5. ADAPTIVE IMMUNE SYSTEM GOALS & CHARACTERISTICS 1. Detect specifically the pathogen. B and T lymphocytes 2. Specialize the response to eliminate efficiently. T cells specialize in differentiating to several profiles over different pathogens. 8 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME 3. Expand the components. T and B cells start a clonal expansion of specific cells. 4. Memorize the response. 1st exposure makes the 2nd response more efficient. 5. Only attacks the foreign (processes eliminate T and B cells that recognize the self). How does the Adaptive IS monitors de body? PROBLEMS SOLUTIONS The organism to be There are specialized tissues that concentrate Ag: lymph defended is big nodes, spleen… There are scarce defense Naive lymphocytes arrive, contact the Ag, proliferate, and cells differentiate to effector and memory lymphocytes Places far away from The effector and memory cells migrate to the infected tissues infection must be defended 5.1. Components Lymphocytes Immature Mature (Naive) Effector Tαß TCD4 - Diverse TCR Helper: TH TH1: virus and bacteria → NK & MAC (95%) - Ag presented by TH2: helminths → eosinophils & mast DC cells TH17: bacteria → neutrophils THF: in the lymph nodes, B cells TREG: inhibit other T cells → DC TCD8 Cytotoxic: Against intracellular pathogens CTL Tγδ (5%) Tγδ - Few TCR LTγδ - Frequent Ag - Intraepithelial T cells 9 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Immature Mature (Naive) Effector / Plasma cells B2 B2F - 95%, lymph nodes - Produce antibodies - Diverse BCR - Rich cytoplasm and rough - Collaboration with THF endoplasmic reticulum - High antibody affinity. IgG - Stop expressing BCR B2MZ - Spleen / Cavities: peritoneal, pleural, heart B1 B1 - BCR frequent pathogens → not diverse - Lipids, protein, and glucids Ag - Low antibody affinity. IgM F = Follicular. Region of the lymphoid organs Receptors, antibodies, and cytokines Antigen Recognition Receptors (TCR and BCR) - Provide the SPECIFICITY with which T and B cells recognize Ag - Each lymphocyte expresses one type of Receptor on it´s surface - Each Receptor and lymphocyte recognizes a different Ag - TCR recognizes peptidic Ag presented by DC, while BCR recognizes peptidic and nonpeptidic Ag, which are soluble Antibodies - Secreted by effector molecules of B cells (Plasmatic Cells) - Specifically recognize Ag from the pathogen - They have the same SPECIFICITY as the BCR - Eliminate the pathogen by neutralization, opsonization or activating the Complement system Cytokines Messenger molecules that provide communication between cells. a. From DC → guide the appropriate response b. Of the newly activated T cells → clonal expansion c. From the effector T cells → help other cells to eliminate the pathogen 5.2. Organs Primary Generate and mature immune cells: hematopoiesis (generation of blood cells) 10 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Bone marrow Found in the medullar cavity of flat bones, where hematopoiesis takes places Thymus Bilobed organ located in the chest, T cells arrive from the bone marrow to mature. We can find T cells (cortex) and Ag’s presenting cells (medulla). Capsule → Layer of connective tissue Trabecules → Connective tissue septum Cortex → Rich in T & epithelial cells Cortex - medullar frontier → Rich in DC & epithelial cells Medulla → Rich in DC, epithelial cells (MEC) & MAC Secondary Meeting point for Ag and lymphocytes for activation and organize the adaptive response Lymph nodes Trap Ag from tissues (lymphatic system) Structure: Capsule Subcapsular and trabecular sinus: MAC Cortex / follicle: B cells and follicular DC Paracortex: T cells and DC Medulla: All cells Spleen Traps Ag from blood Eliminates aging cells Structure: Capsula and trabecules Red pulp: MAC and aged erythrocytes White pulp: around the arteriole ○ Marginal zone with MAC and LB2MZ ○ B cell follicular area ○ Periatherioral T cell sheath We can live without the spleen, but there is an increased susceptibility to infection with 3 pathogens: Pneumococcus, Hemophilus and Meningococcus Mucosal associated lymphoid tissue Types: ○ NALT: Naso-pharyngeal Tonsils and adenoids ○ BALT: Bronco-pulmonary ○ Placas de Peyer in the intestine ○ GALT: Genito-urinary Structure ○ Follicular area with few T cells and DC and abundant B cells ○ M cells: they pass the Ag through the epithelial layer 11 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Lymphatic system System of vessels and nodes that collect the excess of interstitial fluid: 1. Collects Ag and DC from tissues to lymph nodes 2. Transports lymphocytes from lymph nodes to the blood through the chest duct 3. Transports lipids from the diet Lymphocytes in the circulatory system Lymphocytes: Lymph → blood (irrigates organs) → lymphocytes extravasate B and T cells extravasate from blood to lymph nodes continuously. In addition: All leukocytes extravasate from blood to infected tissues during inflammation B and T memory cells are continuously extravasated to peripheral tissues We can find the lymphocytes in the lymphatic and circulatory system: LYMPHOCYTIC RECIRCULATION Transport of T and B cells between blood vessels and lymph nodes 1. Tissue antigens are transported by the lymphoid vessels to lymph nodes 2. T and B cells extravasate from blood to lymph nodes a. If T and B cells don’t encounter an Ag they continue recirculating 3. Activation and differentiation to effector cells 6. PROCESSING AND PRESENTATION OF ANTIGEN TO T CELLS 6.1. Antigen presentation Exposure on the cell surface of a pathogen’s peptide peptides to a T lymphocyte. Self non-pathogen’s peptides are also exposed, but T cells have the ability to recognize only the foreign ones in a specific way. 6.2. Ag for a T-cell Peptide that attaches to the T-cell receptor and induces a response. Any cell can present intracellular peptides, but there are some that also present extracellular ones (APC): 1. DC. Take the Ag to naive T cells and activate them 2. MAC. Retain the Ag and present it to effector T cells 3. B lymphocytes 4. Thymus epithelial cells 12 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Why are DC the most effective cells to activate naive T cells 1. Privileged location. On entrance sites, like epidermis and mucous membranes 2. Capture of Ag. a. Phagocytosis → ingestion of large particles through receptor molecules b. Endocytosis → ingestion of small particles through receptor molecules c. Macropinocytosis → ingestion of fluids and small molecules 3. Maturation. Capture changes the expression of R a. Worse Ag capturers b. Migrate c. Best Ag presenters 4. Migration to the lymph nodes. Released from the entrance site, access the lymph vessels and migrate to the lymph nodes. 5. Guidance of the T cells response. Collect information in PAMP, DAMP, and cytokines to secrete other cytokines to activate and guide T cell differentiation. Macrophages Retain Ag in the entrance sites of infection, and present them to effector T cells, triggering MAC B cells In the lymph nodes: capturing and retaining Ag, present them to THF, triggering B cells 6.3. Ag Presenting pathways HLA are the molecules responsible for collecting the Ag inside the cells to present it on the surface of T cells. Ubiquitin breaks pathogen Phagocytosis apoptotic body Phagocytosis Proteosome forms Ag Phagolysosome Endolysosome Ag gets into ER through TAP Proteosome forms Ag Ag vesicle Ag attaches to a HLA-I Ag gets into ER through TAP Blocked HLA-II (chip) HLA-I vesicle → membrane Ag attaches to HLA-I HLA-II rich compartment Present to an effector CTL HLA-I vesicle → membrane Present to a naive TCD4: Present to a naive TCD8 MAC/B cells: TH, DC: naive 13 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME 6.4. HLA molecules Function and structure Human Leukocyte Ag: molecules on the surface of cells responsible for presenting Ag to the T cells. HLA-I Intracellular pathogens to any type of cell STRUCTURE: Dipeptide α and ß2-microglobulin chains ○ α chain: area for Ag binding ○ α3 region: CD8 receptor binding Ag-HLA BINDING - Peptides of 8-10 aa - Slit ends closed Each HLA-I molecule can bind and present a set of Ag, which have a couple of similar aa. That pair makes up the Ag's "anchor sites" that bind to HLA HLA-II Extracellular pathogens to professional APC STRUCTURE: Dipeptide α and ß chains ○ α and ß chains: area for Ag binding ○ ß2 region: CD4 receptor binding Ag-HLA BINDING - Peptides of 20-30 aa - Opened slit ends Each HLA-II molecule can bind and present a set of peptides of variable length. They have 3 or 4 "anchor sites", preserved between different peptides With few HLA many antigens are presented: HLA also binds the TCR, very specifically. HLA molecules expression There are 3 HLA-I subtypes (A, B, C) and 3 HLA-II subtypes (DR, DQ, DP), with many subtypes each: greater the chance of presenting different pathogen peptides = increased defense. 14 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Each individual expresses 1 or 2 molecules (mother & father) of each HLA subtype, but these are different between individuals: POLYMORPHISM HLA genes A maximum of 6 HLA-I and 12 HLA-II are expressed, forming the halotype. Codominance Transassociation: HLA-II molecules have 2 binding sites (α and ß) Each individual expresses many genes: small variations between individuals: ○ Polygenism ○ Mutations due to the incorrect alignment between similar genes: gene conversion Transplants rejection of HLA Most proteins present in the same species are identical, only some are polymorphic (HLA). Each individual has their ID of HLA proteins, the halotype. Rejection at the molecular level TCR can only recognize and bind to self HLA. If the HLA is different, our body will reject it: Indirect presentation (99%): HLA is processed like a protein and presented as an Ag to T cells, initiating an immune response. Direct presentation (1%): Initiated by the donor cell (HLA peptide), which is recognized by the TCR, but rejected. Rejection at the clinical level Depending on the time after transplantation: a. Hyperacute → immediate b. Acute → days or weeks c. Chronic → years They differ in the immune mechanism of rejection and in the clinical consequences: the immune system removes the transplanted organ. 6.5. Surveillance of HLA by NK cells Contact of NK with any cell to monitor its status, by recognizing: a. Normal HLA → inhibitory signals b. HLA with alterations → activation signals, less inhibitory signals When another NK tries to recognize the cell, if there are activatory signals or less inhibitory signals, it will be activated and start the process of cytotoxicity. 15 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME 8. ANTIGEN RECEPTORS: BCR and TCR 8.1. Ag and Ag receptors Antigen: molecule from the pathogen that induces an immune response, which is initiated by the binding of the Ag to the receptor. We have TCR, BCR and antibodies (Ab). 1. High specificity → distinguish between two Ag that only differ in one aa 2. Huge diversity → an individual possess up to 1020 several BCR and TCR TCR BCR Antibodies Antigens Peptides presented by APC Soluble → do not require APC Proteins, lipids, polysaccharides… Epitopus: Ag region in contact with the BCR Info At the beginning of the In effector response adaptive response Soluble mol. secreted Membrane receptors by activated LB Recognizes the Ag and Recognize, eliminate endocytoses it the Ag Structure Anchored to the membrane Tetrapeptides: two heavy and two light chains Dipeptide: α and ß Fab region: unique for each BCR, antigen binding In each chain: Fc region: different for Ab and BCR - Variable unique region: Fc region Ag binding Membrane anchorage Binds Fc receptors and - Constant region complement proteins Binding Adhesion between TCR and Collaboration with Fab region Very HLA-Ag is weak, it requires effectors T cells specific, other membrane molecules: 1. BCR endocytoses deficient - Co-Receptors CD4 or the Ag and presents to activate CD8 → bind to HLA-I or it T and B HLA-II 2. T cell recognizes it cells: - Adhesion molecules: and activates the B need help integrins cell The cytoplasmic region is Binding of various very short → protein binding signals and crosslinking to send activation signals: - TCR Complex: TCR α, ß + CD3 (γ, δ, ε, ζ) 16 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Antibodies There are 5 types (isotypes) of Antibodies / immunoglobulins, depending on their Fc region: IgG > IgA > IgM > IgD > IgE Ab-Ab receptor (Ab-Fc region) 1. Opsonins for Phagocytosis: Bind to Fc Receptors of phagocytes 2. Recognized by NK cells: Bind an activator Fc Receptor of NK to induce citotoxicity 3. Recognized by eosinophils / mast cells: Bind to Fc Receptors in these cells to induce degranulation and cytotoxicity against helminths 4. Use the Fc region to activate the complement system Linkage Some antibodies are linked by their Fc region: IgM 10 binding sites Polyvalent Very high avidity IgA 4 binding sites Bivalent High avidity IgG 2 binding sites Monovalent Low avidity They can bind several Ag simultaneously: multivalence interactions Affinity: strength of each Ag-Ab union Avidity: binding to several Ag at once, increasing in multivalence interactions ○ An Ab with only 2 binding sites can interact bivalently Complexes Ag excess = Small complexes ○ Free Ag displace Ag-Ab complexes ○ Beginning of the response Equivalence = Large complexes ○ Harmful → Rheumatoid arthritis, Glomerulonephritis ○ Make deposits Ab excess = Small complexes ○ Breakage of the Ag-Ab complexes ○ End of the response 9. DIVERSITY OF ANTIGEN RECEPTORS How can we defend ourselves from different pathogens? With different BCR/TCR Do we have so many genes? No, They wouldn't fit in the nucleus of the cell. There are many gene segments that encode for the variable regions of the TCR and BCR chains Genes of the Ag’s receptors There are 3 types of gene segments in each variable region of each receptor chain: V: Variability D: Diversity J: Junction 17 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME TCR Alpha and Beta (with D segments) chains BCR Light and Heavy (with D segments) chains Diversity mechanisms Segment recombination Segments V, D and J are recombined with each other: Light: V-J Heavy: D-J and V-DJ Irregular binding of segments Nucleotides are added and removed at the edges between the segments: filling (P nucleotides) and new (N nucleotides) Adding and removing of nucleotides - Recombination enzymes (RAG) cut and generate a DNA loop - RAG cut at the end of each DNA chain - Palindromic sequences are generated and filled with P nucleotides - New N nucleotides are added - DNA chains are associated - Nucleotides are eliminated Chain association 1. One chain is recombined a. Chain H → BCR b. Chain β → TCR 2. The other a. Chain L → BCR b. Chain α → TCR 3. They associate to express the full Receptor 4. Each lymphocyte associates different chains that have been recombined differently. Diversity generation phases Phase 1: Proliferation → Pro-T cell Phase 2-3: Recombination and expression 1st chain (β chain) → Pre-T cell* Phase 4: Proliferation → Pre-T cell Phase 5-6: Recombination and expression 1st chain (α chain) → Immature T cell** *1st control: many lymphocytes die (2 out of 3) 1. Gene recombination can lead to an erroneous exon: a. Doesn't translate correctly into protein → reading phase is changed b. Results in proteins with a different structure 18 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME 2. The 1st receptor chain is not expressed on the surface. It fails to pass to the next phase. 3. The recombination of the other allele coding for H or coding for β begins. If it's not expressed either, the B or T cell dies. **2nd control: selection TYPES OF RECEPTORS GENERATED Receptors that recognize pathogens _ Receptors that recognize their own proteins _ Receptors that recognize our presenting molecules: HLA _ Receptors that do not recognize our HLA presenting molecules _ Receptors that never recognize pathogens _ The generation of diversity and the selection of T cells happens in the thymus 1. Cortex. Proliferations and recombinations → DIVERSITY GENERATION 2. Cortico-medullary area. Selection of useful T cell → POSITIVE SELECTION a. The cortico epithelial cells (CEC) of the thymus are APC that process their own proteins and express HLA-I and HLA-II i. If the TCR of the new T cell recognizes its own HLA, the T cell survives ii. If the TCR does not recognize its own HLA, T cell dies by apoptosis b. During positive selection T cell differentiates into TCD4 or TCD8 c. The immature T cells express the two co-receptors: Double Positives (CD4+ CD8+) i. If the TCR binds HLA-I, CD8 is selected ii. If the TCR binds HLA-II, CD4 is selected d. T cell expresses a single co-R: Single Positive 3. Medulla. Self-reactive T cell selection → NEGATIVE SELECTION a. T cells move into the medulla of the thymus b. Medullary epitelial cells (MEC) and DC express tissue specific proteins, which are processed and presented as own peptides c. Selection i. Little or no interaction: T cell doesn't recognize self HLA → Death ii. Intermediate interaction: T cell recognizes its own HLA, but not self peptides → Survival iii. Very strong interaction: Self-reactive cell → Death 10. T LYMPHOCYTES’ ACTIVATION Pre-activation phases of T cell 1. DC uptake Ag on skin or mucous membranes 2. DC leave the skin and migrate to the lymph nodes 3. DC mature and improve their ability to present Ag 4. Naïve T cell activation 5. T cells extravasate from the blood to the lymph nodes 19 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME Recognition phase T cells go from blood to lymph node → DC in the paracortex T cells "scan" DC through contacts with adhesion molecules: integrins They might encounter their specific Ag ○ Ag is not found: unstable contact → T cell is released ○ Ag is found: stable contact (immunological synapse) Activation phase DC activate T cells using 2 signals: 1. Specific presented Ag from DC bind to the TCR from the T cell 2. Co-stimulatory molecules (CD80, CD86…) on the DC bind to the CD28 from the T cell. a. Expressed on DC during maturation after recognizing pathogenic PAMP → increased efficiency in Ag presentation. Recognition by the innate IS is essential to activate T cells a. PAMP (RRP) → expression of co-stimulating molecules b. 1st signal (Ag) + 2nd signal (co-stimulatory) → i. T cell ativation ii. Clonal expansion iii. Differentiation In the absence of the costimulus: 1. Immature DC, don’t express co-stimulatory molecules: a. Self-peptide presentation (they haven’t recognized PAMP) b. Doesn’t activate the T cell c. Permanent inactivation of T cell: anergy 2. Anergic T cells don't respond, they tolerate self Ag How we battle self-Ag: A. Negative selection: self-reactive T cells die (apoptosis), but a few escape B. DC that don’t recognize PAMP, don’t express costimulatory molecules. Presentation of self Ag without 2nd signal, induces anergy. Clonal expansion When activation is correct T cells change: 1. Synthesis and secretion of IL-2 cytokine 2. Increased expression of IL-2 R → IL-2 is autocrine: acts on the IL-2 R of the same T cell 3. T cell responds to IL-2 with clonal expansion a. Several proliferation cycles over days b. Each specific T cell results in 10 000 000 T cell differentiation: helper or cytotoxic DC activate T cells, and inform about the type of pathogen infected with cytokines a. TCD4 cells → helper T cells: TH1, TH2, TH → CD40 Ligand (CD40L): help b. TCD8 → cytotoxic T cells: CTL → Fas Ligand (CD40 L): cytotoxicity 20 a64b0469ff35958ef4ab887a898bd50bdfbbe91a-9976081 Reservados todos los derechos. No se permite la explotación económica ni la transformación de esta obra. Queda permitida la impresión en su totalidad.  Laia Piñol Olabegoya 1º BME TCD4 receptors: 1. Naive T cells → CD28 2. Activated T cells → RIL-2 + CD28 3. Helper T cells → CD40L + RIL-2, CD28 4. Exhausted / Inhibitory T cells → CTLA-4 + CD40L, RIL-2, CD28 Peculiarities of CD8+ T cell activation 1. DC capture intracellular Ag without being infected: cross-presentation pathway 2. DC need a more intense coestimulus to be activated 3. CD8+ T cells need more co-stimulus: a. DC express co-stimulatory molecules when detecting PAMP, but it is not enough b. They need the additional collaboration of TH cells through