ilovepdf_merged (1)_compressed.pdf

Stem Cell: Cells with ability to self renew and differentiate to diverse cell types Embryonic Stem Cell: Pluripotent cells with capacity to generate all cell type in organism Adult Stem Cells (Somatic Stem Cells): Organs harboring stem cells, that can only differentiate to diverse cell types o...

Stem Cell: Cells with ability to self renew and differentiate to diverse cell types Embryonic Stem Cell: Pluripotent cells with capacity to generate all cell type in organism Adult Stem Cells (Somatic Stem Cells): Organs harboring stem cells, that can only differentiate to diverse cell types of a particular tissue. Example: Hematopoietic Stem Cells (HSC), Mesenchymal Stem Cells (MSC) in bone marrow (dedifferentiation, trans-differentiation, IPSc) Hematopoietic Stem Cell (HSC): Cells that can differentiate into all types of blood cells. Present less than 1 in 5x105 bone marrow cells Generally quiescent, but in need displays immense proliferative ability. Hematopoeisis: Process of HSC differentiation into different blood cells Rate of Hematopoeisis as well as production of specific cell lineages is environment deoendent Human Blood Corpuscle Types Hematopoiesis Overview CMP CLP  Cells of Myeloid-erythroid Lineage lineage Cells of this lineage act as first responders to Infection Common Myeloid Progenitor (CMP) differentiates into: Erythroid Progenitor Erythrocytes Platelets Myeloid progenitor Granulocytes Neutrophils Basophils Eosinophils Mast cells Myeloid Antigen Presenting cells Monocytes Macrophages Dendritic cells  Granulocytes Neutrophils: Life span of few days Dominant first responders to infection and major cellular component of pus Leukocytosis: Number of circulating neutrophils significantly increase during infection Recruited to site of infection in response to chemokines secreted by innate cells Kills by phagocytosis as well as release proteins with antimicrobial and tissue remodeling effects Basophils: Contains large granules filled with basic proteins (Histamine is best example responsible for vasodilation) In response to circulation antibodies, basophils release granule contents Like neutrophils can secret cytokines Has role in allergies Mast cells: Found in variety of tissues including skin, digestive, genitourinary tracts etc. Released into blood as undifferentiated cells, but differentiate in blood. Performs mostly similar functions to basophil Eosinophils: Phagocytotic cells, that can also secrete cytokines that can regulate lymphocytes Thought to play important role against defense of multicellular organisms. Also contribute to asthma and allergy symptoms  Myeloid Antigen-Presenting cells Group of phagocytic cells that have antigen presentation ability Act as bridge between innate and adaptive immunity Monocytes: Heterogeneous group of cells that differentiate into diverse tissue resident phagocytic cells Can be categorized into two broad categories: Inflammatory monocytes and Patrolling monocytes Inflammatory monocytes enter tissue in response to infection whereas Patrollling monocytes lie along blood vessel that act as reservoir of tissue resident monocytes Macrophages: Tissue resident monocytes Tissue resident macrophages play role in repair and regeneration Others are inflammatory macrophages that can engulf pathogens as well as act as APC Examples are Osteoclasts, Microglial cells and Alveolar Macropahges Dendritic cells: Arise from Both myeloid and Lymphoid lineage Cells have large membranous extension like nerve cells, that help it to have increased surface area Most efficient activator of T cells Different from follicular dendritic cells  Cells of Lymphoid lineage Lymphocytes- Key Players to adaptive immunity Represent 20-40% of circulating lymphocytes in blood and 99% of blood cells of lymph Broadly subdivided into 3 Types: 1. B cells 2. T cells 3. Natural Killer cells (NK Cells) Unlike other WBCs, they are difficult to differentiate morphologically Usually differentiated by the signature of Surface proteins expressed on the surface, often referred as Cluster of Differentiation (CD) In addition to CD signature on surface, B and T cells Express BCR and TCR respectively  Cells of Lymphoid lineage B- Lymphocytes Site of maturation: Bursa fabricus in Birds and Bone marrow in mammals Mature B-cells are distinguished from other lymphocytes by the presence of BCR. BCR and B-Cells maturation to be read in detail. Mature B cells differentiate to Plasma cells (effector; antibody secreting) cells, whereas few develop into Memory cells T- Lymphocytes Site of maturation: Thymus Express TCR on its surface Differentiated into 3 Types: 1. T- Helper Cells 2. T cytotoxic cells 3. T regulatory cells  Cells of Lymphoid lineage T cytotoxic Lymphocytes (TC) Express CD8 on its surface that recognizes antigen-MHC1 complex, after which they activate to form effector cells called Cytotoxic T-Lymphocytes (CTL) Functionally eliminate infected cells, cancer cells, foreign graft etc. T helper Lymphocytes (TH) Express CD4 on its surface that recognizes antigen-MHCII complex, after which they proliferate to T- Helper Type 1 (TH1) or T- Helper Type 2 (TH2) cells TH17- secrete IL-17 and play role in cell mediated immunity to provide defense against Fungi T follicular Helper Cells (TFH) play role in B-cells development in germinal centers. T Regulatory Lymphocytes (TREG) Inhibit an immune response Identified by presence of CD4 and CD25 on cell surface and expression of FoxP3 transcription factor Natural TREG- Arise during maturation in Thymus from auto-reactive T cells Induced TREG- Arise at the site of immune response in response to antigen  Cells of Lymphoid lineage Natural Killer cells (NK cells) No antigen specific receptors on surface and considered part of innate immune response Comprise 5-10% of circulating Lymphocytes Express surface marker NK1.1 and contain cytotoxic ganules Kill abnormal cells (tumour cells, virus infected cells), by recognizing the absence of MHC-1 molecules on target cells. Also express receptor for Immunoglobulins that help it to recognize infected cells. NKT cells Share feature of T cells and NK cells Like T cells they express TCR (some even express CD4), hat recognize specific lipids/Glycolipids presented on CD1. Like NK cells, they also have surface antibody receptors and release contents of cytotoxic granules to kill cells.  Innate Immunity-Overview Physical barrier - epithelial layers of skin, mucosal and glandular tissue Chemical barrier – Acidic pH, Antimicrobial peptides, enzymes etc Cellular Innate response – Phagocytosis, Inflammation Physiochemical barriers to infection Antimicrobial Proteins and Peptides at epithelial surfaces Antimicrobial Peptides Collectins Innate immune response to infection Phagocytosis-Overview  PAMPs and PRRs PAMPs (Pathogen Associated Molecular Patterns)/MAMPs (Microbe associated molecular patterns: Conserved motifs usually present in many copies on the surface of pathogens. PAMPs get recognized by conserved receptors called as PRRs (Pattern Recognition Receptors) DAMPs (Damage-associated Molecular patterns): Components of dead/dying cells that get recognized by PRRs and usually get cleared by Phagocytosis.  Innate Opsonins Innate Opsonins: Soluble proteins of innate immunity that bind to conserved, repeating components on microbial surface and enhance phagocytosis (Opsonization). Also termed as soluble pattern recognition proteins Examples: Surfactant Collectin Protein- SP-A and SP-D in blood and mucosal secretions of lungs, bind to microbes and get recognized by CD91 opsonin receptor. MBL (Mannose Binding Lectin) in blood and respiratory fluids L-Ficolin in blood bind to acetylated sugars including streptococcal bacteria Complement component C1q that bind to bacterial cell wall components as well as viral proteins CRP (C-reactive protein) recognizes phosporylcholine and carbohydrates of pathogens and then bind to FcRs.  Phagocytosis-Microbial Killing Microbes interbalised into a phagosome, fuse with lysosome to form phagolysosome Phagolysosomes contains an arsenal of anti-microbial agents that kill the microbe. The include: a. Anti-microbial Proteins and Peptides (incudig defensins and cathelicidin) b. Low pH c. Acid activated Hydrolytic Enzymes (lysozyme and other proteases) d. Molecules that Mediate oxidative attack (ROS & RNS) Respiratory Burst: Metabolic process that enhances oxygen uptake by several fold to support RNS or ROS production ROS and RNS alter the microbial molecules by oxidation, hydroxylation, chlorination, nitration and S-nitrosylation along with formation of sulphonic acids and destruction of Iron Sulphur clusters in proteins Chronic granulomatous disease (CGD)- defect in NADPH Phagosome oxidase that destroys its ability for ROS generation  Toll Like Receptors (TLRs) First Family of PRRs to be discovered and characterized. (weird in German- Toll, discovered first in drosophila) Volhard, Eric Wieschaus and Edward B. Lewis were awarded Nobel prize in Physiology & Medicine in 1995 for its discovery Toll Like Receptors (TLRs) LRRs: Repeating segments of 24-29 aminoacids with signal sequence LxxLxLxx that make up the horse shoe shaped extra cellular Ligand binding domain of TLR TIR Domain: Toll/IL-1R domain that interacts with TIR domains of other members of the TLR signaling Pathway Binding of Ligand induces Dimerization Toll Like Receptors (TLRs) Toll Like Receptors (TLRs)-Signalling Signal transduction pathway activated by TLR is determined by TLR type an the initial adaptor protein involved TLR-adaptor interaction occurs through TIR domain Adaptor Proteins: MyD88 (Myeloid differentiation factor 88) TIRAP (TIR-domain containing adaptor Protein) TRIF (TIR domain containing adaptor-inducing IFN-β factor) TRAM (TRIF-Related Adaptor molecule) MyD88 Signalling Pathway: All TLRs except TLR3 and endosomal TLR4 TLRs that bind to extracellular ligands activates NF-κB and MAPK pathways Endosomal TLRs, can also activate IRFs as well as NF-κB and MAPK TRIF signaling pathway: TLR 3 and endosomal TLR 4  Inflammatory Response When physical barriers of innate immunity are damaged, innate immunity can mount an inflammatory response characterized by vasodilation and and local edema  PRRs CLR (C-Type Lectin Receptor) Membrane receptors expressed on Monocytes, Macrophages, Dendritic cell, Neutrophil and Lymphocytes Recognize carbohydrate components on pathogensand allergens Signalling events may promote phagocytosis or synthesis of Interferons, chemokines etc RLRs (Retinoic acid Inducible gene-I-Like receptors) Soluble cytoplasmic PRRs and act as sensors for viral infection Activates IRF3, 7 and NF-κB to express IFNs α & β and other chemokines antimicrobials NLRs (Nod Like receptors and Nucleotide Oligomerization domain/leucine-rich repeat containing receptors) Cytosolic PRRs activated by intracellular PAMPs or DAMPs. Major Role in Innate immune and inflammatory respobnse 3 major groups based on Domain architecture NLRC (with Caspase Recruitment Doamin, CARD), NLRB (with Bacculovirus inhibitory repeats, BIR), NLRP (with Pyrin domains) 23 in Human and 34 in Mouse and mostly uncharacterized. Sone NLRs assemble with other proteins to activate protease that can convert large precursor inactive cytokines to active forms. These NLRs comples with other proteins and proteases is calles as inflammasome Ex: NOD1 and 2 recognize degraded bacterial cell wall and signal interferon response.  Organs of the Immune system (Intro) Primary Lymphoid organs: Sites where immune cells develop form their immature precursors. Example: Bone marrow and Thymus. Secondary Lymphoid Organs: Sites where the mature antigen specific lymphocytes encounter the antigen and begin their differentiation. Examples: Spleen, Lymph nodes, Specialized sites in gut (GALT) and mucosal surfaces (MALT).  Primary Lymphoid organs Bone Marrow: Found in the center of bones (e.g., femur, pelvis). Production of immune cells, including B cells and T cells. Thymus: In the chest behind the sternum. Maturation and differentiation of T cells  Secondary Lymphoid organs Lymph Nodes: Found throughout the body, interconnected by lymphatic vessels. Filter lymphatic fluid; site of immune cell activation and interaction. Spleen: Located in the upper left abdomen. Filters blood; site of immune response to blood-borne pathogens; stores blood cells. Mucosa-Associated Lymphoid Tissue (MALT): Locations: GALT (Gut-Associated Lymphoid Tissue, e.g., Peyer’s patches, appendix), BALT (Bronchus-Associated Lymphoid Tissue, e.g., Tonsils); NALT (Nasopharynx-Associated Lymphoid Tissue) Defense against pathogens at mucosal surfaces (respiratory tract, gastrointestinal tract, etc.).  Other Organs and Tissues Skin: First line of defense; contains immune cells (Langerhans cells). Liver: Filters blood; involved in immune responses like production of acute phase proteins, complement proteins and cytokines.  Organs that act as barriers Skin and Mucous membranes are the first line of defense against germs entering from outside the body. They act as a physical barrier with support from the following: Antibacterial substances can kill germs right from the start. A certain enzyme found in saliva, the airways and tear fluid destroys the cell walls of bacteria. Mucus in the bronchi helps trap many of the germs we breathe in so they can be moved out of the airways by hair-like structures called cilia. Stomach acid stops most of the germs that enter the body in the food we eat. Harmless bacteria on our skin and many of the mucous membranes in our body are also a part of the immune system. The reflexes that cause us to cough and sneeze help us to remove germs from our airways, too. Cytokines and Chemokines K. Sony Reddy  Background Cytokine – group of small proteins that act as messengers of the immune system Chemokine- Cytokines that share the purpose of mobilizing immune cells from one region to another. Belong to chemoattractant class. Most cytokines exhibit autocrine and/or paracrine action. Very few exhibit endocrine action. Cytokines exert their action by binding to specific receptors on target cells. Binding affinity between cytokine and its receptor is very high (10-8 to 10-12 M) Cytokines regulate the intensity and duration of immune response. Cytokines exhibit attributes of pleiotropy, redundancy, synergism, antagonism and cascade induction Cytokine attributes Six Cytokine Families  Interleukin 1 Family Secreted early by dendritic cells and macrophages/monocytes on recognition of viral, bacterial and parasitic antigen by PRRs Proinflammatory cytokines that induce increase in capillary permeability and enhance level of leukocyte migration into infected tissues. IL-1 can signal liver to secrete acute phase proteins (type 1 Interferon, CXCL8 and IL-6), which then can induce protective effects including destruction of viral rna and generation of systemic fever response IL-1 also activate B and T cells at induction of adaptive immune response. IL-1α and Il-1β both synthesized as 31kDa precursors that gets trimmed to their active form (17kDa) by enzyme caspase-1. (Pro IL-1α when present in membrane bound form is active) Il-18 secreted by macrophages and dendritic cells have similar function to IL-1 and requires caspase-1 processing Il-33 induces TH2 cytokines that promotes T-cell interaction with B cells, mast cell and eosinophil  Hematopoietin (Class I) Family Cellular origin and target cells are diverse Functions include T and B cell proliferation, onset of B-cell differentiation to plasma cells, T helper cell differentiation and initiating differentiation of particular leukocyte lineages Defining feature of this family of cytokines is a four-helix bundle motif  Interferon (Class II) Family Type I Interferon Composed of Interferon α (20 related protein family) and Interferons β Secreted by activated macrophages, dendritic cells and virus infected cells after recognition of vial components by PRR. Type 1 interferons, interact with their receptors induce ribonucleases that destroy viral RNA and cease protein synthesis. Type-1 IFNs are dimers of 18-20kDa predominantly helical polypeptides, which may sometimes be glycosylated Type-1 interferons used in treatment of hepatitis infections. Type II Interferon IFN-γ secreted by activated T and NK cells IFN- γ modulator of adaptive immune response, biasing T- cell help to Th1 subtype IFN- γ used medicinally to bias adaptive immune system to cytotoxic response to disease like leprosy or toxoplasmosis. IL-10 secretd by monocytes, T, B and dendritic cells. With similar structure to IFN-γ , binds to same class of receptors Type III Interferon family Interferon- λ family, composed of Interferon -λ1 (Il-29), Interferon –λ2 (IL-28A) and Interferon –λ3 (IL-28B). Antiviral response similar to Type-I  Tumor Necrosis (TNF) Family Regulate development, effector function and homeostasis of cells participating in skeletal, neuronal and immune systems TNF family cytokines can be soluble or membrane anchored. If Membrane anchored, they are Type 2 transmembrane proteins with short cytoplasmic N-terminal region and long extracellular C-terminal region. Examples: Lymphotoxin β- Lymphocyte differentiation BAFF and APRIL- B cell development CD40L- expressed on surface of T cells and required signal for B-cell differentiation Fas Ligand (FasL/CD95L)- induction of Apoptosis Soluble cytokines include TNF-α and TNF-β (Lymphotoxin-α) TNF- α secreted primarily by activated macrophages, but sometimes by other cells in response to infection, inflammation or environment stress. TNF-β (Lymphotoxin-α) primarly produced by activated lymphocytes. Provides activation signal to neutrophils, endothelial cells and osteoclasts, whereas in other cells it enhances expression of MHC glycoproteins and Adhesion Molecules Active TNF family cytokines assemble into trimers [homotrimer as well as heterotrimer (Ex: April and BAFF; Lymphotoxin β and Lymphotoxin α)] that have a conserved tertiary structure and fold into β sandwich.  Interleukin-17 (IL-17) Family Proinflammatory cytokines with receptors on neutrophils, keratinocytes and other nonlymphoid cells. Mostly acts as homodimers but heterodimers (IL-17Aand IL17-F) has been reported.  Chemokines Chemokine: Structurally related family of small cytokines that induce movement of leukocytes up a concentration gradient towards the chemokine source (chemotaxis). Relatively low molecular weight (7.5-12.5 kDa) and structurally homologous and constrained by set of highly conserved disulphide bonds. Chemokines classified into 6 categories based on presence of the cysteines residues. Within one category chemokines share 30-99% sequence identity. ELR subclass bind to CXCR2 receptor, attract neutrophils and are angiogenic Non-ELR chemokines use CXCR4 receptor and are angiostatic 4C CC and 6C CC attract monocytes and macrophages Complement system K. Sony Reddy  Background Complement- Paul Ehrlich, which meant activity of blood serum that complets the action of antibody Most complement components synthesized in liver, with some produced by other cell types Group of around 30 glycoproteins that comprises of about 15% of plasma globulin fraction  Complement components: seven categories 1. Initiator complement components 2. Enzymatic mediators 3. Opsonins 4. Inflammatory mediators 5. Membrane attack complex (MAC) Ex: C3a, C4a, C5a 6. Complement Receptors Ex: C3b, C4b Ex: CR1, C5aR 7. Regulatory complement components Ex: Factor I Ex: Protectin Major Pathways of complement activation Major Pathways of complement activation  C1 complex of classical pathway C1 complex- C1qr2s2 C1q- 18 polypeptide chains/6 collagen like triple helixes C1 macromolecular complex bind by C1q globular heads to Fc sites Atleast 2 Fc site interaction necessary for stable C1-ab interaction Pentameric IgM bound to antigen has 3 binding sites, whereas none antigen bound none Monomeric IgG contain 1 binding site. Less efficient than IgM to activate complement. Upon C1q binding to Fc region, conformational change in C1r (Serine protease) leads to activation C1r then can activate the C1s (serine protease) Classical pathway  Lectin pathway MBL-Mannose binding lectin MASP: MBL associated serine proteases Alternate pathway  Alternative Protease activated pathway Protein factors involved in blood clotting (Plasmin, thrombin) can also activate complement by cleaving C3 and C5 The C3b and C5b are involved in complement whereas C3a and C5a can act as anaphylatoxins  Membrane Attack Complex C5b binds C6 and C7. Binding induces conformational change in C7 exposing hydrophobic regions. C8 made of 2 polypeptide chain (C8β, C8αγ). C8β binds to C5b67 complex whereas C8αγinsert into phospholipid bilayer Final step is binding of C9 (10-19 molecules) to the complex and its polymerization. Mac complex has a tubular form with pore diameter of 70-100 Angstrom.  Membrane Attack Complex Pores formed by MAC facilitate free flow of small molecules and ions, thus compromising the osmotic integrity resulting in cell lysis Smaller pores generated by MAC using few molecules of C9, can result in influx of calcium into the cytoplasm and mediate apoptotic type response called as MAC induced apoptosis. However this apoptosis do not share all biochemical features of apoptosis, thereby its also termed as apoptotic necrosis. MACs can be removed from cell surface, either by shedding MAC containing membrane vesicles into extracellular fluid or by internalizing and degrading MAC vesicles. Gram positive bacteria efficiently repel complement assault as complement proteins cant penetrate its cell wall Opsonization and phagocytosis  Promotion of Inflammation C3a and C5a (anaphylotoxins) are structurally similar, 9kDa proteins that promote inflammation as well as serve as chemoattractants for certain class of Leukocytes. Bind to G-protein coupled receptors and in some cells trigger secretion of cytokines like IL-6 and TNF-α Promote phagocytosis of pathogens by dendritic cells and localized degranulation of granulocytes