B-Lymphocytes and T- lympocytes

B-Lymphocytes and T- lympocytes - ‫بسم اللة...

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Unformatted text preview: ‫بسم اللة الرحمن‬ ‫الرحيم‬ Cells of Immune System Cells of Immune System Cells of Immune System Cells Stem cells of bon marrow cytokines (IL­&, IL­3) differentiate into colony stimulating factor Lymphoid series Myeloid series B­lymphocytes T­lymphocytes NK monocytee­macrophages dendritic cells eosinophils mast cells The Life Of The B Cell The B lymphocytes are formed within the bone marrow and undergo their development there They have the following functions: To interact with antigenic epitopes, using their immunoglobulin receptors To subsequently develop into plasma cells, secreting large amounts of specific antibody, or To circulate as memory cells To present antigenic peptides to T cells, consequent upon interiorization and processing of the original antigen * B cells become plasma cells, which produce antibodies when a foreign antigen triggers the immune response immune B-lymphocytes B-lymphocytes in bon marrow * The lymphoid stem cells differentiate into B cells * B­cells precursors mature, differentiate into immunocomptent B­cells with a single antigen specificity * Immature B­cells that express high affinity receptors for self antigens, die or fail to mature i.e negative selection or clonal deletion * This process induces central self tolerance and reduces autoimmune diseases B-lympocytes B-lympocytes * Immature B cells express IgM receptors on the surface * Mature B cells express IgM, IgD molecules on surfaces * IgM and IgD molecules serve as receptors for antigens * Memory B­cells express IgG or IgA or IgE on the surface * B­cells bear receptors for Fc portion of IgG and a receptor for C3 component of the complement * They express an array of molecules on their surfaces that are important in B­cells interactions with other cells such as MHC II, B7 and CD40 Mechanism of Humoral immunity Mechanism * Antibodies induce resistance through: 1) Antitoxin neutralize bacterial toxins (diphtheria,tetanus) Antitoxin are developed actively as a result of: a­ Previous infection b­ Artificial immunization c­ Transferred passively as antiserum * Neutralization of toxin with antitoxin prevents a combination with tissue cells Mechanism of Humoral immunity Mechanism 2) Antibodies attach to the surface of bacteria and a­ act as opsonins and enhance phagocytosisd b­ prevent the adherence of microorganisms to their target cells, e.g. IgA in the gut c­ Activate the complement and lead to bacterial lysis d­ Clump bacteria (agglutination) leading to phagocytosis Activation of B cells to make antibody Activation T-Lmphocytes T-Lmphocytes T­lmphocytes migrate from bon marrow to enter thymus T­lmphocytes migrate from bon marrow to enter thymus 1) In the outer cortex of thymus: ­ T­lymphocytes acquire specific receptors (TCRs) ­ This receptor commit lymphocyte to a single antigen specificty ­ Responding by proliferation and production of a clone of cells (clonal selection) ­ They differentiate to express CD3, both CD4 and CD8 coreceptors (double positive cells) * T lymphocytes become CD4+ (helper T cells) or * CD8+ cells (which in turn CD8+ can become killer T cells) also called cytotoxic T cells T-Lmphocytes T-Lmphocytes 2) In the medulla of thymus: ­ TCRs recognize MHC molecules, loaded with normal self­peptides (p­MHC) ­ TCRs capable of binding with low affinity to p­MHC will receive positive selection signals to divide and establish clones ­ TCRs that bind too strongly to p­MHC undergo (negative selection) ­ This selection process will eliminate the potentially most harmful self reactive T­cells (central self tolerance) T-Lmphocytes T-Lmphocytes 3)Immature T­cells express both CD4 and CD8 (DP) As they mature * T­cell with TCRs that have affinity to bind to MHC class II will become helper T­cells with CD4 molecule only * T­cell with TCRs that have affinity to bind with MHC class I will become cytotoxic T­cells with CD8 molecule only T-Lmphocytes T-Lmphocytes 4) Mature positively selected T­cells are MHC restricted * CD4 T­cells are MHC II restricted and only recognize specific foreign peptide only when they are presented in association with specific MHC II molecules * CD8 T­cells are MHC I restricted and recognize specific foreign peptidees only when they are presented in association with specific MHC I molecules T-cell surface markers T-cell These are molecules that by witch we can identify T­cells and divide them to subsets They are required to for interactions between T­cells and APC and for antigen recognition These are TCRs, CD3, CD4, CD8, CD2, CD28,and CD40 on activated T­cells T-cell subpopulation T-cell 1) CD4 T helper lymphocytes (TH) ­ TH lymphocytes recognize antigen on the surface of APC in association with class II MHC molecules ­ They are activated and secrete several cytokines ­ There are two main subsets of TH cells (THI and TH2) ­ The two subsets are differentiated on basis of the cytokine they produce 1) CD4 T helper lymphocytes Subsets 1) Th1 produce mainly : ­ Cytokines of CMI and inflammation e.g. IFN­γ, TNF­ β, IL­3 and IL­2 TH2 produce mainly: ­ Cytokines that stimulate B­cells ­ Suppressor cytokines e.g. Il­4, IL­5, IL­6 and IL­10 2) CD8 Cytotoxic T-lymphocytes (CTLs) (CTLs) * They constitute 35% 0o peripheral T­cells * They constitute 35% 0o peripheral T­cells * CTLs recognize antigen on suurface of target cells (infected APC or other infected nucleotid cell) in association with MHC­ I * They are activated and kill the virus infected cell or tumour cell Professional APCs Professional Dendritic cells, macrophages, and B­lymphocytes Dendritic cells: ­ They are the most efficient APCs ­ They are the main inducers of primary immune response ­ Presenting antigen to and activating native T­cells in the recognition phase ­ They express class I and class II MHC molecules ­ Dendritic cells are primarly located under skin and mucosa of most organs ­ They capture foreign antigens and transport them to local lymph nods ­ They present antigen to native helper T­cells Macrophages Macrophages * Derived from myeloid stem cells in bon marrow * They exist as free cells in blood e.g. monocytes and fixed cells in tissues e.g. Kupffer cells of liver * They are important link between innate and aquired immune responses * They are activated and attracted to the site of foreign material by action of different cytokines e.g IFN­γ , C5a Functions of Macrophages Functions 1) Pagocytosis 2) Opsonization 3) APCs: they ingest foreign material, process it, and fragments of antigen are presented on its surface (in association with MHC molecules) for interaction with T­ cells 4) Macrophages may kill antibody coated infected cells or tumour cells through release of lytic enzymes 5) They produce IL­1, IL­6, IL­12, IL­15, TNF­alpha 6) They secret prostaglandins and synthesize complement compononts Natural killer (NK) Cells Natural * Large granular lymphocytes which lack most surface markers of B and T­cells * They comprise 5­10% of the peripheral lymphocytes * They function mainly in innate immunity * They have spontaneous non­specific cytotoxic activity on virus infected cells, tumour cells and graft cells * They are not MHC restricted and MHC I inhibits their killing functions * The mechanism of NK mediated cytolysis is as that of CTLs NK cells differ from CTLs in NK 1)They are non­specific 2)They act spontaneously without prior recognition or activation 3)They do not require antigen presentation by MHC 4)They destroy cells coated with antibodies, a mechanism called antibody dependant cellular cytotoxicity (ADDCC) Antibodies produced by B­cells of the immune system recognize foreign antigens and mark them for destruction Activation of cytotoxic T cells Primary And Secondary Response Primary Primary Response: Slow in Onset Low in Magnitude Short Lived IgM Secondary Response: Rapid in Onset High in Magnitude Long Lived IgG (Or IgA, or IgE Thanks Thanks ...
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