FUNCTIONS OF IMMUNE SYSTEM.pptx

THE IMMUNE SYSTEM CELLS/ORGANS The lymphoid system consist of the organs of our bodies that provide the products of immunity. PRIMARY & SECONDARY LYMPHOID ORGANS BONE MARROW AND THYMUS LYMPH NODES, SPLEEN, ADENOIDS, TONSIL, PEYER’S PATCHES VARIOUS MUCOSAL ASSOCIATED LYMPHOID TISSUE (MALT) LYMPHOID C...

THE IMMUNE SYSTEM CELLS/ORGANS The lymphoid system consist of the organs of our bodies that provide the products of immunity. PRIMARY & SECONDARY LYMPHOID ORGANS BONE MARROW AND THYMUS LYMPH NODES, SPLEEN, ADENOIDS, TONSIL, PEYER’S PATCHES VARIOUS MUCOSAL ASSOCIATED LYMPHOID TISSUE (MALT) LYMPHOID CELLS (CENTRAL CELLS OF THE IMMUNE SYSTEM) Lymphocytes constitute 20% - 40% of the body’s White Blood Cells and 99% of the cells in the lymph. Lymphocytes can be subdivided into 3 populations based on function/ cell- membrane components: B cells, T cells and Null cells B cells, T cells and Null cells are small, motile and nonphagocytic Plasma cells are the effector cell for the B cell lineage The effector cell of the T cell lineage include; Th cell & CTL LYMPHOCYTES CONT. Some of the progeny of B & T lymphoblast differentiate into memory cells The persistence of these population of cells is responsible for the life-long immunity observed for many pathogens Different maturational stages of lymphocytes can be distinguished by their expression of membrane molecules recognized by particular monoclonal Ab All the monoclonal Abs that react with a particular membrane molecule are grouped together as a cluster of differentiation (CD) The CD nomenclature was originally developed for human leukocyte molecules COMMON CD AG USED TO D/GUISH FUNC. LYMPHOCYTE SUB-POPULATN CD DEG FUNCTION W/FOUND CD2 Adhension molecule/Signal transduction Th, Tc, NK CD3 Signal transduction element of T cell Th & Tc CD4 Adhension molecule that binds to class11 MHC/Signal transduction Th CD8 Adhension molecule that binds to class 1 MHC/Signal transduction Tc CD16 Low affinity receptor for Fc of IgG NK cell CD40 Signal transduction B cell CD45 Signal transduction Th, Tc, NK & B cell CD56 Adhension molecule NK cell CELLS OF HUMORAL & CELL MEDIATED IMMUNITY Mature B cells can be distinguished from other lymphocytes by the presence of Igs (antibody), which serve as receptors for antigen Other molecules expressed on the membrane of mature B cells are; CD45(B220); earliest marker of B cell lineage, function in signal transduction Class 11MHC molecules; permit B cell to function as an APC CR1(CD35) & CR2 (CD21); receptors for certain complement products CD32; receptor for the carboxyl terminal region of IgG B7; Co-stimulatory molecule that interacts with CD28 on Th cells LYMPHOCYTE CONT Activated B cell generates both Plasma cells and memory cells Plasma cells, which lack membrane bound antibody actively secrete one of the five classes of Immunoglobulins All clonal progeny from a given B-cell secrete antibody molecules with the same antigen binding specificity Unlike the membrane bound antibody on B cells, TCR recognizes antigen only when associated with a self molecule encoded by genes within MHC B-cell is capable of binding soluble antigen; T-cell is restricted to binding antigen displayed on self cells. This antigen must be displayed together with MHC molecules on the surface of antigen-presenting or virus-infected cells, cancer cells & grafts B cell play a large role in humoral immune response LYMPHOCYTE CONT. All T-cell subpopulations express the TCR (T-Cell Receptor) CD4+ T cells; generally function as T helper cells T cells that express CD4 recognize antigen associated with class 11 MHC T cells expressing CD8 recognize antigen associated with class 1 MHC The expression of CD4 & CD8 defines 2 major functional subpopulations of Tlymphocytes; CD8+ T cells; generally function as T cytotoxic cells Ratio of Th to Tc cells is approx. 2:1 in normal human peripheral blood T cell play central role in Cell mediated immune response LYMPHOCYTE CONT. T-helper cells secrete various cytokines, which play a central role in the activation of B cells, Tc cells & variety of other cells that participate in the immune response A response designated as TH1 response, results in a cytokine profile that activates mainly T cytotoxic cells & macrophages TH 2 response activates mainly B cells In contrast to T- helper cells, CTL generally secrete few cytokines CTL acquire cytotoxic activity & function to recognize & eliminate altered self-cells (virus infected cells) NULL CELLS Null cells are large granulated lymphocytes Lack surface markers or membrane associated proteins from B or T lymphocytes They lack attributes of immunologic specificity and memory Natural Killer (NK) cells are null cells NK cells constitute 5%-10% of peripheral blood lymphocytes NK cells attack pathogens and abnormal cells (tumor cells) MONONUCLEAR CELLS Phagocytic system; consist of monocytes in the blood & macrophages in tissues Monocytes are part of the innate immune system Monocytes replenish resident macrophages & dendritic cells under normal states Macrophages function in both innate/adaptive immunity They are specialized phagocytic cells Stimulate lymphocytes & other immune cells to respond to pathogens Macrophages are the hallmark of chronic inflammation Free macrophages move by amoeboid movement in the tissues MONONUCLEAR CELLS CONT. Fixed macrophages are named to reflect their tissue location; Alveolar macrophages in the lungs Histiocytes in connective tissues Kupffer cells in the liver Mesangial cells in the kidney Microglial cells in the brain GRANULOLYTIC CELLS Granulocytes are classified on the basis of cellular morphology & cytoplasmic staining characteristics; Neutrophils (Polymorphonuclear Leukocyte or PMN ) Eosinophils Basophils GRANULOCYTIC CELLS CONT. Neutrophils & Eosinophils are phagocytic, basophils are not Neutrophils constitute 50%-70% of circulating WBCs Eosinophil (1% - 3%) Basophils (< 1%) GRANULOLYTIC CELLS CONT. Neutrophils are recruited to site of injury within minutes of injury & they are the hallmark of acute inflammation Predominant cells in pus, accounting for its whitish/yellowish appearance Essential part of the innate immune system Eosinophils are involved in combating multicellular parasites & certain infections Along with mast cells, control mechanisms associated with allergy & asthma ANTIGEN PRESENTING CELLS * Group of diverse cell types that assist other cells in immune response Cells which do not have antigen-specific receptors They capture & process antigens, present them to T cell receptors These cells include; macrophages, B cells and dentritic cells PRIMARY & SECONNDARY ANTIBODY RESPONSE PRIMARY & SECONDARY ANTIBODY RESPONSE Initial exposure; there is slow appearance of antibody in the primary response Response to a second contact with the same antigen is faster & greater Assuming the initial exposure had been a non-pathogenic vaccine, subsequent infection would lead directly to a secondary response The Lymphoid System RECAP QUESTIONS Which antibody is first produced in a primary response to antigen? The most abundant antibody in secretions is -------Which antibody is predominant in a secondary response? ……. Is the only antibody that can cross the placenta What are the major functions of macrophages and Polymorphonuclear neutrophils?