Cells of immune system

Cells of immune system

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  B Y D SS R I M AT H I M S C M I C R O B I O L O G Y CELLS OF IMMUNE SYSTEM (B CELL,T CELL, NK CELLS)
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  B CELL INTRODUCTION  Derivedfrom its site of maturation, in the bursa of Fabricius in birds; the name turned out to be apt, for bone marrow is its major site of maturation in a number of mammalian species, including humans and mice  In humans it matures in Bone marrow.  The lymphocyte which arise and develop in the bone marrow is called B lymphocyte.
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  B LYMPHOCYTE  MatureB cells are distinguished from other lymphocytes by their synthesis and display of membrane-bound immunoglobulin (antibody) molecules  Memory B cells express IgG,IgA,or IgE on the surface  Mature B cells express IgM , IgD molecules on the surface serve as receptors for antigen  B cells - receptors for FC portion of IgG and a receptor for a C3 component - complement system  They express array of molecule on their surface that are important in B cells interaction with the other cells such as MHC II ,B7 and CD40.
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  ACTIVATION OF B CELL
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  FUNCTIONS OF BCELL  Production of many plasma cells - result of activation of B cells.  The plasma cells in turn produce large amounts of immunoglobulins specific for the epitope of the antigen.  Some activated B cells also produce memory cells, which remain in a stage of quiescence for months or years.  Most memory B cells have surface IgG that acts as the antigen receptor, but some even have surface IgM.  These memory cells are activated rapidly on re-exposure to antigen.  Memory T cells produce interleukins that facilitate antibody production by the memory B cells.  The presence of these cells is responsible for the rapid appearance of antibody in the secondary immune responses.
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  T - LYMPHOCYTE Type of lymphocyte ( subtype of White blood cell)  Play an major role in cell -mediated immunity  They are distinguished from other lymphocyte by the presence of T cell receptor  They mature in thymus gland
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  TYPES OF TCELL
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  T CELL RECEPTOR Found on the surface of T cells, • Responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules.
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  CD4 AND CD8CO-RECEPTORS  glycoproteins found on the surface of T cells • Both have abilities to recognize peptide-MHC complex and signal transduction CD4 : • CD4 T-cells recognize antigen combined with MHC class II  function largely as helper cells CD8 : • CD8 T-cells recognize antigen combined with MHC class I  function as cytotoxiccells
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  T CELLACTIVATION
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  NK CELLS  thebody contains a small population of large, granular lymphocytes that display cytotoxic activity against a wide range of tumor cells  play an important role in host defense both against tumor cells and against infected cells  constitute 5%–10% of lymphocytes in human peripheral blood, do not express the membrane molecules and receptors that distinguish T- and B-cell lineages.
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  MECHANISM  NK cellsparalyze target cells using the cytolytic protein perforin and a variety of protease enzymes.  An NK cell will first use perforin to create pores in a target cell, allowing it to inject granzymes through an aqueous channel. The granzymes then break down the target cell, inducing death by either apoptosis or osmotic cell lysis.  NK cells also alert the greater immune system by secreting chemicals
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  Although NK cellshave no TCR or immunoglobulin in their cell membrane, they can recognize potential target cell by two ways: i. NK cell receptor mediated:  NK cell employs NK cell receptors to distinguished abnormal host cell, notably a reduction in display of class-I MHC molecule and unusual profile of surface antigen displayed by some tumor cell and virus infected cells. ii. ADCC (antibody dependent cell mediated cytotoxicity):  NK cell recognize target cell because tumor cell or virus infected cell express some antigen on their surface which is recognized by specific antibody.  It also express CD16 which recognize Fc region of IgG antibody. they attach to these antibody and subsequently destroy the target cells.
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  FUNCTIONS OF NKCELLS:  Provide antitumor immunity  Provide antiviral immunity  provide antibody dependent cell mediated cytotoxicity (ADCC).  secretes cytokines