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NAJRAN UNIVERSITY College of Medicine

NAJRAN UNIVERSITY College of Medicine. Microbiology &Immunology Course Lecture No. 12. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. HUMORAL IMMUNITY ANTIBODY MEDIATED IMMUNITY ANTIBODIES :

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NAJRAN UNIVERSITY College of Medicine

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  1. NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 12 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

  2. HUMORAL IMMUNITY ANTIBODY MEDIATEDIMMUNITY ANTIBODIES : These are specialized serum proteins capable to react specifically with antigens that stimulated their production or with antigens of similar chemical determinant. These are called immunoglobulins.

  3. Mechanism of Antibody Production : I‑ Clonal selection : During embryonic development, a large pool of B-lymphocytes are produced (about 107 cells). Each B cell is programmed to produce one antibody, so each B lymphocyte carries on its surface a specific receptor that can react with one antigen or a closely related group of antigens i.e.. there are about 107 different specificities. The B lymphocytes that carry antigen receptor for self proteins are killed i.e. clonal selection.

  4. After the antigen binds, the B cell is stimulated to proliferate and form a clone of cells. These selected B cells soon become plasma cells and secrete antibody specific for the antigen.

  5. 2‑ Activation of B cells Generally, antigen contact alone is not sufficient to activate B cells, because most protein antigens are T-dependent antigens which require the interaction with T helper cells as follows: 1‑ The antigen is processed and epitopes appear on the surface. B cells are used as the antigen presenting cells. 2‑ This complex is recognized by a helper T cell with a TCR on its surface. 3‑ The T helper cells now produce various cytokines, IL‑2, IL-4 and IL‑5 that stimulate the growth and differentiation of the B cells to plasma cells.

  6. 4‑Two costimulatory interactions are required for activation of B cells to produce a full range of antibodies: a‑ CD28 on the TH cell must interact with B7 on the B cell for activation of T cells to produce IL‑2. b‑ CD40 L on the T cells must interact with CD40 on the B cell, for class switching from one to other immunoglobulin classes to occur.

  7. 5‑ Many plasma cells that produce large amounts of immunoglobulin specific for the epitope are the end result. Plasma cells secrete thousands of antibody molecules presented for a few days then die. Some activated B cells form memory cells, which can remain quiescent for long periods but are capable of being activated rapidly upon reexposure to antigen.

  8. IMMUNOGLOBULINS (ANTIBODIES) ‑ Immunoglobulins are glycoproteins present in the gamma globulin fraction of the serum. ‑ They are produced by B‑lymphocytes in response to exposure to an antigen and react specifically with that antigen. ‑ Immune response by antibodies is called the humoral immune response.

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