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2422011FallOutlC21Part2

2422011FallOutlC21Part2 - 21 The Immune System Innate and...

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21: The Immune System: Innate and Adaptive   Body Defenses PART 2: ADAPTIVE DEFENSES [ACQUIRED OR SPECIFIC IMMUNITY] (pp. 775–895; Figs.  21.7–21.22) III. Antigens (pp. 776–777; Fig. 21.7) A. Aspects of the Adaptive (also called acquired or specific immunity) Immune Response   1.    Adaptive (acquired) immunity is considered the third line of defense after intact skin/mucous membranes                and innate immunity. 2. The adaptive defenses recognize and destroy the  specific  antigen that initiated the response. 3. The immune system must be ready to confront any  antigen at any  time and its  versatility  results in part  from the large diversity of lymphocytes present in the body, and in part from the variability of the  synthesized antibodies.  4. The immune response is a  systemic  response; it is not limited to the initial infection site. 5. The immune system also exhibits  tolerance . 6. After an initial exposure the immune response is able to recognize the same antigen and mount a faster  and stronger defensive attack ( memory ).  7. Humoral immunity  is provided by  antibodies  produced by  B lymphocytes and plasma cells  present in  the body’s “humors” or fluids. 8. Cellular immunity  is associated with  T lymphocytes  and has living cells as its protective factor. 9.   Adaptive immunity overlaps with innate immunity  [e.g., cytokines released by the inflammatory  responses attracts lymphocytes which in turn release more cytokines to rev up the inflammation].  In  particular,  macrophages and dendritic cells play important roles in both innate and adaptive  immunity . B. Antigens  are substances that can mobilize the immune system and provoke an immune response. 1.     Complete antigens (immunogens)  are able to stimulate the proliferation of specific lymphocytes and  antibodies, and to react with the activated lymphocytes and produced antibodies.  The most potent  immunogens are protein with molecular weights above 100,000. 2. Haptens  are molecules that are not immunogenic by themselves but they can react with specific antibody.  Haptens are usually small molecules, but some high-molecular weight nucleic acids are haptens as well.  Many drugs such as penicillins are haptens as are the chemicals in plant oils that cause poison oak or ivy.  Haptens are not immunogenic because they cannot activate helper T cells.  The failure of haptens to  activate is due to their inability to bind MHC proteins; they cannot bind because they are not polypeptides  and only polypeptides can be presented by MHC proteins.  Also, haptens are univalent and therefore 
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