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17 Specific Defenses of the Host by HC120325012542

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									                 MICROBIOLOGY
                             Chapter 17
             Specific Defenses of the Host:
                    The Immune Response
Dr. Abdelraouf A. Elmanama
Ph. D Microbiology

          Medical Technology Department, Faculty of Science, Islamic University-Gaza

                                               2008
       Specific Defenses of the Host:
          The Immune Response
• Innate (nonspecific)   Defenses against any pathogen
• Immunity               Specific antibody and lymphocyte
                         response to an antigen
• Antigen (Ag)           A substances that causes the
                         body to produce specific
                         antibodies or sensitized T cells
• Antibody (Ab)          Proteins made in response to an
                         antigen
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                    Terminology



 • Serology             Study of reactions between
                        antibodies and antigens
 • Antiserum            Generic term for serum because
                        it contains Ab
 • Globulins            Serum proteins
 • Gamma () globulin   Serum fraction containing Ab




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       Serum Proteins




                        Figure 17.2
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               The Immune Response




 • Acquired immunity        Developed during an
                            individual's lifetime
 • Humoral immunity         Involves Ab produced by
                            B cells
 • Cell-mediated immunity   Involves T cells




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                     Acquired Immunity


 • Naturally acquired active immunity
       • Resulting from infection
 • Naturally acquired passive immunity
       • Transplacental or via colostrum
 • Artificially acquired active immunity
       • Injection of Ag (vaccination)
 • Artificially acquired passive immunity
       • Injection of Ab


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               Antigenic Determinants
 • Antibodies recognize and react with antigenic
   determinants or epitopes.




                                                   Figure 17.3
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       Haptens




                 Figure 17.4
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       Antibody Structure




                            Figure 17.5a-c
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                     IgG antibodies


 • Monomer
 • 80% of serum antibodies
 • Fix complement
 • In blood, lymph, intestine
 • Cross placenta
 • Enhance phagocytosis;
   neutralize toxins & viruses;
   protects fetus & newborn
 • Half-life = 23 days


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                        IgM antibodies


 • Pentamer
 • 5-10% of serum
   antibodies
 • Fix complement
 • In blood, lymph, on B
   cells
 • Agglutinates microbes;
   first Ab produced in
   response to infection
 • Half-life = 5 days

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                        IgA antibodies



 • Dimer
 • 10-15% of serum
   antibodies
 • In secretions
 • Mucosal protection
 • Half-life = 6 days




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                        IgD antibodies



 • Monomer
 • 0.2% of serum antibodies
 • In blood, lymph, on B cells
 • On B cells, initiate immune
   response
 • Half-life = 3 days




2008
                        IgE antibodies



 • Monomer
 • 0.002% of serum
   antibodies
 • On mast cells and
   basophils, in blood
 • Allergic reactions; lysis of
   parasitic worms
 • Half-life = 2 days



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                     Clonal Selection



• Bone marrow gives rise to B cells.
• Mature B cells migrate to lymphoid organs.
• A mature B cells recognizes epitopes.




 2008
       Clonal Selection




                          Figure 17.8
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                       Self-tolerance


• Body doesn't make Ab against self
• Clonal deletion
    • The process of destroying B and T cells that react to
      self antigens




 2008
       The Results of Ag-Ab Binding




                                      Figure 17.9
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                    Antibody titer:
 • Is the amount of Ab in serum




                                      Figure 17.10
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               Monoclonal Antibodies

 • Hybridomas are produced by fusing a cancer cell with
   an Ab-secreting plasma cells
 • The hybridoma cell culture is immortal and produces
   monoclonal Abs (Mabs)
 • Immunotoxins: Mabs conjugated with a toxin to target
   cancer cells
 • Chimeric Mabs: Genetically modified mice that produce
   Ab with a human constant region
 • Humanized Mabs: Mabs that are mostly human, except
   for mouse antigen-binding


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       Monoclonal Antibodies




                               Figure 17.11
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  Immune system cells communicate via cytokines



 • Interleukin-1    Stimulates TH cells
 • Interleukin-2    Activates TH, B, TC, and NK cells
 • Interleukin-12   Differentiation of CD4 cells
 • -Interferon     Increase activity of macrophages
 • Chemokines       Cause leukocytes to move to an
                    infection




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                Cell-Mediated Immunity



 • Specialized lymphocytes, mostly T cells, respond to
   intracellular Ags
 • After differentiating in the thymus, T cells migrate to
   lymphoid tissue
 • T cells differentiate into effector T cells when
   stimulated by an Ag
 • Some effector T cells become memory cells




2008
        Pathogens entering the gastrointestinal or
             respiratory tracts pass through:
• M (microfold) cells in
• Peyer's patches which contains
• Dendritic cells which are antigen-presenting cells
  and
• T cells




 2008
       Dendritic cells present antigens




                                          Figure 17.12
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                             T Cells



 • Helper T Cells (CD4, TH)
       • T H1  Activate cells related to cell-mediated
         immunity
       • T H2   Activate B cells to produce eosinophils, IgM,
         and IgE
 • Cytotoxic T Cells (CD8, TC)
       • Destroy target cells with perforin



2008
                             T Cells




 • Delayed Hypersensitivity T Cells (TD)
       • Associated with allergic reaction, transplant
         rejection, and tuberculin skin test
 • Suppressor T cells (TS)
       • Turn off immune response when Ag no longer
         present




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       Helper T Cells




                        Figure 17.13
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       Cell-mediated Cytotoxicity




                                    Figure 17.14
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                     Nonspecific Cells


 • Activated
   macrophages:
   Macrophages
   stimulated by
   ingesting Ag or by
   cytokines
 • Natural killer cells:
   Lymphocytes that
   destroy virus-
   infected cells,
   tumor

                                         Figure 17.15
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       T-independent Antigens




                                B cell




                                         Figure 17.17
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       T-independent Antigens




                                Figure 17.16
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  Antibody-Dependent Cell-Mediated Cytotoxicity




                                           Figure 17.18
2008

								
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