16. Adaptive Host Defense Mechanisms

• Immunology


  The scientific study of the immune system and immune responses

  
• Primary functions of the immune system

  • Differentiate between "self" and "nonself"
  • Destroy that which is "nonself"

  
• Lymphocytes


  Cells involved in immune responses that originate in bone marrow, including B lymphocytes (B cells), T lymphocytes (T cells), and natural killer cells (NK cells)
• Types of T cells

  • Helper T cells
  • Cytotoxic T cells
• Humoral immunity


  Where special glycoproteins called antibodies are produced by B cells to destroy specific microbes
• Cell-mediated immunity


  Involves a variety of cell types, with antibodies playing only a minor role, if any

  
• Acquired immunity


  Immunity that results from the active production or receipt of antibodies during one's lifetime

  
• Types of acquired immunity

  • Active acquired immunity
  • Passive acquired immunity

  
• Active acquired immunity


  Antibodies are produced within the person, usually providing long-lasting protection

  
• Passive acquired immunity


  Antibodies produced in one person are transferred to another person to provide temporary protection
• Vaccine


  Material that can artificially induce immunity to an infectious disease, usually following injection or ingestion
• Types of vaccines


  • Attenuated vaccines
  • Inactivated vaccines
  • Subunit vaccines
  • Conjugate vaccines
  • Toxoid vaccines
  • mRNA Vaccines
• Antigen


  Foreign organic substances that are large enough to stimulate the production of antibodies
• Antibody


  Proteins produced by lymphocytes in response to the presence of an antigen, belonging to a class of proteins called immunoglobulins (Ig)
• 1. dependent antigens


  Antigens that require T cells in their processing
• 1. independent antigens


  Antigens that require only B cells in their processing
• Primary immune response


  The initial immune response to an antigen, taking 10 to 14 days for antibodies to be produced
• Secondary immune response


  The increased production of antibodies following the second exposure to a particular antigen
• Monoclonal antibodies


  Specific antibodies produced by long-lived, antibody-producing cells called hybridomas
• Antigen-antibody complex


  The complex formed when an antibody combines with an antigen
• Cell-mediated immunity (CMI)


  A complex system of interactions among many types of cells and cellular secretions (cytokines), capable of controlling chronic infections by intracellular pathogens

  
• Natural killer (NK) cells

  A subpopulation of lymphocytes that kill target cells, including foreign cells, host cells infected with viruses or bacteria, and tumor cells
• Hypersensitivity


  An overly sensitive immune system
• Types of hypersensitivity reactions

  • Immediate-type (types I, II, and III)
  • Delayed-type (type IV)
• Type I hypersensitivity reactions

  Also known as anaphylactic reactions, including classic allergic responses such as hay fever symptoms
• NK cells


  • Lack typical T or B cell surface markers
  • Do not proliferate in response to antigen and appear not to be involved in antigen-specific recognition
  • Kill target cells, including foreign cells, host cells infected with viruses or bacteria, and tumor cells
• Types of hypersensitivity reactions

  • Immediate-type (types I, II, and III)
  • Delayed-type (type IV)
• Immediate-type hypersensitivity


  Occurs from within a few minutes to 24 hours after contact with a particular antigen
• Delayed-type hypersensitivity


  Usually takes more than 24 hours to manifest themselves
• Type I hypersensitivity reactions

  Also known as anaphylactic reactions, include classic allergic responses such as hay fever symptoms, asthma, hives, and gastrointestinal symptoms that result from food allergies, allergic responses to insect stings and drugs, and anaphylactic shock
• Allergic response in type I hypersensitivity

  1. Atopic persons produce IgE antibodies when exposed to allergens

  2. IgE antibodies bound to basophils in the blood or to mast cells in connective tissues
• Factors in the development of type I hypersensitivity

  • Presence of IgE antibodies bound to basophils or mast cells
  • Exposure to allergen
• Events in type I hypersensitivity reactions

  1. Allergen binds to IgE on mast cells or basophils

  2. Mast cells or basophils degranulate and release chemical mediators

  3. Chemical mediators cause symptoms
• Transmission electron micrographs


  • Showing degranulation of a rat mast cell
  • Showing phagocytosis of rat mast cell granules by a rat eosinophil
• Localized type I hypersensitivity reactions

  Involve mast cell degranulation, result in allergic reactions like hay fever, asthma, and food allergies
• Systemic type I hypersensitivity reactions

  Involve basophil degranulation, occur throughout the body, can lead to anaphylactic shock, and can be life-threatening
• Allergens involved in systemic anaphylaxis

  • Drugs
  • Insect venom
• Latex allergy


  Can trigger irritant contact dermatitis, allergic contact dermatitis, or immediate type hypersensitivity
• Allergy skin testing and allergy shots

  1. Skin tests (scratch tests) used to identify offending allergens

  2. Positive test indicated by cutaneous anaphylaxis at scratch site

  3. Immunotherapy (allergy shots) used to treat, producing IgG blocking antibodies
• Type II hypersensitivity reactions

  Cytotoxic reactions where body cells are destroyed