Specific 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"

  
• Cells involved in immune responses

  • B lymphocytes (B cells)
  • T lymphocytes (T cells)
  • 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 active acquired immunity

  • Natural active acquired immunity
  • Artificial active acquired immunity

  
• Vaccine


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

  • Attenuated vaccines
  • Inactivated vaccines
  • Subunit vaccines
  • Conjugate vaccines
  • Toxoid vaccines
• Passive acquired immunity


  Antibodies produced in one person are transferred to another person to protect the latter from infection—provides temporary protection
• Types of passive acquired immunity

  • Natural passive acquired immunity
  • Artificial passive acquired immunity
• Antigen


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


  Proteins produced by lymphocytes in response to the presence of an antigen
• 1. dependent antigens


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


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


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


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


  Globular glycoproteins in the blood that participate in immune reactions
• Types of antibodies/immunoglobulins


  • IgA
  • IgD
  • IgE
  • IgG
  • IgM
• Monoclonal antibodies


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


  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) that can control chronic infections by intracellular pathogens

  
• Natural killer (NK) cells

  A subpopulation of lymphocytes that can 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, asthma, hives, and food allergies, as well as allergic responses to insect stings and drugs
• Types of hypersensitivity reactions

  • Immediate-type (types I, II, 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 like hay fever, asthma, hives, and food allergies, as well as allergic responses to insect stings and drugs, and anaphylactic shock
• Type I hypersensitivity


  • Probably the most common type of hypersensitivity
  • People prone to allergies (atopic persons) produce IgE antibodies when exposed to allergens
  • The allergic reaction results from the presence of IgE antibodies bound to basophils or mast cells
• Events in type I hypersensitivity reactions

  1. Exposure to allergen

  2. IgE antibody production

  3. IgE binds to basophils/mast cells

  4. Allergen binds to IgE

  5. Degranulation of basophils/mast cells

  6. Release of chemical mediators
• Localized type I reactions

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

  Involve basophil degranulation, occur throughout the body, can lead to anaphylactic shock, life-threatening
• Systemic anaphylaxis


  Results from the release of chemical mediators from basophils in the bloodstream, occurs throughout the body, much more serious than localized anaphylaxis
• Latex allergy


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

  1. Skin tests used to identify offending allergens

  2. Positive test indicated by cutaneous anaphylaxis

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

  Cytotoxic reactions where body cells are destroyed
• Sequence of events in type II hypersensitivity

  1. Drug binds to cell surface

  2. Antidrug antibodies bind to drug

  3. Complement activation on cell surface

  4. Complement cascade leads to cell lysis