Properties and Overview of Immune Responses Chapter 1

1. Definitions
   1. Immunity - (L. immunitas = protection from legal prosecution)
      1. historical = protection from disease (esp. infectious disease)
   2. Immune system = cells & molecules responsible for immunity
   3. Immune response = collective and coordinated response to foreign substances
      1. = reaction to components of microbes as well as to macromolecules that are recognized as foreign
      2. note - immune responses can occur against nonliving largish molecules
   4. Immunology = study of immune responses
      1. includes the cellular and molecular events that occur after an organism encounters microbes & other foreign macromolecules
      2. experimental science
2. Innate Immunity = natural or native immunity
   1. Defined
      1. = early line of defense against microbes
      2. cellular and biochemical defense mechanisms that are in place before exposure
         1. born with
      3. **+** respond rapidly
      4. **+** recognize & react only to limited # of molecules
      5. **-** respond the same way (vigor/amt) even with repeated exposure
   2. Components
      1. physical & chemical barriers
         1. epithelia, antimicrobial substances
      2. cells
         1. phagocytic (neutrophils & macrophages)
         2. natural killer cells
      3. blood proteins
         1. complement system proteins
         2. inflammation mediators
      4. cytokines
         1. proteins that regulate & coordinate reactions
   3. Defense lines
      1. First line - goal - block entry
         1. epthelial barriers - skin & mucosal membranes
         2. natural antibiotics
      2. Second line - if epithelia breached
         1. phagocytes, NK cells, plasma proteins
      3. Third line - enhance adaptive immunityAdaptive immunity = Acquired immunity
   4. Defined
      1. **-** responses that are stimulated by exposure to infectious agents - delay
      2. **+** increase in magnitude by successive exposure - can "remember"
      3. specific responses are not present before exposure
      4. **+** can distinguish btw many many different & closely related microbe & non-microbioal molecules
   5. Types of adaptive immune responses
      1. humoral - in blood
         1. antibodies - proteins circulating blood
            1. specifically recognize and bind to infectious molecules
            2. proteins, carbohydrates, NAs, & lipids
         2. antigens - Ag - molecules that provoke the synthesis of Abs
            1. thereby targeting them for elimination
            2. or preventing them from binding targets
         3. principle defense against extracellular microbes & toxins
         4. down side only present outside cells so not "see" intracellular paracites
         1. active immunity
            1. here the individual is exposed to the infection and mounts an immune response themselves
            2. before exposure = naive
            3. after successful immune response - individual is protected from subsequent exposures = immune
            4. Inidiv. can also be exposed to weak microbe or parts of microbe = vaccination
            5. Key = make own Abs
         2. passive immunity
            1. when transfer serum containing Abs from an immune indiv. to one not exposed
            2. the recipient becomes immune to the particular infections without being exposed
            3. confers resistance rapidly but only for short time (half life of Abs)
      2. cell mediated = cellular immunity
         1. mediated by T lumphocytes / cells
         2. targets - intracellular microbes (ex. viruses & some bacteria)
            1. here inaccessible to Abs
         3. promotes the destruction of the infected cell
         4. very good against proteins
   6. Properties of Adaptive Immune Responses
      1. diversity = lymphocyte repertoire
         1. quite large - 10⁷ - 10⁹ (10 million -> gazillion) diff. molecules (epitopes, determinants)
         2. comes from lymphocyte ability to randomly rearrange DNA for Abs & T cell receptors
         3. problem -  #
            1. 1 in 100,000 to 1 in 1,000,000 can bind Ag
            2. results in about 1000 - 10,000 cells that can recognize Ag
            3. to mount an effective defense need many, many more cells
               1. so when a unique lymphocyte binds an Ag (& is confirmed) it induces division
               2. so the cells divides & divides & divides = clonal selection
      2. specificity - ability to distinguish btw many diff Ags.
         1. immune responses are specific for distinct molecules
            1. even specific for diff regions of same molecule
               1. epitope = determinants = part(s) of molec. recognized by individual lymphocytes
         2. during clonal selection the gene is slightly altered
            1. those alterations that result in better binding receive more stimulation to divide
            2. those alterations that result in  binding receive less stimulation so don't divide
      3. memory = secondary immune responses
         1. inital exposure = 1° immune resonse (see above)
            1. when exposed later to same Ag = 2° immune response & . . .
         2. immune response is ...
            1. more rapidly
            2. with greater intensity
            3. more specificity
         3. during first response long-living "memory" cells are created
            1. notice plural
            2. so upon re-exposure more cells ready to respond
            3. reason for success of vaccination
      4. contraction and homeostasis
         1. homeostasis = resting state of immune responses
            1. feedback loops  &  response
            2. after response to infection the immune response diminishes to homeostasis - resting
         2. without stimulation in response to infection many responding immune cells under go programed cell death = apoptosis
      5. immunological self tolerance - nonreactivity to self
         1. norm. an individual's immune sys does not recognize or respond to self potential Ags
         2. abnormalities in tolerance = autoimmune disease