HUMAN SYSTEMS QUESTIONS: 1991              L. PETERSON/AP BIOLOGY
  
   The graph below shows the response of the human immune system to an antigen. 
     Use this graph to answer part a and part b in this question.
	
      a.  Describe the events that occur during period I as the immune system responds to
           the initial exposure to the antigen.

      b.  Describe the events that occur during period II following a second exposure to the 
           same antigen.



		Period I			Period II
	




Antibody
Titer in       Antigen	  Antigen
  Serum       Injected	  Injected

	0	40	80	120	160	200	240	280

				Time in Days



      c.  Explain how infection by the AIDS virus (HIV) affects the function of both T and B
           lymphocytes.


  
  STANDARDS:
  The question as represented on the graph is predicated on a "humoral response". That approach
  is reflected in the standards. The capitalized term in the concept that receives the point (column
  left). The information in the right column expresses a perfect response, i.e. specific information.
  The point can be gained with general information as long as it is in context.
  Part A.       Max at four points
  __OVERVIEW        _ clonal selection theory
               _ humoral response
  __RECOGNITION     _ Ag bind with appropriate cell receptor; B cell response to T cell
                                         (T cell signaling)
  __PROLIFERATION   _ B cells divide (and differentiate)
               _ B cells produce plasma cells (effectors), memory cells
  __AB PRODUCTION   _ B cells produce antibody (to epitope of Ag)
               _ Antibody specificity to Ag
  __AB CHARACTERS   _ Ab types (IgM, IgE, IgA, IgG), structure of Ab
               _ Ab switching (between types)
  __GRAPH      _ dynamics of response (lag, exponential, plateau, decline)
               _ reasons for decline (suppression, turnover, Ag binding)
  __OTHER      _ factors affecting time scale, degree of response
     (such as)      _ Ag presentation (macrophage to T cell) (HLA compt. cell)
               _ IgD strip from B cell
  
  
  Part B.      Max at four points
  __SPEED      _ near immediate response
  __MEMORY          _ memory B cell fast response, stronger response
  __GRAPH      _ short lag, fast rise, extended plateau, slow decline
  __QUANTITY        _ high Ab titer, 10-100 fold increase
  __QUALITY         _ greater binding affinity
               _ more discrimination
               _ not IgM response (rather IgG, A, E)
  __OTHER      _ basis for vaccination
     (such as)      _ location of memory cell (lymphoid tissue)
  
  Part  C.     Max at four points
  __INFECTIVITY     _ T cells but not B cells
               _ T4 cells of CD4+, or T helper (TH) or effector T 
  __CELL DEATH _ decreased T cell population
               _ loss of T cell function (loss of CMI, loss of cytotoxicity, 
                      decreased lymphokines)
  __CONSEQUENCES    _ decreased B cell proliferation (such decrease leads to a
                      decrease of overall immunity)
               _ loss of T cell signalling to B cell
  __VIRAL INTERACT I     _ viral glycoproteins (gp 120, 41) bind to CD4 sites on T4 cell
               _ receptor mediated endocytosis (RME)
  __VIRAL INTERACT II  _ reverse transcription incorporation of viral genome into
                      lymphocyte genome
               _ budding leads to cell disruption (impaired function/death)
               _ viral latency
  __OTHER      _ infection leads to decreasing low Ab titer (anti HIV titer)
     (such as)      _ Ab produced to HIV forms basis for testing
               _ mutagenesis of HIV (antigenic drift)
               _ infected T cells make immunosuppressants