The following set of questions is mostly taken from Ettinger�s book.  It turned out shorter than I thought. :)

QUESTIONS

1. What do CD4 & CD8 refer to?
    
2. An antibody is Y shaped and has 2 light chains & 2 heavy chains.  Where are they?
    
3. Why do we run 2 mercapto ethanol titers?
    
4. What are the components of an IgA molecule?
   
   
   
   
    

ANSWERS

1. These are glycoproteins on T cells.  CD4 is on the helper T cell  while CD8 is on the killer T cell.
   
   
   
   
    
2.             \\   //    
                \\ //
                  II
                  II
   
   I hope this illustration works.  The light chains are on the outside of the arms of the Y.  The heavy chains are on the inside & include the stem of the Y.  The arms of the Y have a �variable region�  at the tips of the arms.  This is the antigen receptor.  the constant regions  (Fc) are pretty much the rest of the antibody.  The �variable region� is also called the �idiotype� of the antibody.
   
   
   
   
    
3. I guess we don�t really run these so much anymore.  First run a titer for say parvo.  then treat the sample with 2 ME.  This will destroy IGM.  The titer is rerun and if it drops dramatically this means that most  of the antibodies in the originial titer were IgM and therefore recently produced.  This indicates that the titer is from a recent infection or recent vaccination.  If there is no history of recent vaccination, then it must be a recent (active) infection.
   
   
   
   
    
4. IgA is a dimer.  It has two antibodies and a J chain.  (IgM also has a J chain - it is involved in polymerization.)  IgA also has �secretory component� which is synthesized by epithelial cells.