The following set of questions is taken from the  ABVP review of immunology presented at A.C.V.I.M. this June 1994.  The transfusion questions came from a lecture on the subject also presented at this last A.C.V.I.M. conference.

QUESTIONS

1. A T cell has receptors which recognize antigen bound to something.  What is antigen bound to?  (Hint: antigen is not recognized unless it is bound to this famous membrane bound protein.)
    
2. Antigens may enter a Class I pathway or a Class II pathway and be presented to T cells in different ways.  What is the difference between a Class I  and a Class II pathway?
    
3. Do T cells recognize soluble antigen?
    
4. Some individuals simply cannot respond to vaccination.  How can this be explained considering what we know about antigen presentation?
    
5. What antibody class does an immature B cell express on its membrane as it anticipates meeting its antigen?
    
6. What is the significance of V7 membrane protein?
    
7. What does it mean when a condition is mediated by �superantigens?�
    
8. What is �Apoptosis?�
    
9. What does DEA stand for in transfusion medicine?
    
10. Which canine red cell antigens are considered clinically significant and why?
     
11. What are the most common and the rarest blood groups in the cat?
     
12. What breed of cat has never been documented as having an individual with Type B blood?
     
13. When you give a Type B cat a transfusion of Type A blood, how long do red cells last?
     
14. When you give a Type A cat a transfusion of Type B blood, how long do red cells last?
     
15. What does ACD stand for?   What does CPD-A stand for.  How long does blood last in these anticoagulants?
     
16. What is the approximate PCV of a unit of packed red cells?
     
17. What kind of freezer do you need to store frozen plasma?
     
18. Can frozen plasma be thawed in a microwave oven?
     
19. What would be a good use for Cryo-poor plasma?  (Er, you do know what cryopoor plasma is, don�t you?)
    
    
    
    
     

ANSWERS

1. The Major Histo Compatibility Complex binds antigen and together MHC & antigen is recognized by the T cell receptor.  T cells are totally unable to recognize free floating antigen. Antigen must be presented to them in combo with MHC.
   
   
   
   
    
2. The classes actually represent types of MHC:Ag complexes.  Class I peptides (antigens) are fragments originating from inside a cell (peptides floating around in the cytoplasm).  CD8  T cells recognize Class I MHC:Ag complexes and kill cells expressing non-self peptides in their MHCÕs.  Every nucleated cell in your bod presents Class I MHC:Ag complexes, mostly with self peptides.  Class II complexes are expressed on B cells, macrophages, and dendritic cells.  These MHC complexes contain peptides from outside cells.  CD4 T cells are stimulated by the Class II pathway.
   
   (FYI:  CD8 T cells = killer T cells   & CD4 T cells = helper T cells.  Easy way to remember = 8 is like �(h)ate� a destructive thing,  4 is like �for,� a helpful kind of thing.)
   
   
   
   
    
3. Nope.  They can only recognize antigen if it is bound to MHC.
   
   
   
   
    
4. Vaccines consist of peptides that enter a Class II pathway to potentially stimulate helper T cells which will in turn facilitate B cells.  In order to stimulate a helper T cell, the peptide has to be presented by an MHC.  The peptide has to structurally fit into one�s individual MHC.  If there are no peptides in the vaccine that fit an individual�s MHC there won�t be any stimulation.
   
   
   
   
    
5. B cells express IgM on their membranes.  Each B cell is programmed to be stimulated by a specific antigenic shape and the IgM it is expressing is a receptor for this specific antigenic shape.
   
   
   
   
    
6. The V7 is a membrane protein present on cells.  Helper T cells possess receptors for V7.  These receptors are noted as CD28.  When a helper T cell meets an Ag:MHC complex, before it is stimulated it checks out the V7 protein.  If V7 is present, the T cell proceeds with stimulation.  If V7 is not present,  not only is the T cell not stimulated, it actually becomes hyporesponsive.  This is one mechanism for protecting self cells.  Tumor cells do not have V7 and thus do not stimulate helper T cells (bummer!).  You can, however (in mice anyway) inject V7 right into the tumor where it is taken up by local cells and the tumor will be rejected like an incompatible graft.  Conversely, there is an antibody called CTLA4 which binds V7 with greater affinity than CD28 binds V7.  If you have a mouse with a tissue graft,  you can give CTLA4 and cover up V7 and the graft will take.  
   
   
   
    
7. There are some antigens which can actually stimulate many T cells at the same time.  These antigens have much less specific binding than regular antigens.  Rheumatoid arthritis & SLE may be superantigen mediated certainly toxic shock syndrome is.
   
   
   
    
8. Apoptosis is basically programmed cell death.  Cells have a sort of a timer that tell them that their time is up and they die.  Cytotoxic T cells kill cells not only by lysis but by activating this timer and causing cell death.  (Does anyone remember on Star Trek the Next Generation when Data entered the Borg collective computer and gave the Borg an instruction to all go to sleep?  It�s sort of the same.)
   
   
   
    
9. DEA stands for Dog Erythrocyte Antigen.
   
   
   
    
10. DEA 1.1, DEA 1.2, and DEA 7 are considered clinically significant though 1.2 & 7 are some what controversial.  DEA 1.1 & 1.2 are considered hemolytic.  If you give DEA 1.1 or  1.2 to a recipient, you can cause a massive hemolytic reaction.  This is why canine donors should be negative for these antigens.  (Also note that in a cross match DEA 1 antigens can cause a hemolytic reaction in the tube rather than the usual hemagglutination & fool you into thinking the cross match is compatible.).  DEA7 is significant because naturally occuring antibodies against DEA7 have been documented and could potentially exist in a recipient.  Donors should also be negative  for DEA 7.
    
    
    
     
11. Type A is by far the most common and type AB is very  very rare.
    
    
    
     
12. The Siamese cat appears not to have Type B individuals as far as anyone knows.
    
    
    
     
13. Giving Type A blood to a Type B  cat is a very bad thing.  There is a 30% mortality rate with this combination and red cells last less than 2 hours.
    
    
    
     
14. This isn�t as bad as the above combination.  Transfusion reactions are not as common  (apparently not every Type A cat has anti-B antibodies--- only 35% of them).  Red cells last about 2 days.  In a compatible transfusion, red cells last about a month.
    
    
    
     
15. ACD = Acid Citrate Dextrose
    Citrate inhibits the calcium dependent steps of coagulation. (However, if you mix lactated ringers into blood, the calcium in the ringers will overwhelm the citrate and clot your transfusion :(   
    
    Dextrose is used as fuel/food for the stored RBC�s
    
    CPD-A = Citrate Phosphate Dextrose with Adenine
    Phosphate and adenine are used by stored red cells as substrate for ATP production. 
    
    Blood is said to last 21 days in ACD.  Blood lasts 35 days in CPD-A for humans.  Most of us were taught 35 days in CPD-A for dogs but it turns out not to be the same as for humans.  Dog blood only lasts 21 days in CPD-A (and probably less in ACD). Feline blood lasts 28-30 days in CPD-A.
    
    
    
     
16. The PCV of packed red cells is about 80%.
    
    
    
     
17. To freeze plasma you need any old freezer but you have to know something first.  If you have a modern freezer (ie no de-frost freezer)  this freezer will continually freeze & thaw so as not to built up ice.  In such a freezer, plasma lasts 3 months.  In an old fashioned freezer that just stays frozen & doesn�t do any of this thawing business, plasma lasts 1 year.
    
    
    
     
18. Well, yes, you can use a microwave to thaw plasma but I wouldn�t recommend it as it is easy to cook the plasma.  In this event, you have ruined the unit and have a bag full of cooked egg whites (albumen  you recall) and rather expensive ones at that.
    
    
    
     
19. To make cryoprecipitate, you take a unit of frozen plasma.  Thaw it in a refrigerator until it is slushy.  Centrifuge it at an especially fast rate and extract the cryopoor plasma leaving the foamy cryoprecipitate in the bag.  Cryoprecipitate is especially rich in Factor VIII.  Cryopoor plasma is an excellent source of K factors.