Immunology Assignment #1
Terra MacDonald
October 16th, 2013
1) The cross-matching procedure by which we determine whether the donor and recipient are compatible involves a hemagglutination reaction. Red blood cells have antigens on their surface and if the blood of the transfusion recipient does not have the same “type” of antigens on their red blood cells, the recipient will produce antibodies against the donor’s red blood cells which will cross-link with the antigens, causing agglutination or “clumping” of the red blood cells or even hemolysis which can be damaging or potentially fatal. If only one transfusion is to occur, and it is the first transfusion the dog in question has received, then it is not necessary to cross-match. If more than one transfusion is to occur, however, a cross-matching test should be done to ensure that the donor and the recipient are of the same type.
The primary and most important part involves mixing red blood cells from the donor and serum from the recipient. These are washed and incubated together and observed for hemolysis. If hemolysis occurs, the transfusion should not be carried out. If no hemolysis is observed, a minor cross match (described below) should be performed in order to thoroughly determine if the two dogs are compatible.
The secondary procedure is less important and involving mixing serum obtained from the donor and red blood cells from the recipient (the opposite of the primary hemolysis reaction). They will be washed and incubated together and observed for hemagglutination. If hemagglutination occurs then it can be said that the two blood types are not a “match” but the transfusion may still go ahead under certain circumstances. Especially in larger size recipients (larger dogs, for example), sufficient hemodilution will occur so that the likelihood of a transfusion reaction is quite low. If the transfusion is to occur for a small recipient, the donor serum should be appropriately diluted before transfusion.
2) DEA1.1 testing is important in order to ensure that no DEA1.1 positive dogs are allowed to donate to dogs that are not also DEA1.1 positive. DEA1.1 negative dogs can donate blood to both DEA1.1 positive and negative dogs. It is also important to know that certain breeds have a higher incidence of DEA1.1 such as Labrador Retrievers, where breeds such as Greyhounds have almost no incidence of this blood “type”.
In order to test for DEA1.1 antigens, several methods could be used including the cross-matching test mentioned above, using serum from a known DEA1.1 negative dog. If agglutination or hemolysis occurs in this instance, it can be said that the dog is most likely DEA1.1 positive. This test is not the most accurate method, however, since levels of DEA1.1 antigens can vary from sparse to widely expressed, depending on the individual dog and this may have an effect on the degree of agglutination and hemolysis, influencing the results.
A more accurate method which is currently being used in commercial tests for DEA1.1 antigen is the immunochromatography or lateral flow immunoassay. A membrane is impregnated with a known DEA1.1 antibody. If present, the antigen will react with the known antibody which has been labelled with a colored product. These antigen-antibody complexes will migrate towards the test zone and control zone respectively. If the test is positive, that is the antigen is present and has bound to the known antibody, it will be “captured” at the test zone and a colored band will appear. Regardless of whether or not the sample is positive for DEA1.1 antigens, a colored band will appear at the control zone. This is to ensure that the test has worked properly. This test is much more accurate and sensitive as it can determine if even small levels of DEA1.1 antigen are present.
