ANTIGEN-ANTIBODY REACTIONS IN BLOOD GROUP SEROLOGY
a. Antibodies may react with their specific antigens in a number of ways. The
following reactions have all been used to demonstrate "in vitro" antigen-antibody
reactions in blood transfusion science:
Absorption and elution.
b. The first two methods are the most commonly used in blood group serology
and will be discussed in more detail. Inhibition and absorption/elution techniques,
although not used every day in the routine blood bank, are used regularly in the forensic
laboratory (for example, blood grouping of blood stains) and in reference laboratories.
Absorption techniques lead to a decrease in antibody activity following treatment of a
serum with RBCs having the appropriate antigens; elution refers to the technique used
to dissociate or remove antibody bound to sensitized RBCs. Precipitation, complement-
fixation, and radioimmunoassay have been utilized more in blood banks in the last few
years, particularly for the detection of hepatitis virus. Fluorescence has been used to
demonstrate blood group antigens (for example, ABH) in tissues.
a. Background. It is convenient to consider antibody-mediated agglutination of
RBCs as involving two distinct stages. First, there is physical attachment of antibody to
the antigenic determinant on the RBC surface. This stage, representing the specific
immunochemical reaction, is referred to as sensitization. It may go on to involve the
binding or fixing of complement components. The second stage involves agglutination
of the sensitized cells. Agglutination results from collision of sensitized cells, allowing
cross-linking of cells to occur by the formation of antibody bridges. As the aim of blood
group serology is to obtain maximum sensitivity without loss of specificity, it is important
to understand and recognize the factors that influence the complex agglutination