Blood Group Antibodies is Involved in AHG
Generally antibodies involved in AHG reactions are of two types, namely the complete and the incomplete, anti-bodies. Whereas the complete antibodies agglutinate red cells in saline medium, the incomplete types of antibody sensitize red cells without agglutination. AHG is a balanced ready to use blend of highly purified immunoglobulins.
It contains anti human lgG antibodies and antibodies reactive with human complement components C3b and C3d and they are the incomplete antibodies.
In Anti-lgG, AHG must contain antibody activity to non- agglutinating blood group antibodies. The majority of these antibodies are a mixture of lgG1 and lgG3 subclass. Rarely, non agglutinating lgM antibodies may be found; however, they have always been shown to fix complement and may be detected by anti-complement (Mollison, 1983). lgG anti-bodies with Rh specificity have been reported; however, lgG antibodies activity has always been present as well.
The only Red blood cell alloantibodies that have been reported as being solely lgA have been examples of anti-Pr, (Garratty, 1973), and those antibodies were agglutinating. lgA auto antibodies have been reported, although very rarely. (Petz, et al., 1980). Therefore, anti-lgG activity must be present in the AHG reagent. Anti-lgM and anti-lgA activity may be present but neither is essential. The presence of anti-light chain activity allows detection of all immunoglobulin class.
In the case of Anti-complement, some antibodies “fix” complements to the red blood cell membrane after complexing of the antibodies with its corresponding antigen. These membrane-bound complement components can be detected by the anti complement activity in AHG. Each AHG reagents were prepared using a crude globulin fraction as the immunogen. In 1947, Coombs and Mourant demonstrated that the antibodies activity that detected Rh antibodies was associated with the anti-gamma globulin fraction in the reagent.
The first indication that there might be another antibody activity present that had an influence on the final reaction was presented by Dacie in 1951. (Dacie, 1951). He observed that different reaction patterns were obtained when dilutions of AHG were used to test cells sensitized with ‘warm’ as compared with ‘cold’ antibodies.
In 1957, Dacie and Coworkers (Dacie, 1957) published data showing that the reactivity of AHG to cells sensitized with “warm” antibodies resulted from anti-gammglobulin activity, whereas anti-nongamma globulin activity was responsible in the activity of cells sensitized by “cold” antibodies. The nongamma globulin component was shown to be the globulin and had specificity for complement. Later studies (Harboe, 1963; Jenkins, 1960) revealed that the complement activity was a result of C3 and C4.
In 1960s, there were many reports published indicating the need for anticomplement activity in AHG to allow the detection of anti-bodies by the indirect antihumanglobulin test (IAT). (Polley 1961, Stratton 1986). Examples of the antibodies that were generally considered to be of little clinical significance are anti-Lea, anti-p1, and anti-H. Evidence was also presented showing that the presence of anticomplement activity would enhance the reactions of clinically significant antibodies such as anti-Fya and anti-K. (Polley 1961).
Table 4: antibodies capable of binding complement.