Multiple Differences in Red Cell Antigens and Isoimmunization

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Abstract
Data available for 175 families with maternal isoimmunization to red blood cell antigens, exclusive of A, B, and Rh0, were analyzed for interaction of unrelated antigens. In 153 families the mother developed antibodies for single antigens, distributed among seven blood group systems; rare, high frequency antigens; and unclassified antigens. The immunizing fetal red blood cells were ABO‐incompatible with the mother in less than 5 per cent of instances, a finding attesting to the impact of ABO incompatibility on immunogenicity of most red blood cell antigens. No evidence was found for interference with immunization to one particular red blood cell antigen by simultaneous differences in unrelated antigens. Maternal immunization to more than one red blood cell antigen, encountered in 22 families, was associated in 13 instances with preceding blood transfusion to the mother and/or pregnancies in which fetal red blood cells contained only one of the immunizing antigens. In six of the remaining nine instances of multiple isoimmunization, Kidd antibodies were involved. Preceding immunization to a variety of red blood cell antigens was noted to interfere with immunization to potent immunogens: Rh0 (nine instances of complete, and one instance of partial, suppression), hr‘ (eight instances of suppression), and K (two instances of suppression). A mechanism, designated as “diversion of antigen,” was proposed in order to explain the phenomena observed in human isoimmunization as well as in animal models in which preceding immunization to one red blood cell antigen affects immune responses to red blood cells carrying the immunizing and additional antigens.