Subdivisions of Group A and Group AB

Abstract

Summary and Conclusions Evidence is presented to show that the agglutinogens A and B are probably regularly antigenic for human beings whose blood lacks the corresponding properties. A case is described which illustrates the immunization of a group B individual against agglutinogen A as a result of a transfusion of 150 ml of group AB blood. Two cases are described which illustrate the isoimmunization of A2 individuals to A1 blood. In one the antigenic stimulus was provided by a transfusion of A1 blood; in the other, the source of the antigen was a fetus in utero. Because of the presence of immune α1 isoagglutinins in these patients' sera only A2 donors were used for subsequent transfusions, with satisfactory results. Evidence is presented which indicates that had A1 donors been used, hemolytic reactions most likely would have resulted. The fact that cases similar to the two described in this paper have not been described previously indicates that isoimmunization based on subgroup differences must be rare, and probably even less frequent than isoimmunization against property Rh. This suggests that some equally rare constitutional anomaly may be required for an individual to produce immune α1 (or α2) isoantibodies. One possibility is that the A agglutinogen in the cells is poorly developed (as in the rare individuals of subgroup A3 and A3B); our two patients had typical A2 blood cells, however. Another possibility is that the serum contains weak irregular α1 (or α2) isoagglutinins to begin with. Observations are described which indicate that this was the probable explanation in at least one of our patients. Reference to only one instance of immunization of A1 individuals by transfusions of A2 blood could be found in the literature. There is some evidence that the transfusion of group O blood into group A1B individuals can stimulate the formation of immune anti-O isoantibodies. This would be a source of danger where “universal” donors are used for transfusing group AB patients. When selecting donors for patients of subgroups A and AB, it is probably safe to disregard the subgroups except in the rare cases where the patient's serum contains an irregular isoagglutinin, α1 or α2. Where the irregular isoagglutinin is present only donors of the homologous subgroup should be used.