Minimal expression of blood group A antigen on thrombocytes from A2 individuals

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Abstract
Two multiply transfused group O patients developed refractoriness to random-donor platelet transfusions. Both had high-titer IgG antibodies to group A and B antigens. Subsequent transfusions with ABO-compatible platelets were successful, suggesting that the ABO blood group system is significant in the development of refractoriness to platelet transfusions. By indirect immunofluorescence, the patients'' IgG anti-A reacted with platelets from group A1 donors but not with those from group A2 donors. A2 platelets were at least 38 times less efficient at adsorbing a mouse monoclonal anti-A; the difference between the absorbance capacities of A2 and O platelets was minimal. Transfusion of A2 platelets, unlike that of A1 platelets, effected as good increment in the platelet counts of these two patients. The results indicate that the expression of A2 antigen on platelets from A2 subjects is minimal.