Blood group A and B antigens are strongly expressed on platelets of some individuals

It is widely thought that expression of ABH antigens on platelets is insuff icient to materially affect the survival of ABH-incompatible platelets in t ransfusion recipients, but anecdotal reports of poor survival of A and B mi smatched platelets suggest that this is not always the case. The A and B an tigen expression on platelets of 100 group A(1) and group B blood donors wa s measured, and 7% and 4%, respectively, had platelets whose A and B antige n levels consistently exceeded the mean plus 2 SD, On the basis of flow cyt ometric and statistical analysis, donors whose platelets contained higher t han normal levels of A antigen were subdivided into 2 groups, designated Ty pe I and Type II ("high expressers"). Serum A(1)- and B-glycosyltransferase levels of A and B high expressers were significantly higher than those of group A(1) and B individuals with normal expression. H antigen levels were low on the red cells of high expressers, indicating that the anomaly affect s other cell lineages, Immunochemical studies demonstrated high levels of A antigen on various glycoproteins (GPs) from high-expresser platelets, espe cially GPIIb and PECAM (CD31). The A(1) Type II high-expresser phenotype wa s inherited as an autosomal dominant trait in one family. The sequences of exons 5, 6, and 7 of the A(1)-transferase gene of one Type II A(1) high exp resser and exon 7 from 3 other genes were identical to the reported normal sequences, Further studies are needed to define the molecular basis for the high-expresser trait and to characterize its clinical implications, (Blood , 2000;96:1574-1581) (C) 2000 by The American Society of Hematology.