The Amount of Blood Group A Substance on Platelets is Proportional to the Amount in the Plasma

To investigate whether platelet ABO antigens are intrinsic to platelets or adsorbed from plasma, the amount of A-antigen on washed platelets was determined and related to the Lewis and secretor phenotypes, as these genes control the amount A, B. or H antigen present in plasma. The A-antigen on platelets was quantitated using a plate-let-erythrocyte mixed agglutination assay in 28 A, individuals of different Lewis and secretor phenotype. There was a direct correlation (r = 0.6, p < 0.01) between the agglutination score and the predicted amount of A-antigen in the plasma. The highest agglutination scores were obtained with platelets from Le(a–b–) secretors, and the lowest score with platelets from Le(a–b–) nonsecretors. The quantity of A-substance on platelets from A, individuals was significantly higher than from A2 individuals of the same Lewis and secretor phenotype (n = 17; p < 0.01). Group 0 platelets were incubated with A-plasma in order to