Alloantibody-induced platelet serotonin release is blocked by antibody to the platelet PLA1 antigen

Anti-platelet antibodies are known to activate the platelet release mechanism, usually measured by [14C]serotonin secretion. We have made immunoglobulin preparations of antibodies to HLA antigens, blood group A and platelet-specific PlA1 antigen on the platelet surface and have defined the optimal conditions for [14C]serotonin secretion by washed platelets. For optimal [14C]serotonin release, platelets were washed in apyrase and suspended in Tyrode-albumin with Ca++ and Mg++ and fibrinogen. Anti-PlA1 at high concentration did not cause [14C]serotonin release and inhibited serotonin release by other alloantibodies to antigens on the platelet surface. This was shown to be a result of the inhibition of fibrinogen binding to the platelet by bound anti-PlA1.