Posttransfusion Purpura: Conversion of PL A1 -Negative Platelets to the PL A1 -Positive Phenotype by Stored Plasma is not due to the Presence of Soluble PL A1 Antigen

Abstract

Abstract

Three previous articles have reported a PL^A1 antigen in the plasma of stored blood which is capable of binding to PL^A1-negative platelets in the presence of divalent cations, rendering them PL^A1 positive. Such a mechanism could explain the enigma of posttransfusion purpura (PTP), i.e., severe thrombocytopenia in a healthy subject with PL^A1-negative platelets secondary to the infusion of blood containing PL^A1-positive platelets. We find that the PL^A1 antigen of stored blood is due to the presence of platelet fragments which can be removed by centrifugation and that divalent cation-chelating agents play no role in the apparent binding of these fragments to platelets. The apparent conversion of PL^A1-negative platelets to the PL^A1-positive phenotype by incubation with stored plasma from a PL^A1-positive subject is due to the cosedimentation of platelet fragments with the platelets. No soluble PL^A1 antigen was found in the plasma of five patients with acute posttransfusion purpura.