FREQUENCY AND SPECIFICITY OF PLATELET-SPECIFIC ALLOANTIBODIES IN HLA-IMMUNIZED HEMATOLOGIC-ONCOLOGIC PATIENTS

The frequency and specificity of platelet-alloantibodies to human plat elet antigens (HPA) -1, -3 and -5 was investigated in 59 multitransfus ed, HLA-immunized patients. Using the MAIPA test (monoclonal antibody specific immobilization of platelet antigens) platelet alloantibodies could be demonstrated in 10 (17%) patients. In one patient the antibod y was present prior to any transfusions and probably induced by multip le previous pregnancies. This antibody was directed to HPA-Sb. The rem aining nine antibodies were found in patients (n = 36) with HLA-antibo dies reacting with over 95% of unselected lymphocytes. In these patien ts the target antigens were HPA-lb in six, HPA-3a in one and both anti gens in two patients. Our findings demonstrate platelet alloimmunizati on induced by transfusions to be restricted to patients with high HLA- immunization. 25% of these patients (9/36) show platelet-specific anti bodies, primarily HPA-1b.