STUDIES ON THE HLA CLASS-II ANTIGENS OF A PATIENT PRESENTING A DOUBLEALLOIMMUNIZATION FOLLOWING POSTTRANSFUSION PURPURA

In the Caucasian population, platelet incompatibility within the HPA-1 (Pl(A1/A2)) and HPA-5 (Br-a/b) alloantigen systems are the two most l ikely causes of post-transfusion purpura (PTP) and neonatal alloimmune thrombocytopenia. However, the way in which HLA (class-II) antigens p articipate in alloantibody formation is unclear. The patient (M-J.G.) is a middle aged woman with two children who developed a severe PTP (< 2000 platelets/mu l) 8 days after receiving red cell concentrates duri ng coronary bypass surgery. During treatment with intravenous gamma-gl obulin and corticosteroids, her platelet count peaked, fell again, and returned to normal over a period of several months. Western blotting and/or the monoclonal antibody specific-immobilization of platelet ant igens (MAIPA) assay performed with serum prepared at the height of her initial thrombocytopenia revealed antibodies to both the Pl(A1) and t he Br-a alloantigens. This rare combination prompted us to study the e xpression of specific HLA class II antigens in the patient. HLA-DR and DQ typing was performed from genomic DNA by the recently developed po lymerase chain reaction-restriction fragment length polymorphism proce dure (PCR-RFLP). The patient was found to express the DRB1()1302/1303 and DRB3()0101/0301 alleles (serological specificities: HLA-DR6 and DR52a/c respectively). She also expressed the DQA1()0102/0501, DQB1(* )0601 and DQB1()0301 alleles. Thus, this case provides further eviden ce linking an immune response to Pl(A1) and Br-a antigens with HLA-DR5 2a/c and DR6.