Studies on the HLA Class-II Antigens of a Patient Presenting a Double Alloimmunization Following Posttransfusion Purpura

Abstract

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 likely causes of post-transfusion purpura (PTP) and neonatal alloimmune thrombocytopenia. However, the way in which HLA (class-II) antigens participate 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/µ1) 8 days after receiving red cell concentrates during coronary bypass surgery. During treatment with intravenous gamma-globulin 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 antigens (MAIPA) assay performed with serum prepared at the height of her initial thrombocytopenia revealed antibodies to both the Pl^A1 and the Br^a alloantigens. This rare combination prompted us to study the expression of specific HLA class II antigens in the patient. HLA-DR and DQ typing was performed from genomic DNA by the recently developed polymerase chain reaction-restriction fragment length polymorphism procedure (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 evidence linking an immune response to Pl^A1 and Br^a antigens with HLA-DR52a/c and DR6.