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

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.