Association of HLA-DRw2 with autoimmune thrombocytopenic purpura

Peripheral blood lymphocytes from 38 paitients with autoimmune thrombocytopenic purpura (AITP) were tested for HLA-A, -B, and -C alloantigens. Isolated B lymphocytes from 20 of these patients were tested for HLA-DRw(Ia) alloantigens. The profile of HLA alloantigens in the patients with AITP was significantly different from that of a matched control population. The most significant finding was the presence of the HLA-DRw2 alloantigen in 75% of patients as compared with 23% in the control population, P <0.001, relative risk 10.0. (A relative risk of 1 would indicate no association between the presence of the antigen and the disease). The co-occurrence of either A3 and B7 (known to be in linkage disequilibrium with DRw2) or A26 and Bw38 was significantly increased as compared with the control population (P<0.001). Of the patients positive for DRw2, 47% had the association A26 and Bw38 as compared with the control population association incidence of 21% (P<0.1). Thus, in the patient population, A26-Bw38 appears to be a haplotype that is in linkage disequilibrium with DRw2 (as presumably is the case with A3-B7). These data indicate that a predisposition to AITP is inherited with a DRw2 gene of the major histocompatibly system.