Association of HLA-DRw2 with autoimmune thrombocytopenic purpura.

Peripheral blood lymphocytes from 38 patients 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 less than 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 less than 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 less than 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 histocompatibility system.