OBJECTIVETo study the relationship between HLA-DRB1 alleles and idiopathic thrombocytopenic purpura (ITP) in children.

METHODSPCR-SSO was used to identify DRB1 alleles of 42 children with ITP. Among them, anti-GPIIb/IIIa and anti-GPIb/IX autoantibody were detected in 36 cases by modified monoclonal antibody specific immobilization of platelet antigens (MAIPA).

RESULTS(1) Compared with healthy controls, HLA-DRB1 * 17 was significantly increased (relative risk = 2.76, P < 0.05, etiologic factor = 0.106 4) and HLA-DRB1 * 1202 decreased (relative risk = 0.20, P < 0.025, prophylactic factor = 0.761 6) in children with ITP. (2) In comparison with patients with good response to steroids and IgG therapy, HLA-DRB1 * 11 was significantly increased (P < 0.025) in patients with a poor response, furthermore, most (5/6) of HLA-DRB1 * 11-positive patients were female teen-ager. (3) Twenty-seven patients (75%) had anti-GPIIb/IIIa and seventeen (47.22%) had anti-GPIb/IX autoantibodies, the positivity rates of both anti-GPIIb/IIIa (P = 0.02) and anti-GPIb/IX (P = 0.01) were associated with HLA-DRB1 * 02. However, the pos./itivity rates of autoantibodies between refractory and non-refractory patients showed no significant difference.

CONCLUSION(1) The DRB1 * 17 seems to predict susceptibility to ITP in children, while DRB1 * 1202 appears to be protective to against ITP. (2) The DRB1 * 11 plays an important role in resistance to steroid and IgG therapy in children with ITP. (3) It seems that the response to the antigenic epitope of GPIIb/IIIa and GPIb/IX is restricted by DRB1 * 02, while the presence of the autoantibodies couldn't predict prognosis. Our preliminary findings indicate that genetic factors influence the clinical course of ITP, but its exact mechanism needs to be further investigated.