ObjectiveTo investigate the expression of costimulatory molecules( B7，CD28, and CTLA-4) of peripheral blood lymphocytes in patients with Behcet′s disease(BD).MethodsLymphocytes were obtained in 24 patients with BD and 20 healthy individuals, and the expression of CD80(B7-1), CD86(B7-2), CD28 and CTLA-4 on T and B cells were detected by direct three-color immunofluorescence flow cytometry.ResultsSignificantly increased expression of CTLA-4 on CD 4+ T cells[(3.18±1.18)%]was found in BD patients compared with that in controls[(1.73±0.66) %](t=－3.722,P＜0.01). The expression of CD86 on CD19+B cells was also significantly increased in BD patients[(4.49±1.73)%]compared with that in controls[(2.40±1.49) %] (t=-2.071,P＜0.05). No significant difference in the expression of the other costimulatory molecules was found.ConclusionsInteraction of B7 and CD28 on peripheral lymphocytes promote the occurrence of uveitis in BD patients. Intervention with these costimulatory signals may lead to a new prevention or treatment for uveitis patients.(Chin J Ocul Fundus Dis, 2003,19:357-359)