CD80 (B7-1) and CD86 (B7-2/B70) have recently been identified in cultured human Langerhans cells (LCs), although their role and regulatory properties remain unclear. We present our comparison of the expression of the molecules, mRNAs and the function between CD80 and CD86 in human LCs treated by interferon gamma (IFN-gamma). We examined the regulatory properties of CD80 and CD86 expression in human LCs pretreated with IFN-gamma. Flow cytometric analysis indicated that the mean fluorescence intensity of CD86 but not CD80 was enhanced. However, the percentage modulation of both CD80 and CD86 positive cells were significantly up-regulated in a dose-dependent manner, after 48-h culturing with IFN-gamma. The regulatory properties of CD80 and CD86 mRNA expressions in human LC were studied using polymerase chain reaction methods. We found that both CD80 and CD86 mRNA of enriched LCs following IFN-gamma pretreatment for 12 h were higher than those without pretreatment. We have demonstrated that the primary allogeneic mixed epidermal cell-lymphocyte reaction induced by human LCs treated by IFN-gamma increased in a dose-dependent manner. There was a 61.5% inhibition by anti-CD86 monoclonal antibody and a 32.5% inhibition by anti-CD80 monoclonal antibody. These data indicate that the CD80 and CD86 expression of human LCs may be differently regulated by IFN-gamma.