Objective To study CD40 expression on melanocytes induced by IFN-?and its significance. Methods CD40 expression was detected by flow cytometry. The capacity of melanocytes to stimulate T lymphocytes was evaluated by mixed ly mphocyte reaction and the supernatant cytokine levels were determined by ELISA. ResultsHuman melanocytes(MC) cultured in vitro expressed low but detectable CD40 surf ace protein. The surface expression of CD40 was markedly up-regulated by stimul ation with interferon(IFN)-?with different concentrations for 24 hours,48 hour s and 72 hours, respectively. The expression of CD40 was correlated with IFN-? levels after 24 hour incubation. MC underwent a morphologic change with an incre ased capacity to stimulate allogenic lymphocytes to proliferate after IFN-?sti mulation. Optimal enhancement of stimulating index(SI) was observed at an IFN-?concentration of 300 IU/ml after 72 hour treatment. Meanwhile concentrations o f interleukin-12 but not interleukin-8 or 10 were obviously increased in the s upernatants of cultured MC. Furthermore, ligation of CD40 via soluble CD40 ligan d(SCD40L) could enhance CD80 and ICAM-1 expression, which could be blocked by s pecific monoclonal antibody to CD40L. Conclusions Since CD40-CD40L is a pair of important and special costimulating signal, it is of great value to elucidate t he fact that CD40 is functionally expressed on MC, thus for a better understandi ng of MC′s role in cellular immune responses. MC might activate cytotoxic T lym phocyte directly and not via CD4 positive lymphocyte.