Melanocytes are potential immunocompetent cells: evidence from recognition of immunological characteristics of cultured human melanocytes.

The dendritic nature, the strategic location, and other accumulated evidence about the immunologic characteristics of melanocytes suggest that they are not only professional melanin producing cells but are also immunocompetent cells. In this study, we demonstrated that cultured melanocytes express low levels of some immunologically important surface markers such as intercellular adhesion molecule-1 and CD 40. Moreover, we report for the first time CD 40 expression by melanocytes can be up-regulated by interferon-gamma (IFN-gamma) stimulation. Optimal enhancement of CD 40 expression was observed at an IFN-gamma concentration of 300 U/ml after a co-culture period of 72 h. Maximal melanocyte-driven T lymphocyte proliferation and interleukin-12 secretion were also observed following the same treatment and proved to be CD 40-dependent. Our data further suggest that upon CD 40 ligation, melanocytes up-regulate their co-stimulating and adhesion molecules. In addition to previous descriptions about the melanocyte's antigen processing and presenting capacity, we therefore hypothesize a dynamic model in which melanocytes alternatively work as heterogeneous antigen presenting cells. As a result of CD 40 expression on the cell surface, melanocytes might contact and subsequently stimulate CD8+ cytotoxic T lymphocytes directly via CD 40-CD 40 L interaction in some cases.