PUVA treatment of human keratinocytes suppresses the surface expression of intercellular adhesion molecule 1 (ICAM-1) and inhibits adherence of PHA-blasts in vitro.

To determine the basis of the therapeutic efficacy of Psoralens and UVA (PUVA) in inflammatory skin diseases, the effect of PUVA on the expression of cell adhesion molecules of keratinocytes was investigated in vitro. The addition of IFN-gamma and TNF-alpha to human keratinocytes in culture up-regulated the expression of ICAM-1 and HLA-DR on the cell surface. The cultured human keratinocytes were exposed to UVA light in the presence of 8-methoxypsoralen (PUVA). The ICAM-1 and HLA-DR surface molecules were stained by monoclonal antibodies, and the intensity of the resultant fluorescence was analyzed by FACS-can. PUVA treatment suppressed the expression of these cell surface molecules, with increasing UVA fluence. Moreover, PHA-blasts failed to adhere to PUVA treated keratinocytes. When keratinocytes were treated with PUVA prior to the addition of IFN-gamma and TNF-alpha, ICAM-1 and HLA-DR expression was suppressed. These results suggest that one of the therapeutic mechanisms of PUVA in inflammatory skin diseases is by inhibition of the adhesion of activated lymphocytes to keratinocytes due to suppression of cell surface molecules. It also suggests that PUVA may be useful as maintenance therapy for inflammatory skin diseases.