Effects of cyclosporin A on resident and passenger immune cells of normal human skin and UV-induced erythema reactions.

Cyclosporin A (CyA) has proved effective in various dermatological diseases, but its mechanisms of action within the skin are still ill-defined. In order to characterize more clearly the cellular targets of CyA we examined its effects on skin immune cells in normal and UVB- and PUVA-irradiated skin by means of a three-step immunoperoxidase reaction and immunofluorescence double-labelling technique. The CyA-induced depletion of epidermal Langerhans cells equals that seen with UVB or PUVA alone. CyA alone has no effect on the number and distribution of dermal cells. CyA modulates the UV irradiation-induced changes by: (i) inhibiting the UVB- and PUVA-induced ICAM-1 expression by keratinocytes and (ii) suppressing the PUVA-induced upregulation of CD11a expression by macrophages (72 +/- 12% of Ki-M8+ macrophages express CD11a with PUVA, compared with 20 +/- 5% with CyA + PUVA, P < 0.001). Neither treatment affected ICAM-1 expression by endothelial cells. In addition, CyA increases PUVA minimal phototoxicity dose from 10 +/- 2.6 J/cm2 (PUVA alone) to 15.3 +/- 3.1 J/cm2 (CyA + PUVA), (P < 0.001). In conclusion, the effects of CyA on the skin include a down-modulation of the PUVA-erythema reaction, associated with a direct or indirect modulation of adhesion molecule expression.