Induction of suppression of delayed type hypersensitivity to herpes simplex virus by epidermal cells exposed to UV-irradiated urocanic acid in vivo.

Urocanic acid (UCA), the putative photoreceptor for ultraviolet radiation (UV)-induced suppression, undergoes a UV-dependent trans to cis isomerisation. Epidermal cells from mice painted with UCA, containing a known proportion of the cis-isomer, generate suppression of the delayed type hypersensitivity response to herpes simplex virus type 1 (HSV-1) when transferred to naive syngeneic recipients at the same time and site as infection with HSV-1. One T suppressor cell subset, of phenotype (Thy1+, L3T4+, Ly2-), is induced by the cis-UCA modified epidermal cell transfer. Flow cytometric analysis of the epidermal cells from skin treated with UV or cis-UCA indicates an overall reduction from normal in the number of cells expressing MHC Class II antigens, but no alteration in the number expressing I-J antigens.