DIFFERENTIAL-EFFECTS OF A MONOCLONAL-ANTIBODY TO CIS-UROCANIC ACID ONTHE SUPPRESSION OF DELAYED AND CONTACT HYPERSENSITIVITY FOLLOWING ULTRAVIOLET-IRRADIATION

Urocanic acid (UCA) occurs naturally in the stratum corneum of the ski n as the transisomer and, upon exposure to UVB radiation, converts to cis-UCA. It has been proposed that trans-UCA is the photoreceptor for and, following its isomerization to cis-UCA, a mediator of the suppres sive effects of UVB irradiation on systemic T cell-mediated immune res ponses, such as contact hypersensitivity (CH) and delayed-type hyperse nsitivity (DTH). To address this question directly, we studied the con sequence of deleting the in vivo function of cis-UCA on systemic suppr ession of CH and DTH, by injecting mice with a anti-cis-UCA mAb severa l hours before exposure to UVB radiation. We found that while DTH resp onses were completely restored, the anti-cis-UCA Ab had no effect on U V-induced immunosuppression of the CH response, even though suppressor cell formation was inhibited in both cases. Further, the kinetics of IL-10 expression in the skin of irradiated mice injected with the anti -cis-UCA mAb was altered and the diminished APC function of spleen-adh erent cells from UVB-irradiated mice was totally reversed by the Ab. T hese findings suggest that cis-UCA acts as a mediator for some but not all of the systemic suppressive effects of UVB irradiation. They also suggest that cis-UCA may act indirectly via IL-10 to modulate immune function.