Ultraviolet B-induced loss of HLA class II antigen expression on lymphocytes is dose, time, and locus dependent.

Ultraviolet B (UVB) irradiation interferes with the afferent and efferent loops of the immune response. One mechanism that has been suggested is the decline of class II histocompatibility antigen expression on the cell surface. However, data in the literature are controversial. In the present study, we examined the effect of UVB light (peak emission at 302 nm), at doses of 0.05-300 mJ/cm2, on class II antigen expression on normal peripheral blood lymphocytes enriched for non-T cells. Monoclonal antibodies directed at nonpolymorphic determinants on HLA-DR, -DQ, and -DP were used to label cells before and at time intervals up to 72 h after irradiation. Immediately following UVB exposure, fluorescence intensity for all three antigens was equal to or slightly increased above control values. Subsequently, there was a decline in antigen expression that was UVB dose dependent and varied for HLA-DR, -DP and -DQ. Although there was only a very moderate loss of surface labeling for HLA-DR up to 72 h, there was a steep decline for HLA-DQ and -DP. There was no significant decline in class II antigen expression on cells exposed to 2000 or 4000 cGy of gamma irradiation. Also, there was no effect of either gamma or UVB irradiation on class I antigen expression. These data explain some of the discrepancies in previous reports on the effects of UVB on class II antigens; they show not only a dose effect but also an effect of time after exposure and, most importantly, the class II antigen under study.