SUPPRESSIVE AND ENHANCING EFFECTS OF ULTRAVIOLET-B RADIATION ON EXPRESSION OF CONTACT HYPERSENSITIVITY IN MAN

Ultraviolet B (WB) radiation has multiple effects on the immune system , and these effects contribute to the development of UVB-induced skin cancers in mice, and probably man. Depending upon dose and duration of WB exposure, the resultant immune aberrations may be strictly local ( at the irradiated skin site) or systemic, One important local effect o f acute, low-dose UVB regimens is impaired induction of contact hypers ensitivity (CH), Because a significant proportion of humans who develo p CH when hapten is painted on UVB-exposed skin fall to display a prim ary allergic reaction at that site, we inquired into the effects of UV B radiation on the expression of CH in man, A high proportion of indiv iduals who were first exposed to a sensitizing dose of hapten via UVB- exposed skin displayed CH when challenged on unirradiated (normal) ski n 11 d later, However, only 50% of these subjects developed CH when ch allenged simultaneously on skin that had been exposed to UVB radiation 11 d previously, Because the density of epidermal antigen-presenting cells was comparable in both responders and non-responders, we interpr et these findings to mean that UVB radiation can create a sustained im munosuppressive microenvironment that inhibits the expression of CH, I n separate experiments, when normal volunteers were sensitized with ha pten via unirradiated (normal) skin, expression of CH at UVB-exposed c hallenge sites 11 d later was found to be enhanced, at least in some i ndividuals, compared to expression of CH at unirradiated challenge sit es, Thus, the local effects of UVB radiation on expression of CH in ma n may be enhancing or inhibitory, depending upon whether initial sensi tization occurred through normal or through UVB-exposed skin.