UVA-induced immune suppression through an oxidative pathway

Although ultraviolet B (UVB) irradiation induces local immune or systemic i mmune suppression, depending on the dose, the immune suppression by ultravi olet A (UVA) has not been fully investigated. In this study, we investigate d the effect of UVA on the immune response in vitro and in vivo. The effect of UVA on the antigen-presenting function of epidermal cells was measured in terms of antigen-specific T cell proliferation. A murine epidermal cell suspension was exposed to UVA in vitro, pulsed with trinitrobenzenesulfonic acid, and cultured with T cells prepared from syngeneic mice previously se nsitized with trinitrochlorobenzene. UVA (5-20 J per cm(2)) suppressed the antigen-presenting function of epidermal cells in a dose-dependent manner, accompanied with suppression of the expression of costimulatory molecules o n Langerhans cells. In order to investigate the effect of an antioxidant on the immune suppression, an epidermal cell suspension was irradiated with U VA in the presence or absence of glutathione. The suppressions of antigen-p resenting function and ICAM-1 expression were significantly prevented by gl utathione in a dose-dependent manner. Further, the effect of UVA on the imm une response at the induction phase of contact hypersensitivity was evaluat ed in terms of lymph node cell proliferation ex vivo. UVA irradiation suppr essed the endogenous proliferation of lymph node cells in trinitrochloroben zene-painted mice, and this suppression was significantly reversed by the a pplication of glutathione to the skin during irradiation. These results sug gest that UVA-induced immune suppression may be mediated by reactive oxygen species, at least in part.