Effect of X-irradiation on epidermal immune function: decreased density and alloantigen-presenting capacity of Ia+ Langerhans cells and impaired production of epidermal cell-derived thymocyte activating factor (ETAF).

The mechanisms involved in the modulation of cutaneous immune responses by UV radiation have been extensively investigated; by contrast, few studies have addressed the effects of x-irradiation on epidermal immune function. We therefore investigated the effect of x-irradiation of mice on: (a) the density of epidermal Ia+ Langerhans cells (LC) in immunofluorescence studies, (b) epidermal cell (EC) allostimulatory capacity in the allogeneic EC-lymphocyte reaction (ELR), and (c) production of epidermal cell-derived thymocyte activating factor (ETAF). C3H/He and BALB/c mice were irradiated with 900, 1,800, 2,700, or 3,600 rad from a 137Cs source, and sacrificed 10 h or 3 days later. X-irradiation of mice 10 h previously only slightly decreased the density of epidermal Ia+ LC and did not affect the capacity of their EC to stimulate allogeneic responder lymphocytes in the ELR. X-irradiation of mice 3 days previously, however, resulted in a dose-dependent decrease in the density of Ia+ LC. This decrease was accompanied by a substantial reduction in EC allostimulatory capacity in the ELR at all doses of x-irradiation. ETAF production by cultured EC from mice x-irradiated 3 days previously was also found to be diminished at all doses of x-irradiation. Trypan blue exclusion studies demonstrated that the observed decreases in EC allostimulatory capacity and ETAF production were not the result of a generalized lethal effect of x-irradiation on EC. The reduction in EC allostimulatory capacity following in vivo x-irradiation could not be reversed by addition of exogenous ETAF or interleukin-1 in the ELR. Taken together, these results indicate that x-irradiation decreases the density of Ia+ LC, impairs LC alloantigen-presenting function, and reduces ETAF production. Thus cutaneous x-irradiation may affect inflammatory and neoplastic processes not only by its antimitotic activity, but also by a direct effect on EC which subserve immunologic functions.