Effect of a single exposure to in vivo UVB radiation on the allogeneic mixed lymphocyte reaction of spleen cells.

We investigated the effect of a single exposure to in vivo UVB radiation on the splenic T cell alloreactivity and antigen presenting cell (APC) function needed for alloantigen presentation. Splenic T cells from UVB-irradiated C57BL/6 mice were used as responders, and spleen cells from UVB-irradiated BALB/c mice were used as stimulators for a source of APCs in mixed lymphocyte culture. A single UVB radiation suppressed T cell alloreactivity, although the proliferative response to T cell mitogens was still normal. Moreover, UVB radiation impaired APC function. FACS analysis revealed a reduction not in the number of APCs but the intensity of class II alloantigen expression on APCs. Our findings suggest that, unlike repeated UVB exposure which impairs splenic APC function by the decrease in the number of APCs, a single UVB exposure impairs APC function by decreasing class II alloantigen expression.