Suppression of graft-versus-host reactivity in the mouse popliteal node by UVB radiation.

A single exposure of recipient (C57BL6 X C3H-) F1 (B6C3F1) mice to UVB radiation suppressed the graft-versus-host (GVH) reaction to injected C3H- lymphoid cells, as measured by the popliteal lymph node weight gain assay. Several observations provided evidence to suggest that this effect of UVB radiation is nonspecific and involves an alteration of the host lymphoid cell component of the reaction. First, the nonspecific trauma of mild thermal injury also suppressed the GVH reaction. Second, although treatment of mice with rose bengal and visible radiation suppresses contact hypersensitivity while treatment with eosin and visible radiation does not, both types of phototoxic treatment suppressed the GVH reaction. Third, implantation of spleens from normal B6C3F1 mice into UVB-treated or thermally injured recipient mice at the time of injection of graft cells overcame the suppression of the GVH reaction. Finally, treatment of donor B6C3F1 mice with UVB radiation did not suppress the host-versus-graft reaction in recipient C3H- mice, which suggests that radiation does not alter the stimulatory function of B6C3F1 cells. These findings are all consistent with a hypothesis that UVB radiation suppresses GVH reactivity by reducing the host component of this immune response through diversion of cells from the site of the reaction. Thus an alteration of cell trafficking appears to be an additional pathway by which UVB radiation can produce immunosuppression.