Specific suppression of allograft rejection after treatment of recipient mice with ultraviolet radiation and allogeneic spleen cells.

Sensitization of UV-irradiated mice with alloantigen results in suppression of the immune response against that antigen. The induction of delayed hypersensitivity and the proliferative response of spleen cells isolated from the UV-irradiated mice are significantly suppressed. We demonstrate here that the rejection of tissue allografts is also suppressed after treatment of the recipient animals with UVR. Two signals, UVR and antigenic sensitization are required to suppress allograft rejection, exposure to UVR alone is not sufficient. The resulting immunosuppression is specific for the antigen used to sensitize the UV-irradiated animal. The induction of graft-versus-host disease was also significantly suppressed when spleen cells from UV-irradiated alloantigen sensitized mice were used to reconstitute lethally irradiated allogeneic mice. Our interpretation of these data is that the antigen-specific suppressor T cells present in the spleens of the UV-irradiated alloantigen sensitized mice are suppressing the immune response against the alloantigen. Thus, the induction of suppression by UVR serves as a novel method of suppressing graft rejection.