Suppression of contact hypersensitivity by short-term ultraviolet irradiation: I. Immunosuppression by serum from irradiated mice.

Serum from UV-irradiated mice was shown to be immunosuppressive in vitro and in vivo. It suppressed leucocyte adherence inhibition reactions of cells from sensitized syngeneic and allogeneic mice, and suppressed the development of contact hypersensitivity after passive transfer to mice. Supernatants of cultures of spleen cells from irradiated mice were also suppressive. The suppressive factors in sera and culture supernatants were non-dialysable. The suppressive effect of UV irradiation was abrogated by cyclophosphamide, but this restored reactivity was still inhibited by serum from irradiated donors; this suggests that the serum factor requires T suppressor cells for its production but not for its action. The level of interleukin 1 (IL-1) was not raised in serum from UV-irradiated mice; thus the serum factor appears not to be IL-1.