Suppressor cells and soluble factors from the spleens of UV-irradiated mice

Several indices of splenic reactivity were measured daily after ultraviolet (UV) irradiation of mice. Spleen weight increased to a maximum after 5 days. Suppressor cell activity, manifested in various assays, peaked slightly earlier. The ability of passively transferred spleen cells to suppress the induction of contact hypersensitivity (CHS) was maximal after 4 days, as was the production of soluble suppressor factors in culture. The factors were detected by suppression of CHS in vivo and leucocyte adherence inhibition (LAI) in vitro. These assays appeared to detect different factors: an I-J- factor active in CHS assays and an I-J+ factor active in LAI assays. The latter factor required CD4-, CD8+ lymphocytes for its production