Regulatory role of suppressor T cells in the expression of delayed-type hypersensitivity in mice. II. Soluble factor from thymic suppressor cells stimulated with antigen in vitro and its possible interaction with macrophages.

Thymus cells from mice primed s.c. with a high dose (10 mg) of lysozyme (Lys) specifically suppressed delayed footpad reaction (FPR) in mice previously immuned with lipid-conjugated lysozyme (D.Lys), and also suppressed the transfer of FPR by D.Lys-immune spleen cells into normal mice. Furthermore, they inhibited antigen-stimulated DNA synthesis of D.Lys-immune spleen cells in vitro. If the suppressor thymus cells were cultured with Lys in vitro, they produced soluble factor which depressed the ability of D.Lys-immune spleen cells to transfer FPR. Both supernatant of culture without Lys and extract of suppressor thymus cells were inactive in supression of FPR. The suppressor factor was antigen-specific because its suppressive activity was absorbed with Lys but not with an unrelated antigen lactalbumin. The factor failed to depress the ability of D.Lys-immune spleen cells to transfer FPR when the spleen cells were depleted of glass-adherent cells. In addition, incubation of peritoneal exudate cells from normal mice with the factor rendered the cells suppressive for passive transfer of FPR. These results suggest that the suppressor factor depresses the effector function of T cells responsible for FPR possibly via macrophage.