The suppressive effect of immunization on the proliferative responses of rat T cells in vitro. II. Abrogation of antigen-induced suppression by selective cytotoxic agents.

Rats given large i.v. doses of ovalbumin or sheep erythrocytes manifest suppressed spleen cell responses (3H-thymidine incorporation) to PHA within hours. Removal of glass wool-adherent cells totally restores responsiveness to that of normal nonadherent spleen cell cultures. Carrageenan, selectively toxic for macrophages, partially restores responses of antigen-suppressed spleen cells in culture, suggesting a supportive role for macrophages in the suppression phenomenon. Treatment of donors with low doses of cyclophosphamide (20 to 50 mg/kg) at the time of antigen injection abrogates the ability of their spleen cells to suppress the responses of normal cells to PHA. The low dose of cyclophosphamide required indicates a target other than the B cell or macrophage and suggests the possibility that cyclophosphamide eliminates the suppressor T cell component of the macrophage-T cell complex.