Suppression of T-cell mediated lymphokine production but not cytotoxic activity by macrophages.

We directly compared the effects of macrophages from infiltrating MSV-induced regressing tumors (T-M0) or from the peritoneal cavity of mice previously injected with light mineral oil (LMO-M0) on two functions of alloimmune spleen cells (ISC), the cytotoxic activity and production of a lymphokine, macrophage inhibitory factor (MIF). Addition of T-M0 or LMO-M0 to ISC did not inhibit their cytotoxicity. In contrast, T-M0, but not LMO-M0, mixed with ISC inhibited their ability to produce MIF. We propose that the differential sensitivity of the two immune functions to the macrophage-dependent suppressor activity is due to the ability to M0 to inhibit lymphocyte protein synthesis, with MIF production, but not T cell killing, requiring active protein synthesis.