Role of protein synthesis in the activation of cytotoxic mouse macrophages by lymphokines

The role of protein synthesis during the activation of macrophages (M phi) by lymphokines (LK) was studied. Peritoneal murine macrophages elicited by proteose-peptone (pM phi) were activated with LK (supernatants from normal mouse spleen cells pulsed with concanavalin A) and tested for cytotoxicity in an 18 hr assay against 111In-labeled L5178Y lymphoma target cells. Reversible (cycloheximide and puromycin) or poorly reversible (emetine and pactamycin) inhibitors of protein synthesis were added during activation, and their effects on pM phi-mediated cytotoxicity and pM phi protein synthesis were measured. Minimal concentrations of inhibitors, reducing the rate of protein synthesis by more than 90% without toxic effects on macrophages, were chosen. Exposure of pM phi to LK for 2 to 18 hr in the presence of reversible inhibitors of protein synthesis did not affect the induction of cytolytic activity, indicating that protein synthesis was not required during the activation period. In contrast, activation of macrophages for 2 hr in the presence of poorly reversible inhibitors of protein synthesis resulted in a considerable reduction of cytolytic activity. The impairment of cytotoxic activity was also evident when pM phi were treated with such drugs during the first 2 hr of an 18 hr exposure to LK or when LK-activated macrophages were treated for 2 hr with the drugs before the addition of the targets. These results demonstrate that active protein synthesis is not required during the exposure of pM phi to LK, but that new proteins have to be synthesized to allow the expression of the cytotoxic activity in LK-activated pM phi.