Mouse macrophage functions under the influence of factors released by spleen cells preincubated with the methanol extraction residue (MER) tubercle bacillus fraction.

Exposure of mouse peritoneal macrophages in vitro to the nonspecific immunomodulator MER (methanol extraction residue fraction of phenol killed, acetone washed tubercle bacilli) failed to heighten their phagocytic and bacteriostatic activities toward Staphylococcus albus, even when amounts of the agent below the threshold of gross toxicity were employed. In contrast, exposure of such macrophages to supernatants of whole splenocyte suspensions that had been obtained from normal donors and were incubated with MER resulted in consistent potentiation of both phagocytosis and bacteriostasis. The findings suggest that the MER effect on macrophages function is mediated, in this system, by soluble lymphocyte product(s).