Induction of tumor necrosis factor in mice by recombinant human macrophage colony-stimulating factor

The effect of recombinant human macrophage colony-stimulating factor (rhM-CSF) on endogenous production of tumor necrosis factor (TNF) was investigated in mice. The intravenous injection of lipopolysaccharide (LPS) after the administration of rhM-CSF via the same route induced the production of endogenous cytotoxic activity in serum as assessed by using TNF-sensitive murine L929 cells. The intravenous injection of LPS alone or rhM-CSF alone did not induce cytotoxic activity. The priming effect of rhM-CSF was transient and the optimal duration between injections of primer and trigger was 3 h, while the optimal duration between trigger injection and serum sampling was 1 h after LPS injection. Moreover, preinjection of rhM-CSF enhanced the priming effect of recombinant mouse interferon-gamma. No triggering effect of rhM-CSF was observed. The cytotoxic activity in the serum was completely neutralized by anti-mouse TNF-alpha polyclonal antibody. These results indicate that rhM-CSF can be used as a priming agent for endogenous production of TNF in vivo, and raise the possibility of using rhM-CSF in cancer immunotherapy.