Production of reactive nitrogen intermediates by bone marrow‐derived macrophages on treatment with cisplatin in vitro
L929 culture medium (a source of macrophage colony stimulating factor (M‐CSF) or recombinant granulocyte‐macrophage colony stimulating factor (rGM‐CSF)‐derived bone marrow macrophages treated with cisplatin or lipopolysaccharide (LPS) (10 μ/ml) were effective in the production of L‐arginine‐dependent reactive nitrogen intermediates (RNI) and generation of tumouricidal activity. The abilities of RNI secretion and related tumouricidal activity against P 815 mastocytoma cells were compared. These parameters were found to be closely correlated in various experiments, RNI secretion and generation of bone marrow macrophage‐mediated tumouricidal activity were significantly inhibited by L‐N‐monomethyl arginine (L‐NMMA), a specific inhibitor of the L‐arginine pathway, but L‐NMMA did not inhibit macrophage‐mediated killing of tumour necrosis factor (TNF)‐sensitive Wehi cells, suggesting that activated macrophages exhibit at least two cytolytic mechanisms, one by L‐arginine‐dependent nitric oxide pathway and another by TNF‐mediated killing. The present findings suggest that the mechanism of tumour cell killing by activated macrophages may differ, depending on the tumour cell type, and reactive nitrogen intermediates play a major role in cisplatin‐mediated activation of bone marrow‐derived macrophages.