Rat macrophage‐mediated toxicity to cancer cells: effect of endotoxins and endotoxin inhibitors contained in culture media

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Abstract
The cytotoxic effect of normal or BCG‐activated rat macrophages on a syngeneic line of cancer cells was compared in media containing rat or bovine sera. Normal macrophages were usually cytotoxic to cancer cells in fetal or newborn bovine serum; however, they enhanced cancer cell growth in normal rat serum. BCG‐activated macrophages were toxic to cancer cells regardless of the serum used in the assay. Many cell culture media or sera obtained commercially were found to be contaminated by bacterial endotoxins. When endotoxin‐free reagents were used in the toxicity assay, different results were observed: normal macrophages were not cytotoxic, but rather, they often enhanced cell growth even in fetal bovine serum; toxicity of activated macrophages was significantly reduced in normal rat serum. These results suggest that endotoxin and endotoxin inhibitors play a role in the modulation of macrophage‐mediated cytotoxicity. These results emphasize the importance of monitoring endotoxin contamination in cell culture reagents used in assays involving macrophages.