Cytotoxicity of human macrophages for tumor cells: enhancement by bacterial lipopolysaccharides (LPS).

Bacterial lipopolysaccharide (LPS) stimulates human macrophages derived from peripheral blood monocytes to kill tumor cells in vitro. Maximum cytotoxicity was observed after 8 to 24 hr of incubation with LPS. However, if the macrophages are activated with LPS for 8 hr and then maintained in medium for an additional 16 hr before assay, their cytotoxic capacity is lost. In comparison to normal macrophages, LPS-activated macrophages were cytotoxic to the three malignant cell lines tested but had no effect on the three nonmalignant cell lines. Human macrophages can be made tumoricidal by the addition of greater than or equal to 10 microgram/ml LPS, and the effect is abolished in the presence of polymyxin B.