Human peripheral blood monocyte and bronchoalveolar macrophage cytotoxicity for cultured human lung tumor cells

Human peripheral blood monocytes (PBM) and bronchoalveolar macrophages (BAM) were tested for cytotoxicity toward a cultured human lung tumor cell line, A549, using a 75Se-methionine post-labelling assay. Cytotoxicity of increasing numbers of PBM plateaud at an effector cell (E):target cell (T) ratio of 3:1. In contrast, BAM cytotoxicity was significantly lower than that of PBM at low E:T ratios but increased in a dose-dependent manner approaching 100% at an E:T ratio of 20:1, this increased cytotoxicity being due to cytolysis. PBM cytotoxicity appeared to be suppressed at least partly by a factor(s) liberated by PBM themselves. The different nature of the two effector cell populations' cytotoxic dose response curves and kinetic studies, and the inability of lipopolysaccharide to stimulate a level of PBM cytotoxicity attainable by BAM, suggested that the mechanism of cytotoxicity of the two cell populations differed or that BAM were more activated than PBM, or both.