In vitro generation of tumoricidal properties in human alveolar macrophages following interaction with endotoxin

Human alveolar macrophages (AM) obtained by bronchoalveolar lavage from healthy nonsmoking donors exhibited primarily low levels of cytolytic activity against allogeneic tumor target cells. These AM acquired enhanced capacity to kill tumor cells following a 24-hr incubation in vitro with endotoxin [lipopolysaccharide (LPS)]. Maximal tumoricidal activity of LPS-activated AM as measured by lysis of tumor target cells was obtained after incubation with tumor cells for 72 hr. LPS-activated AM lysed allogeneic tumor cell lines of different origins but did not affect normal, nonneoplastic cells. We conclude that LPS induces human AM to become tumoricidal. This method should be useful in studies on therapeutic agents enhancing AM-mediated cytotoxicity in situ.