title: Tumor necrosis factor production by human monocytes is a regulated event: induction of TNF-alpha-mediated cellular cytotoxicity by endotoxin.
abstract: Expression of cellular cytotoxicity by monocytes or macrophages has been conceived as an induced function secondary to collaboration in the immune response or to other agonists. However, a form of spontaneous cellular cytotoxicity by monocytes analyzed with unseparated human peripheral blood mononuclear cells (PBM) has been described by using the 6-hr 51Cr release from actinomycin D (ActD)-treated murine WEHI 164 cells, a target cell refractory to the cytotoxic effects of natural killer and cytolytic T cells. We observe that when cells are isolated under rigorously endotoxin-free conditions, there is no cytotoxicity. Inclusion of serum does not induce cellular cytotoxicity; however, cytotoxic activity is induced by the presence of as little as 1 pg/ml of bacterial lipopolysaccharide (LPS). PBM required 2 hr of preexposure to endotoxin in order to express full cytotoxic activity. We investigated the basis of the cytotoxicity of WEHI 164 cells and the effect of ActD. ActD-treated target cells are highly susceptible to the effects of TNF-alpha and TNF-beta (alpha-lymphotoxin), whereas untreated target cells were resistant. In contrast, ActD does not affect susceptibility to the cytotoxic effects of H2O2, and interleukin 1 is not cytotoxic to the target cells. With the use of a neutralizing monoclonal antibody specific for TNF-alpha, the cytotoxic activity induced by LPS greatly diminished and the amount of TNF-alpha neutralized is similar to that required for equivalent cytotoxicity. We conclude that monocytes present in human PBM are not "spontaneously" cytotoxic for ActD-treated WEHI 164 target cells, but that the reported cytotoxicity results from exposure to a level of endotoxin or endotoxin-like agonists to which the cells are exposed. The cytotoxicity is mediated mostly if not entirely by TNF-alpha, an established product of monocytes/macrophages. With the use of endotoxin-free conditions, PBM can be isolated in a cytotoxically latent state, suitable for analysis of the immunologic regulation of TNF-alpha-mediated monocyte cellular cytotoxicity.
mesh_terms: D002460:Cell Line; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic; D003609:Dactinomycin / Q000494:pharmacology; D004731:Endotoxins / Q000494:pharmacology; D006023:Glycoproteins / Q000096:biosynthesis* / Q000276:immunology; D006801:Humans; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D009000:Monocytes / Q000187:drug effects / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha
chemical_list: D004731:Endotoxins; D006023:Glycoproteins; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin