Tolerance to endotoxin in vitro: independent regulation of interleukin-1, tumor necrosis factor and interferon alpha production during in vitro differentiation of human monocytes.

Bacterial lipopolysaccharide (LPS)-induced production of three known endogenous pyrogens, interferon alpha (IFN-alpha), interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) was studied during in vitro differentiation of human peripheral blood monocytes. In freshly seeded cells, secretion of IL-1 and TNF-alpha, but not IFN-alpha were readily induced by LPS. After 24 hr and for up to 14 days of culture, monocytes became irreversibly tolerant to LPS for the release of IL-1. IFN-alpha secretion was not induced by LPS in cells cultured for up to 8 days. Monocytes also became tolerant to LPS for TNF-alpha production 48 hr after an initial stimulation with LPS. This tolerant state, however, was transient, lasting from 6 to 8 days, after which competence for TNF secretion resumed. These observations demonstrate that regulation of production of IL-1, TNF-alpha and IFN-alpha by human mononuclear phagocytes is mutually independent, related to the stage of cell differentiation and modulated by cell stimulation. Since in vitro tolerance to LPS mimics the in vivo tolerance to LPS with respect to fever, we speculate that they are closely related.