Tumor necrosis factor release from lipopolysaccharide-stimulated human monocytes: lipopolysaccharide tolerance in vitro.

Human peripheral blood monocytes secrete tumor necrosis factor (TNF) in response to stimulation with bacterial lipopolysaccharide (LPS). We have shown that isolated human monocytes pretreated with LPS for 24 h secrete lower levels of TNF on a second stimulation with LPS than monocytes that have been stimulated with a single dose of LPS either immediately after isolation or 24 h after isolation. The levels of TNF released by monocytes after the second stimulation with LPS are proportional to the LPS concentration over a range from 1 ng/mL to 10 micrograms/mL. Increasing concentrations of LPS used during the first 24-h stimulation induce greater suppression of TNF release after a second stimulation with LPS. After an initial stimulus of 10 micrograms/mL LPS, a second stimulation of monocytes even with 10 micrograms/mL LPS will result in TNF secretion similar to that of unstimulated cells. This in vitro tolerance apparently can be overcome by stimulating previously activated cells with phorbol myristate acetate. We have also shown that neither prostaglandin E2 nor dexamethasone added during the initial stimulation with LPS had an effect on the subsequent reduction in TNF release on a second stimulation of monocytes with LPS.