The pyrogenic cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) appear in the circulation during infections and injuries, but TNF-alpha and IL-6 are regulated differently in macrophages. We compared the effects of elevated temperatures within the usual febrile range on the expression of TNF-alpha and IL-6 in vitro in lipopolysaccharide (LPS)-stimulated human macrophages derived from peripheral blood monocytes (HuMoM phi). During an 18-h incubation at 37 degrees C with 5 ng/ml LPS, these cells released 5,030 +/- 1,460 pg TNF-alpha/10(6) cells (means +/- SE) and 1,380 +/- 280 pg IL-6/10(6) cells. In LPS-stimulated HuMoM phi incubated at 40 degrees C, TNF-alpha release was almost completely inhibited (76 +/- 76 pg TNF-alpha/10(6) cells; P < 0.01 compared with LPS-stimulated HuMoM phi at 37 degrees C), but release of IL-6 was preserved (1,600 +/- 780 pg IL-6/10(6) cells). Western and Northern analyses showed that levels of TNF-alpha mRNA and cell-associated and secreted TNF-alpha protein were decreased, but IL-6 expression was unchanged at 40 degrees C in LPS-stimulated macrophages. Incubating HuMoM phi at 40 degrees did not alter their viability after 18 h but induced a 75-fold increase in levels of the inducible heat-shock protein 72 (HSP-72) mRNA in the face of a 56% inhibition in total protein synthesis. Our results show that IL-6 expression persisted at incubation temperatures in the upper end of the physiological range that induced heat shock and attenuated the expression of functionally active TNF-alpha in LPS-stimulated HuMoM phi.

We have previously reported that sustained tumor necrosis factor (TNF)-alpha expression is suppressed by temperatures in the febrile range in human macrophages. In this study, we examined the mechanisms of high-temperature-induced macrophage TNF suppression in the RAW 264.7 macrophage cell line. Incubating lipopolysaccharide (LPS)-stimulated RAW 264.7 cells at 40 degrees C reduced TNF secretion by 92% and peak TNF mRNA levels by 43% compared with cells incubated at 37 degrees C (P < 0.05) but did not affect levels of glyceraldehyde-3-phosphate dehydrogenase, beta-actin, or interleukin-6 mRNA. TNF mRNA half-life, measured after transcriptional arrest with actinomycin D, was reduced from 21.8 +/- 3.6 min in LPS-stimulated RAW 264.7 cells at 37 degrees C to 16.0 +/- 1.8 min at 40 degrees C (P < 0.03), but these cells at 40 degrees C did not alter transcription rate or TNF mRNA polysome association. TNF mRNA destabilization occurred at temperatures below the threshold (43 degrees C) for the generalized heat shock response in these cells. We conclude that heating macrophages to febrile-range temperatures attenuates sustained TNF expression by modulating posttranscriptional processing, including acceleration of TNF mRNA decay.

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