Suppression of tumor necrosis factor a production by cAMP in human monocytes: Dissociation with mRNA level and independent of interleukin-10

Background. Elevation of cellular cAMP inhibits lipopolysaccharide (LPS)-st imulated tumor necrosis factor alpha (TNF-alpha) production and increases t he expression of interleukin (IL)-10 in mononuclear cells. TNF-alpha gene e xpression obligates activation of the transcription factor nuclear factor k appaB (NF-kappaB). Exogenous IL-10 inhibits NF-kappaB in monocytes and thus attenuates TNF-alpha production. We examined the role of endogenous IL-10 in the regulation of NF-kappaB activation and TNF-alpha production in human monocytes by cAMP. Methods. Human monocytes were stimulated with Escherichia coli LPS (100 ng/ ml) with and without forskolin (FSK, 50 muM) or dibutyryl cyclic AMP (dbcAM P, 100 muM). Cytokine (TNF-alpha and IL-10) release was measured by immunoa ssay. TNF-alpha mRNA was measured by reverse transcription polymerase chain reaction, and NF-kappaB DNA binding activity was assessed by gel mobility shift assay. Results. cAMP-elevating agents inhibited LPS-stimulated TNF-alpha release ( 0.77 +/- 0.13 ng/10(6) cells-in LPS + dbcAMP and 0.68 +/- 0.19 ng/10(6) cel ls in LPS + FSK, both P < 0.05 vs 1.61 +/- 0.34 ng/10(6) cells in LPS alone ). Conversely, cAMP enhanced LPS-stimulated IL-10 release (100 +/- 21.5 pg/ 10(6) cells in LPS + dbcAMP and 110 +/- 25.2 pg/10(6) cells in LPS + FSK, b oth P < 0.05 vs 53.3 +/- 12.8 pg/10(6) cells in LPS alone). Neither TNF-alp ha mRNA expression nor NF-kappaB activation stimulated by LPS was inhibited by the cAMP-elevating agents. Neutralization of IL-10 with a specific anti body did not attenuate the effect of cAMP-elevating agents on TNF-alpha pro duction. Conclusion. The results indicate that cAMP inhibits LPS-stimulated TNF-alph a production through a posttranscriptional mechanism that is independent of endogenous IL-10. (C) 2001 Academic Press.