Suppression of Tumor Necrosis Factor α Production by cAMP in Human Monocytes: Dissociation with mRNA Level and Independent of Interleukin-10

Abstract

Background. Elevation of cellular cAMP inhibits lipopolysaccharide(LPS)-stimulated tumor necrosis factor α (TNF-α) production and increases the expression of interleukin (IL)-10 in mononuclear cells. TNF-α gene expression obligates activation of the transcription factor nuclear factor κB (NF-κB). Exogenous IL-10 inhibits NF-κB in monocytes and thus attenuates TNF-α production. We examined the role of endogenous IL-10 in the regulation of NF-κB activation and TNF-α production in human monocytes by cAMP.Methods. Human monocytes were stimulated with Escherichia coli LPS (100 ng/ml) with and without forskolin (FSK, 50 μM) or dibutyryl cyclic AMP (dbcAMP, 100 μM). Cytokine (TNF-α and IL-10) release was measured by immunoassay. TNF-α mRNA was measured by reverse transcription polymerase chain reaction, and NF-κB DNA binding activity was assessed by gel mobility shift assay.Results. cAMP-elevating agents inhibited LPS-stimulated TNF-α release (0.77 ± 0.13 ng/106 cells in LPS + dbcAMP and 0.68 ± 0.19 ng/106 cells in LPS + FSK, both P < 0.05 vs 1.61 ± 0.34 ng/106 cells in LPS alone). Conversely, cAMP enhanced LPS-stimulated IL-10 release (100 ± 21.5 pg/106 cells in LPS + dbcAMP and 110 ± 25.2 pg/106 cells in LPS + FSK, both P < 0.05 vs 53.3 ± 12.8 pg/106 cells in LPS alone). Neither TNF-α mRNA expression nor NF-κB activation stimulated by LPS was inhibited by the cAMP-elevating agents. Neutralization of IL-10 with a specific antibody did not attenuate the effect of cAMP-elevating agents on TNF-α production.Conclusion. The results indicate that cAMP inhibits LPS-stimulated TNF-α production through a posttranscriptional mechanism that is independent of endogenous IL-10.