Interleukin-10 stabilizes inhibitory κB-α in human monocytes

Interleukin-10 (IL-10) protects animals from lethal endotoxemia. This beneficial effect is mediated, in part, by inhibition of inflammatory cytokine production, including tumor necrosis factor-alpha (TNF-alpha). Evidence suggests that IL-10 may inhibit activation of the transcription factor nuclear factor-kappa B (NF-kappa B) through an unknown mechanism. NF-kappa B activation in response to inflammatory signals is dependent upon degradation of its associated inhibitory peptide, inhibitory kappa B-alpha (I kappa B-alpha). We hypothesized that IL-10 prevents human monocyte NF-kappa B activation and resultant TNF-alpha production by stabilization of I kappa B-alpha. The purpose of this study was to determine the effect of IL-10 on lipopolysaccharide (LPS)-induced human monocyte TNF-alpha production, NF-kappa B activation, and I kappa B-alpha degradation. Monocytes were isolated from human donors. Cells were stimulated with endotoxin (LPS, 100 ng/mL) with and without human IL-10 (10 ng/mL). Following stimulation, TNF-alpha was measured in cell supernatants by ELISA, NF-kappa B activity by electrophoretic mobility shift assay, and I kappa B-alpha levels by Western blot. We observed that after LPS stimulation of human monocytes, TNF-alpha increased to 798 +/- 67 pg/mL (p < .001 versus control). IL-10 attenuated LPS-stimulated TNF-alpha production (297 +/- 54; p < .001 versus LPS alone). After LPS stimulation in human monocytes, I kappa B-alpha protein levels decreased, and NF-kappa B DNA binding increased. IL-10 pretreat ment prevented LPS-induced decreases in I kappa B-alpha protein levels and attenuated NF-kappa B DNA binding. IL-10 appears to prevent activation of NF-kappa B by preserving I kappa B-alpha protein levels, leading to a reduction in TNF-alpha release.