Interleukin-10 Induction of Nitric-oxide Synthase Expression Attenuates CD40-mediated Interleukin-12 Synthesis in Human Endothelial Cells

Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine in Th1 cell-mediated chronic inflammatory diseases such as, e.g. Crohn's disease. Moreover, IL-10 has been shown to limit the progression of atherosclerosis, presumably by influencing endothelial cell function. Here we demonstrate that under pro-inflammatory conditions expression of the human IL-10 receptor gene is enhanced in endothelial cells in vitro and in vivo. Subsequent exposure to IL-10 results in an up-regulation of both endothelial nitric-oxide synthase (NOS-3) expression and activity. Gel mobility shift analyses and decoy oligonucleotide experiments suggest that this effect of IL-10 is mediated through activation of the transcription factor STAT-3 (signal transducer and activator of transcription-3). One functional consequence of IL-10 up-regulation of NOS-3 abundance in cultured endothelial cells is the attenuation of CD154-induced IL-12 p40 expression. Moreover, CD154-induced IL-12 p40 expression is enhanced after blockade of NOS-3 activity but attenuated in the presence of exogenous nitric oxide. Increased NOS-3 expression may, thus, be one mechanism by which IL-10 exerts its anti-inflammatory effects in Th1 cell-mediated chronic inflammatory diseases.