Lipopolysaccharide-induced production of interleukin-10 is promoted by the serine/threonine kinase Akt

Abstract

The bacterial endotoxin lipopolysaccharide (LPS), is a potent inducer of the inflammatory response. Previous studies demonstrated that LPS-induced toxicity is reversed upon FcγR clustering by IgG immune complexes (IC) through upregulation of the anti-inflammatory cytokine IL-10. The PI3K-Akt pathway is also reported to reverse LPS-induced inflammation. In this study, we have examined the role of Akt in LPS-induced IL-10 production. First, we compared Akt activation in macrophages stimulated with either LPS alone, or with a combination of LPS and ICs. Our experiments revealed that while Akt was activated under both conditions, the level of activation was significantly higher in cells stimulated with LPS and ICs, suggesting that Akt may be involved in IC-induced upregulation of IL-10 production. Using several independent models we have then tested the notion that enhanced Akt activation may lead to enhanced LPS-induced IL-10 production. Over-expression of constitutively active Myr-Akt in the mouse macrophage cell line Raw 264.7 led to significant increase in IL-10 production in response to LPS. In addition, down-regulation of Akt by siRNA resulted in a decrease in LPS-induced IL-10 production. Peritoneal macrophages from transgenic mice with macrophage-specific expression of Myr-Akt produced significantly higher levels of IL-10 when stimulated with LPS, compared to their wild-type counterparts. Consistent with this observation, serum levels of IL-10, post-LPS challenge, was higher in the Myr-Akt transgenic mice compared to the wild-type mice. Taken together, these data demonstrate that Akt plays a critical role in LPS-induced production of IL-10.