132 Mechanism of Induction of Inflammatory Bowel Disease Associated Gene TL1A (TNFSF15) By Microbes in Antigen Presenting Cells

Abstract

mucosal CMV infection has been associated with IBD exacerbation, relapse and steroid refractoriness. Therefore, we investigated the mechanism by which CMV blocks intestinal stroma (TGF-β) down-regulation of monocyte cytokine production. Methods: Intestinal macrophages and monocytes were isolated by enzyme digestion and/or elutriation. Intestinal stroma was isolated from normal mucosa to generate stroma-conditioned media (S-CM). Cytokines were assayed by ELISA, RNA by RT-PCR, signal proteins by western blot, surface proteins by FACS, and NF-κB by immunofluorescence. Results: S-CM down-regulated monocyte receptors and the production of pro-inflammatory cytokines, thereby inducing the phenotype and function of non-inflammatory intestinal macrophages. Intestinal macrophages, which did not express CD14 or MD-2, remained unresponsive to LPS, even in the presence of exogenous CD14 andMD-2 transfection. Consistent with these findings, intestinal macrophages did not activate NF-κB. To study the mechanism of this down-regulation, stromal TGF-β blocked NF-κB activation in blood monocytes through the down-regulation of NF-κB signal proteins. These findings indicate a mechanism by which pro-inflammatory monocytes recruited to the mucosa become non-inflammatory intestinal macrophages. However, CMV-infected monocytes spontaneously produced TNF-α mRNA and released fold higher levels of inducible TNF-α than mock-infected monocytes. Moreover, CMV-infected monocytes were resistant to stromal TGF-β down-regulation of inducible cytokine production compared to mock-infected monocytes. Importantly, CMV induced NF-κB phosphorylation and nuclear translocation of NF-κB in monocytes. Finally, CMV infection of monocytes induced resistance to stromal TGF-β down-regulation of NF-κB phosphorylation and nuclear translocation. Conclusions: CMV infection blocks the stroma-induced differentiation of proinflammatory monocytes into non-inflammatory macrophages through NF-κB activation. The recruitment of such cells to the mucosa in IBD would enhance the LPS responsiveness of intestinal macrophages, thereby increasing mucosal inflammation.