EBI3 blocking peptide

Although the protective functions by T helper 17 (Th17) cytokines against extracellular bacterial and fungal infection have been well documented, their importance against intracellular bacterial infection remains unclear. Here, we investigated the contribution of Th17 responses to host defense against intracellular bacteria Listeria monocytogenes and found that Th17 cell generation was suppressed in this model. Unexpectedly, mice lacking both p35 and EBI3 cleared L. monocytogenes as efficiently as wild-type mice, whereas p35-deficient mice failed to do so. Furthermore, both innate cells and pathogen-specific T cells from double-deficient mice produced significantly higher IL-17 and IL-22 compared to wild-type mice. The bacterial burden in the liver of double-deficient mice treated with anti-IL-17 was significantly increased compared to those receiving a control Ab. Transfer of Th17 cells specific for listeriolysin O as well as administration of IL-17 and IL-22 significantly suppressed bacterial growth in p35-deficient mice, indicating the critical contribution of Th17 responses to host defense against the intracellular pathogen in the absence of IL-12 and proper Th1 responses. Our findings unveil a novel immune evasion mechanism whereby the intracellular bacteria exploit IL-27EBI3 to suppress Th17-mediated protective immunity.

Members of the interleukin (IL)-12 family constitute subunits of IL-12, -23, and -27. These ILs represent pivotal mediators in the regulation of cell-mediated immune responses and in animal models of human inflammatory bowel disease. Recent work has suggested that intestinal endothelial cells might serve as a second line of defense in bacterial sensing of invading pathogens. The purpose of this study was to examine the production of IL-12 family members in intestinal endothelial cells (HIMEC). HIMEC were stimulated with proinflammatory agents (TNF-alpha, IFN-gamma, IL-1 beta) and microbial antigens [LPS, lipoteichoic acid, peptidoglycan, CpG-DNA, flagellin, poly(I:C)]. Expression of IL-12 family members and of Toll-like receptor (TLR)3 in HIMEC was assessed by real-time RT-PCR, immunostaining, flow cytometry, and immunoblot analysis. HIMEC display an induction of Epstein-Barr virusinduced gene 3 (EBI3), IL-12p35, and IL-23p19, whereas no expression of IL-12p40 and IL-27p28 was detectable. The strongest induction was induced by proinflammatory factors known to utilize the NF-kappa B pathway, and expression of EBI3 and IL-23p19 was diminished by an NF-kappa B inhibitor. HIMEC display regulated expression of TLR3. Adhesion and transmigration assays showed proinflammatory responses after HIMEC stimulation. HIMEC are capable of producing IL-12 family members as a response to microbial stimuli. The TLR3 agonist, poly( I: C), was shown to enhance leukocyte adhesion in vitro in HIMEC. Our data suggest that the intestinal microvasculature is responsive to ligands of TLR3 expressed on intestinal endothelial cells, thereby adding to the regulation of adaptive immunity and leukocyte recruitment.