CCR4-dependent regulatory T cell function in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is an idiopathic inflammatory disease of the intestine. CD4(+) T lymphocytes play an important role in both initiating and regulating intestinal inflammatory immune responses. CD4(+)CD25(+)CD45RB(low) regulatory T (T reg) cells are capable of preventing the development of colitis in a mouse model of IBD. The precise mechanism of T reg cell-mediated prevention of colitis in this model is unclear, and the role of chemokine receptors in the trafficking and function of T reg cells in this model has not been determined. We examined the role of the chemokine receptor CCR4 in in vivo trafficking and suppressive function of T reg cells in a mouse adoptive transfer model of IBD. CCR4-deficient T reg cells failed to accumulate in the mesenteric lymph nodes (MLNs) at early time points (2-5 d) after adoptive transfer, resulting in a failure to suppress the generation of pathogenic T cells and the development of colitis. Moreover, although CCR4-deficent T cells had equivalent in vitro suppressive activity and accumulated in MLNs at later time points (42-56 d), they were unable to suppress colitis. Our study demonstrates that CCR4 plays an important role in T reg cell trafficking in LNs and that this is critical for T reg cell suppressive function in vivo.

Membrane-bound eotaxin-3 mediates eosinophil transepithelial migration in IL-4-stimulated epithelial cells.

Epithelial cells play an important role in orchestrating mucosal immune responses. In allergic-type inflammation, epithelial cells control the recruitment of eosinophils into the mucosa. Th2-type cytokine-driven release of eosinophil-active chemokines from epithelial cells directs eosinophil migration into the mucosal epithelium. CCR3, the main eosinophil chemokine receptor, regulates this process; however, the respective contribution of individual CCR3 ligands in eosinophil transepithelial migration is less well understood. Using an in vitro transepithelial chemotaxis system, we found that eotaxin-3 produced by IL-4-stimulated airway epithelial cells and CCR3 on eosinophils exclusively mediate eosinophil transepithelial migration. Eotaxin-3 protein levels were also increased in the nasal mucosal epithelium recovered from allergic patients as compared to non-allergic patients. Surprisingly, eotaxin-3 in IL-4-stimulated airway epithelial cells was predominantly cell surface bound, and the cell surface form was critical for eosinophil transepithelial migration. Eotaxin-3 cell surface association was partially glycosaminoglycan (GAG) dependent, but was completely protein dependent, suggesting that eotaxin-3 associates with both GAG and cell surface proteins. We thus provide evidence that cell surface-associated eotaxin-3 is the critical IL-4-dependent chemotactic signal mediating eosinophil transepithelial migration in the setting of allergic inflammation.