Background & aims: In the present work, we address the requirement for intestinal-specific homing molecules, the chemokine/chemokine receptor pair CCL25/CCR9 and beta7 integrin, in the pathogenesis of the CD8(+) T cell-dependent Tnf(DeltaARE) mouse model of Crohn's-like inflammatory bowel disease.
Methods: We investigated by flow cytometry lymphocyte recruitment in the intestinal epithelium and lamina propria (LP); cytokine production by intraepithelial and LP lymphocytes; and peripheral expression of CCR9, alpha4beta7, and alphaEbeta7 integrin. The functional significance of CCL25/CCR9 and beta7 integrin in inflammatory lymphocyte recruitment and intestinal disease development was assessed in Tnf(DeltaARE) mice genetically lacking these molecules.
Results: Intestinal inflammation in the Tnf(DeltaARE) mice is associated with early reduction of CD8alphaalpha-expressing intraepithelial lymphocytes, decreased T helper cell 1 and increased T helper cell 17 responses by LP CD4(+) lymphocytes, increased alphaEbeta7 integrin expression in peripheral activated/memory intestinal-homing CD8alphabeta lymphocytes, and predominance of tumor necrosis factor/interferon-gamma-producing CD8alphabeta lymphocytes in the epithelium. Although CCL25/CCR9 have been strongly implicated in T-lymphocyte recruitment to the small intestine, inflammatory pathology develops unperturbed in the genetic absence of CCL25/CCR9. Furthermore, CD8alphabeta lymphocyte recruitment in the intestinal epithelium and inflammatory infiltration in the LP are not impaired in CCR9- or CCL25-deficient Tnf(DeltaARE) mice. In contrast, genetic ablation of beta7 integrin results in complete amelioration of intestinal pathology.
Conclusions: Our findings demonstrate that development of intestinal inflammation in the Tnf(DeltaARE) mice is critically dependent on beta7 integrin-mediated T-lymphocyte recruitment, whereas the function of the CCL25/CCR9 axis appears dispensable in this model.