Evaluation of the immunoregulatory activity of intraepithelial lymphocytes in a mouse model of chronic intestinal inflammation

Intraepithelial lymphocytes (IELs) represent the first line of lymphocyte defense against the intestinal bacteria. Although previous studies have demonstrated a protective role of IELs in the development of colitis, the data supporting a regulatory role for IELs are limited. The objective of this study was to examine the suppressive activity of IELs in vitro and in vivo using a mouse model of chronic small and large bowel inflammation. Adoptive transfer of CD8α⁺ IELs isolated from small intestines of wildtype (WT) mice into TCR βxδ-deficient (TCR βxδ^-/-) recipients did not prevent or delay the onset of the disease induced by WT CD4⁺CD45RB^high T cells. On the contrary, we observed a more rapid onset of wasting and clinical signs of intestinal inflammation when compared with animals injected with CD4⁺CD45RB^high T cells alone. Histopathological scores of small and large bowel did not differ significantly between the two groups. Transfer of IELs alone did not produce any pathological changes. Real-time PCR analysis of intestinal tissues showed up-regulation of message for T_h1- and macrophage-derived cytokines in colon and small bowel. Using Foxp3-GFP reporter mice, we were unable to detect any Foxp3⁺ cells within the CD8α⁺ IELs but did find a small population of Foxp3⁺CD4⁺ IELs in the small and large bowel. Using in vitro suppression assay, we found that neither TCRαβ⁺CD8αα⁺, TCRαβ⁺CD8αβ⁺ nor TCRγδ⁺CD8αα⁺ IELs were capable of suppressing CD4⁺ T-cell proliferation. Taken together, our data do not support an immunoregulatory role for CD8α⁺ IELs in a mouse model of small and large bowel inflammation.