Notch-STAT5b Signaling Regulates the TCRαβ+CD8αα+ Intraepithelial Lymphocytes in the Small Intestine.

Intraepithelial lymphocytes (IELs) in the small intestine are divided into several subsets. It has been reported that TCRαβ⁺CD8αα⁺IELs and TCRγδ⁺IELs have suppressive roles in colitis model. However, the molecular mechanisms underlying IELs development and their functions are largely obscure.

We found that TCRαβ⁺CD8αα⁺IELs and their maturation from Thy1⁺ to Thy1^negGranzyme B ⁺ cells in the small intestine were markedly decreased in CD4-Cre dependent Notch1, 2-Rbpj signal deficient mice compared with control mice. We did not find any reduction of IELs precursors in the thymus and their ability to differentiate toward CD8αα⁺ cells in CD4-Cre Rbpj^f/f mice in vitro. Villin1-Cre dependent Jagged1 and/or Dll1 deficient mice had normal number of IELs. Those data indicate that both Notch1 and Notch2 regulate the differentiation of TCRαβ⁺CD8αα⁺Thy1^negIELs but Jagged1 or Dll1 in the intestinal epithelium is not involved in the differentiation. TCRαβ⁺CD8αα⁺IELs from CD4-Cre Rbpj^f/f mice have reduced expression of STAT5b and phospho-STAT5 but not STAT5a and receptors for IL-2, 7, or 15. CD4-Cre Stat5a/b^f/f mice had few numbers of TCRαβ⁺CD8αα⁺IELs, suggesting that STAT5a/b is required for the regulation of TCRαβ⁺CD8αα⁺IELs. Furthermore, overexpression of constitutive-active STAT5b in CD4-Cre Rbpj^f/f mice could partially rescue the reduction of TCRαβ⁺CD8αα⁺IELs but not their maturation.

These data indicate that Notch1 and Notch2 signaling controls the differentiation of TCRαβ⁺CD8αα⁺IELs in the small intestine without affecting the development of its precursor. Furthermore, Notch-mediated differentiation of TCRαβ⁺CD8αα⁺IELs would be, at least partly, regulated by the activation of Stat5 signaling.