LAUSR

CD8αα + intestinal intraepithelial lymphocytes (iIELs) are known for their unique role in keeping the integrity of the intestinal epithelial barrier, but factors affecting the development of these cells have not been thoroughly understood. Here we found that the transcriptional regulator interferon regulatory factor-2 (IRF-2) plays a cell-intrinsic, indispensable role in establishing iIEL populations. CD8αα +, but not CD8αβ +, iIELs bearing TCRαβ or TCRγδ were severely reduced in numbers in mice lacking this factor (Irf2-/- mice). Moreover, the majority of residual CD8αα +TCRαβ + iIELs in these mice were immature as judged from their Thy1.2 high phenotype and inefficient T-bet expression. Thymic IEL precursors isolated from Irf2-/- mice failed to efficiently generate CD8αα +TCRαβ + and TCRγδ + IELs upon transfer in vivo and CD8αα +TCRαβ + cells in response to IL-15 in vitro. Double mutant mice lacking both IL-15 and IRF-2 showed an even more severe iIEL defect than in mice lacking IL-15 alone. Upon increasing agonistic TCR signal strength through OT-II TCR transgenesis, CD8αα +TCRαβ + iIELs became more abundant but remained immature on the Irf2-/- background. Our current observations thus revealed the unique bimodal role that IRF-2 plays in promoting not only generation of IEL progenitors in the thymus but also maturation of iIELs in the periphery in IL-15-dependent and -independent manners.