Osteopontin provides a survival signal for intestinal intraepithelial lymphocytes in mice

Abstract

Abstract Intraepithelial lymphocytes (IEL) are a diverse immune population residing in between intestinal epithelial cells, which possess important roles during mucosal immune responses. The IEL family comprises cells such as TCRαb+CD4+, TCRαb+CD8+, TCRgd+, TCRab+CD8aa+, iCD8a and iCD3+, among others. Osteopontin (OPN), a pleiotropic cytokine encoded by the Spp-1 gene, is well known for its function in tissue remodeling, modulation of Th1 responses development, maintenance of Th17 function, and homeostasis of NK cells. Herein, we investigated the impact of OPN in the IEL compartment. We compared the cell numbers of IEL, lamina propria (LP) lymphocytes and splenocytes from Spp-1−/− and wild-type (WT) mice. OPN deficiency reduced the number of TCRγδ+, TCRβ+CD4+, TCRβ+CD8α+ and TCRβ+CD4+CD8α+ IEL, but had no effect on LP and spleen lymphocytes. In in vitro studies, IEL from WT mice cultured in the presence of rOPN showed better survival rates than IEL incubated alone. The increased survival was blunted to control levels when CD44, a receptor for OPN, was blocked with anti-CD44 antibody. When total T cells (including Tregs) from WT splenocytes were transferred into Spp-1−/−Rag-2−/− and Rag2−/− mice, we observed that although OPN deficiency did not affect donor-derived IEL reconstitution at day 7 post-transfer, it decreased the number of CD4+ and CD4+CD8α+ IEL at day 28 post-transfer. As expected, Rag-2−/− mice remained healthy throught the experiment; however, Spp-1−/−Rag-2−/− recipient mice presented a remarkably loss of body weight and colon inflammation. Together, our results indicate that OPN is a critical survival signal for IEL via CD44, and that OPN-deficiency promotes development of colitis even in the presence of Tregs.