Myeloid cells and sphingosine-1-phosphate are required for TCRαβ +intraepithelial lymphocyte recruitment to the colon epithelium

Abstract

Abstract Intraepithelial lymphocytes (IELs) of the colon are essential for barrier maintenance and repair after injury. As bacterial depletion or global MyD88 deficiency results in a significant reduction of colon IELs and impaired barrier integrity, we aimed to connect the signals of how bacteria recruit colon IELs to the epithelium using conditional knockouts of MyD88 to target T cells (Lck-Cre), IECs (Villin-Cre), and myeloid cells (LysM-Cre). Only in the colons of LysM-Cre +mice were TCRαβ +IELs reduced, at 3.3-fold (p<0.005 compared to Cre −littermate controls) without effect on lamina propria T cells or myeloid cells. TCRγδ +IELs were unaffected in all knockouts, suggesting they are recruited via different mechanisms. We then examined upregulated cell surface gene expression of IELs during recruitment, identifying sphingosine-1-phosphate receptor 1 (S1PR1) as a candidate for further study. Indeed, S1PR1 expression is significantly increased at 3.7-fold in IELs (p<0.05 compared to lamina propria T cells). In accordance with these findings, we demonstrated that TCRαβ+ IEL recruitment is blocked by administration of the S1PR1 receptor agonist FTY720 (p<0.05 compared to vehicle treatment). Furthermore, myeloid cell production of sphingosine-1-phosphate (S1P) was required for colon TCRαβ +IEL recruitment in a MyD88-dependent manner. In the TNF ΔARE/+model of spontaneous colitis, loss of myeloid MyD88 resulted in protection from disease (p<0.05 compared to Cre-littermate controls). Overall, these data demonstrate the requirement for myeloid-produced S1P for TCRαβ+ IEL recruitment to the colon and suggest that TCRαβ +IELs can contribute to intestinal inflammation under a specific genetic predisposition.