Critical role for Slam/SAP signaling in the thymic developmental programming of IL-17- and IFN-γ-producing γδ T cells

During thymic development, γδ T cells commit to either an IFN-γ- or an IL-17-producing phenotype through mechanisms that remain unclear. Here, we investigated whether the SLAM/SAP signaling pathway played a role in the functional programming of thymic γδ T cells. Characterization of SLAM family receptor expression revealed that thymic γδ T cell subsets were each marked by distinct co-expression profiles of SLAMF1, SLAMF4, and SLAMF6. In the thymus, immature CD24hi Vγ1 and Vγ4 γδ T cells were largely contained within a SLAMF1+SLAMF6+ double positive (DP) population, while mature CD24low subsets were either SLAMF1+ or SLAMF6+ single positive (SP) cells. In the periphery, SLAMF1 and SLAMF6 expression on Vγ1, Vγ4, and Vγ6 T cells distinguished IL-17- and IFN-γ-producing subsets, respectively. Disruption of SLAM family receptor signaling through deletion of SAP resulted in impaired thymic γδ T cell maturation at the CD24hiSLAMF1+SLAMF6+ DP stage that was associated with a decreased frequency of CD44+RORγt+ γδ T cells. These defects were in turn associated with impaired γδ T cell IL-17 and IFN-γ production in both the thymus as well as in peripheral tissues. The role for SAP was subset-specific, as Vγ1, Vγ4, Vγ5, but not Vγ6 subsets were SAP-dependent. Together, these data suggest that the SLAM/SAP signaling pathway regulates a critical checkpoint in the functional programming of IL-17 and IFN-γ-producing γδT cell subsets during thymic development.