PSGL-1 regulates the extent of TCR-dependent activation in T cells and prevents their suppression by Tregs

Abstract

We recently demonstrated that PSGL-1 (P-selectin glycoprotein-1) could act as a T cell-intrinsic checkpoint inhibitor during chronic viral infection. As such, PSGL-1 may be a viable target to control T cell responses in the setting of autoimmune disease. In this study, we investigated the role of PSGL-1 on the activation of T cells and in mouse models of autoimmune disease. Here we find that the lack of PSGL-1 on T cells results in clinically worse disease in both EAE and adoptive transfer colitis, which supports its function as a negative regulator of T cell activation. However, in vivo treatment with an anti-PSGL-1 antibody known to block binding of the ligand, P-selectin, from the time of disease initiation had little effect on disease severity in the transfer colitis model and led to exacerbated disease in the EAE model. Crosslinking PSGL-1 on naïve T cells in vitro in the presence of TCR signals results in up-regulation of PD-1 but also up-regulation of other activation markers, suggesting that PSGL-1 exerts regulatory effects during the early activation program in T cells. Surprisingly, however, in an in vitro assay, crosslinking PSGL-1 on effector T cells resulted in resistance to regulatory T cell suppression. Therefore, anti-PSGL-1 treatment results in enhanced T cell activation and resistance to Treg suppression, thereby leading to more severe autoimmune disease by altering/blocking PSGL-1 signaling to phenocopy PSGL-1-deficiency.