Abstract
INTRODUCTION: Previous work from our laboratory has demonstrated in vivo persistence of CD103(+) CD69(+) brain resident memory CD8(+) T-cells (bT(RM) ) following viral infection, and that the PD-1: PD-L1 pathway promotes development of these T(RM) cells within the brain. Although glial cells express low basal levels of PD-L1, its expression is upregulated upon IFN-γ-treatment, and they have been shown to modulate antiviral T-cell effector responses through the PD-1: PD-L1 pathway. METHODS: We performed flow cytometric analysis of cells from co-cultures of mixed glia and CD8(+) T-cells obtained from wild type mice to investigate the role of glial cells in the development of bT(RM) . RESULTS: In this study, we show that interactions between reactive glia and anti-CD3 Ab-stimulated CD8(+) T-cells promote development of CD103(+) CD69(+) CD8(+) T-cells through engagement of the PD-1: PD-L1 pathway. These studies used co-cultures of primary murine glial cells obtained from WT animals along with CD8(+) T-cells obtained from either WT or PD-1 KO mice. We found that αCD3 Ab-stimulated CD8(+) T-cells from WT animals increased expression of CD103 and CD69 when co-cultured with primary murine glial cells. In contrast, significantly reduced expression of CD103 and CD69 was observed using CD8(+) T-cells from PD-1 KO mice. We also observed that reactive glia promoted high levels of CD127, a marker of memory precursor effector cells (MPEC), on CD69(+) CD8(+) T-cells, which promotes development of T(RM) cells. Interestingly, results obtained using T-cells from PD-1 KO animals showed significantly reduced expression of CD127 on CD69(+) CD8(+) cells. Additionally, blocking of glial PD-L1 resulted in decreased expression of CD103, along with reduced CD127 on CD69(+) CD8(+) T-cells. CONCLUSIONS: Taken together, these results demonstrate a role for activated glia in promoting development of bT(RM) through the PD-1: PD-L1 pathway.