Reactive glia promote development of CD103⁺CD69⁺ CD8⁺ T‐cells through programmed cell death‐ligand 1 (PD‐L1)

Abstract

IntroductionPrevious work from our laboratory has demonstrated in vivo persistence of CD103+CD69+ brain resident memory CD8+ T‐cells (bTRM) following viral infection, and that the PD‐1: PD‐L1 pathway promotes development of these TRM 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.MethodsWe 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 bTRM.ResultsIn 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 TRM 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.ConclusionsTaken together, these results demonstrate a role for activated glia in promoting development of bTRM through the PD‐1: PD‐L1 pathway.

Brain-Resident T Cells Following Viral Infection

“…Recent in vitro studies have identified a role for activated microglia in promoting generation and retention of bT RM . In these studies, upregulation of CD69, CD103, and CD127 on CD8 + T cells was noted in the presence of glial cells (66). Additionally, blocking of PD-L1 on glia led to decreased expression of CD103, and CD127, on CD69 + CD8 + T cells.…”

“…In brain, the majority of persisting CD8 + T cells co-express CD103 and CD69 (10,67). Local conversion of brain-infiltrating CD8 + T cells to a CD69 + CD103 + population has been reported in various disease settings (10,12,66,89,90). CD103 functions through aiding in tissue retention through interaction with BRAIN-RESIDENT T CELLS FOLLOWING VIRAL INFECTION E-cadherin, which has been well established in epithelial cells (14,15).…”

“…Upon Ag restimulation, T RM exhibit rapid production of cytokines like IFN-g, TNF-a, IL-2, and IL-17 (21,29,30,50,66). As in other tissues, bT RM also produce high levels of IFN-g following pathogen restimulation (10,42,85).…”

“…Ag-experienced CD8 + T cells upregulate PD-1 as an activation marker. Paradoxically, despite the fact that T RM exert immediate and effective immune responses upon Ag restimulation (66,89), in a variety of experimental models, the upregulation of immune inhibitors like PD-1, LAG-3, TIM-3, and CTLA-4 has been demonstrated on these cells. Ag-specific bT RM have been shown to express high levels PD-1 and blockade of this pathway, correspondingly, resulted in increased IFN-g production during chronic infection (83).…”

“…Ag-specific bT RM have been shown to express high levels PD-1 and blockade of this pathway, correspondingly, resulted in increased IFN-g production during chronic infection (83). Additionally, fewer bT RM were detected within PD-1 KO animals (66). The maintenance of PD-1 on T RM has been reported to be independent of Ag or inflammation (83).…”