Tregs Modulate Lymphocyte Proliferation, Activation, and Resident-Memory T-Cell Accumulation within the Brain during MCMV Infection.

Sujata Prasad,Amar Singh,Wen S Sheng,Shuxian Hu,James R Lokensgard,Steven M Varga

doi:10.1371/journal.pone.0145457

Abstract

Accumulation and retention of regulatory T-cells (Tregs) has been reported within post viral-encephalitic brains, however, the full extent to which these cells modulate neuroinflammation is yet to be elucidated. Here, we used Foxp3-DTR (diphtheria toxin receptor) knock-in transgenic mice, which upon administration of low dose diphtheria toxin (DTx) results in specific deletion of Tregs. We investigated the proliferation status of various immune cell subtypes within inflamed central nervous system (CNS) tissue. Depletion of Tregs resulted in increased proliferation of both CD8+ and CD4+ T-cell subsets within the brain at 14 d post infection (dpi) when compared to Treg-sufficient animals. At 30 dpi, while proliferation of CD8+ T-cells was controlled within brains of both Treg-depleted and undepleted mice, proliferation of CD4+ T-cells remained significantly enhanced with DTx-treatment. Previous studies have demonstrated that Treg numbers within the brain rebound following DTx treatment to even higher numbers than in untreated animals. Despite this rebound, CD8+ and CD4+ T-cells proliferated at a higher rate when compared to that of Treg-sufficient mice, thus maintaining sustained neuroinflammation. Furthermore, at 30 dpi we found the majority of CD8+ T-cells were CD127hi KLRG1- indicating that the cells were long lived memory precursor cells. These cells showed marked elevation of CD103 expression, a marker of tissue resident-memory T-cells (TRM) in the CNS, in untreated animals when compared to DTx-treated animals suggesting that generation of TRM is impaired upon Treg depletion. Moreover, the effector function of TRM as indicated by granzyme B production in response to peptide re-stimulation was found to be more potent in Treg-sufficient animals. Taken together, our findings demonstrate that Tregs limit neuroinflammatory responses to viral infection by controlling cell proliferation and may direct a larger proportion of lymphocytes within the brain to be maintained as TRM cells.

Highlights

Regulatory T-cells (Tregs) are well-known to play crucial roles in suppression of immune responses during infection, as well as autoimmunity, and several recent studies describe their role in antiviral immunity [1, 2]
Recent findings from our laboratory have demonstrated that following murine cytomegalovirus (MCMV) infection, regulatory T-cells are present within the central nervous system (CNS)-infiltrating CD4+ T-lymphocyte population and accumulate within the brain from acute through chronic phases of infection [8]
In this study, using the well-established technique of in-vivo Foxp3+ cell ablation by administration of diphtheria toxin (DTx) to Foxp3-DTR animals (Fig 1A), we first assessed the presence of Tregs within the brains of both DTx-treated and untreated animals from acute through chronic phases of viral infection

Summary

Introduction

Regulatory T-cells (Tregs) are well-known to play crucial roles in suppression of immune responses during infection, as well as autoimmunity, and several recent studies describe their role in antiviral immunity [1, 2]. Evidence from recent reports demonstrates that Treg cells accumulate within the brains of mice upon viral infection and play distinct roles in immune modulation [7, 8]. Several previous studies have reported that the presence of Tregs within the brain has a significant impact on neuroimmune responses They serve to limit tissue damage in many chronic infections. It has been shown that depletion of Tregs leads to more robust generation of effector T-cells, as well as short lived effector cells, in response to viral infection [7, 9]

Methods

Results

Conclusion