CD4+CD25+Foxp3+ Regulatory T Cells Are Dispensable for Controlling CD8+ T Cell-Mediated Lung Inflammation

Abstract

Every person harbors a population of potentially self-reactive lymphocytes controlled by tightly balanced tolerance mechanisms. Failures in this balance evoke immune activation and autoimmunity. In this study, we investigated the contribution of self-reactive CD8+ T lymphocytes to chronic pulmonary inflammation and a possible role for naturally occurring CD4+CD25+Foxp3+ regulatory T cells (nTregs) in counterbalancing this process. Using a transgenic murine model for autoimmune-mediated lung disease, we demonstrated that despite pulmonary inflammation, lung-specific CD8+ T cells can reside quiescently in close proximity to self-antigen. Whereas self-reactive CD8+ T cells in the inflamed lung and lung-draining lymph nodes downregulated the expression of effector molecules, those located in the spleen appeared to be partly Ag-experienced and displayed a memory-like phenotype. Because ex vivo-reisolated self-reactive CD8+ T cells were very well capable of responding to the Ag in vitro, we investigated a possible contribution of nTregs to the immune control over autoaggressive CD8+ T cells in the lung. Notably, CD8+ T cell tolerance established in the lung depends only partially on the function of nTregs, because self-reactive CD8+ T cells underwent only biased activation and did not acquire effector function after nTreg depletion. However, although transient ablation of nTregs did not expand the population of self-reactive CD8+ T cells or exacerbate the disease, it provoked rapid accumulation of activated CD103+CD62Llo Tregs in bronchial lymph nodes, a finding suggesting an adaptive phenotypic switch in the nTreg population that acts in concert with other yet-undefined mechanisms to prevent the detrimental activation of self-reactive CD8+ T cells.