Regulatory T Cell Stability and Migration Are Dependent on mTOR.

CD4+ Foxp3+ regulatory T cells (Treg) are essential to maintain immune tolerance, as their loss leads to a fatal autoimmune syndrome in mice and humans. Conflicting findings have been reported concerning their metabolism. Some reports found that Treg have low mechanistic target of rapamycin (mTOR) activity and would be less dependent on this kinase compared with conventional T cells, whereas other reports suggest quite the opposite. In this study, we revisited this question by using mice that have a specific deletion of mTOR in Treg. These mice spontaneously develop a severe and systemic inflammation. We show that mTOR expression by Treg is critical for their differentiation into effector Treg and their migration into nonlymphoid tissues. We also reveal that mTOR-deficient Treg have reduced stability. This loss of Foxp3 expression is associated with partial Foxp3 DNA remethylation, which may be due to an increased activity of the glutaminolysis pathway. Thus, our work shows that mTOR is crucial for Treg differentiation, migration, and identity and that drugs targeting this metabolism pathway will impact on their biology.

Tumor necrosis factor receptor family costimulation increases regulatory T-cell activation and function via NF-κB.

Several drugs targeting members of the TNF superfamily or TNF receptor superfamily (TNFRSF) are widely used in medicine or are currently being tested in therapeutic trials. However, their mechanism of action remains poorly understood. Here, we explored the effects of TNFRSF co-stimulation on murine Foxp3+ regulatory T cell (Treg) biology, as they are pivotal modulators of immune responses. We show that engagement of TNFR2, 4-1BB, GITR, and DR3, but not OX40, increases Treg proliferation and survival. Triggering these TNFRSF in Tregs induces similar changes in gene expression patterns, suggesting that they engage common signal transduction pathways. Among them, we identified a major role of canonical NF-κB. Importantly, TNFRSF co-stimulation improves the ability of Tregs to suppress colitis. Our data demonstrate that stimulation of discrete TNFRSF members enhances Treg activation and function through a shared mechanism. Consequently, therapeutic effects of drugs targeting TNFRSF or their ligands may be mediated by their effect on Tregs.

The NF-κB RelA Transcription Factor Is Critical for Regulatory T Cell Activation and Stability.

Regulatory T cells (Tregs) play a major role in immune homeostasis and in the prevention of autoimmune diseases. It has been shown that c-Rel is critical in Treg thymic differentiation, but little is known on the role of NF-κB on mature Treg biology. We thus generated mice with a specific knockout of RelA, a key member of NF-κB, in Tregs. These mice developed a severe autoimmune syndrome with multi-organ immune infiltration and high activation of lymphoid and myeloid cells. Phenotypic and transcriptomic analyses showed that RelA is critical in the acquisition of the effector Treg state independently of surrounding inflammatory environment. Unexpectedly, RelA-deficient Tregs also displayed reduced stability and cells that had lost Foxp3 produced inflammatory cytokines. Overall, we show that RelA is critical for Treg biology as it promotes both the generation of their effector phenotype and the maintenance of their identity.

A Diet-Sensitive Commensal Lactobacillus Strain Mediates TLR7-Dependent Systemic Autoimmunity.

Western lifestyle is linked to autoimmune and metabolic diseases, driven by changes in diet and gut microbiota composition. Using Toll-like receptor 7 (TLR7)-dependent mouse models of systemic lupus erythematosus (SLE), we dissect dietary effects on the gut microbiota and find that Lactobacillus reuteri can drive autoimmunity but is ameliorated by dietary resistant starch (RS). Culture of internal organs and 16S rDNA sequencing revealed TLR7-dependent translocation of L. reuteri in mice and fecal enrichment of Lactobacillus in a subset of SLE patients. L. reuteri colonization worsened autoimmune manifestations under specific-pathogen-free and gnotobiotic conditions, notably increasing plasmacytoid dendritic cells (pDCs) and interferon signaling. However, RS suppressed the abundance and translocation of L. reuteri via short-chain fatty acids, which inhibited its growth. Additionally, RS decreased pDCs, interferon pathways, organ involvement, and mortality. Thus, RS exerts beneficial effects in lupus-prone hosts through suppressing a pathobiont that promotes interferon pathways implicated in the pathogenesis of human autoimmunity.