No abstract

Key Points CD161 defines proinflammatory FoxP3+ cells that have classic Treg signatures, yet share effector T-cell properties. CD161+ Treg proinflammatory phenotype is stable upon Treg expansion and thus should be considered in therapeutic strategies using Treg.

Bending et al. establish a new tool, Timer of cell kinetics and activity (Tocky), revealing the temporal dynamics of cellular activation and differentiation in vivo. The tool analyzes the temporal sequence of molecular processes during cellular differentiation and can classify cells based on the frequency they receive signaling events in vivo.

Bacterial-induced intestinal inflammation is crucially dependent on interleukin (IL)-23 and is associated with CD4(+) T helper type 1 (Th1) and Th17 responses. However, the relative contributions of these subsets during the induction and resolution of colitis in T-cell-sufficient hosts remain unknown. We report that Helicobacter hepaticus-induced typhlocolitis in specific pathogen-free IL-10(-/-) mice is associated with elevated frequencies and numbers of large intestinal interferon (IFN)-γ(+) and IFN-γ(+)IL-17A(+) CD4(+) T cells. By assessing histone modifications and transcript levels in IFN-γ(+), IFN-γ(+)IL-17A(+), and IL-17A(+) CD4(+) T cells isolated from the inflamed intestine, we show that Th17 cells are predisposed to upregulate the Th1 program and that they express IL-23R but not IL-12R. Using IL-17A fate-reporter mice, we further demonstrate that H. hepaticus infection gives rise to Th17 cells that extinguish IL-17A secretion and turn on IFN-γ within 10 days post bacterial inoculation. Together, our results suggest that bacterial-induced Th17 cells arising in disease-susceptible hosts contribute to intestinal pathology by switching phenotype, transitioning via an IFN-γ(+)IL-17A(+) stage, to become IFN-γ(+) ex-Th17 cells.

Understanding the mechanisms of cellular differentiation is challenging because differentiation is initiated by signaling pathways that drive temporally dynamic processes, which are difficult to analyse in vivo. We establish a new Tool, Timer-of-cell-kinetics-and-activity (Tocky [toki], time in Japanese). Tocky uses the Fluorescent Timer protein, which spontaneously shifts its emission spectrum from blue-to-red, in combination with computer algorithms to reveal the dynamics of differentiation in vivo. Using a transcriptional target of T cell receptor (TCR)-signaling, we establish Nr4a3-Tocky to follow downstream effects of TCR signaling. Nr4a3-Tocky reveals the temporal sequence of events during regulatory T cell (Treg) differentiation and shows that persistent TCR signals occur during Treg generation. Remarkably, antigen-specific T cells at the site of autoimmune inflammation also show persistent TCR signaling. In addition, by generating Foxp3-Tocky, we reveal the in vivo dynamics of demethylation of the Foxp3 gene. Thus, Tocky is a Tool for cell biologists to address previously inaccessible questions by directly revealing dynamic processes in vivo.SummaryThe authors establish a new Tool, Timer-of-cell-kinetics-and-activity (Tocky) revealing the temporal dynamics of cellular activation and differentiation in vivo. The tool analyses the temporal sequence of molecular processes during cellular differentiation and identifies cells that receive persistent signals in vivo.