Type 1 regulatory T cells control autoinflammatory diseases. In two linked papers, groups led by Kuchroo and Quintana demonstrate the role of the aryl hydrocarbon receptor in the differentiation of these cells. Type 1 regulatory T cells (Tr1 cells ) that produce interleukin 10 (IL-10) are instrumental in the prevention of tissue inflammation, autoimmunity and graft-versus-host disease. The transcription factor c-Maf is essential for the induction of IL-10 by Tr1 cells, but the molecular mechanisms that lead to the development of these cells remain unclear. Here we show that the ligand-activated transcription factor aryl hydrocarbon receptor (AhR), which was induced by IL-27, acted in synergy with c-Maf to promote the development of Tr1 cells. After T cell activation under Tr1-skewing conditions, the AhR bound to c-Maf and promoted transactivation of the Il10 and Il21 promoters, which resulted in the generation of Tr1 cells and the amelioration of experimental autoimmune encephalomyelitis. Manipulating AhR signaling could therefore be beneficial in the resolution of excessive inflammatory responses.

IL-27 has recently been identified as a differentiation factor for the generation of IL-10-producing regulatory type 1 (Tr1) T cells. However, how IL-27 induces the expansion of Tr1 cells has not been elucidated. In this study we demonstrate that IL-27 drives the expansion and differentiation of IL-10-producing murine Tr1 cells by inducing three key elements: the transcription factor c-Maf, the cytokine IL-21, and the costimulatory receptor ICOS. IL-27-driven c-Maf expression transactivates IL-21 production, which acts as an autocrine growth factor for the expansion and/or maintenance of IL-27-induced Tr1 cells. ICOS further promotes IL-27-driven Tr1 cells. Each of those elements is essential, because loss of c-Maf, IL-21-signaling, or ICOS decreases the frequency of IL-27-induced differentiation of IL-10-producing Tr1 cells.

IL-23, an IL-12 family member, has been implicated in the development of Th17 cells and the progression of autoimmune diseases. However, due to the lack of availability of sensitive Ab reagents specific for the IL-23 receptor (IL-23R), it has been difficult to characterize the cell types that express the IL-23R and are responsive to IL-23 in vivo. To address the role of IL-23 in vivo, we have generated a novel “knock-in” mouse in which we have replaced the intracellular domain of the IL-23R with the GFP. We show that in addition to Th17 cells, a subset of myeloid cells express IL-23R and respond to IL-23 by producing IL-17 and IL-22. Our studies further demonstrate that IL-23R expression is crucial for generation of encephalitogenic Th17 cells, but its expression on the innate immune system is dispensible in the development of experimental autoimmune encephalomyelitis.

MS symptoms affect many functional domains. Knowing the specific impact of symptoms on health-related quality of life (HRQoL) is vital for successful disease and symptom management in MS. We aimed at investigating how specific MS symptoms contribute to the disease burden in individuals and from a population perspective. We included 855 Swiss Multiple Sclerosis Registry participants with a relapsing-remitting form (RRMS) or a progressive form (PMS). HRQoL was measured with the EuroQol 5-Dimension EQ-5D-index and EQ-Visual Analogue Scale (EQ-VAS) on 0-100% scales. Their associations with 20 symptoms, socio-demographic and clinical information were explored in median regression models, stratified by RRMS and PMS. We included 611 participants with RRMS and 244 with PMS. In RRMS, gait (-6.5%) and balance problems (-5.1%) had the largest EQ-5D-index reductions, and were also important at the population level (frequencies 45% and 52%). Fatigue, depression, and spasticity (frequencies 74.1%, 31%, 38%) also contributed to the population disease burden. In PMS, spasticity, paralysis, and bowel problems had the largest impact on EQ-5D-index, both at the individual and population levels. The largest impact on EQ-VAS at population level was associated in RRMS with balance problems, depression, dizziness, and spasticity, while in PMS with weakness, pain, and paralysis. While HRQoL at population level is most affected by balance problems, spasticity, and depression in RRMS, the biggest HRQoL losses in PMS are caused by spasticity, paralysis, weakness, and pain. Many symptoms with the largest effects in individuals substantially contribute to the population disease burden.