Sunlight exposure exerts immunomodulatory effects to reduce multiple sclerosis severity.

Multiple sclerosis (MS) disease risk is associated with reduced sun-exposure. This study assessed the relationship between measures of sun exposure (vitamin D [vitD], latitude) and MS severity in the setting of two multicenter cohort studies (nNationMS = 946, nBIONAT = 990). Additionally, effect-modification by medication and photosensitivity-associated MC1R variants was assessed. High serum vitD was associated with a reduced MS severity score (MSSS), reduced risk for relapses, and lower disability accumulation over time. Low latitude was associated with higher vitD, lower MSSS, fewer gadolinium-enhancing lesions, and lower disability accumulation. The association of latitude with disability was lacking in IFN-ß-treated patients. In carriers of MC1R:rs1805008(T), who reported increased sensitivity toward sunlight, lower latitude was associated with higher MRI activity, whereas for noncarriers there was less MRI activity at lower latitudes. In a further exploratory approach, the effect of ultraviolet (UV)-phototherapy on the transcriptome of immune cells of MS patients was assessed using samples from an earlier study. Phototherapy induced a vitD and type I IFN signature that was most apparent in monocytes but that could also be detected in B and T cells. In summary, our study suggests beneficial effects of sun exposure on established MS, as demonstrated by a correlative network between the three factors: Latitude, vitD, and disease severity. However, sun exposure might be detrimental for photosensitive patients. Furthermore, a direct induction of type I IFNs through sun exposure could be another mechanism of UV-mediated immune-modulation in MS.

Production of IL-17 by MAIT Cells Is Increased in Multiple Sclerosis and Is Associated with IL-7 Receptor Expression.

Multiple sclerosis (MS) is a T cell-driven inflammatory disease of the CNS. Research on T cell subsets involved in MS pathogenesis has mainly focused on classical CD4+ T cells, especially Th17 cells, as they produce the proinflammatory, MS-associated cytokine IL-17. However, the abundant unconventional mucosal-associated invariant T (MAIT) cells are also able to produce IL-17. MAIT cells are characterized by high CD161 expression and a semi-invariant Vα7.2 TCR, with which they recognize bacterial and yeast Ags derived from the riboflavin (vitamin B2) metabolism. In this study, we characterized MAIT cells from the peripheral blood of MS patients in comparison with healthy individuals with respect to their type-17 differentiation. We found a specific increase of IL-17+ MAIT cells as well as an increased expression of retinoic acid-related orphan receptor (ROR)γt and CCR6 in MAIT cells from MS patients, whereas the expression of T cell activation markers HLA-DR and CD38 was not different. IL-17 production by MAIT cells furthermore correlated with the surface expression level of the IL-7 receptor α-chain (CD127), which was significantly increased on MAIT cells from MS patients in comparison with healthy individuals. In summary, our findings indicate an augmented type-17 differentiation of MAIT cells in MS patients associated with their IL-7 receptor surface expression, implicating a proinflammatory role of these unconventional T cells in MS immunopathology.

The value of animal models for drug development in multiple sclerosis.

The rodent model for multiple sclerosis, experimental allergic (autoimmune) encephalomyelitis (EAE), has been used to dissect molecular mechanisms of the autoimmune inflammatory response, and hence to devise and test new therapies for multiple sclerosis. Clearly, artificial immunization against myelin may not necessarily reproduce all the pathogenetic mechanisms operating in the human disease, but most therapies tested in multiple sclerosis patients are nevertheless based on concepts derived from studies in EAE. Unfortunately, several treatments, though successful in pre-clinical EAE trials, were either less effective in patients, worsened disease or caused unexpected, severe adverse events, as we review here. These discrepancies must, at least in part, be due to genetic and environmental differences, but the precise underlying reasons are not yet clear. Our understanding of EAE pathogenesis is still incomplete and so, therefore, are any implications for drug development in these models. Here, we suggest some potential explanations based on new thinking about key pathogenic concepts and differences that may limit extrapolation from EAE to multiple sclerosis. To try to circumvent these rodent-human dissimilarities more systematically, we propose that pre-clinical trials should be started in humanized mouse models.