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Sunlight exposure exerts immunomodulatory effects to reduce multiple sclerosis severity.

Proc Natl Acad Sci U S A. 2021 Jan 5;118(1):e2018457118. doi: 10.1073/pnas.2018457118. PMID: 33376202.

Authors/Editors: Ostkamp P, Salmen A, Pignolet B, Görlich D, Andlauer TFM, Schulte-Mecklenbeck A, Gonzalez-Escamilla G, Bucciarelli F, Gennero I, Breuer J, Antony G, Schneider-Hohendorf T, Mykicki N, Bayas A, Then Bergh F, Bittner S, Hartung HP, Friese MA, Linker RA, Luessi F, Lehmann-Horn K, Mühlau M, Paul F, Stangel M, Tackenberg B, Tumani H, Warnke C, Weber F, Wildemann B, Zettl UK, Ziemann U, Müller-Myhsok B, Kümpfel T, Klotz L, Meuth SG, Zipp F, Hemmer B, Hohlfeld R, Brassat D, Gold R, Gross CC, Lukas C, Groppa S, Loser K, Wiendl H, Schwab N; German Competence Network Multiple Sclerosis (KKNMS) and the BIONAT Network.
Publication Date: 2021

Abstract

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-β–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.

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