UV irradiation of skin regulates a murine model of Multiple Sclerosis

Objective: The prevalence of multiple sclerosis follows a latitude gradient, with increased disease at higher latitudes. Previous studies have focused on a vitamin D hypothesis; although recent evidence suggests that exposure to ultraviolet radiation (UVR) itself may be important. In this study, the effects of UVR on the development of experimental autoimmune encephalomyelitis (EAE) were examined. Methods: C57BL/6 mice were irradiated with a single erythemal dose of UVR (8 kJ/m2), or 4 daily sub-erythemal doses (1 kJ/m2), before sensitisation to myelin oligodendrocyte glycoprotein peptide. The UV irradiation protocols used do not increase 25-hydroxyvitamin D concentrations in serum of vitamin D-sufficient mice. The onset of EAE was recorded and mice were clinically monitored for 40 days. Results: A single dose of erythemal UVR (8 kJ/m2) significantly suppressed EAE onset and severity. Four daily exposures of sub-erythemal UVR (1 kJ/m2) also significantly delayed disease onset but was less effective than the erythemal dose. Conclusion: UV irradiation delayed the onset and reduced the severity of EAE. Continued administration of lower dose UVR following disease onset may be necessary to achieve similar results to a single higher dose delivered pre-sensitisation. Our results give further weight to suggestions that UVR exposure may delay MS onset and progression and UVB phototherapy may provide an option for treatment of MS.