DOES IMMUNOSUPPRESSIVE ULTRAVIOLET-RADIATION EXPLAIN THE LATITUDE GRADIENT FOR MULTIPLE-SCLEROSIS

Multiple sclerosis is regarded as an autoimmune disease. The autoimmun e process is thought to be triggered by early-life exposure to viral/b acterial antigens that share key peptide sequences with myelin protein (the target of autoimmune attack in multiple sclerosis). It has long been known that the incidence of multiple sclerosis is positively corr elated with latitude, particularly in Caucasian populations. There is no agreed explanation for this latitude gradient, however. Ultraviolet radiation level is negatively correlated with latitude. Recent eviden ce suggests that ultraviolet-B is immunosuppressive, affecting particu larly T-cell activity and delayed-type hypersensitivity. We hypothesiz e here that the latitude gradient of multiple sclerosis may reflect di fferential ultraviolet-induced suppression of autoimmune activity, par ticularly since the autoimmune profile of multiple sclerosis is charac terized by disturbances of those T-cell-related activities that are sp ecifically affected by ultraviolet-B. We propose some specific tests o f this hypothesis.