The low incidence of multiple sclerosis in areas near the equator may be due to ultraviolet light induced suppressor cells to melanocyte antigens.

It has been shown by Elmets et al. (1) that ultraviolet irradiation of the skin followed by the application of a normally sensitizing antigen results in tolerance induction to the antigen. This tolerance is due to the induction of suppressor T-cells specific for the antigen. Multiple sclerosis is more common in certain climates distant from the equator where there is less ultraviolet light (sunlight). I postulate that people near the equator are exposed to more sunlight and that the ultraviolet light from the sunlight aids in the induction of suppressor cells specific for melanocyte associated antigens. Since melanocytes are of neural crest origin and share antigenic determinants with neural tissues these suppressor cells may act to protect against multiple sclerosis which is probably an autoimmune disease directed against neural tissues.