MELANIN, MELATONIN, MELANOCYTE-STIMULATING HORMONE, AND THE SUSCEPTIBILITY TO AUTOIMMUNE DEMYELINATION - A RATIONALE FOR LIGHT THERAPY IN MULTIPLE-SCLEROSIS

Multiple sclerosis is a central nervous system demyelinating disease. Significant evidence, including similarities with its animal model, ex perimental autoimmmune encephalomyelitis, supports an autoimmune mecha nism, activated by putative environmental factors in genetically predi sposed individuals. Genetic factors strongly influence the susceptibil ity to demyelinating diseases in humans and rodents. Understanding the mechanisms governing susceptibility versus resistance may help to ide ntify individuals at risk or design therapeutic strategies. The hypoth esis formulated here is based on the observation that resistance to mu ltiple sclerosis and experimental autoimmune encephalomyelitis is asso ciated with dark skin pigmentation. While this may signify a protectiv e role for melanin against environmental factors producing oxidative d amage, the mechanism postulated here is that susceptibility to autoimm une demyelination is influenced by hormonal factors, i.e. the neurohor mones melatonin and melanocyte stimulating hormone, which have opposin g effects on immune functions and, at the same time, are important det erminants of the individual's production of melanin.