Autoimmune diseases ultraviolet radiation

One of the primary reasons ultraviolet radiation is of interest in the context of autoimmune diseases is because of induction of photosensitive cutaneous lesions (cutaneous lupus erythematosus)82 and dermatomyositis.83 A recent global evaluation of the frequency of dermatomyositis and associated autoantibodies in referral centers around the world showed a positive correlation with the intensity of ultraviolet irradiation at those locations.84... 

Okada, S., et al., International Myositis Collaborative Study Group. Global surface ultraviolet radiation intensity may modulate the clinical immunologic expression of autoimmune muscle disease, Arthritis Rheum., 48, 2285, 2003. 

Ponsonby, A.L., McMichael, A., and van derMei, I., Ultraviolet radiation and autoimmune disease insights from epidemiological research, Toxicology, 181-182, 71, 2002. 

A characteristic of some autoimmune disorders is the strong geographical variation. There seems to be a clear latitude gradient in incidence of autoimmune diseases, also indicating the effect of sun exposure. This is well known for multiple sclerosis but has now also been described for diabetes mellitus type 1 and polymyositis. A similar gradient is seen both north and south of the equator (Staples et al., 2003), with the incidence of these diseases rising as one moves away from the equator. In this situation, ultraviolet radiation would be protective against some autoimmune disorders (McMichael Hall, 1997 Ponsonby et al., 2005). 

A prime effect of ultraviolet radiation is on Langerhans cells in the skin, inducing them to leave the skin and affecting their functionality (Schwarz et al., 2000), resulting in dendritic cells that support tolerance rather than activation. Thus, ultraviolet radiation-induced damage in the skin plays a role in the stimulation of the autoimmune disease systemic lupus erythematosus. 

Most of the human studies of vitamin D and autoimmune diseases have focused on diabetes mellitus type 1 and multiple sclerosis. Higher risks of these diseases are generally seen at higher latitudes (e.g. farther north in the northern hemisphere and farther south in the southern hemisphere), which would be areas of relatively low exposure to ultraviolet radiation (Ponsonby et al., 2002). Case-control and prospective studies of maternal and child vitamin D intake have provided some evidence of a protective effect of vitamin D on risk of developing diabetes mellitus type 1... 

---