New hypotheses on sunlight and the geographic variability of multiple sclerosis prevalence.

Multiple sclerosis is an autoimmune demyelinating disorder of the central nervous system. Its etiology continues to be elucidated. The debate about the environmental impact on the disease etiology and progression has focused on sun light exposure in the recent past, but mainly as it applies to vitamin D and its derivatives. This paper will discuss how sunlight stimulus may effect neuronal and microglial antigenic presentation based on sunlight-dependent neuronal activity, as well as how sunlight may alter the amount of vitamin A and melatonin levels during immune development in the central nervous system. Changes in the number of antigens presented to lymphocytes by antigen-presenting cells for self-selective removal during immune development could therefore alter the number of circulating self-recognizing B and T-lymphocytes. This situation would increase susceptibility to a significantly greater number of self-antigens, and lead to autoimmune disorders such as multiple sclerosis.