Environmental factors and their regulation of immunity in multiple sclerosis.

Epidemiological and clinical studies have shown that environmental factors such as infections, smoking and vitamin D are associated with the risk of developing multiple sclerosis (MS). Some of these factors also play a role in the MS disease course. We are currently beginning to understand how environmental factors may impact immune function in MS on a cellular and molecular level. Here we review epidemiological, clinical and basic immunological studies on the environmental factors, viral and parasitic infections, smoking, and vitamin D and relate epidemiological findings with their likely pathophysiology in MS.