Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system (CNS) in humans. Patients with MS normally experience a chronic progressive loss of motor and/or sensory functions. The origin of MS is unknown, although some investigators have postulated than an environmental agent (i.e. a virus or bacteria) may trigger the disease. My laboratory utilizes a mouse model of virus-induced demyelination (Theiler's murine encephalomyelitis virus) to study immune factors involved in the development of pathology and clinical disease.