The symptoms of MS are caused by the destruction of a protein called myelin in the central nervous system. Because of a misfunction, the myelin is destroyed by the body's own immune system. Normally, myelin protein forms a multilayered coating around nerve cells. In MS, the loss of myelin, called demyelination , affects the way that nerve cells conduct signals in the brain and spinal cord, causing neurologic symptoms.
The immune cells thought to lead the attack on myelin are called T lymphocytes. T lymphocytes mediate the immune responses that protect our bodies from foreign agents such as viruses and bacteria. Usually, T lymphocytes are able to distinguish between foreign material and the body's own tissues and suppress attacks on the self. In MS, the T lymphocytes are thought to inappropriately attack parts of the central nervous system as though it was a foreign substance. The attack upon myelin in MS initiates a cascade of events called an inflammatory response that leads to further damage to the central nervous system and disruption of central nervous system functions. Because MS appears to be affected by the body's own immune system, MS is considered to be an "autoimmune" disease.