Multiple sclerosis is a disease of the central nervous system. It most commonly occurs in individuals between the ages of twenty and forty (1) and in higher numbers of women than men (2). In Multiple Sclerosis (or "MS") a loss of the nerves' axon coating myelin prohibits the nerve axons from efficiently conducting action and synaptic potentials. Scar tissue (called plaques or lesions) forms at the points where demyelination occurs in the brain and spinal cord, hence the name "Multiple Sclerosis"or "many scars" (3). The demyelination found in MS is thought to be caused by an autoimmune process, in which the body's immune system attacks its own healthy tissue (4). Other diseases thought to have an autoimmune basis are rheumatoid arthritis, systemic lupus and the insulin dependent form of diabetes mellitus(5).
In the immune system, there are two types of white blood cells, B-cells and T-cells. T-cells exist in three forms, all responsible for different immune system responses. Helper T-cells recognize foreign antigens (the substance the immune system aims to destroy), stimulate antibody production, and produce cytokines (chemicals which act as biological messengers) which activate other T-cells. These T-cells are able to recognize antigens through their receptors, made of protein molecules that selectively bind to certain other molecules. Suppressor T-cells perform a function converse to that of their helper counterparts, turning off the immune system response. Cytotoxic T-cells directly attack and destroy antigenic material (6). In MS, an unknown trigger activates helper T-cells whose antigen specific receptors recognize central nervous system myelin as an antigen. While what exactly activates these T-cells is unknown, but there is speculation that the trigger may be environmental or viral (7). Once triggered, the activated T-cells reproduce clones that have the same myelin-specific activation. All of the activated T-cells then release cytokines and adhesion molecules that enable the T-cells to adhere to and cross over the blood-brain barrier, which normally prohibits the flow of substances into the brain (8,9). The proteins in these T-cells bind to myelin fragments on microglial cells and undergo a secondary activation (10), after which they multiply and release more cytokines, further invading the nervous system (11) and inflaming and damaging the blood-brain barrier. The greatly weakened barrier becomes easily permeable, allowing additional immune system cells, such as B-cells and cytotoxic T-cells to cross over (12). Once through the barrier, B-cells produce antibodies which bind to the oligodendracytes (the cells of the CNS which create myelin) and the myelin itself. Associated macrophages procede to destroy the myelin and may also damage the oligodendracytes (13).
Myelin, found only in vertebrate nervous systems, is a fatty substance that surrounds the axons and long dendrites of nerves in the brain and spinal...