The Autoimmune Disease Process

Multiple sclerosis is referred to as an autoimmune disease. The general theory for the development of MS is that a genetically damaged immune system is unable to distinguish between virus proteins and the body's own myelin and so produces antibodies that attack. In other words, the body becomes allergic to itself, a condition known as autoimmunity.

Autoimmunity may develop when the body's immune system is damaged by genetic or environmental factors or both, causing it to attack its own tissues. In the case of MS, the immune system attacks the tissues that make up myelin:

• Myelin is made from layers of cell membranes that are produced in the brain and spinal cord by specialized cells called oligodendrocytes. The destruction of this myelin sheath during the disease process is the hallmark for multiple sclerosis.
• The myelin coat is distributed in segments along the axons, the long filaments that carry electric impulses away from a nerve cell.
• The segments are separated from each other by tiny clusters called nodes of Ranvier, which house channels for sodium ions. These sodium ions are important for boosting the electrical charge required to pass signals from one nerve to another.
• As the myelin insulation is destroyed, signals transmitted from nerve cell to nerve cell throughout the central nervous system are disrupted.
• Experts once believed that axons themselves were spared during the disease process. Research, however, has shown that many are severed in MS and, in fact, axon destruction appears to start at an early stage in the disease and may be a major cause of its irreversibility.

The body often makes corrective actions to offset the effects of the nerve cell destruction:

• For example, researchers have observed an increase in the density of the sodium channels, which carry electric charges. By increasing their numbers, the nerve cells can continue to communicate, in spite of the loss of myelin.
• The nerves also retain some capacity to remyelinate (to restore the insulating myelin).

Such processes are probably responsible for the remissions that most patients experience. Unfortunately, the disease process nearly always eventually outpaces these corrective actions.

Onset of Multiple Sclerosis: The Autoimmune Process and the Inflammatory Response

The Normal Immune Response.

• The most important critical immune factors in the disease process are white blood cells called lymphocytes, which consist of T cells and B cells. These cells are the warriors in the immune defense system.
• Receptors on T cells acquire the ability to recognize specific molecules called antigens. Antigens are typically proteins from infecting organisms, such as bacteria or viruses, and perceived as a threat to the body.
• Once the antigen is identified, specific T cells, called helper T cells, trigger the B cells to release antibodies. These molecules are designed to attach to and destroy the targeted antigen.

Autoimmunity.