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Multiple Sclerosis (MS)
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The Immune System & MS
To understand what is happening when a person has Multiple Sclerosis (MS), it is first necessary to know a little about how the healthy immune system works. The immune system - a complex network of specialized cells and organs - defends the body against attacks by "foreign" invaders such as bacteria, viruses, fungi, and parasites. It does this by seeking out and destroying the interlopers as they enter the body. Substances capable of triggering an immune response are called * antigens.
The immune system displays both enormous diversity and extraordinary specificity. It can recognize millions of distinctive foreign molecules and produce its own molecules and cells to match up with and counteract each of them. In order to have room for enough cells to match the millions of possible foreign invaders, the immune system stores just a few cells for each specific antigen. When an antigen appears, those few specifically matched cells are stimulated to multiply into a full scale army. Later, to prevent this army from overexpanding, powerful mechanisms to suppress the immune response come into play.
* T Cells, so named because they are processed in the * thymus, appear to play a particularly important role in MS. They travel widely and continuously throughout the body patrolling for foreign invaders. In order to recognize and respond to each specific antigen, each T cell's surface carries special * receptor molecules for particular antigens.
T cells contribute to the body's defenses in two major ways. Regulatory T cells help orchestrate the elaborate immune system. For instance, they assist other cells to make antibodies, proteins programmed to match one specific antigen much as a key matches a lock. Antibodies typically interact with circulating antigens, such as bacteria, but are unable to penetrate living cells. Chief among the regulatory T cells are those known as helper (or inducer) cells. Helper T cells are essential for activating the body's defenses against foreign substances. Yet another subset of regulatory T cells acts to turn off, or suppress, various immune system cells when their job is done.
Killer T cells, on the other hand, directly attack diseased or damaged body cells by binding to them and bombarding them with lethal chemicals called * cytokines. Since T cells can attack cells directly, they must be able to discriminate between "self" cells (those of the body) and "nonself" cells (foreign invaders). To enable the immune system to distinguish the self, each body cell carries identifying molecules on its surface. T cells likely to react against the self are usually eliminated before leaving the thymus - the remaining T cells recognize the molecular markers and coexist peaceably with body tissues in a state of self-tolerance.
In * autoimmune disease such as MS, the detente between the immune system and the body is disrupted when the immune system seems to wrongly identify self as nonself and declares war on the part of the body - * myelin - it no longer recognizes. Through intensive research efforts, scientists are unraveling the complex secrets of the malfunctioning immune system of patients with MS.
Components of myelin such as myelin basic protein have been the focus of much research because, when injected into laboratory animals, they can precipitate * experimental allergic encephalomyelitis (EAE), a chronic (lasting a long time) relapsing brain and spinal cord disease that resembles MS. The injected myelin probably stimulates the immune system to produce anti-myelin T cells that attack the animal's own myelin.
Investigators are also looking for abnormalities or malfunctions in the * blood/brain barrier, a protective membrane that controls the passage of substances from the blood into the central nervous system. It is possible that, in MS, components of the immune system get through the barrier and cause nervous system damage.
Scientists have studied a number of infectious agents (such as viruses) that have been suspected of causing MS, but have been unable to implicate any one particular agent. Viral infections are usually accompanied by inflammation and the production of gamma interferon, a naturally occurring body chemical that has been shown to worsen the clinical course of MS. It is possible that the immune response to viral infections may themselves precipitate an MS attack. There seems to be little doubt that something in the environment is involved in triggering MS.
Definitions For This Page - In Alphabetical Order
* Antigen
Antigen is a structure foreign to the body, such as a virus. The body usually responds to antigens by producing antibodies.
* Autoimmune Disease
Autoimmune disease is a disease in which the body's defense system malfunctions and attacks a part of the body itself rather than foreign matter.
* Blood/Brain Barrier
Blood/Brain Barrier is a membrane that controls the passage of substances from the blood into the central nervous system.
* Cytokines
Pronounced - SY-toh-kines
Cytokines are powerful chemical substances secreted by T cells. Cytokines are an important factor in the production of inflammation and show promise as treatments for MS.
* Experimental Allergic Encephalomyelitis (EAE)
Experimental Allergic Encephalomyelitis (EAE) is a chronic (lasting a long time) brain and spinal cord disease similar to MS which is induced by injecting myelin basic protein into laboratory animals.
* Myelin
Pronounced - MY-eh-lin
Myelin is a fatty covering insulating nerve cell fibers in the brain and spinal cord, myelin facilitates the smooth, high-speed transmission of electrochemical messages between these components of the central nervous system and the rest of the body. In Multiple Sclerosis (MS), myelin is damaged through a process known as demyelination, which results in distorted or blocked signals.
* Receptor
Pronounced - reh-SEP-ter
Receptor is a protein on a cell's surface that allows the cell to identify antigens.
* T Cells
T cells are immune system cells that develop in the thymus gland. Findings suggest that T cells are implicated in myelin destruction.
* Thymus
Thymus is an organ that is part of the lymphatic system, in which T lymphocytes grow and multiply. The thymus is in the chest behind the breastbone.
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References:
NIH Publication No. 96-75
September 1996
www.ninds.nih.gov
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