Autoimmune disease occurs when the immune system mistakes our own tissue for a microbial pathogen. What are the consequences? The immune cells infiltrate the tissue and start destroying it, in the same way as it usually does with invading microbial organisms. The symptoms of autoimmune disorders depend on the organ that is affected. Treatment is challenging, but recently developed approaches are promising.
Immune System Function
The immune system protects the body against vast number of microorganisms. Critical players in this task are T and B lymphocytes. These cells have receptors on their surface, epitopes, that interact with specific structures on the microbes. When a microbial organism attempts to invade the body, the immune system activates only T and B cells with receptors for relevant epitopes. These individual clones then rapidly multiply, so that there are enough soldiers for one-on-one battle with the invading microbes.
Vulnerable Points
Some structures on microbial pathogens mimic those of bodily organs. The presence of lymphocytes reactive to such structures presents danger because the immune system may initiate autoimmune destructive processes. For that reason, there is a period in development of the immune system when lymphocytes reacting strongly with our tissue are induced to die. However, lymphocytes with only moderate reactivity to the body's own tissues are not deleted. These cells are kept under control by several mechanisms. The most important seems to be the existence of a small subset of regulatory T cells--about 1 percent of all lymphocytes--that have the ability to suppress immune responses. Their numbers in autoimmune diseases consistently decrease.
Causes of Autoimmune Disorders
Causes of autoimmune disorders often remain obscure. Genetic predisposition and female gender play an important role. Chronic stress, such as post-traumatic stress disorder, seems associated with autoimmune diseases. Nutrition also seems to contribute, as suggested by the role of vitamin D deficiency in multiple sclerosis. Interestingly, vitamin D was shown to be beneficial for adequate function of regulatory T cells that normally suppress autoimmune processes.
How Frequently Autoimmunity Occurs?
Except rheumatic arthritis and Type 1 diabetes, individual organ-specific autoimmune disorders are relatively rare. All together, however, they affect 5 percent of the population. Autoimmune diseases may involve only one organ--as in type 1 diabetes, Graves' disease and multiple sclerosis--or they may be systemic--as in autoimmune polyendocrinopathies and systemic lupus erythematosus.
Treatment
Treatment of autoimmune disorders has two main components: giving the body substitutes for the products of the organ destroyed by autoimmune inflammation--as in replacing insulin in type 1 diabetes--and controlling the inflammatory process with immunosuppressants, such as corticosteroids, methotrexate and non-steroidal anti-inflammatory drugs. Researchers also have developed antibodies against a major inflammatory molecule and are working on enriching the body's regulatory T cells.
References
- "Janeway's Immunobiology"; Kenneth Murphy, Paul Travers, Mark Walport; 2008
- "Lancet Neurology"; "Vitamin D and Multiple Sclerosis; Alberto Ascherio, Kassandra L. Munger, K. Claire Simon; June 2010
- "Current Opinion in Immunology"; Novel Ttargeted Therapies for Autoimmunity; E. William St. Clair; Dec. 2009
- "Immunological Reviews"; Human Regulatory T Cells; T. M. Brusko et al.; June 2008
