Autoimmune Disorders

The immune system defends the body against attack by infectious microorganisms and inanimate foreign objects. Immune recognition and attack of an invader is a highly specific process. A particular immune system cell will only recognize and target one type of invader. The immune system must develop this specialized knowledge of individual invaders, and learn to recognize and not destroy cells that belong to the body itself.

Immune recognition depends upon the chemistry of the surface of cells and tissues. Every cell carries protein markers on its surface. The markers—called major histocompatability complexes (MHCs)—identify the cell as to its type (e.g. nerve cell, muscle cell, blood cell, etc.), and also to which organ or tissue the cell comprises. In a properly functioning immune system, the class of immune cells called T cells recognizes the host MHCs. Conversely, if the T cells encounter a MHC that is not recognized as that belongs to the host, another class of immune cell called B cells will be stimulated to produce antibodies. There are a myriad of B cells, each of which produces a single characteristic antibody directed toward one specific antigen. The binding of an antibody to the antigen on the invading cell or particle initiates a process that destroys the invader.

In autoimmune disorders, the immune system cannot distinguish between "self" cells and invader cells. As a result, the same destructive operation is carried out on the body's own cells that would normally be carried out on bacteria, viruses, and other invaders. The reasons why the immune systems become dysfunctional are still not clearly understood. It is conceded by the majority of immunologists that a combination of genetic, environmental, and hormonal factors contribute to the development of autoimmunity.

A number of other mechanisms may also trigger autoimmunity. A substance that is normally restricted to one part of the body—and so not usually exposed to the immune system—is released into other areas of the body. The substance is vulnerable to immune attack in these other areas. In a second mechanism, the antigenic similarity between a host molecule and a molecule on an invader may fool the immune system into mistaking the host's component as foreign. Additionally, drugs, infection, or some other environmental factor can alter host cells. The altered cells are no longer recognizable as "self" to the immune system. Finally, the immune system can become damaged and malfunction by, for example, a genetic mutation.