Autoimmune Diseases

Sometimes the immune system's recognition apparatus breaks down, and the body begins to manufacture antibodies and T cells directed against the body's own constituents-cells, cell components, or specific organs. Such antibodies are known as autoantibodies, and the diseases they produce are called autoimmune diseases. (Not all autoantibodies are harmful; some types appear to be integral to the immune system's regulatory scheme.)

Autoimmune reactions contribute to many enigmatic diseases. For instance, autoantibodies to red blood cells can cause anemia, autoantibodies to pancreas cells contribute to juvenile diabetes, and autoantibodies to nerve and muscle cells are found in patients with the chronic muscle weakness known as myasthenia gravis. Autoantibody known as rheumatoid factor is common in persons with rheumatoid arthritis.

Persons with systemic lupus erythematosus (SLE), whose symptoms encompass many systems, have antibodies to many types of cells and cellular components. These include antibodies directed against substances found in the cell's nucleus-DNA, RNA, or proteins-which are known as antinuclear antibodies, or ANAs. These antibodies can cause serious damage when they link up with self antigens to form circulating immune complexes, which become lodged in body tissue and set off inflammatory reactions (Immune Complex Diseases).

Autoimmune diseases affect the immune system at several levels. In patients with SLE, for instance, B cells are hyperactive while suppressor cells are underactive; it is not clear which defect comes first. Moreover, production of IL-2 is low, while levels of gamma interferon are high. Patients with rheumatoid arthritis, who have a defective suppressor T cell system, continue to make antibodies to a common virus, whereas the response normally shuts down after about a dozen days.

No one knows just what causes an autoimmune disease, but several factors are likely to be involved. These may include viruses and environmental factors such as exposure to sunlight, certain chemicals, and some drugs, all of which may damage or alter body cells so that they are no longer recognizable as self. Sex hormones may be important, too, since most autoimmune diseases are far more common in women than in men.

Heredity also appears to play a role. Autoimmune reactions, like many other immune responses, are influenced by the genes of the MHC. A high proportion of human patients with autoimmune disease have particular histocompatibility types. For example, many persons with rheumatoid arthritis display the self marker known as HLA-DR4.

Many types of therapies are being used to combat autoimmune diseases. These include corticosteroids, immunosuppressive drugs developed as anticancer agents, radiation of the lymph nodes, and plasmapheresis, a sort of "blood washing" that removes diseased cells and harmful molecules from the circulation.

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A little deeper explanation.

Autoimmune Diseases, illnesses in which the immune system reacts to normal components of the body as if they were foreign substances and produces antibodies (see Antibody) against them.

Antibodies are manufactured by cells called lymphocytes. It is thought that, during development of the embryo, lymphocytes capable of reacting with the body's own tissues are somehow inactivated so that the self is distinguished from the nonself and is not destroyed by antibodies. Self-reactive lymphocytes can still be found in some adults, however, which suggests that they are actively suppressed in some way rather than eliminated. Another mechanism for protecting components of the self from destruction is sequestration during early development. Mature sperm cells, for example, do not appear until after the immune system has matured and are then automatically separated from the bloodstream. After vasectomy, these cells enter the bloodstream, where they can provoke formation of antibodies against themselves (autoantibodies).

One theory to explain autoimmune disease proposes that suppression of reaction against the self is disrupted when viruses infect the antibody-forming cells. In the infectious form of mononucleosis, in which lymphocytes are invaded by a virus, antibodies against a variety of body tissues are found in the bloodstream. Rheumatic heart disease is believed to be a result of childhood infection by streptococcal bacteria, which have a surface molecular arrangement identical to one found in heart muscle; antibody formed against the bacteria can also damage the heart.

In most other autoimmune diseases the cause of antibody formation is unknown. Persons with myasthenia gravis make an antibody that blocks the transmission of nerve impulses to muscle; this causes the muscle weakness and breathing difficulty associated with the disease. In autoimmune hemolytic anemia, the red blood cells are destroyed by autoantibodies. Persons with lupus erythematosus make antibodies that attack cell components, including genetic material. Clumps of matter formed by antibodies bound to the cell components can damage the kidneys. The blood of some persons with arthritis contains rheumatoid factor, an antibody that binds to other antibodies in the blood; whether this factor also causes the joint injury of arthritis is not known.

Lupus, arthritis, and the skin diseases scleroderma and dermatomyositis are called collagen diseases because of the damage the associated antibodies cause to connective tissue, which is made up of collagen.

A few severe cases of diabetes are caused by an antibody that destroys insulin-forming cells in the pancreas. Another antibody attacks the thyroid gland, producing chronic thyroiditis. Addison's disease in some cases may result from autoimmune destruction of the adrenal gland.

One of the most intensively studied autoimmune diseases is multiple sclerosis. In this illness the myelin sheath covering the spinal cord is destroyed, leading to difficulty in walking and other movements. The damage in multiple sclerosis is not produced by an autoantibody but by a lymphocyte that reacts directly with the protective sheath.

Autoantibodies are often found in the blood of older persons who have no disease, a phenomenon that is not understood.

Treatment of autoimmune diseases usually entails therapy with steroids , which suppress the immune system. Currently under investigation is a procedure called plasmapheresis, in which the patient's blood is passed through a machine that removes gamma globulin, the blood fraction that contains antibodies. 

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Autoimmunity is the immune response of the body turned against its own cells and tissues. Autoimmune diseases may involve either cell-mediated responses, humoral responses, or both. For example, in type I diabetes, the body makes an immune response against its insulin-producing cells and destroys them, with the result that the body cannot use sugars. In myasthenia gravis, the immune system makes antibodies against the normal molecules that control neuromuscular activity, causing weakness and paralysis. In rheumatic fever, the immune system makes antibodies that bind to the heart’s valves, leading to permanent heart damage. In systemic lupus erythematosus, commonly known as lupus, the body makes antibodies against many different body tissues, resulting in widespread symptoms.

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