A Closer Look at Autoimmune Disease and Complexes

With Autoimmune Disease Autoantibodies and Immune Complexes Do Damage

Colourised SEM image of Two Cytotoxic T Cells; T lymphocytes that kill cells infected with viruses
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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 Diseases

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. An autoantibody known as a rheumatoid factor is common in persons with rheumatoid arthritis.

Autoimmune diseases affect the immune system at several levels. In patients with systemic lupus erythematosus (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.

What Causes an Autoimmune Disease?

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 has particular histocompatibility types. For example, many persons with rheumatoid arthritis display the self-marker known as HLA-DR4.

How Is Autoimmune Disease Treated?

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.

Immune Complexes

Immune complexes are clusters of interlocking antigens and antibodies. Under normal conditions, immune complexes are rapidly removed from the bloodstream by macrophages in the spleen and Kupffer cells in the liver. In some circumstances, however, immune complexes continue to circulate. Eventually, they become trapped in the tissues of the kidneys, lung, skin, joints, or blood vessels. Just where they end up probably depends on the nature of the antigen, the class of antibody--for instance, IgG instead of IgM--and the size of the complex.

Once they make it to an anatomic site or organ they set off reactions that lead to inflammation and tissue damage.

Immune complexes work their damage in many diseases. Sometimes, as is the case with malaria and viral hepatitis, they reflect persistent low-grade infections. Sometimes they arise in response to environmental antigens such as the moldy hay that causes the disease known as farmer's lung. Frequently, immune complexes develop in autoimmune disease, where the continuous production of autoantibodies overloads the immune complex removal system.

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