To better understand autoimmune diseases, one must understand how the immune system works.
The immune system is a network of organs, cells and molecules that work together to defend the body against attacks by foreign (not of the body) invaders such as germs, bacteria, viruses, parasites and fungi. When one of these invaders (antigens) tries to break into the body, the body's first line of defense is the skin and mucous membranes.
The skin and mucous membranes house macrophages (white cells of the tissues) and antibodies. The macrophages job is to digest the antigens while the antibodies trap the antigens that got away. If the antigens break through these barriers, the body reacts by producing lymphocytes (B and T cells) programmed to attack and kill the antigen.
In general terms, when antibodies are directed against the body's own cells, or when B and T cells attack and destroy their own body's cells and not foreign antigens, an autoimmune disorder can result.
The autoimmune process can have varied consequences. For example, slow destruction of a particular type of cell or tissue, stimulation of an organ into excessive growth or interference in its functions. Organs and tissues frequently affected include the thyroid, pancreas, adrenal glands as well as red blood cells and connective tissues (skin, muscle and joints).
Autoimmune disorders are classified into two types, organ-specific (directed mainly at one organ) and non-organ-specific (widely spread throughout the body).
Examples of organ-specific autoimmune disorders are insulin-dependent diabetes (Type I) which affects the pancreas, Hashimoto's thyroiditis and Graves' disease which affects the thyroid gland, pernicious anemia which affects the stomach, Addison's disease which affects the adrenal glands, and chronic active hepatitis which affects the liver.
Examples of non-organ-specific autoimmune disorders are rheumatoid arthritis, multiple sclerosis, lupus and myasthenia gravis.
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