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A wide variety of disorders are classified as autoimmune diseases, ranging from systemic lupus erythematosus to type I diabetes, and many other disorders are suspected of having an autoimmune component. Autoimmune diseases can thus affect a wide variety of bodily tissues and processes, such as the skin, liver, kidneys, or other organs, or the chemical reactions essential to metabolism. Each disease has a characteristic set of autoantibodies (antibodies that attack normal cells or structures in the body itself). In some of these diseases, the autoantibodies that are produced actually cause the tissue and organ damage. In other cases, the antibodies are considered to be characteristic markers of the disease but do not cause disease themselves. It is thought that the autoantibodies are generated by an immunologic reaction with bodily proteins, but the reasons that a specific set of bodily proteins should provoke an immune response that results in disease remain obscure. The genetic makeup of the individual, environmental influences, and infectious disease organisms may all contribute to a person's susceptibility to autoimmune disease. For reasons that are not clear, the prevalence of many autoimmune diseases is much higher in women than in men. Recently there have been dramatic improvements in the diagnosis and treatment of autoimmune disorders. New tests for diagnostically important autoantibodies have been discovered. Corticosteroids are used to reduce inflammation, and anticancer drugs that kill rapidly dividing cells are used to deplete activated cells in the immune system. The most promising new drugs consist of genetically engineered monoclonal antibodies that block just one part of the immune system. By selectively shutting down the part of the immune system involved in the autoimmune response, the drugs allow some people to see dramatic improvement in their symptoms with minimal side effects.