Autoimmune diseases refer to diseases caused by the body's immune response to its own antigens, which leads to damage to its own tissues. Many diseases have been listed as autoimmune diseases. It is worth pointing out that the existence of autoantibodies and autoimmune diseases are not two equivalent concepts. Autoantibodies can exist in normal people without autoimmune diseases, especially the elderly, such as anti-thyroglobulin, thyroid epithelial cells, gastric parietal cells, and nuclear DNA antibodies. Sometimes, damaged or antigenically changed tissues can stimulate the production of autoantibodies. For example, when myocardial ischemia occurs, necrotic myocardium can lead to the formation of anti-myocardial autoantibodies, but these antibodies have no pathogenic effect and are a secondary immune response.