The term immunity refers to the resistance exhibited by the humans towards injury caused by micro-organisms and their products, Autoimmunity is a condition in which structural or functional damage is produced by the action of immunologically competent cells or antibodies against normal components of the body. Many diseases are considered to be of autoimmune origin based on their association with cellular or humoral responses against self antigens. Once initiated, most autoimmune responses tend to be self perpetuating. Their progress can be arrested by immunosuppressive therapy, though the degree of response to such therapy varies in different diseases.