Immunology defined as the study of organism’s defense (immune) system in both health and disease. The principal role of the immune system is to defend the body against possible infections by discriminating between self and non-self. A key part of immunology involves studying how the many different organs, cells, and molecules of the immune system work to react with each other and many diseases are caused when the immune system malfunctions. Immunology deals with immunodeficiency and autoimmunity, as well as with producing vaccines to respond to an invading foreign organisms and prevent and control infections.