The immune system is composed of a complex network ofcells, tissues, and organs that function together as the body’sdefense against infectious organisms, diseases, and otherinvasive agents. Representing a duality of responsibilities,the immune system initiates the body’s quick and efficientresponse to harmful agents, while also distinguishing thesethreats from the body’s healthy cells and working to avoidautoimmunity, which is an attack against the host.