The Immune System is the body’s defense against a wide variety of infections, such as bacterial, viral, fungal and parasitic, as well as illnesses, such as tumor cells. It includes the lymph nodes, the spleen, bone marrow and white blood cells among others. The role of the immune system — a collection of structures and processes within the body — is to protect against disease or other potentially damaging foreign bodies. When functioning properly, the immune system identifies a variety of threats, including viruses, bacteria and parasites, and distinguishes them from the body's own healthy tissue. Disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer.