Immunodeficiency disordersoccur when the body's immune response is reduced or absent.
See also: Autoimmune disorders
Causes, incidence, and risk factors:
The immune system is made up of lymphoid tissue in the body, which includes the bone marrow, lymph nodes, thymus, tonsils, and parts of the spleen and gastrointestinal tract.
The immune system helps protect the body from harmful substances called antigens . Examples of antigens include bacteria, viruses, toxins , cancercells, and foreign blood or tissues from another person or species.
When the immune system detects an antigen, it responds by producing antibodiesthat destroy the harmful substances. The immune system response also involves a process called phagocytosis. During this process, certain white blood cells swallow and destroy bacteria and other foreign substances.
Immune system disorders occur when the immune system does not fight tumors or harmful substances as it should. The immune response may be over active or under active.
Immunodeficiency disorders may affect any part of the immune system. Most commonly, such a condition occurs when specialized white blood cells called T or B lymphocytes (or both) do not work as well as they should, or when your body doesn't produce enough antibodies.