Immunodeficiency Disorders
"Immunodeficiency disorders occur when the body's immune response is reduced or absent.
When the immune system detects an antigen, it responds by producing antibodies that 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.
Acquired immunodeficiency may be a complication of diseases such as HIV infection and AIDS (acquired immunodeficiency syndrome). Malnutrition, particularly with lack of protein, and many cancers, may also cause immunodeficiency.
Persons who have had their spleen removed are at higher risk for from certain bacteria that the spleen would normally help fight. Patients with diabetes are also at higher risk for certain infections.
Increasing age reduces the effectiveness of the immune system to some degree. Immune system tissues (particularly lymphoid tissue such as the thymus) shrink, and the number and activity of white blood cells drop.
Interferon (used to treat viral infections and some types of cancer) and Zidovudine (AZT, used to treat AIDS) are 2 immunostimulant drugs (medications that increase the efficiency of the immune system)."
From a MedlinePlus Article (opens in new tab or window)