Immunodeficiency disorders occur when the body’s immune response is reduced or absent.

Causes

The immune system is made up of lymphoid tissue in the body, which includes:

• Bone marrow

• Lymph nodes

• Parts of the spleen and gastrointestinal tract

• Thymus

• Tonsils

• Proteins and cells in the blood are also part of the immune system.

The immune system helps protect the body from harmful substances called antigens. Examples of antigens include bacteria, viruses, toxins, cancer cells, and foreign blood or tissues from another person or species.

People are said to be immunosuppressed when they have an immunodeficiency disorder due to medicines that weaken the immune system (such as corticosteroids). Immunosuppression is also a common side effect of chemotherapy given to treat cancer.

Acquired immunodeficiency may be a complication of diseases such as HIV infection and malnutrition

(especially if the person does not eat enough protein). Many cancers may also cause immunodeficiency.

People who have had their spleen removed have an acquired immunodeficiency, and are at higher risk for infection by certain bacteria that the spleen would normally help fight. Patients with diabetes are also at higher risk for certain infections.

As you get older, the immune system becomes less effective. Immune system tissues (especially lymphoid tissue such as the thymus) shrink, and the number and activity of white blood cells drop.

The following conditions and diseases can lead to an immunodeficiency disorder:

• Ataxia-telangiectasia

• Complement deficiencies

• DiGeorge syndrome

• Hypogammaglobulinemia

• Job syndrome

• Leukocyte adhesion defects

• Bruton disease

• Wiscott-Aldrich syndrome