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

See also: Autoimmune disorders

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, cancer cells, and foreign blood or tissues from another person or species.

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.

Inherited immunodeficiency disorders that affect B cells include:

• Hypogammaglobulinemia, which usually causes mild to moderate respiratory infections
• Agammaglobulinemia, which results in frequent severe infections and is often deadly

Inherited immunodeficiency disorders that affect T cells may cause increased susceptibility to fungi, resulting in recurring candida (yeast) infections. Inherited combined immunodeficiency affects both T lymphocytes and B lymphocytes. It may be deadly within the first year of life if it isn't treated early.

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

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.

The following conditions and diseases can result in an immunodeficiency disorder:

• Ataxia-telangiectasia
• DiGeorge syndrome
• Chediak-Higashi syndrome
• Job syndrome
• Leukocyte adhesion defects
• Panhypogammaglobulinemia
  • Bruton disease
  • Congenital agammaglobulinemia
• Selective deficiency of IgA
• Combined immunodeficiency disease
• Wiscott-Aldrich syndrome
• Complement deficiencies
• Hypogammaglobulinemia

The symptoms vary with the specific disorder.

Persistent, recurrent infections, or severe infection by microorganisms that do not usually cause severe infection, may be a sign that an immunodeficiency disorder is present. Other signs include:

• Poor response to treatment
• Delayed or incomplete recovery from illness
• Certain types of cancers (such as Kaposi's sarcoma or non-Hodgkin's lymphoma)
• Certain infections (such as pneumocystis carinii pneumonia or recurrent fungal yeast infections)

Tests used to help diagnose an immunodeficiency disorder may include:

• White blood cell count
• Antibody/immunoglobulin levels
• T (thymus derived) lymphocyte count
• Complement levels or other measurements of immune-response components