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 overactive or underactive.
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 cells and B cells. 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. Malnutrition, particularly with lack of protein, and many cancers may also cause immunodeficiency.
People who have had their spleen removed 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.
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
- Chediak-Higashi syndrome
- Combined immunodeficiency disease
- Complement deficiencies
- DiGeorge syndrome
- Hypogammaglobulinemia
- Job syndrome
- Leukocyte adhesion defects
- Panhypogammaglobulinemia
- Bruton disease
- Congenital agammaglobulinemia
- Selective deficiency of IgA
- Wiscott-Aldrich syndrome
