Complete or partial failure of the immune system, developing after birth
Immunodeficiency is the term used for failure of the immune system to combat infections effectively. As a result of immunodeficiency, infections develop more frequently than normal and are a greater threat to health. Infections that would not normally seriously affect a healthy person may be life-threatening in someone who has immunodeficiency. They include viral infections, such as shingles and chickenpox, both of which are caused by herpes zoster and cause only mild illnesses if the immune system is normal.
Immunodeficiency may be present from birth, in which case it is often inherited (see Congenital immunodeficiency). More commonly, the deficiency in a person’s immune system develops later in life, and in such cases the condition is given the name acquired immunodeficiency.
Worldwide, acquired immunodeficiency is most often associated with malnutrition or with infection with the human immunodeficiency virus (see HIV infection and AIDS).
In AIDS, the human immunodeficiency virus (HIV) destroys a particular type of white blood cell, and this causes progressive immunodeficiency.
Infections such as influenza or measles damage the body’s ability to fight infection. They do this partly by reducing the number of white blood cells involved in fighting the infection. Usually, this type of immunodeficiency is mild, and the immune system returns to normal once the person has recovered from the infection.
A mild form of immunodeficiency may occur in some long-term disorders, including diabetes mellitus and rheumatoid arthritis. This may occur partly because these diseases put stress on the immune system, reducing its ability to resist other diseases.
Certain types of cancer, particularly tumours of the lymphatic system (see Lymphoma), may cause a more severe form of immunodeficiency by damaging the cells of the immune system and by reducing the production of normal white blood cells.
The long-term use of corticosteroids suppresses the immune system and has the inevitable effect of causing immunodeficiency. Immunosuppressant drugs, which may be given to prevent the rejection of an organ following transplant surgery, also produce immunodeficiency and affect the body’s ability to fight infections. Chemotherapy can damage the bone marrow, where the majority of blood cells are made, and may also lead to acquired immunodeficiency.
Immunodeficiency may also develop after surgical removal of the spleen, an organ in which some of the white blood cells are produced. Splenectomy may be performed if the spleen has been damaged by an injury, or it may be carried out to treat various disorders including hereditary spherocytosis, which is a type of haemolytic anaemia.
There are many other types of acquired immunodeficiency, the causes of which are not clear. One type is immunoglobulin A (IgA) deficiency, in which levels of immunoglobulin A antibodies are lower than normal.
Your doctor may suspect immunodeficiency if you have recurrent infections. To confirm the diagnosis of acquired immunodeficiency, you may need to have blood tests that measure the levels of white blood cells and antibodies.
If immunodeficiency is due to drug treatment, it may be possible to reduce the dose or stop taking the drug. If the underlying cause cannot be cured or reversed, treatment is aimed at reducing the risk of infection and combating infections as they occur. Your doctor may suggest regular intravenous infusions of immunoglobulin; continual low doses of antibiotics, antiviral drugs, and/or antifungal drugs; and various immunizations, such as the pneumococcus vaccine (see Vaccines and immunoglobulins) to protect against pneumococcal pneumonia.
The effects of immunodeficiency can usually be controlled by treatment, although immunodeficiency due to HIV infection may worsen over time.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.