Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Synonyms and keywords: Primary immunosuppression, inherited immunosuppression, familial immunosuppression, secondary immunosuppression, acquired immunodeficiency, secondary immunodeficiency, immunosuppressive disorder, immune deficiency disease
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immuno-suppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other conditions. Deliberately induced immunosuppression is generally done to prevent the body from rejecting an organ transplant, treating graft-versus-host disease after a bone marrow transplant, or for the treatment of auto-immune diseases such as rheumatoid arthritis or Crohn's disease. This is typically done using drugs, but may involve surgery (splenectomy), plasmapharesis, or radiation. A person who is undergoing immunosuppression, or whose immune system is weak for other reasons (for example, chemotherapy and HIV patients) are said to be immunocompromised. When an organ is transplanted, the immune system of the recipient will most likely recognize it as foreign tissue and attack it. The destruction of the organ will, if untreated, end in the death of the recipient. In the past, radiation therapy was used to decrease the strength of the immune system, but now immunosuppressant drugs are used to inhibit the reaction of the immune system. The downside is that with such a deactivated immune system, the body is very vulnerable to opportunistic infections, even those usually considered harmless. Also, prolonged use of immunosuppressants increases the risk of cancer.
Dr. Joseph Murray of Harvard Medical School and chief plastic surgeon at Children's Hospital Boston from 1972-1985 was awarded the Nobel Prize in Physiology or Medicine in 1990 for his work on immunosuppression. Dr. Murray and his team are credited with first successful human kidney transplant at Peter Bent Brigham Hospital, Boston on 23 December 1954.
Cortisone was the first immunosuppressant identified, but its wide range of side effects limited its use. The more specific azathioprine was identified in 1959, but it was the discovery of cyclosporine in 1970 that allowed for significant expansion of kidney transplantation to less well-matched donor-recipient pairs as well as broad application of liver transplantation, lung transplantation, pancreas transplantation, and heart transplantation.
Immunodeficiency can be:
- B cell immunodeficiency
- T cell immunodeficiency
- NK cell immunodeficiency
- Mixed immunodeficiency
Immunodeficiency can be classified as:
- Inherited immunodeficiency
- Acquired immunodeficiency
Congenital immunodeficiency may be caused by disorders of the bone marrow (site of immunocyte production). However, many primary immunodeficiency syndromes are caused by mutations that result in abnormalities in either the maturation of immunocytes or their function outside the bone marrow and are thus not considered bone marrow disorders per se. Accordingly, immunodeficiency syndromes are usually not listed under bone marrow failure syndromes and are often discussed separately.
Inherited immunodeficiency syndromes may involve:
Acquired immunodeficiency may be secondary to a disease of the bone marrow or the reticuloendothelial system. Bone marrow etiologies of acquired immunosuppression include either post-transplant immunosuppression, viral disease (eg HIV and AIDS), or drugs among other causes.
Acquired immunodeficiency syndromes may involve:
- T-cells (e.g. AIDS), or
- B-cells aka humoral immune deficiency (e.g. acquired hypogammaglobulinemia), or
- NK cells (e.g. AIDS), or
- Mixed (more than one line of cells)