# T cell deficiency

T cell deficiency is a deficiency of T cells, caused by decreased function of individual T cells, it causes an immunodeficiency of cell-mediated immunity. T cells normal function is to help with the human body's immunity, they are one of the two primary types of lymphocytes (the other being B cells).

## Symptoms and signs

Presentations differ among causes, but T cell insufficiency generally manifests as unusually severe common viral infections (respiratory syncytial virus, rotavirus), diarrhea, and eczematous or erythrodermatous rashes. Failure to thrive and cachexia are later signs of a T-cell deficiency.

## Mechanism

In terms of the normal mechanism of T cell we find that it is a type of white blood cell that has an important role in immunity, and is made from thymocytes. One sees in the partial disorder of T cells that happen due to cell signaling defects, are usually caused by hypomorphic gene defects. Generally, (micro)deletion of 22Q11.2 is the most often seen.

### Pathogens of concern

The main pathogens of concern in T cell deficiencies are intracellular pathogens, including Herpes simplex virus, Mycobacterium and Listeria. Also, intracellular fungal infections are also more common and severe in T cell deficiencies. Other intracellular pathogens of major concern in T cell deficiency are:
* Mycobacterium avium intracellulare
* Salmonella species
* Rhodococcus equi
* Pneumocystis jirovecii
* Toxoplasma gondii
* Cryptosporidium parvum
* Leishmania species
* Herpesviridae (herpes simplex, cytomegalovirus and varicella zoster)
* Cryptococcus neoformans
* Histoplasma capsulatum

## Diagnosis

The diagnosis of T cell deficiency can be ascertained in those individuals with this condition via the following:
* Delayed hypersensitivity skin test
* T cell count
* Detection via culture(infection)

### Types
#### Primary or secondary

* Primary (or hereditary) immunodeficiencies of T cells include some that cause complete insufficiency of T cells, such as severe combined immunodeficiency (SCID), Omenn syndrome, and Cartilage–hair hypoplasia.
* Secondary causes are more common than primary ones. Secondary (or acquired) causes are mainly:
   * AIDS
   * Cancer chemotherapy
   * Lymphoma
   * Glucocorticoid therapy

##### Complete or partial deficiency

* Complete insufficiency of T cell function can result from hereditary conditions (also called primary conditions) such as severe combined immunodeficiency (SCID), Omenn syndrome, and cartilage–hair hypoplasia.
* Partial insufficiencies of T cell function include acquired immune deficiency syndrome (AIDS), and hereditary conditions such as DiGeorge syndrome (DGS), chromosomal breakage syndromes (CBSs), and B-cell and T-cell combined disorders such as ataxia-telangiectasia (AT) and Wiskott–Aldrich syndrome (WAS).

## Treatment

In terms of the management of T cell deficiency for those individuals with this condition the following can be applied:
* Killed vaccines should be used(not live vaccines in T cell deficiency)
* Bone marrow transplant
* Immunoglobulin replacement
* Antiviral therapy
* Supplemental nutrition

## Epidemiology

In the U.S. this defect occurs in about 1 in 70,000, with the majority of cases presenting in early life. Furthermore, SCID has an incidence of approximately 1 in 66,000 in California.