T cell deficiency is a deficiency of T cells, either caused by lymphocytopenia of T cells or by decreased function of individual T cells. It causes an immunodeficiency of cell-mediated immunity.
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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.[1]
Causes of 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).[1]
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.[1]
Secondary (or acquired) causes are mainly:[2]
Overall, secondary causes are more common than primary ones.[2]
Causes of T cell deficiency by thymic hypoplasia can, in turn, be classified as:
Peripheral (or non-thymic) causes of T cell deficiency include: Purine nucleoside phosphorylase deficiency, hyper IgM syndrome (in turn including, for example, 1)
The main pathogens of concern in T cell deficiencies are intracellular pathogens, including Herpes simplex virus, Mycobacterium and Listeria.[3] Also, intracellular fungal infections are also more common and severe in T cell deficiencies.[3]
Other intracellular pathogens of major concern in T cell deficiency are:[4]
Presentations differ among causes, but T cell insufficiency generally manifests as unusually severe common viral infections (e.g. by respiratory syncytial virus (RSV), enterovirus, rotavirus), mucocutaneous candidiasis, diarrhea, and eczematous or erythrodermatous rashes.[1] Failure to thrive and cachexia are late signs of a T-cell defect.[1]
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