T cell deficiency

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.^[1] Failure to thrive and cachexia are later signs of a T-cell deficiency.^[1]

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.^[5] One sees in the partial disorder of T cells that happen due to cell signaling defects, are usually caused by hypomorphic gene defects.^[6] Generally, (micro)deletion of 22Q11.2 is the most often seen.^[7]

The diagnosis of T cell deficiency can be ascertained in those individuals with this condition via the following:^[1][4][3]

• 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.^[1]
• Secondary causes are more common than primary ones.^[9] Secondary (or acquired) causes are mainly:^[9]

• 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.^[1]
• 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]

Recognition of T cell deficiency

• Recognition of T cell disorders can involve identifying deficiencies in MHC class I or class II molecules. MHC class I and MHC class II molecules are cell-surface proteins that facilitate immune recognition by displaying peptide antigens to T lymphocytes. MHC class I^[10] presents peptides derived from intracellular proteins to CD8⁺ cytotoxic T cells, while MHC class II^[11] presents peptides originating from extracellular sources to CD4⁺ helper T cells. This antigen presentation allows the immune system to distinguish normal cells from those that are infected or otherwise altered, enabling an appropriate and targeted immune response. A deficiency in MHC class I interferes with the maturation of cytotoxic T cells (CD8+), which rely on MHC I for proper development, leading to a deficiency of these cells^[12]. Without functional MHC I, CD8+ T cells cannot effectively destroy virus-infected or abnormal cells. Similarly, MHC class II deficiency disrupts helper T cell (CD4+) maturation, leading to T cell deficiency, impaired activation of other immune cells, and a weakened immune response^[11].

In terms of the management of T cell deficiency for those individuals with this condition the following can be applied:^[2][1]

• Killed vaccines should be used(not live vaccines in T cell deficiency)
• Bone marrow transplant
• Immunoglobulin replacement
• Antiviral therapy
• Supplemental nutrition

In the U.S. this defect occurs in about 1 in 70,000, with the majority of cases presenting in early life.^[1] Furthermore, SCID has an incidence of approximately 1 in 66,000 in California.^[13]

• B cell deficiency