In terms of thenormal mechanism of T cell we find that it is a type ofwhite blood cell that has an important role in immunity, and is made fromthymocytes.[5] One sees in thepartial disorder of T cells that happen due tocell signaling defects, are usually caused byhypomorphic gene defects.[6] Generally, (micro)deletion of 22Q11.2 is the most often seen.[7]
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[13].
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.[14]
