Cellular Immunodeficiency (T Cell Defects)
المؤلف:
APURBA S. SASTRY , SANDHYA BHAT
المصدر:
Essentials Of Medical Microbiology 2021
الجزء والصفحة:
3rd edition , p210
2025-09-29
430
DiGeorge Syndrome (Thymic Aplasia)
DiGeorge syndrome results from a congenital defect in thymic development leading to defect in T cell maturation.
- Infants are extremely vulnerable to viral, fungal, intracellular bacterial and protozoan infections
- Genetic defect: In 90% of cases, there occurs a deletion affecting chromosome 22q11 which leads to developmental malformation affecting the third and fourth pharyngeal pouches in embryonic life
- As a result, all the structures that develop from third and fourth pharyngeal pouches such as thymus, parathyroid glands, and portions of the face and aortic arch become defective
- Thus, in addition to the thymic defects, there may be associated:
* Parathyroid gland hypoplasia resulting in neonatal tetany and hypocalcemia
* Anomalies of the heart and the great vessels (Fallot’s tetralogy)
* Characteristic facial appearance.
- B cells and serum immunoglobulin levels are generally unaffected
- Treatment: Thymus transplantation has been found to be successful in restoration of immune function. In others (with partial defects), immunity may improve spontaneously with age.
Chronic Mucocutaneous Candidiasis
It represents an impaired cell-mediated immunity against Candida albicans leading to superficial infections of the skin, mucous membranes, and nails.
- They do not show increased susceptibility to other infections but often associated with endocrinopathies and autoimmune disorders
- Transfer factor therapy, along with amphotericin B has been reported to be effective.
Purine Nucleoside Phosphorylase Deficiency
It is a rare autosomal recessive disorder (chromosome 14), characterized by deficiency of an enzyme of purine metabolism called purine nucleoside phosphorylase (PNP).
- PNP is a key enzyme required for purine degradation; catalyzes the conversion of guanosine to hypoxanthine
- Its deficiency leads to elevated Deoxyguanosine triphosphate levels resulting in T cell toxicity. However, B cells are not affected
- T cell depletion predisposes to increased susceptibility to infection and autoimmune disorders.
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