Why in News?
Reports on May 3, 2026, highlighted how modern Antiretroviral Therapy (ART) has effectively halted the natural selection of protective HLA-B alleles in populations, ensuring survival no longer depends on a "genetic lottery".
Key Information
- Definition: HLA-B is a gene that provides instructions for making proteins called MHC Class I, which sit on the surface of almost all cells.
- Function: These proteins act as "display cases," showing fragments of proteins (peptides) from inside the cell to the immune system. If the fragments are from a virus, the immune system triggers the cell's destruction.
- Extreme Diversity: HLA-B is the most polymorphic (variable) gene in the human genome, with over 10,870 known versions (alleles) as of early 2026.
- Nomenclature: Alleles are named using a code (e.g., HLA-B*27:05), where the first number identifies the group and the second identifies the specific protein subtype.
Clinical Importance & Disease Links
Specific alleles are used as biomarkers to predict disease risk or drug reactions:
- Autoimmune Diseases:
- HLA-B27: Strongly linked to Ankylosing Spondylitis (spinal inflammation); 90% of patients carry this allele.
- HLA-B51: A primary risk factor for Behçet’s Disease, especially in Asian populations.
- Drug Hypersensitivity:
- HLA-B*15:02: Patients with this allele have a high risk of life-threatening skin rashes (SJS/TEN) when taking the epilepsy drug Carbamazepine.
- HLA-B*57:01: Linked to severe reactions to the HIV drug Abacavir; testing is now mandatory before prescription.
- HLA-B*58:01: Increases the risk of severe reactions to Allopurinol (used for gout).
- Viral Control:
- Elite Controllers: People with HLA-B27 or HLA-B57 often progress much slower to AIDS after HIV infection because their immune systems "see" the virus more effectively.
Practical Application
- Organ Transplants: HLA-B "matching" between donors and recipients is critical to prevent the recipient's immune system from rejecting the new organ.
- Pharmacogenomics: Doctors are increasingly using HLA-B genotyping to "screen" patients before giving them certain medications to avoid fatal side effects.
- Diagnostic Testing: In India, an HLA-B*15:02 test typically costs around ₹5,250, while HLA-B27 tests are routine for diagnosing chronic back pain in young adults.
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