The IGRA (interferon-gamma release assay) for latent TB uses M. tuberculosis-specific antigens absent in BCG and most NTM. These antigens are encoded in the 'region of difference 1' (RD1). Which antigens are used in commercial IGRA assays?
- A ESAT-6 (early secretory antigenic target 6) and CFP-10 (culture filtrate protein 10) ✓
- B PPD (purified protein derivative) antigen mixture
- C Antigen 85A and ESAT-6
- D 38 kDa antigen and 16 kDa antigen
Correct answer: A. ESAT-6 (early secretory antigenic target 6) and CFP-10 (culture filtrate protein 10)
Explanation
IGRA assays (QuantiFERON-TB Gold Plus, T-SPOT.TB) stimulate patient T cells with ESAT-6 (early secretory antigenic target-6) and CFP-10 (culture filtrate protein-10), both encoded in the RD1 locus — a genomic segment absent in BCG vaccine strains and most non-tuberculous mycobacteria except M. kansasii, M. szulgai, and M. marinum. This makes IGRA more specific than TST for latent TB, especially in BCG-vaccinated populations like India. PPD contains hundreds of antigens including BCG cross-reactive antigens.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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