The QuantiFERON-TB Gold Plus (QFT-Plus) IGRA measures IFN-gamma release in response to two TB-specific peptide antigens. Which antigens are used, and why is BCG vaccination not a cause of false-positive IGRA results?
- A ESAT-6 and CFP-10; these antigens are absent from BCG strains and most non-tuberculous mycobacteria (encoded in RD1 region absent from BCG) ✓
- B PPD (tuberculin); BCG-vaccinated individuals produce the same IFN-gamma response
- C MPT-64 and MPT-32; present in both MTB and BCG
- D Lipoarabinomannan (LAM); a shared antigen between all mycobacteria
Explanation
IGRA (QuantiFERON-TB Gold Plus and T-SPOT.TB) uses the MTB-specific antigens ESAT-6 (early secretory antigenic target-6) and CFP-10 (culture filtrate protein-10), both encoded in the RD1 (region of difference 1) genomic region. RD1 was deleted from the BCG vaccine strain and is absent from most NTM, meaning BCG-vaccinated individuals do NOT mount a T-cell IFN-gamma response to these antigens. This makes IGRA far more specific than tuberculin skin test (TST/Mantoux) in BCG-vaccinated populations. QFT-Plus adds a second TB2 tube with CD8+ T-cell epitopes to enhance sensitivity for immunocompromised individuals.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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