The QuantiFERON-TB Gold In-Tube (QFT-GIT) assay measures IFN-γ release in response to M. tuberculosis–specific antigens. Which antigens are used in QFT-GIT that distinguish it from PPD-based tuberculin skin tests and avoid cross-reactions with BCG?
- A MPT64 and MPT51 heat-shock proteins
- B Lipoarabinomannan (LAM) and cord factor (trehalose-6,6-dimycolate)
- C Purified protein derivative containing 200+ antigens
- D ESAT-6 (CFP-10 region of Rv3875) and CFP-10 (Rv3874) from the RD1 genomic region ✓
Explanation
QFT-GIT uses synthetic peptides representing ESAT-6 (Early Secretory Antigen Target-6, encoded by Rv3875) and CFP-10 (Culture Filtrate Protein-10, Rv3874), both located in the region of difference 1 (RD1) of the M. tuberculosis genome — a region absent from BCG vaccine strains and most non-tuberculous mycobacteria (except M. kansasii, M. marinum, M. szulgai). This specificity prevents false-positive results in BCG-vaccinated individuals, a major drawback of TST in India. TB7.7 (Rv3803) is a third antigen added in QFT-GIT. LAM and cord factor are bacterial structural components, not IGRA antigens.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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