An IGRA (interferon-gamma release assay) for tuberculosis infection uses antigens ESAT-6 and CFP-10, which are encoded within the RD1 region. These antigens are absent in BCG strains because:

• A RD1 is deleted from M. bovis BCG during attenuation ✓
• B BCG produces modified ESAT-6 that does not stimulate T cells
• C BCG lacks the ESX-1 secretion system entirely
• D RD1 encodes heat-labile proteins destroyed during BCG lyophilisation

Explanation

The region of difference 1 (RD1) is deleted from M. bovis BCG during laboratory passage and attenuation. This region contains the genes encoding ESAT-6 (early secretory antigenic target 6) and CFP-10 (culture filtrate protein 10), which are secreted via the ESX-1 system. Because BCG lacks RD1, IGRA tests using these antigens are BCG-vaccination-specific and do not produce false-positive results in BCG-vaccinated individuals, which is a key advantage over TST. NTM species other than M. kansasii, M. szulgai, and M. marinum also lack RD1.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.