Early secretory antigenic target-6 of Mycobacterium tuberculosis: enigmatic factor in pathogen-host interactions

T helper (Th) 1 and 17 cells play important roles in host protective responses against tuberculosis. Early Secretory Antigenic Target 6; a Region of Difference 1 (RD1) encoded protein, mounts Th17-responses in the lung. Therefore, lack of RD-1 region makes Bacillus Calmette-Guérin (BCG) less vaccine efficacious than parent strains.