The potential of delayed type hypersensitivity-inducing Mycobacterium tuberculosis-specific antigens in the diagnosis of tuberculosis

The worldwide control of tuberculosis (TB) requires affordable and easy to apply test(s), which could diagnose active/latent TB and differentiate from vaccination with Mycobacterium bovis Bacillus Calmette Guerin (BCG), and exposure to environmental mycobacteria. The currently used test for the diagnosis of TB is the in vivo administered tuberculin skin test that induces delayed-type hypersensitivity (DTH) skin responses in individuals infected with M. tuberculosis. However, this test lacks sensitivity and specificity because of the non-standardized and cross-reactive nature of the antigens used, i.e. purified protein derivative (PPD) of M. tuberculosis. Since PPD contains antigens shared between M. tuberculosis, BCG, and environmental mycobacteria, it cannot differentiate between infection with M. tuberculosis, vaccination with BCG, and exposure to environmental mycobacterial. To overcome the problems associated with PPD, there is a need to identify M. tuberculosis-specific antigens as new tuberculins for in vivo diagnostic applications in humans.