[A view of dynamics of immune responses against tuberculosis infection through QFT]

QFT has been approved as a diagnostic test of TB infection in April 2005 in Japan, and further adopted to health insurance in January 2006. QFT is now a necessary tool to diagnose TB infection, especially in contact investigation. Since QFT uses M. tuberculosis-specific antigens, which are absent from BCG and most of non-tuberculous mycobacteria, to stimulate blood samples, and Interferon-gamma (IFN-gamma) produced with antigen-specific T cells is measured to diagnose TB infection, QFT can specifically diagnose TB infection without influence of BCG vaccination or infection of most of non-tuberculous mycobacteria. There is another diagnostic test, T-SPOT.TB, which uses similar antigens to QFT, and these two tests are called as IGRAs (Interferon-Gamma Release Assays). However, as production of IFN-gamma is a small part of protective immune responses against TB infection, it is difficult from this point of view to understand the dynamics of protective immune responses against TB infection through IGRAs results. Especially, it is impossible to distinguish between active TB and latent TB infection, to identify time of TB infection, or to detect dormancy TB infection using current IGRAs. Using biomarkers other than IFN-gamma or antigens other than antigens used in current IGRAs, development of newer diagnostic tests which have these performances would be awaited.