Interferon gamma release assay measures IFN release against which M.TB antigen:

Interferon gamma release assay (IGRA) measure T cell release of gamma interferon against TB antigen ESAT 6 and CF 10. This test also called as Quantiferon- more specific than Tuberculin skin testing as a result of less cross reactivity due to BCG vaccination and sensitization by nontuberculosis mycobacteria. - It reduces patient visits and gives an ability to perform serial testing without the hassle of boosting phenomenon caused by Tuberculin skin testing.