The percentage of ESAT-6 and CFP-10 specific IFN-γ/IL-2 dual positive CD4 T cells does not allow clear distinction between active tuberculosis (A-TB) and non-active disease states (T-TB or latent <i>M. tuberculosis</i> infection).

<p>This is evident from the fact that 7 of 12 (58%) of latently infected subjects had <56% IFN-γ/IL-2 dual positive ESAT-6-specific CD4 T cells The percentage of dual positive CD4 T cells specific for ESAT-6 and CFP-10 was determined as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0017813#pone-0017813-g002" target="_blank">figure 2</a>. As compared with PPD specific profiles with higher overall frequencies, robust determination of profiles specific for ESAT-6 and CFP-10 could only be determined if overall frequencies of specific cells were above 0.1% (i.e. in 62.5% of patients with active tuberculosis, 35.7% of individuals with successfully treated disease and 56.0% of latently infected individuals). The stippled line indicates the 56% threshold established for PPD specific T cells.