Whole-blood flow-cytometric analysis of antigen-specific cd4 t-cell cytokine profiles distinguishes active tuberculosis from non-active states. PLoS ONE 2011; 6: e17813

T-cell based IFN-c release assays do not permit distinction of active tuberculosis (TB) from successfully treated disease or latent M. tuberculosis infection. We postulated that IFN-c and IL-2 cytokine profiles of antigen-specific T cells measured by flow-cytometry ex vivo might correlate with TB disease activity in vivo. Tuberculin (PPD), ESAT-6 and CFP-10 were used as stimuli to determine antigen-specific cytokine profiles in CD4 T cells from 24 patients with active TB and 28 patients with successfully treated TB using flow-cytometry. Moreover, 25 individuals with immunity consistent with latent M. tuberculosis infection and BCG-vaccination, respectively, were recruited. Although the frequency of cytokine secreting PPD reactive CD4 T cells was higher in patients with active TB compared to patients with treated TB (median 0.81 % vs. 0.39 % of CD4 T cells, p = 0.02), the overlap in frequencies precluded distinction between the groups on an individual basis. When assessing cytokine profiles, PPD specific CD4 T cells secreting both IFN-c and IL-2 predominated in treated TB, latent infection and BCG-vaccination, whilst in active TB the cytokine profile was shifted towards cells secreting IFN-c only (p,0.0001). Cytokine profiles of ESAT-6 or CFP-10 reactive CD4 T cells did not differ between the groups. Receiver operator characteristics (ROC) analysis revealed that frequencies of PPD specific IFN-c/IL-2 dual-positive T cells below 56 % were an accurate marker for active TB (specificity 100%, sensitivity 70%) enabling effective discrimination from non-active states. In conclusion,