Identification of latently
-infected individuals according to IL-2 secretion upon stimulation with PPD and BCG. A) Distribution of the frequencies (%) of IL-2-secreting T cells in PBMC of patients with active TB (TB Act) or individuals with latent TB infection (TB Lat) stimulated for 72 hours with PPD, ESAT-6/CFP-10 or BCG. Horizontal lines indicate the median. Differences among the populations were considered significant when the p-values (indicated by the numbers) were < 0.05. B) ROC curves (on the left) were generated plotting sensitivity (%) versus 100%-specificity% to examine the effect of different cut-points of the percentage of PPD-specific (on the top) or BCG-specific (on the bottom) IL-2 secreting T cells in latently infected individuals versus both control subjects and active TB patients. Squares indicate the various percentage cut-off values used to calculate the corresponding sensitivity and specificity. Arrows indicate the optimum cut-offs (0.35% and 0.25% for PPD and BCG, respectively) with the best combination of sensitivity and specificity. On the right the corresponding AUC and statistical significances of the ROC curves and the sensitivity and specificity corresponding to the optimum cut-offs are indicated.