Level of IFNγ induced by specific antigens in three groups of study participants. Whole blood samples were collected from study participants suspected of pulmonary tuberculosis and apparently healthy subjects directly into tubes containing TB-specific antigens, mitogen and nil. The samples were incubated for 24 hours at 37°C, plasma was collected and IFNγ assay was performed using ELISA. The optical density (OD) of each test was read using a 450 nm filter with a 620 nm reference filter using ELISA plate reader, and the level of IFNγ (IU/ml) was interpreted using QuantiFERON-TB Gold In-Tube (QFTGIT) analysis software developed by the company (Cellestis Ltd., Carnegie, Australia). The subjects were categorized in to three groups based on sputum culture results as CP = sputum culture positive, CN = sputum culture negative and HS = healthy subjects and the mean levels of IFNγ IU/ml were compared for the three groups. Each dot represents the concentration of IFNγ IU/ml of each individual and the solid line shows the mean level of the IFNγ.