CD4 and tuberculosis: QFT-Plus testing was performed at enrollment per the manufacturer’s (Qiagen; Hilden, Germany) protocol.7 The QFT-Plus measures IFN-γ response (IU/ml) in a nil tube (negative control, measuring endogenous IFN-γ), a mitogen tube (positive control, measuring IFN-γ response to a non-specific T-cell stimulator), and two TB-specific tubes (TB1 and TB2) which elicit CD4+ and CD8+ T-cell responses to Mtb-specific antigens.