Abstract
A prospective cross-sectional blinded study of 28 patients (21 male and 7 female patients; mean age, 44 years) with suspected active tuberculosis (TB) attending a TB and chest clinic is described. Blood was taken for immune cell enumeration, a whole-blood enzyme-linked immunosorbent assay (ELISA) for the detection of gamma interferon (IFN-gamma) by the QuantiFERON-TB Gold (QFT-G) assay, and intracellular cytokine flow cytometry (ICC) analysis; and sputum was simultaneously taken for bacteriological culture for Mycobacterium tuberculosis. Twelve healthy subjects were included as controls. The performance characteristics of the QFT-G and ICC assays for the detection of active TB were compared. Among the patients with active TB, we found (i) normal to slightly elevated peripheral CD4(+) and CD8(+) T-cell counts but a significant reduction in the number of NK cells; (ii) CD4(+) T cells were the major cell type producing IFN-gamma, a type 1 cytokine; (iii) small percentages of CD8(+) T cells were also primed for IFN-gamma production; (iv) the production of interleukin-4 (IL-4), a type 2 cytokine, was not prominent; and (v) the sensitivity and the specificity of the QFT-G assay were 88.2% and 18%, respectively, and those of the ICC assay were 94.1% and 36.4%, respectively. The specificities of the blood tests were likely underestimated due to cross-reaction to a non-M. tuberculosis mycobacterial infection and the lack of a confirmatory test that could be used to diagnose latent M. tuberculosis infection. Flow cytometry accurately locates the pool of immunological effector cells responsible for cytokine production during active TB. The ICC assay is an additional useful tool for the diagnosis of active TB.