Discrimination between active and latent tuberculosis based on ratio of antigen-specific to mitogen-induced IP-10 production

Abstract

Mycobacterium tuberculosis is the major causative agent of tuberculosis (TB). The gamma interferon (IFN-γ) release assay (IGRA) has been widely used to diagnose TB by testing cell-mediated immune responses but has no capacity for distinguishing between active TB and latent TB infection (LTBI). This study aims to identify a parameter that will help to discriminate active TB and LTBI. Whole-blood samples from 33 active TB patients, 20 individuals with LTBI, and 26 non-TB controls were applied to the commercial IFN-γ release assay, QuantiFERON-TB Gold In-Tube, and plasma samples were analyzed for interleukin-2 (IL-2), IL-6, IL-8, IL-10, IL-13, tumor necrosis factor-alpha (TNF-α), IFN-γ, monokine induced by IFN-γ (MIG), interferon gamma inducible protein 10 (IP-10), interferon-inducible T cell alpha chemoattractant (I-TAC), and monocyte chemoattractant protein 1 (MCP-1) by using a commercial cytometric bead array. The Mycobacterium tuberculosis antigen-specific production of most of the assayed cytokines and chemokines was higher in the active TB than in the LTBI group. The mitogen-induced responses were lower in the active TB than in the LTBI group. When the ratio of TB-specific to mitogen-induced responses was calculated, IL-2, IL-6, IL-10, IL-13, TNF-α, IFN-γ, MIG, and IP-10 were more useful in discriminating active TB from LTBI. In particular, most patients showed higher IP-10 production to Mycobacterium tuberculosis antigens than to mitogen at the individual level, and the ratio for IP-10 was the strongest indicator of active infection versus LTBI with 93.9% sensitivity and 90% specificity. In conclusion, the ratio of the TB-specific to the mitogen-induced IP-10 responses showed the most promising accuracy for discriminating active TB versus LTBI and should be further studied to determine whether it can serve as a biomarker that might help clinicians administer appropriate treatments.

FIG 1

Cytokine levels in active TB and LTBI. Whole blood was stimulated with M. tuberculosis-specific antigens (ESAT-6, CFP-10, and TB7.7) or with mitogen for 24 h, and the levels of TB-specific and mitogen-induced cytokines and chemokines were measured in active TB patients, LTBI subjects, and non-TB healthy control subjects. *P < 0.05; **P < 0.01; ***P < 0.001; ns, not significant.

FIG 2

Ratio of TB-specific to mitogen-induced responses. Whole blood was stimulated with M. tuberculosis-specific antigens (ESAT-6, CFP-10, and TB7.7) or with mitogen for 24 h, and the levels of TB-specific and mitogen-induced cytokines and chemokines were measured in active TB patients, LTBI subjects, and non-TB healthy control subjects. (A) Ratios of TB-specific to mitogen-induced responses are shown. (B) Comparison of TB-specific and mitogen-induced IP-10 levels. (C) The optimal cutoff value and positive cases are indicated on the graph. *P < 0.05; **P < 0.01; ***P < 0.001; ns, not significant.

FIG 3

ROC curves for TB-specific and mitogen-induced cytokine responses. The AUCs of TB-specific (A) and mitogen-induced (B) IL-13, IFN-γ, and IP-10 levels and the ratios of TB-specific to mitogen-induced responses (C) were compared between active TB patients and LTBI. The AUCs and the P values are indicated on the graphs.