1405. The Accuracy of Mycobacterium tuberculosis Specific IFN-γ/IL-2/TNF-α- FluoroSpot in Differential Diagnosis of Active Tuberculosis and Latent Tuberculosis Infection: A Case-Control Study
Authors: Zhang Lifan , Ma Huimin , Ge Qiping , Zhang Yueqiu , Shi Xiaochun , Cao Qifei , Gao Mengqiu , liu Xiaoqing 
Published: December 2021

Abstract

Background
To establish the Mycobacterium tuberculosis (MTB) specific IFN-γ/IL-2/TNF-α-FluoroSpot assay, and preliminarily evaluate its accuracy of differential diagnosis of active tuberculosis (ATB) and latent tuberculosis infection (LTBI).

Methods
Patients with pathologically confirmed and clinically diagnosed ATB in Peking Union Medical College Hospital and Beijing Chest Hospital from April 2020 to May 2021 were enrolled as case group, while patients with LTBI in the same period were enrolled as control group. The FluoroSpot assay was used to simultaneously detect the secretion of IFN-γ, IL-2 and TNF-α in T cells stimulated by the MTB specific antigens ESAT-6 and CFP-10 at the single-cell level. A binary logistic regression model was used to fit the combined diagnostic parameters, and the sensitivity, specificity, predictive value and likelihood ratio of the differential diagnosis of ATB and LTBI were calculated.

Figure 1. Schematic diagram of FluoroSpot (IFN-γ/IL-2/TNF-α) detecting cytokine-secreting specific T cells after stimulation with MTB specific antigen. A. The green spots are the total IFN-γ-secreting T cells; B. The red spots are the total IL-2-secreting T cells; C. The blue spots are the total TNF-α-secreting T cells; D. The green spots are the single IFN-γ-secreting T cells; the red spots are the single IL-2-secreting T cells; the blue spots are the single TNF-α-secreting T cells; the yellow spots are the dual IFN-γ/IL-2-secreting T cells; the cyan spots are the dual IFN-γ/TNF-α-secreting T cells; the purple spots are the dual IL-2/TNF-α-secreting T cells; the white spots are the triple IFN-γ/IL-2/TNF-α-secreting T cells.

Results
62 patients with ATB (37 pathogen-confirmed ATB, 25 clinical diagnosed ATB), 87 patients with LTBI were included. There was significant correlation of the frequencies of total IFN-γ-secreting T cells detected by IFN-γ/IL-2/TNF-α-FluoroSpot assay compared with T-SPOT.TB after stimulation of MTB-specific antigen (r=0.829 for ESAT-6, P&lt; 0.001, r=0.804 for CFP-10, P&lt; 0.001). ROC curve was drawn for both T-SPOT.TB and Fluorospot. For T-SPOT.TB, the AUROC was 0.669 (95%CI 0.574-0.765), the sensitivity and specificity of differentiating ATB from LTBI were 70.97% (95%CI 58.05%-81.80%) and 56.32% (95CI 45.26%-66.94%) respectively. While for Fluorospot, the AUROC was 0.906 (95 CI 0.856-0.957), the sensitivity and specificity of differentiating ATB from LTBI were 80.65% (95%CI 68.63% - 89.58%) and 88.51% (95%CI 79.88% - 94.35%) respectively.

Figure 2. Correlation between the frequencies of total IFN-γ-secreting T cells detected by FluoroSpot assay and those of T-SPOT.TB. (A) Stimulated by EAST-6. (B) Stimulated by CFP-10.

Figure 3. ROC curves and the corresponding AUROC for measurement of frequencies of specific T cells in differentiating ATB and LTBI under stimulation of ESAT-6 or CFP-10. The blue line is drawn with the frequency of IFN-γ-secreting T cells detected by T-SPOT.TB, and the AUC is 0.669 (95%CI, 0.574-0.765). The red line is drawn with combination of the frequencies and proportion of single IFN-γ-'single IL-2-'single TNF-α-'dual IFN-γ/IL-2-'dual IFN-γ/ /TNF-α-'dual IL-2/TNF-α-secreting T cells detected by FluoroSpot, and the AUC is 0.906 (95% CI, 0.856-0.957).
Table 1. Diagnostic value of T-SPOT.TB and FluoroSpot for differentiating ATB from LTBI

Conclusion
Compared with T-SPOT.TB, the IFN-γ/IL-2/TNF-α-Fluorospot assay may be helpful to distinguish ATB from LTBI, and the results need to be verified by large sample prospective cohort study.

Disclosures
All Authors: No reported disclosures