ABSTRACT
Background: Discriminating latent tuberculosis infection [LTBI] from active TBI may be challenging. The objective of this study was to produce the recombinant L-alanine dehydrogenase [AlaDH] antigen and evaluate individuals with LTBI, those with active TBI, and uninfected individuals by enzyme-linked immunospot assay [ELISPOT] in order to distinguish LTBI from active TBI
Methods: This exploratory study was performed in the Iranian city of Shiraz from 2014 to 2015. The study population [N=99] was divided into 3 groups: individuals with newly diagnosed active TBI [n=33], their household contacts [n=33], and controls [n=33]. AlaDH was produced through PCR and cloning methods. The diagnostic characteristics of AlaDH vs. ESAT-6/ CFP-10 were evaluated in responses to interferon-gamma [IFN-gamma] and interleukin-2 [IL-2] with ELISPOT. Differences between the groups were assessed with the Kruskal-Wallis and Mann- Whitney tests for nonparametric data analysis. The statistical analyses were performed with SPSS, version 16
Results: IFN-gamma responses to both ESAT-6/CFP-10 [P=0.81] and AlaDH [P=0.18] revealed that there were no significant differences between the individuals with LTBI and those with active TBI. The same results were determined for IL-2 responses to ESAT-6/CFP-10 between the 2 groups, while significantly higher IL-2 responses to AlaDH were observed in LTBI than in active TBI. According to the ROC curve analysis, a cutoff value of 275 SFC showed sensitivity of 75.8% and specificity of 78.8% for distinguishing LTBI from active TBI by IL-2 responses to AlaDH
Conclusion: The current study suggests that it may be possible to discriminate LTBI from active TBI by IL-2 responses to AlaDH