Identification and serological characterization of MtbAg1073, a conserved Mycobacterium tuberculosis complex antigen recognized in active tuberculosis.

backgroundTuberculosis (TB) remains a major global health challenge, with delayed diagnosis perpetuating transmission in resource-limited settings. Although the sensitivity of molecular diagnostic methods is high, their dependence on the laboratory infrastructure limits accessibility in many regions. Serological approaches that detect host antibody responses represent a technically simple diagnostic strategy; however, the performance of currently available TB serodiagnostic tests is inconsistent, largely due to suboptimal antigen selection and heterogeneity in host immune responses. Therefore, the identification of conserved antigens naturally recognized during human infection is essential for improving serological diagnostics.

methodsA cDNA expression library derived from Mycobacterium bovis BCG Tokyo was constructed and screened by colony immunoblotting using pooled sera from patients with active TB. Immunoreactive clones were sequenced and analyzed bioinformatically. The full-length coding sequence of the identified antigen was expressed recombinantly using a cold-shock expression system in Escherichia coli. The recombinant protein was purified and evaluated for immunoreactivity using a Western blot analysis. Serological reactivity was further assessed using a dot-blot assay with individual serum samples from microbiologically confirmed TB patients (n = 40) and healthy controls (n = 40) from the Lao People's Democratic Republic. Diagnostic performance was evaluated by a receiver operating characteristic (ROC) curve analysis.

resultsImmunoscreening identified a conserved hypothetical protein corresponding to Rv1073 of M. tuberculosis, designated MtbAg1073, for which no antigenicity had been previously reported. The protein was highly conserved among members of the M. tuberculosis complex. Recombinant expression using a cold-shock system produced soluble His-tagged MtbAg1073, which was specifically recognized by sera from TB patients in the Western blot analysis. Dot-blot assays showed significantly higher antibody responses in TB patients than in controls (median intensity: 761.2 vs. 471.9; the Mann-Whitney U test, P = 0.0002). The ROC analysis demonstrated moderate discriminatory performance (AUC = 0.734; 95% CI: 0.624-0.844), with a sensitivity of 70.0% and specificity of 67.5% at the optimal cut-off value.

conclusionsMtbAg1073 is a conserved and immunoreactive antigen that elicits detectable antibody responses in active TB. These findings provide preliminary evidence of its immunoreactivity and warrant further investigation into its potential utility in serological approaches.