Differentiating Active TB from Latent TB Infection: A New IFN? Release Assay Using Three LTBI Antigens
Objective: Distinguishing between active tuberculosis (ATB) and latent tuberculosis infection (LTBI) poses challenges to TB control efforts. This study aimed to identify LTBI antigens that could differentiate ATB from LTBI in a new interferon-gamma release assay (IGRA).  Methods: We systematically screened and identified potential latent TB antigens using gene synthesis, subcloning, bacterial expression, and purification. A cohort of 128 subjects participated in the study, enabling the development of a novel assay. Three proteins with promising characteristics were selected for further investigation, and various antigen combinations were explored to enhance assay sensitivity and specificity. The diagnostic performance was evaluated using area under the curve (AUC) analysis, with the optimal cutoff determined by the receiver operating characteristic (ROC) curve.  Results: Among the evaluated single antigen stimulators, Rv0475, Rv2028c, and Rv2029c showed potential in distinguishing ATB from LTBI, albeit with individual sensitivities below 70%. Notably, combining these antigens substantially improved sensitivity. For example, the combination of Rv0475 and Rv2029c yielded a positive rate of 78.9% and specificity of 88.9% at a cutoff of 80.4 pg/ml. Similarly, the combination of Rv0475, Rv2028c, and Rv2029c achieved a positive rate of 76.3% and specificity of 92.6% at a cutoff of 86.9 pg/ml.  Discussion: The combination of these three LTBI antigens in the new IFN? release assay represents a promising method for distinguishing ATB from LTBI infection. This finding holds significant potential for clinical diagnosis and tuberculosis control efforts.