Evaluation of Interleukin-2 to Detect Active and Latent Tuberculosis among Household Contacts of Pulmonary Tuberculosis Cases

Background: The interferon-gamma release assays (IGRAs) are the most important diagnostic approach to Mycobacterium tuberculosis infection diagnosis. However, they cannot discriminate between latent tuberculosis infection (LTBI) and active tuberculosis (TB). Some recent studies suggested that interleukin-2 (IL-2) response to M. tuberculosis could be utilized as a potential biomarker to discriminate active disease from LTBI. Objectives: The current study aimed at evaluating the potential role of IL-2 to detect both active TB and LTBI among household contacts of patients with pulmonary TB in two TB-endemic regions of Iran. Methods: A total of 650 household contacts of patients with TB were invited to participate in the current study. All subjects were diagnosed on extensive clinical evaluation of active TB and LTBI based on clinical manifestations and laboratory findings. The IGRA test was performed using QuantiFERON®-TB Gold Plus. The serum level of IL-2 was measured using the ELISA Development Kit. Results: A total of 237 household contacts entered the final analysis, including 132 patients with LTBI and three with active TB. In addition, 14 subjects were included as TB controls and 102 as TB-uninfected controls. The serum level of IL-2 was significantly higher in active TB and LTBI patients than TB-uninfected controls. The ROC curve was plotted between active TB and LTBI, revealing that the cutoff point of 25.5 pg/mL identifies the active form with 88.24% sensitivity and 36.36% specificity. Conclusions: The current study indicated that the IL-2 assay could not discriminate between active TB and LTBI with acceptable sensitivity.