Development and Evaluation of an NTM-IGRA to Guide Pediatric Lymphadenitis Diagnosis

Background: Diagnosis of nontuberculous mycobacteria (NTM) infections remains a challenge. In this study, we describe the evaluation of an immunological NTM-interferon (IFN)-γ release assay (IGRA) that we developed using glycopeptidolipids (GPLs) as NTM-specific antigens. Methods: We tested the NTM-IGRA in 99 samples from pediatric patients. Seventy-five were patients with lymphadenitis: 25 were NTM confirmed, 45 were of unknown etiology but compatible with mycobacterial infection and 5 had lymphadenitis caused by an etiologic agent other than NTM. The remaining 24 samples were from control individuals without lymphadenitis (latently infected with M.Tuberculosis, uninfected controls and active tuberculosis patients). Peripheral blood mononuclear cells were stimulated overnight with GPLs. Detection of IFN-γ producing cells was evaluated by enzyme-linked immunospot assay. Results: NTM culture-confirmed lymphadenitis patient samples had a significantly higher response to GPLs than the patients with lymphadenitis of unknown etiology but compatible with mycobacterial infection (P < 0.001) and lymphadenitis not caused by NTM (P < 0.01). We analyzed the response against GPLs in samples from unknown etiology lymphadenitis but compatible with mycobacterial infection cases according to the tuberculin skin test (TST) response, and although not statistically significant, those with a TST ≥5 mm had a higher response to GPLs when compared with the TST <5 mm group. Conclusions: Stimulation with GPLs yielded promising results in detecting NTM infection in pediatric patients with lymphadenitis. Our results indicate that the test could be useful to guide the diagnosis of pediatric lymphadenitis. This new NTM-IGRA could improve the clinical handling of NTM-infected patients and avoid unnecessary misdiagnosis and treatments.