Is secretion of IFN-gamma in response to Mycobacterium tuberculosis antigens in youngest children sufficient to play a role in TB diagnostics?

ObjectivesTo assess whether children 5 years of age, produce sufficient amounts of interferon gamma (IFN-?) in response to phytohaemagglutinin (mitogen), and Mycobacterium tuberculosis antigens (TB antigens) in the QuantiFERON-TB Gold in-Tube test (QFT-GIT), (Cellestis Ltd., Australia). Working hypothesis: Is TB-antigen-induced IFN-? response in children 5 years sufficient to consider QFT-GIT a possible tool for TB diagnostics? Study design, patient-subject selection, and methods: We recruited children 0-17 years old suspected of TB infection to this cross-sectional study, in whom QFT-GIT and TST were performed. We analyzed the median IFN-? levels in mitogen and TB antigen tubes in children 5 years and >5 years, and the correlation between IFN-? level in both tubes and age. ResultsA total of 153 children were enrolled, age median was 7.8 (IQR:8), 45 (29.4%) aged 5 years (median 3.4, IQR:1.7), 108>5 years (median 10.55, IQR:5.93). In the mitogen tubes, the median IFN-? level was higher in children >5 years (median 17.87, IQR:2.1 vs 16.77, IQR:7.6), but surprisingly in the TB antigen tubes it was higher in the younger group (median 0.12, IQR:0.21vs 0.06, IQR:0.09, P=0.04). We proved a positive correlation between IFN-? level and age in mitogen tubes (r=0.18, P=0.03) and a negative correlation in TB antigen tubes (r=-0.17, P=0.04). In latent tuberculosis infection patients, the latter correlation was found to be even stronger (r=-0.39, P=0.01). ConclusionsThe youngest children release sufficient amount of IFN-? in response to TB antigens thus QFT-GIT might be a useful tool for TB diagnostics in this age group.