Levels of interferon-gamma increase after treatment for latent tuberculosis infection in a high-transmission setting

Abstract

Objectives. We investigated IFN-γ levels before and after a six month course of isoniazid among individuals with latent tuberculosis infection (LTBI) in a high-transmission setting. Design. A total of 26 household contacts of pulmonary tuberculosis patients who were positive for LTBI by tuberculin skin test completed six months of treatment and submitted a blood sample for a follow-up examination. The IFN-γ response to Mycobacterium tuberculosis-specific antigens was measured, and the results before and after the completion of LTBI treatment were compared. Results. Of the 26 study participants, 25 (96%) showed an IFN-γ level higher than their baseline level before treatment (P ≤ 0.001). Only one individual had a decreased IFN-γ level after treatment but remained positive for LTBI. Conclusion. In a high-transmission setting, the IFN-γ level has increased after LTBI treatment. Further studies must be undertaken to understand if this elevation is transient.

Figure 1

The difference between the baseline and follow-up IGRA result according to the number of months elapsed between the completion of H treatment and the follow-up examination. IFN-γ levels were measured by QFT-IT and plotted for each study participant (n = 26). H = isoniazid; IFN-γ = interferon-gamma; QFT-IT = QuantiFERON TB Gold in Tube.

Figure 2

Flow chart of the study population and the study participants. *TST ≥ 10 mm. H: isoniazid; QFT-IT: QuantiFERON TB Gold in Tube; TST: tuberculin skin test.

Figure 3

IFN-γ levels before and after H treatment for LTBI measured by QFT-IT stratified by baseline QFT-IT result; (a) positive QFT-IT and (b) negative QFT-IT. The solid line represents the median value of IFN-γ levels at the two time points. The differences between the median values in each group before and after H treatment are significant by the Wilconxon's signed rank test (P = 0.0007 and P = 0.005, resp.). IFN-γ: interferon-gamma; H: isoniazid; QFT-IT: QuantiFERON-TB Gold in Tube.