Interferon-gamma response by years after tuberculosis infection, measured with QuantiFERON-TB Plus

Introduction: Interferon-gamma (IFN-γ) response wanes by years after tuberculosis infection. CD8+ T cells play a role to control tuberculosis infection mainly in active phase, and also in chronic phase. IFN-γ response by years after tuberculosis (TB) infection measured with QuantiFERON-TB Plus (QFT-Plus) has not been reported. Aims: To evaluate IFN-gamma response by years after TB infection with QFT-Plus. Materials and Methods: From May 2017 to June 2018, we enrolled 36 subjects with previous active TB and divided into 2 groups: the subjects who was diagnosed with TB within 3 years (group 1, n=18) and over 3 years before (group 2, n=18). Positive rate and quantitative IFN-γ response with QFT-Plus were compared among two groups. Results: The average age was 56.6±19.5 years in group 1 and 66.2±15.5 years in group 2, and 13 (72.2 %) were male in both groups. The median years after active TB onset was 1.3 (0.5–2.4) years in group 1 and 11.2 (3–70) years in group 2. Positive rate with QFT-Plus was 83.3% and 55.6%, respectively. The quantitative IFN-γ response was 0.86 (0.01–11.52) and 0.49 (0.01–5.33), respectively. The difference in quantitative values between TB2 and TB1 (TB2-TB1: surrogate CD8+ T cells response) were 0.10 (-0.72–2.46) in group 1 and 0.00 (-1.03–1.54) in group 2. The positive rate, the quantitative IFN-γ response, and TB2-TB1 value were lower in group 2, although there was no significant difference. Conclusion: These results suggested that IFN-γ response might wane over 3 years after TB infection. The median of TB2-TB1 values in group 2 were zero, suggesting CD8+ T cells response might be weaker over 3 years after TB infection.