Waning of the specific interferon-gamma response after years of tuberculosis infection.

HYPOTHESIS: Memory T-cell responses to specific antigens wane over time in subjects with tuberculosis (TB) infection. SETTING: Accumulated evidence indicates that QuantiFERON-TB Gold (QFT-G), a specific whole-blood interferon-gamma (IFN-gamma) based assay, can detect recent TB infections with superior sensitivity and specificity. OBJECTIVE: We applied this technique to the adult population of a Japanese community to determine its epidemiological usefulness. METHOD: A total of 1559 subjects attending periodic health screening volunteered to participate in the study. RESULTS: The QFT-G positive rates were 3.1% for those aged 40-49 years, 5.9% for those aged 50-59 and 9.8% for those aged 60-69. The expected infection prevalence estimated by the authors from a series of studies was 11.1%, 29.6% and 53.1% for those aged 40-49, 50-59 and 60-69 years, respectively. This wide gap between the expected and observed positivity suggests that the IFN-gamma response waned substantially with time after infection. Those with X-rays suggestive of old TB lesions exhibited positivity rates well below 100%. CONCLUSION: The specific IFN-gamma response may wane considerably with time after infection. Longitudinal studies are required to investigate long-term dynamics of cell-mediated immunity in infected donors.