Interferon gamma, interferon-gamma-induced-protein 10, and tuberculin responses of children at high risk of tuberculosis infection.

BACKGROUND

Children in contact with adults with pulmonary tuberculosis (TB) are at risk for infection and disease progression, and chemoprophylaxis may reduce this risk. The identification of infection is based on the tuberculin skin test (TST) and interferon-gamma (INF-gamma) release assays. Other biomarkers such as interferon-gamma-induced-protein 10 (IP-10) may have potential for the diagnosis of latent TB infections.

OBJECTIVES

To describe IP-10 concentrations and their association to TST and INF-gamma responses in children recently exposed to adults with smear-positive TB in Brazil and Nepal.

METHODS

: Two surveys using the same design were undertaken to describe TST, INF-gamma, and IP-10 responses in 146 children in Nepal and 113 children in Brazil.

RESULTS

The concordance of TST and QuantiFERON-TB gold in-tube (QFT-IT) was high (kappa 0.73 in Brazil and 0.80 in Nepal). IP-10 responses were higher in children with both positive TST and positive QFT-IT (medians 1434 pg/mL in Brazil and 1402 pg/mL in Nepal) and lowest in children with both negative TST and negative QFT-IT (medians 206 pg/mL in Brazil and 81 pg/mL in Nepal). Children with negative TST and positive QFT-IT had higher IP-10 concentrations than children with positive TST but negative QFT-IT.

CONCLUSIONS

IP-10 is a potential marker to identify latent TB infections that is expressed in large quantities and with good agreement with QFT-IT. The reasons for the discrepant results observed are discussed.