The assessment of IFN-γ and its regulatory cytokines in the plasma and bronchoalveolar lavage fluid of patients with active pulmonary tuberculosis

OBJECTIVES: To assess the role of IFN-γ and its regulatory cytokines in active pulmonary tuberculosis (TB).

DESIGN: Cytokines were measured in the plasma of TB patients and healthy subjects with different risk for TB exposure. In addition, cytokine profile was assessed in the bronchoalveolar lavage fluid (BALf) of six TB patients and nine normal controls.

RESULTS: Circulating IFN-γ, IL-10 and IL-18 were higher in TB patients than in control groups. Plasma IL-12 levels were extremely variable, and no difference was observed among study groups. An inverse correlation between plasma IFN-γ and IL-10 levels was found in TB patients. Furthermore, circulating IL-18 correlated with IL-10 but not with IFN-γ levels. Finally, IFN-γ, IL-18 and IL-12 were increased in the BALf of TB patients, whereas no difference was observed in IL-10 levels.

CONCLUSIONS: In human TB, at least at certain disease stages, there is a differential compartmentalization of the IFN-γ-regulatory factors IL-12 and IL-10, the former being concentrated in the lungs and the latter being present in peripheral circulation. In addition, our findings address more critically the role of IL-18 in the host response to tuberculosis infection in humans.