Increased levels of interleukin-18 in patients with pulmonary sarcoidosis

interleukin-18 (IL-18) has recently been identified as an interferon-gamma (IFN-gamma)-inducing factor, and it plays an important role in T helper 1 (Th1) response. We measured the serum levels of IL-18 and IFN-gamma in 37 patients with pulmonary sarcoidosis and 25 healthy control subjects. We also measured the levels of IL-18 and IFN-gamma in 10-fold concentrated bronchoalveolar lavage (BAL) fluids of 19 patients with pulmonary sarcoidosis and 9 healthy control subjects (all lifelong nonsmokers). The levels of serum IL-18 and IFN-gamma were significantly increased in patients with sarcoidosis. The levels of BAL fluid IL-18 were significantly elevated in patients with sarcoidosis, however, the IFN-gamma levels of the patients and control subjects were all below sensitivity. Serum IL-18 levels significantly correlated with serum IFN-gamma levels and lysozyme activity. The patients positive for gallium-67 (Ga-67) scan had significantly elevated serum IL-18 levels as compared with those of the negative patients. BAL fluid IL-18 levels significantly correlated with serum IL-18 levels in patients with sarcoidosis, and there was a significant correlation between IL-18 levels and lymphocyte proportions in sarcoid BAL fluids. In patients with sarcoidosis, IL-18 seems to induce IFN-gamma production and IL-18 levels in sera may reflect disease activity of sarcoidosis.