Can circulating interleukin-18 differentiate between sarcoidosis and idiopathic pulmonary fibrosis?

Objective. The aim of the present study was to investigate serum and bronchoalveolar lavage fluid (BALF) interleukin-18 (IL-18) levels in sarcoidosis and idiopathic pulmonary fibrosis (IPF) and to assess the clinical usefulness of IL-18 in these diseases. Methods. Serum and BALF levels of IL-18 were measured in 15 patients with sarcoidosis, 10 patients with IPF and 24 control subjects (8 with lung tumor, 6 with pulmonary tuberculosis and 10 healthy controls). Lymphocyte fractions (T, B and natural killer (NK) cells) in blood and BALF were analysed by flow cytometer. Results. The serum and BALF levels of IL-18 in patients with sarcoidosis were significantly higher (p < 0.05) than those in IPF subjects and control groups. The percentages of T, B and NK cells in blood and BALF did not differ among all groups, while the blood and BALF CD4/CD8 ratios in patients with sarcoidosis were significantly higher (p < 0.05) than those in the other groups. Among all subjects, the serum levels of IL-18 correlated positively with the CD4/CD8 ratios in BALF (r - 0.693, p < 0.001). Conclusions. As to the levels of IL-18 in serum and BALF, there were differences between sarcoidosis and IPF indicating a different role of IL-18 in the pathogenesis of these diseases. Measurement of circulating IL-18 might have a potential of clinical utility in the differential diagnosis of sarcoidosis versus IPF.