Elevated interleukin-18 levels in bronchoalveolar lavage fluid of patients with eosinophilic pneumonia

Background: Interleukin (IL)-18 can induce Th2 cytokine production particularly in collaboration with IL-2. Accumulation of Th2 cells and increased levels of Th2 cytokines are found in bronchoalveolar lavage fluid (BALF) from patients with eosinophilic pneumonia (EP). To evaluate the role of IL-18 in the pathogenesis of EP, we measured the concentration of IL-2, IL-12, IL-18, and Th2 cytokines in BALF from patients with EP. Methods: The concentrations of interferon (IFN)-gamma, IL-2, IL-5, IL-10, IL-12, IL-13, and IL-18 in BALF were measured in patients with idiopathic acute eosinophilic pneumonia (AEP), with idiopathic chronic eosinophilicpneumonia (CEP), with sarcoidosis and healthy volunteers (HV). Results: The BALF concentrations of Th2 cytokines, IL-5, IL-10, and IL-13, were higher in patients with EP than in sarcoidosis and control. The IL-2 level in BALF was higher in EP than in sarcoidosis and control. The IL-18 and IL-12 (p40 + p70) levels were higher in patients with EP than sarcoidosis, while the level of IL-12 (p70) was below the detection limit in patients with EP. There was a significant correlation between IL-2 level and both IL-5 and IL-13 in BALF of patients with EP. Conclusions: Our findings suggest that IL-18 may contribute to Th2 cytokine-dominant responses in patients with EP in collaboration with IL-2.