Interleukin-18 expression in BAL cells of sarcoidosis patients is decreased in vivo but protein secretion is not impaired in vitro

Recently, increased expression of interleukin- 18 (IL- 18) has been shown in sarcoid airway epithelium. However, IL-18 expression has not been investigated extensively in bronchoalveolar lavage (BAL) cells in sarcoidosis yet. Expression of IL-18 and tumour necrosis factor-alpha (TNFalpha) mRNA in cells of the BAL of 23 patients with sarcoidosis and nine healthy volunteers was determined using semiquantitative RT-PCR. IL-18 protein in BAL cells was investigated by immunocytochemistry (ICC). IL- 18 protein levels in BAL cell culture supernatants from patients and controls with and without LPS stimulation were measured by enzyme-linked immuno-sorbent assay. BAL cells from patients were stimulated with either IL- 10 or IL- 13 and IL- 18 protein levels were determined. IL- 18 m RNA expression was significantly decreased in BAL cells of patients compared to control subjects (1.62 +/- 0.27 vs. 4.29 +/- 0.77, P < 0.05). TNFalpha m RNA expression was significantly increased in BAL cells of patients in comparison to control subjects (0.63 +/- 0.09 vs. 0.11 +/- 0.08, P < 0.05). ICC showed less positive alveolar macrophages in sarcoidosis patients than in control subjects (26 vs. 53%). IL- 18 protein levels did not differ significantly between both groups. Stimulation with IL- 10 significantly reduced IL- 18 protein concentration in sarcoidosis patients. Our results suggest that BAL cells may not be the main source of IL- 18 production in sarcoidosis in vivo. Since IL- 18 production of BAL cells was not impaired in culture anti inflammatory cytokines might contribute to decreased IL- 18 expression in vivo. (C) 2003 Elsevier Science Ltd. All rights reserved.