IL-18 expression in salivary gland ducts of patients with Sjögren's syndrome (SS) (a–d) and nonspecific chronic sialoadenitis (e,f). IL-18-positive ducts were detected in all the SS samples but in only a minority of those from chronic sialoadenitis. A considerable range of variability of IL-18 expression was observed in ducts among different samples. Within the same glandular lobule, positive and negative (arrowheads) adjacent ducts were observed (a). Ductal IL-18 expression was found in ducts surrounded (b) and not surrounded (c) by focal infiltrate, as well as in ducts characterized by periductal fibrosis (d). In contrast to ductal epithelial cells, no staining for IL-18 was found in acinar cells (a,d, stars). In a minority of patients with chronic sialoadenitis, we observed similar ductal staining patterns. Representative examples of positive (e) and negative (f) ductal IL-18 staining in different patients with chronic sialoadenitis are shown. Original magnification × 200.