Immunohistochemical (IHC) detection of IL-18 in salivary glands of patients with Sjögren's syndrome (SS) (a–c,g–i) and in nonspecific chronic sialoadenitis (d–f). (a,b) Paraffin-embedded section of glands in SS, showing high amounts of IL-18-expressing cells distributed in a scattered fashion within the periductal mononuclear infiltrate. (c) IL-18-positive cells were also observed surrounding acini (arrows) in proximity with the inflammatory aggregate. (d–f) Paraffin-embedded sections of glands from patients with nonspecific chronic sialoadenitis, demonstrating the absence of IL-18 expression in mononuclear cells in nonfocal periductal infiltrates. (g) Paraffin-embedded sections of glands from patients with SS, double-stained for CD68 (brown) and IL-18 (purple), showed exclusive co-localization of IL-18 expression in most of the CD68+ macrophages (arrows) within the periductal inflammatory infiltrates. (h) Macrophages expressing a large amount of IL-18 (arrows) were also observed surrounding acini in contiguity with a focal lymphocytic aggregate. (i, same sample as g) Conversely, CD68+ macrophages adjacent to a nonfocal infiltrate remained single-stained. Original magnification (a,b,d) × 100, (c,e–i) × 200.