IL-18 is highly expressed in inflammatory infiltrates of submandibular glands in patients with immunoglobulin G4-related disease.

Immunoglobulin (Ig) G4-related disease (IgG4-RD) is a new disease entity characterized by high serum IgG4 concentrations, infiltration of IgG4-positive plasmacytes, and fibrosis of various organs. Several groups have reported that IgG4-RD is a unique inflammatory disorder characterized by an immune reaction predominantly mediated by T helper (Th) 2 and regulatory T cells. Meanwhile, recent studies have demonstrated that interleukin (IL) 18 has a potential to trigger the production of Th2 cytokines by Th1 cells. We analyzed IL-18 expression in submandibular glands of patients with IgG4-RD (20 cases) and controls (19 cases) by immunohistochemical analysis and quantitative real-time reverse-transcription polymerase chain reaction. We found that IL-18 was highly expressed in submandibular glands of patients with IgG4-RD than in controls with both protein (P < .05, χ(2) test) and messenger RNA levels (P < .05, Mann-Whitney U test). In addition, the expression of IL-18 and IL-13 was correlated in submandibular glands of patients with IgG4-RD. Moreover, by analyzing dual immunofluorescence staining, a few numbers of cells were double positive for IL-13 and interferon γ at the inflammatory infiltrates of submandibular glands of patients with IgG4-RD. These data suggest a possibility that IL-13 is produced by Th1 cells. We speculated that IL-18 stimulates Th1 cells producing Th2 cytokines and enhances the immune reaction of Th2 cytokines in pathogenesis of IgG4-RD.