IL13RA1 and immunoglobulin G4-related sclerosing disease: Since Th2 lymphocytes and the related secreted cytokines are thought to play a dominant role in the pathogenesis of IgG4-RD, we therefore focused on IL-13 and its canonical receptor IL-13Rα1.15 Immunofluorescence staining results revealed that the level of IL-13 (Fig. 1a, c) and IL-13Rα1 (Fig. 1d, e) were markedly elevated in the SMGs of IgG4-RS patients compared with those in controls.