The pathogenesis of IgG4-RD remains unclear; however, up-regulation of T-helper 2 (Th2) and regulatory T (Treg) cell cytokines, including interleukin 4 (IL4), IL5, IL10, IL13, and transforming growth factor-beta 1 (TGFB1), in affected organs is thought to be important3. Here, IL4 is linked to immunoglobulin G4-related sclerosing disease.