The pathogenic role of IL-33 is reflected in its ability to stimulate an aberrant Th2 response with subsequent production of fibrogenic cytokines, such as interleukin 4 (IL-4) and interleukin 13 (IL-13); concentrations of type 1 IFN and IL-33, appear to be increased in both tissue and serum from patients with IgG4-RD, suggesting the use of IL-33 as a novel IgG4-RD biomarker [29]. Here, IL4 is linked to immunoglobulin G4-related sclerosing disease.