The scheme of the pathogenesis of IgG4-RD assumes the increased activity of T regulatory cells (Treg) with overexpression of IL-10, transforming growth factor β (TGF-β) production, and upregulation of Th2 response, in which predominant roles play interleukins 4, 5, and 13 (IL-4, IL-5, Il-13) (Figure 2). Here, IL4 is linked to immunoglobulin G4-related sclerosing disease.