PRTN3 and immunoglobulin G4-related sclerosing disease: When peripheral blood mononuclear cells are stimulated with PR3 or MPO, it results in an elevated production of IL-6 (150), This heightened IL-6 level subsequently promotes fibroblast proliferation as well as the synthesis of collagen and fibronectin, thereby worsening fibrosis in the tissues affected by IgG4-RD (82).