We thus made the following hypothesis regarding the pathogenic process in IgG4-RD; M2 macrophages recognize certain exogenous or endogenous molecules through binding to MARCO which promote the production of factors, including IL-10 and CCL18, which precipitate an exaggerated fibrosis and the pathology noted in IgG4-RD (see Supplementary Figure 4). This evidence concerns the gene CCL18 and immunoglobulin G4-related sclerosing disease.