IL6 and immunoglobulin G4-related sclerosing disease: In iMCD, hyper IL-6 is considered to be a strong inducer of B-cell maturation and immunoglobulin production [1, 24], while IgG4-RD is characterized by the expansion of not only plasma cells, but also other subsets of B cells (e.g., plasmablasts) [25, 26].