IFNG and immunoglobulin G4-related sclerosing disease: Both memory and follicular CD4+ T helper cells are thought to contribute to IgG4-RD via secretion of profibrotic cytokines (e.g., IL-6, IFN-γ and TGF-β), induction of IgG4 class-switching, expansion of plasmablasts, and production of autoantibodies (4).