IL4 and immunoglobulin G4-related sclerosing disease: Although they didn’t directly demonstrate the effect of IL-13 and IL-4 secreted by ILC2 on IgG4-RD fibrosis, multiple studies suggested that IL-13 and/or IL-4 could mediate tissue fibrosis either directly (by acting on fibroblasts) or indirectly (e.g., by acting on alternatively activated macrophage) (22–24).