Yet, the central role of such cells is debated because IL-4 production upon re-stimulation has been shown to be restricted to CD4+GATA3+ T cells in patients with known atopy, suggesting that the role of TH2 responses in IgG4-RD might be confounded by concomitant allergic disease (21). Here, IL4 is linked to immunoglobulin G4-related sclerosing disease.