In line with the positive correlation observed between the serum IFN-α and total IgG, IgG1, or IgG4 levels, we found significant positive correlations between IL-33 and total IgG or IgG4 concentrations in the serum of patients with type 1 AIP/IgG4-RD. Here, IL33 is linked to immunoglobulin G4-related sclerosing disease.