Collectively, these data suggest that the serum of type 1 AIP/IgG4-RD patients contains higher concentrations of total IgG, IgG1, IgG4, IFN-α, and IL-33, and that the activation of IFN-α and IL-33-mediated signaling pathways is involved in IgG4-biased Ig class switch recombination. This evidence concerns the gene IL33 and autoimmune pancreatitis type 1.