IFNA1 and immunoglobulin G4-related sclerosing disease: In addition, the positive correlations between serum concentrations of these cytokines and IgG4 serum levels reported in this study are fully consistent with the results of our in vitro studies, in which peripheral blood pDCs isolated from type 1 AIP/IgG4-RD patients promoted IgG4 production by HC B cells in an IFN-α-dependent manner15.