Among them, we found there were 12 DEPs (IGHG4, ITA2B, URP2, HV118, APOC2, GP1BA, CAP1, TBB1, APOE, DSC2, TSP1, and SODE) overlapped in the comparisons of tissue and serum and all those DEPs upregulated in IgG4-RD patients, suggesting their importance to IgG4-RD. Here, APOE is linked to immunoglobulin G4-related sclerosing disease.