IGHG1 and immunoglobulin G4-related sclerosing disease: Single-cell validation showed that IGHG4 and IGHE, but not IGHG1, were significantly upregulated in plasmablasts/dividing plasmablasts in IgG4-RD patients compared with HCs (Supplemental Figure 2F), which is in line with elevated serum IgG4 and IgE in these patients (4).