CD4 and immunoglobulin G4-related sclerosing disease: In addition to serum biomarkers, changes in the numbers of circulating plasmablasts [33, 34], activated follicular helper 2 T cells [33–35], activated follicular helper 1 T cells [34, 35], and CD4+ cytotoxic T cells [36] were observed in patients with IgG4-RD.