CD4 and immunoglobulin G4-related sclerosing disease: Here, our finding that Tfh2 cells, but not Tfh1 and Tfh17 cells, induce the differentiation of naïve B cells into plasmablasts and the production of IgG4 in patients with active, untreated IgG4-RD suggests that Tfh2 cells are pathogenic CD4+ T cells that play a pivotal role in the T-cell-dependent immune response in patients with IgG4-RD.