CD4 and immunoglobulin G4-related sclerosing disease: It has been reported that antigen exposure resulted in longer CDR3 domains in adults compared to infants in both CD4+ and CD8+ T cell compartments [37], suggesting that longer CDR3 in IgG4-RD patients might be caused by chronic antigen exposure, which is consistent with the previous results showing antigen-driven clonal expansion in IgG4-RD.