IgG4-related disease (IgG4-RD) is a systemic disorder characterized by elevated serum IgG4 level, which is mediated by T follicular helper 2 (Tfh2) cell. However, the cytokines responsible for enhancing IgG4 production remain unclear in IgG4-RD. The aim of this study was to identify responsible Tfh2-related cytokines (interleukin (IL)-4 and IL-21) for enhancing IgG4 production in IgG4-RD. Peripheral blood mononuclear cells obtained from consecutive patients with active, untreated IgG4-RD and healthy controls were examined. The production of both IgG and IgG4 were significantly increased by stimulation with IL-4 alone as well as IL-21 alone compared to background stimulation with anti-CD40 antibody in IgG4-RD. On the other hand, the IgG4/IgG ratio was statistically higher by stimulation with IL-4 alone compared to the other Tfh2-related cytokines including IL-21 in IgG4-RD. IgG4 production was not increased by stimulation with IL-4 in healthy controls. These results suggest that IL-4 can contribute to the shift of balance of IgG subclasses toward IgG4 compared to the other Tfh2-related cytokines in IgG4-RD.
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