Background IgG4-related disease (IgG4-RD) is a lymphoproliferative disorder characterized by elevated serum levels of IgG4 and increased numbers of circulating plasmablast. We have previously reported that class-switching to IgG4 and plasmablast differentiation are mediated by follicular helper type 2 T cells which are known to secrete interleukin (IL)-4, IL-13, IL-10 and IL-21 (1, 2). However, the cytokines which play a role in the IgG4 class-switching and plasmablast differentiation through cell to cell contact remain unclear in IgG4-RD.

Objectives The aim of this study was to elucidate the role of follicular helper type 2 T cell cytokines (IL-4, IL-13, IL-10, and IL-21) and cell to cell interaction in the pathogenesis of IgG4-RD.

Methods Peripheral blood mononuclear cells (PBMCs) were prepared from seven consecutive patients with active, untreated, newly diagnosed IgG4-RD and five healthy controls. To identify the cytokines which induce IgG4 class-switching, the cells were stimulated with IL-4, IL-13 or the combination with other cytokines, such as IL-10 or IL-21. The amounts of IgG4 and IgG in the culture supernatants were measured by cytometric bead arrays. The expression level of activation-induced cytidine deaminase (AID; an enzyme essential for class-switch recombination) was analyzed by quantitative PCR to confirm the induction of class-switching by stimulation with cytokines. The numbers of plasmablasts and plasma cells induced by cytokines stimulation were examined by flow cytometry. Moreover, an anti-CD40 antibody was added to the culture to elucidate the effects of cell to cell interaction on the differentiation of plasmablasts or plasma cells.

Results IL-4 significantly induced CD40-stimulated PBMCs to undergo IgG4 class-switching in patients with IgG4-RD, while IL-13 did not show any positive effects. Moreover, the IgG4/IgG ratio in culture supernatants was also significantly higher in the stimulation with IL-4 compared to other cytokines in IgG4-RD. In addition, the expression levels of AID mRNA were increased by stimulation with IL-4 compared to that by no stimulation or CD40 stimulation in IgG4-RD. On the other hand, PBMCs from healthy controls showed no significant difference in IgG4 production after stimulation with either IL-4 or IL-13. Furthermore, IgG4 production stimulated with IL-4 was significantly higher in IgG4-RD than that in healthy controls. Assessing additional effects of IL-10 or IL-21 on IL-4, IL-10 and IL-21 did not increase IgG4 production and IgG4/IgG ratio compared to IL-4 alone in IgG4-RD. However, importantly, IL-21 synergistically induced plasmablasts or plasma cells differentiation in combination with IL-4, whereas no obvious change was observed in PBMCs stimulated with IL-4 alone in IgG4-RD. Of note, the differentiation of plasmablasts and plasma cells by IL-4 and IL-21 was markedly abolished in the absence of CD40 stimulation.

Conclusions Our results strongly suggest that IL-4 plays a pivotal role in IgG4 class-switching, and the effective collaboration between IL-4 and IL-21 contributes to plasmablasts and plasma cells differentiation via CD40 dependent manner in patients with IgG4-RD.

References

1. Akiyama M, et al. Arthritis Res Ther. 2016;18:167.

2. Akiyama M, et al. Arthritis Rheumatol. 2015;67:2476–81.

References

Acknowledgements We thank all the physicians and others caring for the patients enrolled in our study.

Disclosure of Interest None declared