J Rheum Dis 2017; 24(5): 271-278  
Interleukin-17 Enhances Germinal Center Formation and Immunoglobulin G1 Production in Mice
Jennifer Lee1,2*, Seon-Young Lee1*, Chang-Min Kang1, Joo Yeon Jhun1, Ji Hun Kim2, Mi-La Cho1, Sung-Hwan Park1,2, Ho-Youn Kim1,2, Seung-Ki Kwok1,2
1The Rheumatism Research Center, Catholic Research Institute of Medical Science, The Catholic University of Korea, 2Division of Rheumatology, Department of Internal Medicine, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
Correspondence to: Seung-Ki Kwok, Division of Rheumatology, Department of Internal Medicine, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 06591, Korea. E-mail:seungki73@catholic.ac.kr
*These authors contributed equally to this work.
Received: May 23, 2017; Revised: May 30, 2017; Accepted: May 31, 2017; Published online: October 31, 2017.
© Korean College of Rheumatology. All rights reserved.

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Abstract
Objective. Interleukin (IL)-17 is a pro-inflammatory cytokine that has pleiotropic effects on multiple target cells and thereby contributes to the development of immune-mediated inflammatory disorders. However, the role of IL-17 in the humoral immune response has not been clearly elucidated. Methods. Mice deficient in IL-17A (IL-17A knockout [KO] mice) and wild type (WT) C57BL/6 mice were compared. Distinct B cell (mature/precursor and marginal zone/follicular) and plasma cell populations were compared using fluorescence-activated cell sorting (FACS) and confocal immunostaining. Immunoglobulin production was assessed by enzyme-linked immunosorbent assay. Results. There was no difference in B cell and plasma cell populations between IL-17A KO and WT mice. However, after T cell-dependent antigen challenge, IL-17A KO mice produced lower levels of immunoglobulin (Ig)G1 than wild-type animals. IL-17A KO mice also showed reduced germinal center (GC) formation and lower expression of activation-induced cytidine deaminase, the essential enzyme for class switch recombination (CSR). IL-17 had no effect on the proliferation or survival of naïve B cells in in vitro functional studies. However, IL-17 treatment promoted naïve B cell differentiation into plasma cells in synergy with IL-4, although IL-17 alone had no effect. Conclusion. Our findings suggest that IL-17 contributes to the humoral immune response by enhancing GC formation, CSR to IgG1, and plasma cell differentiation in synergy with IL-4.
Keywords: Interleukin-17, B cell, Germinal center


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