Liu Rui, Wu Qian, Su Dinglei, Che Nan, Chen Haifeng, Geng Linyu, Chen Jinyun, Chen Wanjun, Li Xia, Sun Lingyun
Arthritis Res Ther. 2012 Nov 23;14(6):R255. doi: 10.1186/ar4100.
Interleukin (IL)-21 is a member of type I cytokine family. Recent studies indicate that IL-21 can promote T follicular helper (Tfh) cell differentiation and survival, a specialized T cell subset which provides help for B cell. It can also regulate the activation, proliferation and differentiation of human B cell and immunoglobulin (Ig) production as well as isotype switching of plasma cell. Rheumatoid arthritis (RA) is characterized by auto-antibodies overproduction such as rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibody, suggesting a pivotal role of Tfh cell and B cell in the pathogenesis of RA. This study aimed to investigate whether IL-21 had a regulatory effect on Tfh cell and B cell in RA.
Serum IL-21 concentrations were measured by ELISA. The correlations between serum IL-21 levels and clinical features of RA patients were analyzed by Spearman's rank test. The percentages of Tfh-like cells, IL-21 receptor (R) expression on Tfh-like cells and B cells in peripheral blood (PB) were analyzed by flow cytometry. Peripheral blood mononuclear cells (PBMC) were stimulated by rIL-21 (100 ng/ml) in the presence or absence of anti-CD40 and/or anti-IgM, and changes of IL-21R, activation-associated surface markers (CD25, CD69 and CD40), the proliferation, apoptosis and differentiation of B cells were analyzed by flow cytometry. Production of IgG and IgM in the culture supernatants was determined by ELISA.
The results showed that the serum IL-21 levels in RA patients were significantly higher than that of healthy controls (HC). IL-21 concentrations were positively correlated with 28-joint count disease activity score (DAS28) and anti-CCP antibody in RA patients with high IL-21 levels. Furthermore, the frequencies of peripheral CXCR5+PD-1+CD4+ Tfh-like cells markedly increased in RA patients and the percentages of Tfh-like cells were positively correlated with DAS28 and anti-CCP antibody levels. Moreover, elevated IL-21 levels were also correlated with the frequencies of Tfh-like cells. IL-21R expression on both Tfh-like cells and B cells were significantly enhanced in RA patients. In cultures vitro, exogenous IL-21 upregulated IL-21R expression and activation-associated surface markers on B cells and promoted more B cell proliferation in RA than in HC. This IL-21-mediated effect could be reversed by IL-21R-specific neutralizing antibody. Importantly, IL-21 promoted more differentiation of B cell into plasmablast and higher levels of IgG and IgM production in RA than in HC.
Increased serum IL-21 levels in RA patients correlate with DAS28, anti-CCP antibody and frequencies of Tfh-like cells. IL-21 supports B cell activation, proliferation and antibody secretion via IL-21R pathway. Thus, IL-21 may be involved in the pathogenesis of RA and antagonizing IL-21 could be a novel strategy for the therapy of RA.
白细胞介素（IL）-21是I型细胞因子家族的成员。最近的研究表明，IL-21可促进滤泡辅助性T（Tfh）细胞的分化和存活，Tfh细胞是一种特殊的T细胞亚群，可为B细胞提供帮助。它还可调节人B细胞的激活、增殖和分化、免疫球蛋白（Ig）的产生以及浆细胞的同种型转换。类风湿关节炎（RA）的特征是自身抗体过度产生，如类风湿因子（RF）和抗环瓜氨酸肽（抗CCP）抗体，提示Tfh细胞和B细胞在RA发病机制中起关键作用。本研究旨在探讨IL-21对RA患者Tfh细胞和B细胞是否具有调节作用。
采用酶联免疫吸附测定（ELISA）法检测血清IL-21浓度。采用Spearman秩相关检验分析RA患者血清IL-21水平与临床特征之间的相关性。采用流式细胞术分析外周血（PB）中Tfh样细胞的百分比、Tfh样细胞和B细胞上IL-21受体（R）的表达。在存在或不存在抗CD40和/或抗IgM的情况下，用重组人IL-21（rIL-21，100 ng/ml）刺激外周血单个核细胞（PBMC），采用流式细胞术分析IL-21R、激活相关表面标志物（CD25、CD69和CD40）的变化以及B细胞的增殖、凋亡和分化。采用ELISA法测定培养上清液中IgG和IgM的产生。
结果显示，RA患者血清IL-21水平显著高于健康对照（HC）。在IL-21水平较高的RA患者中，IL-21浓度与28个关节计数疾病活动评分（DAS28）和抗CCP抗体呈正相关。此外，RA患者外周血CXCR5+PD-1+CD4+Tfh样细胞频率显著增加，Tfh样细胞百分比与DAS28和抗CCP抗体水平呈正相关。此外，IL-21水平升高也与Tfh样细胞频率相关。RA患者Tfh样细胞和B细胞上的IL-21R表达均显著增强。在体外培养中
