Interleukin-21 (IL-21), a potent immunomodulatory four-alpha-helical-bundle type I cytokine, is produced by NKT and CD4(+) T cells and has pleiotropic effects on both innate and adaptive immune responses. These actions include positive effects such as enhanced proliferation of lymphoid cells, increased cytotoxicity of CD8(+) T cells and natural killer (NK) cells, and differentiation of B cells into plasma cells. Conversely, IL-21 also has direct inhibitory effects on the antigen-presenting function of dendritic cells and can be proapoptotic for B cells and NK cells. IL-21 is also produced by Th17 cells and is a critical regulator of Th17 development. The regulatory activity of IL-21 is modulated by the differentiation state of its target cells as well as by other cytokines or costimulatory molecules. IL-21 has potent antitumor activity but is also associated with the development of autoimmune disease. IL-21 transcription is dependent on a calcium signal and NFAT sites, and IL-21 requires Stat3 for its signaling. The key to harnessing the power of IL-21 will depend on better understanding its range of biological actions, its mechanism of action, and the molecular basis of regulation of expression of IL-21 and its receptor.

中文翻译：

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白介素21：基本生物学及其对癌症和自身免疫的影响。

白细胞介素21（IL-21）是一种有效的免疫调节I型四α-螺旋束细胞因子，由NKT和CD4（+）T细胞产生，对先天和适应性免疫应答均具有多效作用。这些作用包括积极作用，例如增强淋巴细胞的增殖，增加CD8（+）T细胞和自然杀伤（NK）细胞的细胞毒性，以及B细胞分化为浆细胞。相反，IL-21对树突状细胞的抗原呈递功能也具有直接的抑制作用，并且对B细胞和NK细胞具有促凋亡作用。IL-21也由Th17细胞产生，并且是Th17发育的关键调节因子。IL-21的调节活性受其靶细胞的分化状态以及其他细胞因子或共刺激分子的调节。IL-21具有有效的抗肿瘤活性，但也与自身免疫性疾病的发展有关。IL-21的转录依赖于钙信号和NFAT位点，IL-21的信号传导需要Stat3。利用IL-21的能力的关键将取决于更好地了解其生物学作用范围，其作用机理以及调节IL-21及其受体表达的分子基础。