Interleukin (IL)-21 is a pleiotropic cytokine and plays a vital role in immunity. In the current study, we examined the immune function of Japanese flounder Paralichthys olivaceus IL-21 (PoIL-21). PoIL-21 shares moderate (25.17%-46.25%) sequence identities with other teleost IL-21. PoIL-21 expression occurred in multiple tissues, especially intestine, and was regulated by bacterial infection in a time dependent manner. PoIL-21 was secreted by peripheral blood leukocytes (PBL) upon LPS stimulation. Recombinant PoIL-21 (rPoIL-21) bound to a wide range of Gram-negative and Gram-positive bacteria and inhibited the growth of the fish bacterial pathogen Streptococcus iniae. rPoIL-21 also interacted with PBL, resulting in enhanced cell proliferation, ROS production, and expression of IL-1β, TNF-α, CD8β, T-bet, PoIL-21, PoIL-21 receptor, and STAT. Consequently, the presence of rPoIL-21 significantly reduced bacterial infection in PBL. In vivo study showed that rPoIL-21 upregulated the expression of inflammatory cytokines and PoIL-21. Taken together, these results indicate that PoIL-21 is an inducible, secreted cytokine with a broad range of binding capacities and plays an important role in the regulation of anti-bacterial immunity.

中文翻译：

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日本比目鱼Paralichthys olivaceus interleukin 21诱导炎症反应，并在抵抗细菌病原体的免疫防御中发挥重要作用。

白介素（IL）-21是一种多效细胞因子，在免疫中起着至关重要的作用。在当前的研究中，我们检查了日本比目鱼oliparaeus olivaceus IL-21（PoIL-21）的免疫功能。PoIL-21与其他硬骨鱼IL-21具有中等（25.17％-46.25％）的序列同一性。PoIL-21表达发生在多个组织中，尤其是肠中，并且受细菌感染以时间依赖性方式调节。LPS刺激后，外周血白细胞（PBL）分泌PoIL-21。重组PoIL-21（rPoIL-21）与多种革兰氏阴性和革兰氏阳性细菌结合，并抑制鱼类细菌病原体链球菌的生长。rPoIL-21也与PBL相互作用，导致细胞增殖增强，ROS产生以及IL-1β，TNF-α，CD8β，T-bet，PoIL-21，PoIL-21受体和STAT的表达。因此，rPoIL-21的存在显着减少了PBL中的细菌感染。体内研究表明，rPoIL-21上调了炎症细胞因子和PoIL-21的表达。综上所述，这些结果表明PoIL-21是具有广泛结合能力的可诱导的，分泌的细胞因子，并且在抗细菌免疫的调节中起重要作用。