Urocortin (UCN) is a hormone in the hypothalamic–pituitary–adrenal axis that is expressed in various immune cells. However, the function of teleost UCN in the immune system remains unclear. In this study, we cloned the cDNA sequence of UCN from ayu Plecoglossus altivelis (PaUCN). Sequence and phylogenetic tree analyses showed that PaUCN clustered within the fish UCN 1 group and was most related to the rainbow trout (Oncorhynchus mykiss) UCN. PaUCN was expressed in all tested tissues and its expression increased in the liver, spleen, head kidney, and gill upon Vibrio anguillarum infection. Mature PaUCN protein (mPaUCN) treatment affected the phagocytosis and bacterial killing of monocytes/macrophages (MO/MФ). mPaUCN reduced pro-inflammatory cytokine expression in MO/MФ, which was partially mediated via interaction with ayu interleukin-6. mPaUCN reduced bacterial load and increased the survival of V. anguillarum-infected ayu. Overall, UCN as an endocrine factor regulates the immune response of ayu after infection by activating MO/MФ, thus contributing to enhance fish survival.

尿皮质素 (UCN) 是下丘脑-垂体-肾上腺轴中的一种激素，在各种免疫细胞中表达。然而，硬骨鱼UCN在免疫系统中的功能仍不清楚。在这项研究中，我们从 Ayu Plecoglossus altivelis (PaUCN)中克隆了 UCN 的 cDNA 序列。序列和系统发育树分析表明，PaUCN 聚集在鱼 UCN 1 组内，与虹鳟鱼 ( Oncorhynchus mykiss ) UCN 最相关。PaUCN在所有受试组织中均有表达，在鳗弧菌上其在肝脏、脾脏、头肾和鳃中的表达增加感染。成熟的 PaUCN 蛋白 (mPaUCN) 处理影响了单核细胞/巨噬细胞 (MO/MФ) 的吞噬作用和细菌杀伤作用。mPaUCN 降低了 MO/MФ 中促炎细胞因子的表达，这部分是通过与 ayu interleukin-6 的相互作用介导的。mPaUCN 减少了细菌负荷并增加了V. anguillarum感染的香鱼的存活率。总体而言，UCN作为内分泌因子通过激活MO/MФ来调节香鱼感染后的免疫反应，从而有助于提高鱼类的存活率。