Tumor necrosis factors (TNFs) are pleiotropic cytokines with important functions in homeostasis and disease pathogenesis. Recent advances have shown that TNFs are also involved in the regulation of adaptive immune responses. However, the knowledge about how TNF participates in and regulates adaptive immune response in early vertebrates is still limited. In present study, we identified two isoforms of TNF, TNF-α and TNF-β, from Nile tilapia Oreochromis niloticus (On-TNF-α and β). After analyzing the sequence characteristics, we investigated their regulatory roles in adaptive immune response of this fish species. On-TNF-α and β are evolutionarily conserved compare with their homologs from other vertebrates. Both TNFs were distributed in a wide range of tissues in O. niloticus, and with relative higher expression level in gill. After the animals were infected by Streptococcus agalactiae, mRNA levels of On-TNF-α and TNF-β in spleen lymphocytes were significantly upregulated during the primary response stage of adaptive immunity. Meanwhile, both TNF proteins in spleen lymphocytes were also dramatically elevated during the adaptive immune stage after bacterial infection. These results indicate the potential participation of On-TNF-α and TNF-β in adaptive immune response of Nile tilapia. Furthermore, On-TNF-α and β transcripts were obviously augmented, once spleen lymphocytes were activated by T cell-specific mitogen PHA. More importantly, both recombinant On-TNF-α and β could induce the apoptosis of head-kidney leukocytes of Nile tilapia. And On-TNF-β but not On-TNF-α promoted the apoptosis by activating caspase-8 in the target cells. Altogether, our study revealed that TNF-α and TNF-β participated in the lymphocyte-mediated adaptive immune response of Nile tilapia by initiating the apoptosis, and thus shed novel perspective for the regulatory mechanism of adaptive immunity in teleost.

肿瘤坏死因子 (TNFs) 是多效性细胞因子，在体内平衡和疾病发病机制中具有重要作用。最近的进展表明，TNFs 也参与调节适应性免疫反应。然而，关于 TNF 如何参与和调节早期脊椎动物适应性免疫反应的知识仍然有限。在本研究中，我们从尼罗罗非鱼Oreochromis niloticus（On-TNF-α 和 β）中鉴定了 TNF 的两种同工型，TNF-α 和 TNF-β 。在分析了序列特征后，我们研究了它们在这种鱼类适应性免疫反应中的调节作用。与来自其他脊椎动物的同源物相比，On-TNF-α 和 β 在进化上是保守的。两种 TNF 均分布在尼罗罗非鱼的广泛组织中，并且在鳃中具有相对较高的表达水平。动物感染无乳链球菌后, 在获得性免疫的初级反应阶段, 脾淋巴细胞中 On-TNF-α 和 TNF-β 的 mRNA 水平显着上调。同时，在细菌感染后的适应性免疫阶段，脾淋巴细胞中的两种 TNF 蛋白也显着升高。这些结果表明 On-TNF-α 和 TNF-β 可能参与尼罗罗非鱼的适应性免疫反应。此外，一旦脾淋巴细胞被 T 细胞特异性有丝分裂原 PHA 激活，On-TNF-α 和 β 转录物明显增加。更重要的是，重组On-TNF-α和β均能诱导尼罗罗非鱼头肾白细胞凋亡。并且 On-TNF-β 而不是 On-TNF-α 通过激活靶细胞中的 caspase-8 来促进细胞凋亡。共，