Streptococcus agalactiae is a Gram‐positive facultative intracellular bacterium that leads to severe economic loss of tilapia worldwide. Previous studies demonstrated that CD40 contributes to host protection against intracellular injection. In this study, CD40 was characterized from Nile tilapia (Oreochromis niloticus), named OnCD40. Sequence analysis showed that open reading frame of OnCD40 was 933 bp, containing a single peptide, a transmembrane domain and four cysteine‐rich domains. The qRT‐PCR revealed that OnCD40 was expressed in all examined tissues with the most abundant ones in spleen and thymus. After S. agalactiae stimulation, the expression of OnCD40 was significantly induced in most of the detected organs. Moreover, OnCD40‐overexpressing fish elicited significant protection against subsequent S. agalactiae challenge; approximately 10000‐fold fewer bacteria were detected in spleen of OnCD40‐overexpressing fish in comparison with control fish. Thus, CD40 had protecting function in Nile tilapia against intracellular pathogens.

中文翻译：

---

CD40对尼罗罗非鱼，尼罗罗非鱼中的细胞内病原体无乳链球菌产生抗微生物反应。

无乳链球菌是革兰氏阳性兼性细胞内细菌，导致罗非鱼在全球范围内造成严重的经济损失。先前的研究表明CD40有助于宿主抵抗细胞内注射。在这项研究中，CD40的特征是尼罗罗非鱼（Oreochromis niloticus），名为OnCD40。序列分析表明，OnCD40的开放阅读框为933 bp，包含一个肽，一个跨膜结构域和四个富含半胱氨酸的结构域。qRT-PCR显示OnCD40在所有检查过的组织中都有表达，其中最丰富的是脾脏和胸腺。后无乳链球菌在刺激下，在大多数检测到的器官中均显着诱导了OnCD40的表达。而且，过表达CD40的鱼对随后的无乳链球菌攻击也具有重要的保护作用。与对照鱼相比，在过量表达OnCD40的鱼的脾脏中检测到的细菌减少了约10,000倍。因此，CD40在尼罗罗非鱼中具有针对细胞内病原体的保护功能。