The class B scavenger receptors (scarb) are members of important pattern recognition receptors which play key roles for host immune response to pathogen infection. In the present study, two scarb member 2 paralogous (Onscarb2a and Onscarb2c) were identified and characterized in Nile tilapia. Onscarb2a was identified with an open reading frame (ORF) of 1593 bp which encoded a polypeptide of 530 amino acids, and Onscarb2c was consisting of an ORF of 1446 bp which encoded a polypeptide of 461 amino acids. Both Onscarb2a and Onscarb2c share high sequence identity/similarity with their counterparts from other teleost species. Multiple sequence alignment and phylogenetic tree analyses show that scarb2c from teleost fish is more closely related to other vertebrate scarb2s. Gene expression studies revealed that both scarb2a and scarb2c were highly expressed in liver, with the lowest expression in muscle in healthy tilapia. After challenges with Streptococcus agalactiae and Aeromonas hydrophila, both Onscarb2a and Onscarb2c were markedly up-regulated in liver and head kidney. In addition, the up-regulation of Onscarb2a and Onscarb2c were also detected in head kidney monocytes/macrophages and hepatocytes. In conclusion, this study revealed that Onscarb2a and Onscarb2c might play important roles in the innate immune responses to bacterial invasion in Nile tilapia.

B 类清道夫受体 (scarb) 是重要的模式识别受体的成员，它们在宿主对病原体感染的免疫反应中起关键作用。在本研究中，在尼罗罗非鱼中鉴定并表征了两个旁系同源物（Onscarb2a和Onscarb2c）的疤痕成员 2 。Onscarb2a具有 1593 bp 的开放阅读框 (ORF)，编码 530 个氨基酸的多肽，Onscarb2c由编码 461 个氨基酸的多肽的 1446 bp 的 ORF 组成。Onscarb2a 和 Onscarb2c 与来自其他硬骨鱼类的对应物具有高度的序列同一性/相似性。多序列比对和系统发育树分析表明，来自硬骨鱼的 Scarb2c 与其他脊椎动物的 Scarb2s 更密切相关。基因表达研究表明， Scarb2a 和 Scarb2c 在肝脏中均高度表达，在健康罗非鱼的肌肉中表达最低。在用无乳链球菌和嗜水气单胞菌攻击后，Onscarb2a和Onscarb2c在肝脏和头肾中均显着上调。此外，Onscarb2a和在头肾单核细胞/巨噬细胞和肝细胞中也检测到Onscarb2c。总之，这项研究表明 Onscarb2a 和 Onscarb2c 可能在对尼罗罗非鱼细菌入侵的先天免疫反应中发挥重要作用。