Scavenger receptor B promotes bacteria clearance by enhancing phagocytosis and attenuates white spot syndrome virus proliferation in Scylla paramamosian

• Published in: Fish & shellfish immunology 2018-07, Vol.78, p.79-90
• Main Authors: Kong, Tongtong, Gong, Yi, Liu, Yan, Wen, Xiaobo, Tran, Ngoc Tuan, Aweya, Jude Juventus, Zhang, Yueling, Ma, Hongyu, Zheng, Huaiping, Li, Shengkang
• Format: Article
• Language: English
• Subjects: Apoptosis; Class B scavenger receptors; Phagocytosis; Scylla paramamosain
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2018.04.027

Phagocytosis and apoptosis are key cellular innate immune responses against bacteria and virus in invertebrates. Class B scavenger receptors (SRBs), which contain a CD36 domain, are critical pattern recognition receptors (PRRs) of phagocytosis for bacteria and apoptotic cells. In the present study, we identified a member of SRB subfamily in mud crab Scylla paramamosain, named Sp-SRB. The full-length cDNA of Sp-SRB is 2593 bp with a 1629 bp open reading frame (ORF) encoding a putative protein of 542 amino acids, and predicted to contain a CD36 domain with two transmembrane regions at the C- and N-terminals. Real-time qPCR analysis revealed that Sp-SRB was widely expressed in all tissues tested, and the expression of Sp-SRB was up-regulated upon challenge with Vibrio parahaemolyticus, white spot syndrome virus (WSSV), lipopolysaccharides (LPS) and polyinosinic polycytidylic acid (PolyI:C). Moreover, in vitro experiments indicated that recombinant Sp-SRB protein (rSp-SRB) could bind to fungi, Gram-positive and Gram-negative bacteria. RNA interference of Sp-SRB resulted in significant reduction in the expression level of phagocytosis related genes, antimicrobial peptides (AMPs) and Toll-like receptors (TLRs), which consequently led to impairment in both bacterial clearance and the phagocytotic activity of hemocytes. In addition, we found that Sp-SRB had the ability to attenuate the replication of WSSV proliferation in mud crab S. paramamosain. Collectively, this study has shown that Sp-SRB contributed to bacteria clearance by enhancing phagocytosis and up-regulating the expression of AMPs possibly in a TRLs (SpToll 1 and SpToll 2)-dependent manner. Besides, Sp-SRB inhibited the replication of WSSV in S. paramamosian probably through enhancement of hemocytes phagocytosis of apoptotic cells. •Full-length of Sp-SRB with 2593 bp was isolated from mud crab.•Sp-SRB promoted bacteria clearance by enhancing phagocytosis and up-regulating the expression of AMPs.•Sp-SRB inhibited the replication of WSSV in S. paramamosian.