A class B scavenger receptor from Eriocheir sinensis (EsSR-B1) restricts bacteria proliferation by promoting phagocytosis

Scavenger receptors (SRs) are important pattern recognition receptors (PRRs), which play significant roles in host defense against pathogens by identifying pathogen-associated molecular patterns (PAMPs). In this study, we report the cloning and characterization of a SR from Eriocheir sinensis (EsSR-B1) which is a 500 amino acid protein encoded by a gene comprised of 2726 nucleotides with a 1503 bp open reading frame. The domains of EsSR-B1 were found to be evolutionarily conserved. EsSR-B1 was widely detected in different tissues of E. sinensis and significantly up-regulated in hemocytes after stimulation by Staphyloccocus aureus or Vibrio parahaemolyticus. Recombinant EsSR-B1 protein could bind to bacteria and promote phagocytosis upon bacterial stimulation. Moreover, antimicrobial peptide expression was reduced in EsSR-B1-silenced hemocytes after challenge by S. aureus or V. parahaemolyticus. Thus, EsSR-B1 has a critical role in the binding of bacteria and subsequent promotion of hemocyte phagocytosis.