Functions Of Class C Scavenger Receptor In Innate Immunity Of Kuruma Shrimp

Invertebrates depend on the innate immunity system to resist pathogens.The first step of the innate immunity is recognizing pathogenic microorganisms by pattern recognition receptors(PRRs).Several PRRs were identified in shrimp,but the function of some PRRs needs to be clarified.In this study,we found a class C scavenger receptor in kuruma shrimp,Marsupenaeus japonicus,acting as a pattern recognition receptor,enhanced hemocyte phagocytosis to restrict viral and bacterial systemic infection and regulated the expression of several antimicrobial peptide genes.(1)Class C scavenger receptor enhances hemocyte phagocytosis to restrict viral systemic infectionScavenger receptors are an important class of pattern recognition receptors that play several important roles in host defense against pathogens.The class C scavenger receptors(SRCs)have only been identified in a few invertebrates,and their role in the immune response against viruses is seldom studied.In this study,we firstly identified an SRC from kuruma shrimp,Marsupenaeus japonicus,designated MjSRC,which was significantly upregulated after white spot syndrome virus(WSSV)challenge at the mRNA and protein levels in hemocytes.The quantity of WSSV increased in shrimp after knockdown of MjSRC,compared with the controls.Furthermore,overexpression of MjSRC led to enhanced WSSV elimination via phagocytosis by hemocytes.Pull-down assays demonstrated the interaction between MjSRC and the WSSV envelope protein.Electron microscopy observation indicated that the colloidal gold-labeled extracellular domain of MjSRC was located on the outer surface of WSSV.MjSRC formed a trimer and was internalized into the cytoplasm after WSSV challenge,and the internalization was strongly inhibited after knockdown of Mj?-arresting2.Further studies found that Mj?-arrestin2 interacted with the intracellular domain of MjSRC and induced the internalization of WSSV in a clathrin-dependent manner.WSSV were co-localized with lysosomes in hemocytes and the WSSV quantity in shrimp increased after injection of lysosome inhibitor,chloroquine.Collectively,this study demonstrated that MjSRC recognized WSSV via its extracellular domain and invoked hemocyte phagocytosis to restrict WSSV systemic infection.This is the first study to report an SRC as a pattern recognition receptor promoting phagocytosis of a virus.(2)Function studies of MjSRC from kuruma shrimp in resisting bacterial infectionIn this study,we characterized the anti-bacterial function of a SRC from kuruma shrimp Marsupenaeus japonicus(MjSRC).After challenge of Vibrio anguillarum or Staphylococcus aureus,the mRNA level of MjSRC was up-regulated significantly in hemocytes of kuruma shrimp.The recombinant extracellular domains(MAM and CCP domains)from MjSRC have the ability of binding different bacteria and polysaccharides in vitro.After knockdown of MjSRC,the bacterial clearance ability and phagocytic rate of hemocyte decreased significantly in vivo.Meanwhile,overexpression of MjSRC enhanced the clearance ability and phagocytic rate of hemocytes.In addition,MjSRC could regulate the expression of several antimicrobial peptides(AMPs).All these results indicated MjSRC played an important role in innate immunity by enhancing cellular and humoral immunity of kuruma shrimp.