Abstract
Scavenger 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 and co-immunoprecipitation 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 Mjβ-arrestin2. Further studies found that Mjβ-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.
Highlights
White spot syndrome virus (WSSV), which is a serious pathogen that threatens the aquaculture of shrimp, has led to huge economic losses in the shrimp industry [1]
Pattern recognition is the first step in the innate immune response, initiated by pattern recognition receptors (PRRs) that sense the presence of microorganic structural components, known as pathogen-associated molecular patterns (PAMPs) [2], such as lipopolysaccharides and peptidoglycan from bacteria or some proteins from viruses
We discovered that hemocytes used clathrin-mediated endocytosis to engulf WSSV and that Mjβ-arrestin2 was used as an adaptor protein to mediate the endocytotic process
Summary
White spot syndrome virus (WSSV), which is a serious pathogen that threatens the aquaculture of shrimp, has led to huge economic losses in the shrimp industry [1]. Great advances have been made in both pathogen study, including mechanisms and strategies used by the virus to infect and replicate in host cells, such as the findings of envelope proteins, VP19, 24, 26 and 28 interacting with each other and playing an important role in virus assembly and infection [2]; and host immune responses against the virus, including humoral and cellular immunity [3]. Understanding the mechanisms of the host-virus interaction might help to find new strategies and methods for WSSV control. Host innate immunity plays an important role in protecting the organism from pathogen invasion, in invertebrates, which lack the typical adaptive immune responses [4]. Some receptors have been studied in depth; there are relatively few reports about the immunological roles of scavenger receptors (SRs) in invertebrates
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