Functional Investigation Of A Class B Scavenger Receptor And A C-type Lectin In The Innate Immunity Of Kuruma Shrimp Marsupenaeus Japonicus

Pattern recognition receptors (PRRs) play important roles in innate immunity. After recognizing "self" or "non-self" damage-associated molecular patterns or pathogen-associated molecular patterns, PRRs can transduct the signal to downstreamand induce the expression of effectors to clean the apoptotic cells or kill pathogens. Some PRRs can clear the pathogens directly. Both scavenger receptors and C-type lectins are very important members of the family of PRRs. In this research,a B-type scavenger receptor,MjSR-B1,and a C-type lectin, MjcLec, were identified in Marsupenaeus japonicusand their function in innate immunity were studied.1. Functional research of MjSR-B1 in Marsupenaeus japonicus.Scavenger receptors are involved in innate immunity through recognizing pathogen-associated molecular patterns (PAMPs) and in pathogenesis of diseases through interactions with damage-associated molecular patterns (DAMPs). The roles of SRs in invertebrate innate immunity still need to be elucidated. Here we identify a class B scavenger receptor from kuruma shrimp Marsupenaeus japonicus, designated as MjSR-B1. The recombinant MjSR-B1 agglutinated bacteria in a calcium dependent manner and bound lipopolysaccharide and lipoteichoic acid. After knockdown of MjSR-B1, both the bacterial clearance and phagocytotic ability of M. japonicus against V. anguillarum and S. aureus were impaired, and several phagocytosis related genes were downregulated. The expression levels of antimicrobial peptides were also downregulated. Overexpression of MjSR-B1 led to enhanced bacterial clearance, phagocytosis rate and upregulation of phagocytosis-related and antimicrobial peptide genes. However, overexpression of mutant MjSR-B1 AC, which lacks the carboxyl tail of MjSR-B1, had none of these effects. Our results indicate that MjSR-B1 can protect shrimp from bacteria by promoting phagocytosis and by enhancing the expression of antimicrobial peptides.2. MjcLec participates in the antiviral and antibacterial immunity in Marsupenaeus japontcus.C-type lectin family is a kind of pattern recognition receptors and plays an important role in the immune system. However, its role in invertebrates’ innate immunity still needs to be elucidated. In this research a novel kind of C-type lectins which has a coiled coil region, was identified from Marsupenaeus japonicus, and designated as MjcLec.The structure of MjcLec contains a signal peptide, a coiled coil domain and a carbonhydrate recognition domain. Tissue distribution analysis indicated that MjcLec expressed in all the tissues tested, including hemocytes, heart, hepatopancreas, gills, stomach and intestine,and both WSSV and bacteria challenge could upregulated the expression of MjcLec in hemocytes. The recombinant rMjcLec could recognize bacteria through binding polysaccharides thus agglutinating these bacteria. And in vivo experiments suggested that RNAi of MjcLec facilitated WSSV replication and inhibited crustins expression. All this data implicated that MjcLec participate in both antiviral and antibacterial innate immunity.