The hepatopancreas is an important digestive and immune organ in crustacean. There were low but stable numbers of microbes living in the hemolymph of crustacean, whereas the organs (including hepatopancreas) of crustacean were immersed in the hemolymph. It is very important to study the immune mechanism of the hepatopancreas against bacteria. In this study, a novel CTL (HepCL) with two CRDs, which was mainly expressed in the hepatopancreas, was identified in red swamp crayfish (Procambarus clarkii). HepCL binds to bacteria in vitro and could enhance bacterial clearance in vivo. Compared with the C-terminal CRD of HepCL (HepCL-C), the N-terminal CRD (HepCL-N) showed weaker bacterial binding ability in vitro and stronger bacterial clearance activity in vivo. The expression of some antimicrobial proteins, such as FLP, ALF1 and ALF5, was downregulated under knockdown of HepCL or blocked with Anti-HepCL after challenge with Vibrio in crayfish. These results demonstrated that HepCL might be involved in the antibacterial immune response by regulating the expression of antimicrobial proteins.

The giant freshwater prawn, Macrobrachium rosenbergii, is an economically important crustacean and is farmed in many countries. Since 2009, a larval mortality syndrome of M. rosenbergii has broken out and spread widely in the main breeding area, including Zhejiang, Jiangsu, Guangxi, and Guangdong Provinces in mainland China. A novel virus, named Macrobrachium rosenbergii Taihu virus (MrTV), was isolated from the moribund larvae and was determined to be the causative agent of the M. rosenbergii larval mortality syndrome by experimental infection. Further genomic sequencing suggested that the MrTV genome is monopartite, 10,303 nt in length, and dicistronic with two non-overlapping open reading frames (ORFs) separated by an intergenic region (IGR) and flanked by untranslated regions (UTRs). Phylogenetic analysis using the full-length genomic sequence and the putative amino acid sequences of the capsid protein revealed that MrTV was more closely related to the taura syndrome virus (TSV) than to any other viruses. According to these molecular features, we proposed that MrTV is a new species in the genus Aparavirus, family Dicistroviridae. These results may shed light on controlling larval mortality syndrome in M. rosenbergii.