A negative elongation factor E inhibits white spot syndrome virus replication by suppressing promoter activity of the viral immediate early genes in red claw crayfish Cherax quadricarinatus

The effect of white spot syndrome virus (WSSV) envelope protein VP28 on innate immunity and resistance to white spot syndrome virus in Cherax quadricarinatus

VP28 is the most abundant membrane protein of WSSV, and the recombinant protein VP28 (VP26 or VP24) was constructed for the immune protection experiment in this study. Crayfish were immunized by intramuscular injection of recombinant protein V28 (VP26 or VP24) at a dose of 2 μg/g. The survival rate of crayfish immunized by VP28 showed a higher value than by VP26 or VP24 after WSSV challenge. Compared with the WSSV-positive control group, the VP28-immunized group could inhibit the replication of WSSV in crayfish, increasing the survival rate of crayfish to 66.67% after WSSV infection. The results of gene expression showed that VP28 treatment could enhance the expression of immune genes, mainly JAK and STAT genes. VP28 treatment also enhanced total hemocyte counts and enzyme activities including PO, SOD, and CAT in crayfish. VP28 treatment reduced the apoptosis of hemocytes in crayfish, as well as after WSSV infection. In conclusion, VP28 treatment can enhance the innate immunity of crayfish and has a significant effect on resistance to WSSV, and can be used as a preventive tool.

Recent insights into anti-WSSV immunity in crayfish

White spot syndrome virus (WSSV) is currently the most severely viral pathogen for farmed crustaceans such as shrimp and crayfish, which has been causing huge economic losses for crustaceans farming worldwide every year. Unfortunately, study on the molecular mechanisms of WSSV has been restricted by the lack of crustacean cell lines for WSSV propagation as well as the incompletely annotated genomes for host species, resulting in limited elucidation for WSSV pathogenesis at present. In addition to the findings of anti-WSSV response in shrimp, some of novel cellular events involved in WSSV infection have been recently revealed in crayfish, including endocytosis and intracellular transport of WSSV, innate immune pathways in response to WSSV infection, and regulation of viral gene expression by host genes. Despite these advances, many fundamental gaps in WSSV pathogenesis are still remaining, for example, how WSSV genome enters into nucleus and how the progeny virions are fully assembled in the host cell nucleus. In this review, recent findings in WSSV infection mechanism and the antiviral immunity against WSSV in crayfish are summarized and discussed, which may provide us a better understanding of the WSSV pathogenesis as well as new ideas for the target design of antiviral drugs against WSSV in crustaceans farming.