Study On The Role Of Immune-related Proteins In IHHNV Infection Of Litopenaeus Vannamei At Different Growth Stages

Infectious hypodermal and haematopoietic necrosis virus(IHHNV)is a kind of linearly single-stranded DNA virus,which can infect most shrimps and other crustaceans and has spread worldwide.IHHNV can cause mortality in Penaeus stylirostris and slow growth and deformities in Litopenaeus vannamei.Chronic Runt-Deformity Syndrome(RDS),caused by IHHNV,leads to large economic loss every year.As an invertebrate with no acquired immunity,L.vannamei is one of the most economically valuable shrimp species in China and has to rely on innate immunity against pathogens.Studies have shown that the pathogenicity of IHHNV differs at different growth stages of the host.Therefore,studying the role of immune-related proteins in IHHNV infection in L.vannamei at different growth stages can help us to understand the mechanism of the pathogenicity differences of IHHNV infection to different growth stages of L.vannamei,and provide data to support the prevention and control of IHHNV.In this study,IHHNV infection was conducted to identify the differences of IHHNV pathogenicity in L.vannamei at different growth stages.The effects of the activity of Superoxide Dismutase(SOD),Acid Phosphatase(ACP)and the relative expression of Mn SOD,ACP and CCCH-Zinc Finger Antiviral Protein1(CCCH-ZAP)genes were studied to analyze the role of immune-related proteins in IHHNV infection in L.vannamei at different growth stages.The results of the study are as follows:1.The differences of IHHNV pathogenicity to juvenile and adult L.vannamei were studied by challenge experiment.The PCR results showed that IHHNV positive occurred in the challenge group from 1-4 days of the infection experiment in the juvenile stage,with an infection rate of 30.0%.In the adult stage,IHHNV positive occurred on days 1 to 3,with an infection rate of 16.7%.The IHHNV positive samples were detected by quantitative real-time PCR and the maximum viral loads were 50.1copies/μL DNA and 16.3 copies/μL DNA in juveniles and adults,respectively.The results showed that the infection rate and the level of virus proliferation were higher in juveniles than in adults.Juvenile L.vannamei were more sensitive to IHHNV.2.The SOD and ACP activities in hepatopancreas,gill and muscle tissues during IHHNV infection in juvenile and adult L.vannamei were studied.The results showed that there were no significant differences in SOD and ACP activities in hepatopancreas,gill and muscle tissues of L.vannamei at both the juvenile and adult stages(p > 0.05).3.The relative expression of Mn SOD and ACP in hepatopancreas,gill and muscle tissues of juvenile and adult L.vannamei during the IHHNV infection were studied.For the hepatopancreas and gill tissues of juveniles and adults,the relative expression of Mn SOD and ACP were up-regulated at the initial stage of infection(p < 0.05),but the differences didn’t last long,while no significant differences existed in muscle tissue(p > 0.05).This suggested that SOD and ACP showed a low-level immunological response in the immunization of shrimp.4.The relative expression of CCCH-Zinc Finger Antiviral Protein1 gene in hepatopancreas and gill tissue of juvenile and adult L.vannamei during IHHNV infection were investigated.The results showed that the relative expression of ZC3HAV1 was significantly up-regulated after IHHNV infection(p < 0.05),and the up-regulation was more significant in the adults.It was speculated that ZC3HAV1 might be positively correlated with the antiviral ability of L.vannamei and play an important role in the antiviral immune response of L.vannamei.