The complete genome of Cyprinid herpesvirus 2, a new strain isolated from Allogynogenetic crucian carp

Characteristics and expression profiles of MHC class Ⅰ molecules in Carassius auratus

Major histocompatibility complex class Ⅰ (MHC Ⅰ) molecules play a vital role in adaptive immune systems in vertebrates by presenting antigens to effector T cells. Understanding the expression profiling of MHC Ⅰ molecules in fish is essential for improving our knowledge of the relationship between microbial infection and adaptive immunity. In this study, we conducted a comprehensive analysis of MHC Ⅰ gene characteristics in Carassius auratus, an important freshwater aquaculture fish in China that is susceptible to Cyprinid herpesvirus 2 (CyHV-2) infection. We identified approximately 20 MHC Ⅰ genes discussed, including U, Z, and L lineage genes. However, only U and Z lineage proteins were identified in the kidney of Carassius auratus using high pH reversed-phase chromatography and mass spectrometry. The L lineage proteins were either not expressed or present at an extremely low level in the kidneys of Carassius auratus. We also used targeted proteomics to analyze changes in protein MHC Ⅰ molecules abundance in healthy and CyHV-2-infected Carassius auratus. We observed that five MHC Ⅰ molecules were upregulated, and Caau-UFA was downregulated in the diseased group. This study is the first to reveal the expression of MHC Ⅰ molecules at a large scale in Cyprinids, which enhances our understanding of fish adaptive immune systems.

Development and characterization of monoclonal antibodies specific for cyprinid herpesvirus 2

Infections of Cyprinid herpesvirus 2 in goldfish and farmed crucian carp (Carassius auratus gibelio) are still an urgent problem worldwide. Detection and prevention are necessary for the control of haematopoietic necrosis disease caused by CyHV-2. Although many sensitive molecular diagnostic methods have been developed, effective immunodiagnosis and neutralization approaches based on monoclonal antibodies (MAbs) against CyHV-2 are still important to CyHV-2 study. In this experiment, purified CyHV-2 was used as antigens to produce monoclonal antibodies (Mabs). Six Mabs bound to different proteins were selected by Dot-blot screening and Western-blot analysis, and no one had cross-reactivity with closely related koi herpesvirus. Among them, Mabs 2E1-B10, 1F5-A3 and 4C4-A7 belonged to IgG₁ isotype, while other three Mabs 3G9-B11, 3B4-G5 and 4F4-B7 belonged to IgM isotype. These six Mabs all could specifically detect CyHV-2 in CyHV-2 infected caudal fin of Carassius auratus gibelio (GiCF) cells by immunofluorescence assays. Then, the neutralization ability was tested in vitro, and the result showed that all six Mabs can attenuate CPE by CyHV-2 in vitro among which 2E1-B10 had the best neutralization ability. The virus proteins recognized by these six Mabs were identified by mass spectrometry identification, and the result showed they probably were ORF88, ORF55R, ORF115 and ORF151R. This study is the first to prepare Mabs by purifying CyHV-2, which will provide a practical basis for the in-depth study of CyHV-2 virus.

Complete Genome and Molecular Characterization of a New Cyprinid Herpesvirus 2 (CyHV-2) SH-01 Strain Isolated from Cultured Crucian Carp

Cyprinid herpesvirus 2 (CyHV-2) is a causative factor of herpesviral hematopoietic necrosis (HVHN) in farmed crucian carp (Carassius carassius) and goldfish (Carassius auratus). In this study, we analyzed the genomic characteristics of a new strain, CyHV-2 SH-01, isolated during outbreaks in crucian carp at a local fish farm near Shanghai, China. CyHV-2 SH-01 exhibited a high sensitivity to goldfish and crucian carp in our previous research. The complete genome of SH-01 is 290,428 bp with 154 potential open reading frames (ORFs) and terminal repeat (TR) regions at both ends. Compared to the sequenced genomes of other CyHVs, Carassius auratus herpesvirus (CaHV) and Anguillid herpesvirus 1 (AngHV-1), several variations were found in SH-01, including nucleotide mutations, deletions, and insertions, as well as gene duplications, rearrangements, and horizontal transfers. Overall, the genome of SH-01 shares 99.60% of its identity with that of ST-J1. Genomic collinearity analysis showed that SH-01 has a high degree of collinearity with another three CyHV-2 isolates, and it is generally closely related to CaHV, CyHV-1, and CyHV-3, although it contains many differences in locally collinear blocks (LCBs). The lowest degree of collinearity was found with AngHV-1, despite some homologous LCBs, indicating that they are evolutionarily the most distantly related. The results provide new clues to better understand the CyHV-2 genome through sequencing and sequence mining.

Quick detection of Carassius auratus herpesvirus (CaHV) by recombinase-aid amplification lateral flow dipstick (RAA-LFD) method

Crucian carp (Carassius auratus) is one of the major freshwater species and is also a common food fish in China. Recently, Carassius auratus herpesvirus (CaHV) could induce fatal viral disease with high mortality of crucian carp, which had caused huge economic losses. In this study, we described a rapid and simple recombinase-aid amplification (RAA) assay coupled with lateral flow dipstick (LFD), which could achieve sensitive diagnosis of tumor necrosis factor receptor (TNFR) of CaHV within 35 min at 40°C. Our RAA-LFD method had a satisfactory detection limit of 100 gene copies per reaction, which was 100-fold more sensitive than traditional PCR. In addition, no cross-reaction was observed with other viral pathogens, including koi herpesvirus (KHV), cyprinid herpesvirus 2 (CyHV-2), infectious hematopoietic necrosis virus (IHNV), spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV). Furthermore, the overall cost of the method was cut in half compared to previous studies. In conclusion, RAA-LFD assay is therefore, a promising alternative for point-of-care testing (POCT) of CaHV, which is feasible and of certain value in application of aquatic disease control.

Generation and application of a monoclonal antibody specific for the ORF121 of cyprinid herpesvirus 2

Cyprinid herpesvirus 2 (CyHV-2) is a viral pathogen worldwide and causing high mortality on goldfish and silver crucian carp (Carassius auratus gibelio). In order to establish a stable and sensitive immunological diagnostic approach, the recombinant ORF121 protein encoded by the CyHV-2 ORF121 gene, was selected as a capture antigen to identify cells and tissues infected with CyHV-2 by immunological methods in this study. Firstly, the open reading frame of CyHV-2 ORF121 was cloned into the PGEX-4T-3 vector and expressed in Escherichia coli. Purified recombinant ORF121 protein was then used as an antigen to prepare monoclonal antibodies, and an efficient hybridoma cell line was selected by dot-blot assay. The resulting mAb-3D9 was applied to detect CyHV-2 in infected caudal fin of Carassius auratus gibelio (GiCF) cells and fish tissues by western blotting, immunofluorescence assays and immunohistological asays. The monoclonal antibody could specifically identify CyHV-2 in infected GiCF cells and the gills, the kidney and the spleen tissues, and it could attenuate CPE by CyHV-2 in vitro, suggesting it can be applied for CyHV-2 detection in the crucian carp and ORF121 may be a candidate vaccine against CyHV-2.

Transcriptome analysis provides insights into the antiviral response in the spleen of gibel carp (Carassius auratus gibelio) after poly I: C treatment

Gibel carp (Carassius auratus gibelio) is an important commercial fish that has become one of the most cultured fishes in the region of Yangtze River in China. However, the fish faces increasing hazard due to cyprinid herpesvirus 2 (CyHV-2) infection, which has caused great economic losses. In this study, healthy gibel carp were intraperitoneally injected with different doses of poly I:C at 24 h before CyHV-2 challenge. Results showed that the mortality decreased and peak death time appeared later in the fish injected with poly I:C at a dose of 10 μg/g body weight. To explore what gene plays an important role after poly I:C treatment, the transcriptome analysis of the gibel carp spleen was further performed. Compared with the PBS group, 1286 differentially expressed genes (DEGs) were obtained in the poly I:C-treated fish, including 1006 up-regulated and 280 down-regulated DEGs. GO analysis revealed that the most enriched DEGs responded to "biological regulation", "regulation of cellular process" and "regulation of biological process". Meanwhile, KEGG enrichment analysis showed that the DEGs were mainly mapped on the immune pathways like "TNF signal pathway", "p53 signal pathway" and "JAK-STAT signal pathway", suggesting that these signal pathways may be responsible for the delayed peak of CyHV-2 infection in gibel carp after poly I:C treatment. Taken together, this study provides insights into the immune protection effect of poly I:C against CyHV-2 infection, as well as providing useful information for antiviral defense in gibel carp.

Fish herpesvirus protein (CaHV-138L) can target to mitochondrial protein FoF1 ATPase

Herpesvirus infection usually relies on the interaction between viral protein and host protein to enhance replication of the enveloped virus. Fish Carassius auratus herpesvirus (CaHV) is highly pathogenic pathogen causing gill acute hemorrhages of crucian carp (Carassius auratus) and high moritality rates among those infected fish. The protein of CaHV (CaHV-138 L) containing two transmembrane (TM) domains and an immunoglobulin C-2 Type (IGc2) domain was predicted as a viral membrane protein. In this investigation, fluorescence observation showed that full-length CaHV-138 L mainly localized on the plasma membrane or around nuclear membrane of fish fathead minnow (FHM) cells in a punctate pattern. The TM domain deletion mutants of CaHV-138 L (ΔTM1, ΔTM2, and ΔTM1&ΔTM2) diffusely distributed in both the cytoplasm and the nucleus, mainly presented patchy fashion in the cytoplasm, and mainly presented both in the nucleus and in the cytoplasm, respectively. Obviously, the TM domain deletion mutants significantly affected CaHV-138 L subcellular localization. Meanwhile, colocalization assay showed that the full-length viral protein colocalized with mitochondria. Furthermore, the interaction between CaHV-138 L and host protein was identified by yeast two-hybrid (Y2H) and co-immunoprecipitation (co-IP) assays. The host mitochondrial protein FoF1 ATP synthase (FoF1-ATPase) that interacts with this viral protein was screened. The data indicated that CaHV-138 L can target to mitochondrial protein FoF1-ATPase, which might provide energy for virus replication through mediating mitochondrial ATP synthesis. This study has provided valuable information for better understanding of the links of herpesvirus proteins with aquaculture animal proteins.

Recombinant baculovirus BacCarassius-D4ORFs has potential as a live vector vaccine against CyHV-2

Cyprinid herpesvirus II (CyHV-2) is highly contagious and pathogenic to Carassius auratus gibelio (gibel carp), causing enormous economic losses in aquaculture in Yancheng city, Jiangsu province, China; however, to date, there is no effective way to protect C. auratus gibelio from CyHV-2 infection. In this study, a recombinant baculovirus vector vaccine, BacCarassius-D4ORFs, containing a fused codon-optimized sequence D4ORFs comprising the ORF72 (region 1-186 nt), ORF66 (region 993-1197 nt), ORF81 (region 603-783 nt) and ORF82 (region 85-186 nt) genes of CyHV-2, driven by a Megalobrama amblycephala β-actin promoter, was constructed. Then, qPCR, Western blotting and immunofluorescence assays showed that the fused gene D4ORFs was successfully delivered and expressed in fish cells or tissues by transduction with BacCarassius-D4ORFs. The fused gene D4ORFs could not be detected by PCR in the C. auratus gibelio injected with BacCarassius-D4ORFs after 7 weeks. Specific antibody against ORF72 could be detected in the serum of vaccinated C. auratus gibelio by injection with BacCarassius-D4ORFs. Furthermore, when C. auratus gibelio were vaccinated with BacCarassius-D4ORFs via the oral or injection route, followed by challenge with CyHV-2, the relative survival rate of immunized C. auratus gibelio reached 59.3% and 80.01%, respectively. These results suggested that BacCarassius-D4ORFs has the potential to be used as a vector-based vaccine for the prevention and treatment of disease caused by CyHV-2 infection.