Cloning of a new fibroblast cell line from an early primary culture from mandarin fish (Siniperca chuatsi) fry for efficient proliferation of megalocytiviruses

Development of a Highly Permissive Mandarin Fish (Siniperca chuatsi) Kidney Cell Line for Mandarin Fish Ranavirus Using a Single-Cell Cloning Method

Mandarin fish ranavirus (MRV) infection poses a substantial challenge to the mandarin fish culture industry as no effective preventive or therapeutic measures currently exist. The creation of a highly permissive cell line from a natural host is crucial for developing a vaccine for MRV and understanding its pathogenic mechanisms. In this research, the mandarin fish (Siniperca chuatsi) kidney cell line (SCK) was isolated from mandarin fish kidneys. Subsequently, SCK-a to SCK-g monoclonal cell lines were derived from the SCK cell population, distinguished by morphological variations. Notably, MRV infection induced an advanced cytopathic effect (CPE) in almost all cells of the SCK-f clone. Further tests showed that MRV achieved a peak viral titer of 1010.7 50% tissue culture infectious dose (TCID50)/mL and consistently exceeded 1010 TCID50/mL across nine passages in SCK-f cells. Electron microscopy verified the MRV virion integrity within SCK-f. In vivo experiments revealed that MRV infections led to cumulative mortality rates of 86.9% in mandarin fish and 88.9% in largemouth bass (Micropterus salmoides). Such results suggest that SCK-f is highly permissive to MRV. This study underscores the importance of cellular diversity in developing viral permissive cell lines. The SCK monoclonal cell line pool may offer potential for generating highly permissive cell lines for other mandarin fish viruses.

30-Year Development of Inactivated Virus Vaccine in China

Inactivated vaccines are vaccines made from inactivated pathogens, typically achieved by using chemical or physical methods to destroy the virus's ability to replicate. This type of vaccine can induce the immune system to produce an immune response against specific pathogens, thus protecting the body from infection. In China, the manufacturing of inactivated vaccines has a long history and holds significant importance among all the vaccines available in the country. This type of vaccine is widely used in the prevention and control of infectious diseases. China is dedicated to conducting research on new inactivated vaccines, actively promoting the large-scale production of inactivated vaccines, and continuously improving production technology and quality management. These efforts enable China to meet the domestic demand for inactivated vaccines and gain a certain competitive advantage in the international market. In the future, China will continue to devote itself to the research and production of inactivated vaccines, further enhancing the population's health levels and contributing to social development. This study presents a comprehensive overview of the 30-year evolution of inactivated virus vaccines in China, serving as a reference for the development and production of such vaccines.

Mangiferin and Taurine Ameliorate MSRV Infection by Suppressing NF-κB Signaling

The emergence or reemergence of viruses pose a substantial threat and challenge to the world population, livestock, and wildlife. However, the landscape of antiviral agents either for human or animal viral diseases is still underdeveloped. The far tougher actuality is the case that there are no approved antiviral drugs in the aquaculture industry, although there are diverse viral pathogens. In this study, using a novel epithelial cell line derived from the brain of Micropterus salmoides (MSBr), inflammation and oxidative stress were found to implicate the major pathophysiology of M. salmoides rhabdovirus (MSRV) through transcriptome analysis and biochemical tests. Elevated levels of proinflammatory cytokines (interleukin-1β [IL-1β], IL-6, IL-8, tumor necrosis factor alpha [TNF-α], and gamma interferon [IFN-γ]) and accumulated contents of reactive oxygen species (ROS) as well as biomarkers of oxidative damage (protein carbonyl and 8-OHdG) were observed after MSRV infection in the MSBr cells. Mangiferin or taurine dampened MSRV-induced inflammation and rescued the oxidative stress and, thus, inhibited the replication of MSRV in the MSBr cells with 50% effective concentration (EC50) values of 6.77 μg/mL and 8.02 μg/mL, respectively. Further, mangiferin or taurine hampered the activation of NF-κB1 and the NF-κB1 promoter as well as the increase of phosphorylated NF-κB (p65) protein level induced by MSRV infection, indicating their antiviral mechanism by suppressing NF-κB signaling. These findings exemplify a practice approach, aiming to dampen and redirect inflammatory responses, to develop broad-spectrum antivirals. IMPORTANCE Aquaculture now provides almost half of all fish for human food in 2021 and plays a significant role in eliminating hunger, promoting health, and reducing poverty. There are diverse viral pathogens that decrease production in aquaculture. We developed a novel epithelial cell line derived from the brain of Micropterus salmoides, which can be used for virus isolation, gene expressing, and drug screening. In this study, we focus on M. salmoides rhabdovirus (MSRV) and revealed its pathophysiology of inflammation and oxidative stress. Aiming to dampen and redirect inflammatory responses, mangiferin or taurine exhibited their antiviral capability by suppressing NF-κB signaling. Our findings exemplify a practice approach to develop broad-spectrum antivirals by dampening and redirecting inflammatory responses.

Role and relevance of fish cell lines in advanced in vitro research

Introduction

Cell line derived from fish has been established as a promising tool for studying many key issues of aquaculture covering fish growth, disease, reproduction, genetics, and biotechnology. In addition, fish cell lines are very useful in vitro models for toxicological, pathological, and immunological studies. The easier maintenance of fish cell lines in flexible temperature regimes and hypoxic conditions make them preferable in vitro tools over mammalian cell lines. Great excitement has been observed in establishing and characterizing new fish cell lines representing diverse fish species and tissue types. The well-characterized and authenticated cell lines are of utmost essential as these represent cellular functions very similar to in vivo state of an organism otherwise it would affect the reproducibility of scientific research.

Conclusion

The fish cell lines have exhibited encouraging results in several key aspects of in vitro research in aquaculture including virology, nutrition and metabolism, production of vaccines, and transgenic fish production. The review paper reports the cell lines developed from fish, their characterization, and biobanking along with their potential applications and challenges in in vitro research.

Megalocytiviruses in ornamental fish: A review

Iridoviruses, especially megalocytiviruses, are related to severe disease resulting in high economic losses in the aquaculture industry worldwide. The ornamental fish industry has been affected severely due to Megalocytivirus infections. Megalocytivirus is a DNA virus that has three genera; including red sea bream iridovirus, infectious spleen and kidney necrosis virus, and turbot reddish body iridovirus. Megalocytivirus causes non-specific clinical signs in ornamental fish. Cell culture, histology, immunofluorescence test, polymerase chain reaction (PCR) assay, and loop-mediated isothermal amplification assay have been used to diagnose megalocytiviruses. Risk factors such as temperature, transportation (export and import), and life stages of ornamental fish have been reported for the previous cases due to Megalocytivirus infections. In addition, other prevention and control methods also have been practiced in farms to prevent Megalocytivirus outbreaks. This is the first review of megalocytiviruses in ornamental fish since its first detection in 1989. This review discusses the occurrences of Megalocytivirus in ornamental fish, including the history, clinical signs, detection method, risk factors, and prevention measures.

Isolation and characterisation of an ISKNV-genotype megalocytivirus from imported angelfish Pterophyllum scalare

Using cultures of the SKF-9 cell line, megalocytivirus AFIV-16 was isolated from imported angelfish Pterophyllum scalare held in quarantine at the Australian border. The cytopathic effect caused by isolate AFIV-16 presented as cell rounding and enlargement, but complete destruction of the infected cell cultures did not occur. The infected cells demonstrated immunocytochemical reactivity with monoclonal antibody M10, which is used for diagnosis of OIE-listed red sea bream iridoviral disease. Using electron microscopy, the virus particles, consisting of hexagonal nucleocapsids, were observed in the cytoplasm of SKF-9 cells. The replication of AFIV-16 in cultured SKF-9 cells was significantly greater at 28°C incubation than at 22 and 25°C incubation, whereas no difference in growth characteristics was observed for red sea bream iridovirus (RSIV) isolate KagYT-96 across this temperature range. Whole genome sequencing demonstrated that AFIV-16 has a 99.96% similarity to infectious spleen and kidney necrosis virus (ISKNV), the type species in the genus Megalocytivirus. AFIV-16 was classified into ISKNV genotype Clade 1 by phylogenetic analysis of the major capsid protein gene nucleotide sequence. This is the first report of whole genome sequencing of an ISKNV genotype megalocytivirus isolated from ornamental fish.

Isolation and identification of a viral haemorrhagic septicaemia virus (VHSV) isolate from wild largemouth bass Micropterus salmoides in China

Fish rhabdoviruses are a family of viruses responsible for large-scale fish die-offs worldwide. Here, we reported the isolation and identification of a member of rhabdoviruses from wild largemouth bass (Micropterus salmoides) in the coastal area of the Pearl River Estuary, China. This virus isolate was identified as viral haemorrhagic septicaemia virus (VHSV) by specific RT-PCR. Furthermore, the virus (VHSVLB2018) was isolated by cell culture using fathead minnow cells and confirmed by RT-PCR. Electron microscopy showed the presence of bullet-shaped viral particles in the cytoplasm of infected cells. The complete sequencing of VHSVLB2018 confirmed that it was genome configuration typical of rhabdoviruses. Phylogenetic analysis based on whole-genome sequences and G gene nucleotides sequences revealed that VHSVLB2018 was assigned to VHSV genogroup Ⅳa. The pathogenicity of VHSVLB2018 was determined in infection experiments using specific pathogen-free largemouth bass juveniles. VHSVLB2018-infected fish showed typical clinical signs of VHSV disease, including darkened skin, petechial haemorrhages and pale enlarged livers, with the cumulative mortalities reached 63.3%-93.3% by 7 days post-infection. VHSVLB2018 was re-isolated from dead fish and confirmed by RT-PCR. Together, this is the first report of isolation and identification of a VHSV isolate from wild largemouth bass in China.

Establishment and characterization of a fin tissue cell line derived from silver pomfret, Pampus argenteus

A cell line (PaF) derived from the fin tissue of silver pomfret (Pampus argenteus) was established and characterized in this study. The cell line has been subcultured for more than 50 times in Dulbecco's modified Eagle's medium (DMEM) containing 15% foetal bovine serum (FBS) since the initial primary culture. PaF cells grew well at temperatures from 24°C to 28°C in DMEM supplemented with 15% FBS. Partial amplification and sequence analysis of the cytochrome B gene indicated that PaF originated from silver pomfret. Cytogenetic analysis demonstrated that the modal chromosome number was 48. A significant cytopathic effect was observed in PaF cells during viral haemorrhagic septicaemia virus (VHSV) infection, and the VHSV replication was confirmed by qRT-PCR and viral titre assays. In contrast, PaF cells were resistant to red-spotted grouper nervous necrosis virus infection. Moreover, PaF cells could respond to VHSV and lipopolysaccharide treatments, as indicated by the expression of immune-related genes, TLR5 and TLR9. In conclusion, the establishment of PaF cell line will provide an appropriate in vitro tool for the study of mechanisms of pathogen-silver pomfret interaction.

Screening for Antiviral Medaka Haploid Embryonic Stem Cells by Genome Wide Mutagenesis

Nervous necrosis virus (NNV), one of the most prevalent fish pathogens, has caused significant losses in both yield and economy to the aquaculture. Host factors involved in NNV infection remain to be identified due to the lack of ideal model for the study of NNV and host interaction. Haploid stem cells have proven to be ideal materials in genetic screens. Here, we generated a cell line HX1G1 (simply named G1) with the activity against red-spotted grouper nervous necrosis virus (RGNNV) by N-ethyl-N-nitrosourea (ENU)-mediated whole genome random mutagenesis from the haploid embryonic stem cell HX1a, a cell clone from haploid cell line HX1 that we previously derived from the medaka fish. G1 cells retained the characteristics of haploidy and pluripotency as indicated by the EBs differentiation ability after genetic mutagenesis. Compared with HX1a cells, no typical cytopathic effects were observed, and the expression of RNA-dependent RNA polymerase (RDRP) was significantly reduced in G1 cells post RGNNV infection, indicating the enhanced anti-RGNNV activity of G1. Furthermore, we demonstrated that RGNNV entry into G1 cells was partially inhibited, and this inhibition might be relevant to the induced mutation of heat shock cognate protein 70 (HSC70) which was decisive for NNV entry. Interestingly, G1 cells were to some extent permissive to RGNNV infection, but RGNNV was spontaneously cleared in G1 cells during serial passage. In addition, we also found that the expression levels of interferon (IFN)-related genes were higher in G1 cells than those in HX1a cells, suggesting that viral clearance might be associated with the elevated expression of IFN-related genes in G1 cells.

Establishment of a cell line with high transfection efficiency from zebrafish Danio rerio embryos and its susceptibility to fish viruses

A cell line ZBE3 isolated from a continuous cell culture derived from zebrafish Danio rerio blastomeres by clonal growth was characterized. ZBE3 cells had been subcultured for >120 passages since the initial primary culture of the blastomeres. The ZBE3 cells grow stably at temperature from 20 to 32° C with an optimum temperature of 28° C in ESM2 or ESM4 medium with 15% foetal bovine serum (FBS). The optimum FBS concentration for ZBE3 cell growth ranged from 15 to 20%. Cytogenetical analysis indicated that the modal chromosome number of ZBE3 cells was 50, the same as the diploid chromosome number of D. rerio. Significant cytopathic effect was observed in ZBE3 cells after infection with redspotted grouper nervous necrosis virus, Singapore grouper iridovirus and grass carp reovirus, and the viral replication in the cells was confirmed by real-time quantitative PCR and transmission electron microscopy, indicating the susceptibility of ZBE3 cells to the three fish viruses. After transfected with pEGFP-N3 plasmid, ZBE3 cells showed a transfection efficiency of about 40% which was indicated by the percentage of cells expressing green fluorescence protein. The stable growth, susceptibility to fish viruses as well as high transfection efficiency make ZBE3 cells be a useful tool in transgenic manipulation, fish virus-host cell interaction and immune response in fish.