Protective effects of β-glucan as adjuvant combined inactivated Vibrio harveyi vaccine in pearl gentian grouper

Strategies for Prevention and Control of Vibriosis in Asian Fish Culture

It is estimated that vibriosis account for about half of the economic losses in Asian fish culture. Consequently, the prevention and control of vibriosis is one of the priority research topics in the field of Asian fish culture disease. Relevant measures have been proposed to control some Vibrios that pose a threat to Asian fish culture, but there are currently only a few effective vaccines available to combat these Vibrios. The purpose of our review is to sum up the main prevention methods and the latest control strategies of seven Vibrio species that cause great harm to Asian aquaculture, including Vibrio harveyi, Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio mimicus, Vibrio anguillarum, Vibrio alginolyticus and Vibrio cholerae. Strategies such as antibiotics, probiotics, bacteriophages, antimicrobials from plants and other natural sources, as well as vaccines, are compared and discussed here. We expect this review will provide some new views and recommendations for the future better prevention and control of vibriosis in Asian fish culture.

Current status and development prospects of aquatic vaccines

Diseases are a significant impediment to aquaculture's sustainable and healthy growth. The aquaculture industry is suffering significant financial losses as a result of the worsening water quality and increasing frequency of aquatic disease outbreaks caused by the expansion of aquaculture. Drug control, immunoprophylaxis, ecologically integrated control, etc. are the principal control strategies for fish infections. For a long time, the prevention and control of aquatic diseases have mainly relied on the use of various antibiotics and chemical drugs. However, long-term use of chemical inputs not only increases pathogenic bacteria resistance but also damages the fish and aquaculture environments, resulting in drug residues in aquatic products, severely impeding the development of the aquaculture industry. The development and use of aquatic vaccines are the safest and most effective ways to prevent aquatic animal diseases and preserve the health and sustainability of aquaculture. To give references for the development and implementation of aquatic vaccines, this study reviews the development history, types, inoculation techniques, mechanisms of action, development prospects, and challenges encountered with aquatic vaccines.

β-glucan mimics tissue damage signaling and generates a trade-off between head kidney and spleen to activate acquired immunity in vaccinated tilapia (Oreochromis niloticus)

The association of vaccines with immunostimulants such as β-glucan, promote the production of cytokines, competent immune cells and antibodies. However, differences between β-glucan types and trials make it difficult to understand β-glucan's mechanism of action. In this study, three trials were carried out with control and fish fed β-glucan, the first trial occurred at 15 days; the second trial occurred at 30 days when we associated β-glucan and vaccine; and the third trial occurred at 15 days post-challenge with Streptococcus agalactiae in tilapia (O. niloticus) in order to investigate immune-related gene expression in the head kidney and spleen using real-time qPCR. We found increases in HSP70, IL-6, IL-1β, TNF-α, IL-10, Lys and C3 predominantly in the head kidney, except for IgM expression, which prevailed in the spleen, under vaccinated + β-glucan action. This demonstrates the trade-off presented by the head kidney and spleen after immunostimulation in order to produce acquired immunity, as well as an increase in HSP70 expression in vaccinated + β-glucan fish. The results suggest that β-glucan stimulates the immune response through damage-associated molecular patterns (DAMPs) recognition. Therefore, these dynamics of the immune response promote a more robust defense against disease.

Immune response and protective efficacy of two new adjuvants, Montanide™ ISA 763B VG and Montanide™ GEL02, administered with a Streptococcus agalactiae ghost vaccine in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae is one of the most important pathogens infecting tilapia worldwide and causes meningoencephalitis, septicemia and high mortalities with considerable losses. Various types of vaccines have been developed against S. agalactiae infection, such as inactivated vaccines, live attenuated vaccines and subunit vaccines. Bacterial ghosts (BGs) are nonliving, empty cell envelopes and have been reported as novel vaccine candidates. Therefore, the main aims of this study were to develop an S. agalactiae ghost vaccine (SAGV) and to evaluate the immune response and protective effect of SAGV against S. agalactiae with two novel adjuvants, Montanide™ ISA 763B VG and Montanide™ GEL02. Nile tilapia, mean weight 50 g, were divided into four groups as follows; 1) fish injected with PBS as control, 2) fish injected with the SAGV alone; 3) fish injected with the SAGV+Montanide™ ISA 763B VG; and 4) fish injected with SAGV+Montanide™ GEL02. Following vaccination, innate immunity parameters including serum lysozyme, myeloperoxidase, catalase, and bactericidal activity were all significantly enhanced. Moreover, specific serum IgM antibodies were induced and reached their highest level 2-8 weeks post vaccination. Importantly, the relative percent survival of tilapia vaccinated against the SAGV formulated with both adjuvants was 80-93%. Furthermore, the transcription of immune-related genes (IgM, TCRβ, IL-1β, IL-8 and TNFα) were up-regulated in tilapia after vaccination, indicating that both cellular and humoral immune responses were induced by these adjuvanted vaccines. In summary, Montanide™ ISA 763B VG and Montanide™ GEL02 can enhance immunoprotection induced by the SAGV vaccine against streptococcosis, demonstrating that both have value as potential adjuvants of fish vaccines.

Establishment and characterization of a gill cell line from pearl gentian grouper (Epinephelus lanceolatus♂×Epinephelus fuscoguttatus♀) and its application in cadmium toxicology

A novel gill cell line from pearl gentian grouper (Epinephelus lanceolatus♂×Epinephelus fuscoguttatus♀, PGGG cell line) was established, its application in cadmium (Cd) toxicology was demonstrated in this study. Primary cultures and PGGG subcultures were carried out at 25 °C in Dulbecco's Modified Eagle medium/F12 medium (1:1; pH 7.2) supplemented with 15% fetal bovine serum (FBS). Primary PGGG cells were spindle-shaped, proliferated into a confluent monolayer within two weeks and were continuously subcultured over passage 60. The growth of cells at passages 20, 40, and 60 was examined. Chromosome analysis revealed that the chromosomal number of normal PGGG cells was 48, but the number of cells with the normal chromosomes number decreased during the passaging process. Cadmium is one of the most toxic metals in aquatic systems and has been associated with multiple animal and human health problems. To interpret the cytotoxicity and related mechanisms of cadmium, PGGG cells were used as an in vitro model. After treatment with cadmium at concentrations ranging from 1 µM to 500 µM, PGGG cells demonstrated dose- and time-dependent cytotoxicity, manifested as morphological abnormalities and a viability decline. Further, it was found that the reactive oxygen species (ROS) and malondialdehyde (MDA) levels were elevated following cadmium exposure, and related genes involved in the antioxidant system, including those encoding catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and Kelch-like- ECH-associated protein 1 (Keap1), were regulated differently. In addition, PGGG cells treated with cadmium had the typical features associated with apoptosis, including phosphatidylserine (PS) externalization; upregulated expression of caspase-3, -8, and -9; and apoptotic body formation. In general, the PGGG cell line may serve as a useful tool for studying the toxic mechanisms of cadmium or other toxicants or for toxicity testing and environment monitoring.