Assessment of DNA vaccine potential for gilthead sea bream (Sparus aurata) by intramuscular injection of a reporter gene

The immune-adjuvant effect of Japanese flounder Paralichthys olivaceus IL-1β

IL-1β is known as a pro-inflammatory cytokine and plays a pivotal role in regulating immune response. IL-1β has been shown to influence immune responses in Japanese flounder Paralichthys olivaceus. To investigate the immune responses, a plasmid construct of pcDNA3.1-driven Japanese flounder IL-1β (pcDNA3.1-JFIL-1β) was co-injected into the muscle with Bovine serum albumin (BSA), as an antigen model, or pCI-neo driven with GFP (pCI-neo-GFP) as a vaccine model compared with the antigen or vaccine model alone, respectively. The IL-1β expression in the muscle was dramatically elevated in fish injected with pcDNA3.1-JFIL-1β on a day after injection, and the induction level was significantly higher than control groups. Moreover, pcDNA3.1-JFIL-1β significantly stimulated the gene expression of IL-1β in the kidney. The pcDNA3.1-JFIL-1β enhanced the antibody titer against BSA at 30 days after injection. In the DNA vaccine model, the antibody titer against GFP was also higher in the fish injected with pcDNA3.1-JFIL-1β than the group that injected pCI-neo-GFP alone. These results suggest that the pcDNA-driven Japanese flounder IL-1β could have potential immunoadjuvant effects.

Electrotransfer of the epinecidin-1 gene into skeletal muscle enhances the antibacterial and immunomodulatory functions of a marine fish, grouper (Epinephelus coioides)

Electrotransfer of plasmid DNA into skeletal muscle is a common non-viral delivery system for the study of gene function and for gene therapy. However, the effects of epinecidin-1 (epi) on bacterial growth and immune system modulation following its electrotransfer into the muscle of grouper (Epinephelus coioides), a marine fish species, have not been addressed. In this study, pCMV-gfp-epi plasmid was electroporated into grouper muscle, and its effect on subsequent infection with Vibrio vulnificus was examined. Over-expression of epi efficiently reduced bacterial numbers at 24 and 48 h after infection, and augmented the expression of immune-related genes in muscle and liver, inducing a moderate innate immune response associated with pro-inflammatory infiltration. Furthermore, electroporation of pCMV-gfp-epi plasmid without V. vulnificus infection induced moderate expression of certain immune-related genes, particularly innate immune genes. These data suggest that electroporation-mediated gene transfer of epi into the muscle of grouper may hold potential as an antimicrobial therapy for pathogen infection in marine fish.

Protection of Japanese flounder (Paralichthys olivaceus) against Vibrio anguillarum with a DNA vaccine containing the mutated zinc-metalloprotease gene

Vibrio anguillarum is one of the causative agents of vibriosis, a systemic disease of fish characterized by acute hemorrhagic septicemia. The extracellular zinc metalloprotease (EmpA) is a putative virulence factor involved in pathogenicity of V. anguillarum. Here we described the results of immunization against V. anguillarum with the plasmid expressing the mutated EmpA (m-EmpA7), which had no protelytic activity or cytotoxicity. In vitro protein expression of m-empA7 gene was determined by fluorescent microscopy and Western-blot after transfection of Chinese hamster ovary (CHO) and human embryonic kidney (HEK293T) cell lines. All three groups of fish immunized with a single intramuscular (i.m.) injection of different doses of the m-EmpA7 DNA vaccine showed significant serum antibody levels after vaccination, compared with the fish injected with the control eukaryotic expression vector pEGFP-N1 and PBS. In addition, fish receiving the DNA vaccine developed a protective response to a live V. anguillarum challenge 4 weeks post-inoculation, as demonstrated by increased survival of vaccinated fish over the control and by decreased histological alterations in vaccinated fish. Furthermore, humoral immune responses and protective effects were significantly increased at higher vaccine doses using a single intramuscularly injection route.

What happens to the DNA vaccine in fish? A review of current knowledge

The primary function of DNA vaccines, a bacterial plasmid DNA containing a construct for a given protective antigen, is to establish specific and long-lasting protective immunity against diseases where conventional vaccines fail to induce protection. It is acknowledged that less effort has been made to study the fate, in terms of cellular uptake, persistence and degradation, of DNA vaccines after in vivo administration. However, during the last year some papers have given new insights into the fate of DNA vaccines in fish. By comparing the newly acquired information in fish with similar knowledge from studies in mammals, similarities with regard to transport, blood clearance, cellular uptake and degradation of DNA vaccines have been found. But the amount of DNA vaccine redistributed from the administration site after intramuscular administration seems to differ between fish and mammals. This review presents up-to-date and in-depth knowledge concerning the fate of DNA vaccines with emphasis on tissue distribution, cellular uptake and uptake mechanism(s) before finally describing the intracellular hurdles that DNA vaccines need to overcome in order to produce their gene product.

Specific uptake of plasmid DNA without reporter gene expression in Atlantic salmon (Salmo salar L.) kidney after intramuscular administration

In this study we investigated tissue distribution of pDNA after intramuscular and intravenous administration, cellular localisation, receptor-specific uptake, integrity of pDNA and transgene expression in Atlantic salmon (Salmo salar L). Anatomical distribution of plasmid DNA was determined using both radiotracing and fluorescence microscopy. Cellular uptake was studied in cultures of adherent anterior kidney leucocytes. The integrity of the pDNA in vivo was investigated by Southern blot analysis. Transcription of plasmid DNA encoded luciferase gene and protein synthesis were investigated in salmon tissues by means of real-time reverse transcription-polymerase chain reaction and enzyme activity measurements, respectively. Approximately 50% of the total recovered radioactivity was redistributed from the carcass 168h after intramuscular administration and accumulated mainly in the kidneys (37% of total). The majority of radiolabelled plasmid DNA administered intravenously was taken up within the first 15min mainly by the kidney. Intravenous co-administration of trace amounts of radiolabelled plasmid DNA with excess amounts of unlabelled plasmid DNA or formaldehyde treated albumin (a ligand for the scavenger receptors) significantly inhibited accumulation of the radiotracer in the kidney. Fluorescence microscopy demonstrated that fluorescence was localised intracellularly in cells lining the sinusoids of the kidney after intravenous administration of rhodamine-labelled plasmid DNA. Southern blot analysis demonstrated presence of supercoiled plasmid DNA in all organs and tissue samples 168h after intramuscular administration, but degradation products were only revealed at the administration site. Luciferase transcript and activity were only detectable at the administration site 24-168h after intramuscular administration of plasmid DNA. After incubation with trace amounts of radiolabelled plasmid DNA, only minor amounts of radiolabelled plasmid DNA were cell associated in cultures of adherent anterior kidney leucocytes. These results suggested that a substantial portion of radiolabelled plasmid DNA was redistributed from the carcass and was mainly cleared by a receptor-specific uptake in the kidney. Although intact plasmid DNA was detected in the kidney and other tissues, no luciferase transcripts or activity were detected in these samples at any time points investigated (24-168h), except for the administration site following intramuscular administration.

Towards a metalloprotease-DNA vaccine against piscine cryptobiosis caused by Cryptobia salmositica

Cysteine protease is a metabolic enzyme, whereas metalloprotease is the virulent factor in cryptobiosis caused by Cryptobia salmositica. Recombinant DNA vaccines were produced with the insertion of either the metalloprotease or cysteine protease gene of C. salmositica into plasmid vectors (pEGFP-N). As expected, fishes (Oncorhynchus mykiss and Salmo salar) injected intramuscularly with the metalloprotease-DNA (MP-DNA) vaccine (50 microg/fish) were consistently more anemic (lower packed cell volume, PCV) than controls (injected only with the plasmid) at 3-5 weeks post-inoculation. Also, there were no difference in PCV between fish injected with the cysteine-DNA plasmids and the controls. In addition, agglutinating antibodies against Cryptobia were detected only in the blood of MP-DNA-vaccinated fish at 5-7 weeks post-vaccination and not in cysteine-DNA plasmids and the control groups. MP-DNA-vaccinated fish when challenged with the pathogen had consistently lower parasitemia, delayed peak parasitemia, and faster recovery compared with the controls. All fish vaccinated with attenuated strain were protected when challenged with the pathogen; this positive control group confirmed that the two vaccines operate through different mechanisms.

Effect of photoperiod on the fish innate immune system: a link between fish pineal gland and the immune system

The pineal gland via its secretory product, melatonin, influences the light-dark rhythm in most vertebrates including fish. Apart from the information concerning this circadian rhythm, the interrelation of the melatonin with other physiological processes has not been considered in fish. Thus, we evaluated the changes in the humoral innate immune system of seabream (Sparus aurata L.) and sea bass (Dicentrarchus labrax L.) specimens exposed to a constant light-dark photoperiod (12 hr L:12 hr D). Serum was obtained from blood samples collected at 02:00, 08:00 hr (light-on), 14:00, 20:00 hr (light-off) and at 08:00 hr again. Among the humoral innate immune responses, complement, lysozyme and peroxidase activities were determined. Complement activity was higher during the day than during the night in both fish species. Seabream lysozyme activity reached its maximum at 20:00 and 02:00 hr but was hardly affected in sea bass. Finally, the peroxidase activity of seabream was significantly higher at 08:00 hr than during the rest of the cycle while, in sea bass, it showed little variation. The present results demonstrate that the humoral innate immune system has a circadian rhythm based on the light-dark cycle and that this cycle might be affected by the pineal gland.

Protection of flounder against hirame rhabdovirus (HIRRV) with a DNA vaccine containing the glycoprotein gene

Hirame rhabdovirus (HIRRV) is an important virus of cultured flounder (Paralichthys olivaceus). We tested the protective immunogenicity of DNA-based vaccines against this virus. Genes encoding the nucleocapsid protein (N) and the C-terminal half of the glycoprotein (G) were amplified by RT-PCR and separately cloned into the eukaryotic expression vector pcDNA 3.1. The G protein expressed by transfected cells was detected by western blot analysis. PCR analyses demonstrated the presence of injected plasmids in fish muscle tissue at 14 days post injection. Immunocytochemistry of muscle tissue injected with the plasmid DNA showed expression of the target protein in myofibrils and sarcoplasm. Flounder fry with an average weight of 3 g were injected with 5 microg of plasmid DNA and challenged at 21 days after immunization. Fish injected with vector DNA or PBS showed >95% cumulative mortality by 16 days after inoculation with the virus. In contrast, fish injected with plasmids containing the N gene, G gene, or N + G gene mixture showed 70, 5, and 2.5% cumulative mortality, respectively. These results show that the G gene is effective for the induction of protective immunity against HIRRV infection in injected fish.