Preventive and therapeutic effects of auxotrophic Edwardsiella tarda mutant harboring CpG 1668 motif-enriched plasmids against scuticociliatosis in olive flounder (Paralichthys olivaceus)

Innate immunity and protective effects of orally administered betaine against viral and bacterial diseases in the olive flounder Paralichthys olivaceus (Temminck & Schlegel)

Sustainable methods that increase farmed fish yield while controlling infections are required to prevent economic losses in aquaculture farms. In this study, we evaluated the effects of betaine-supplemented (0%, 0.1%, 0.5%, and 1.0%) feed on the growth and immunity of the olive flounder Paralichthys olivaceus. Feed conversion ratios, post-infection cumulative mortality rates and innate immune responses were monitored. Weight gain was significantly higher with 0.5% and 1.0% than with 0% and 0.1% betaine-supplemented feed. Lysozyme activity was highest with 1.0% betaine. Respiratory burst activity was highest with 0.5% and 1.0% betaine. Serum bactericidal activity against Edwardsiella tarda was highest with 1.0% betaine (40% increase in survival rates compared with those in the control). Furthermore, serum virucidal activity against the viral haemorrhagic septicaemia virus (VHSV) was higher with 1.0% betaine than with other concentrations. With 0.5% and 1.0% betaine, the survival rates against VHSV were higher than those in the control until day 11, after which they declined. Our study suggests that betaine is a promising agent for promoting the growth of and enhancing immunity against E. tarda in olive flounders. Our findings may further contribute to developing necessary alternatives to conventional antibiotics in fish farming.

Protective immunity against CyHV-3 infection via different prime-boost vaccination regimens using CyHV-3 ORF131-based DNA/protein subunit vaccines in carp Cyprinus carpio var. Jian

Cyprinid Herpesvirus 3 (CyHV-3), also known as Koi Herpesvirus (KHV), causes Koi Herpesvirus Disease (KHVD) which leads to serious economic losses worldwide. To exploit DNA/subunit vaccine candidates, CyHV-3 ORF131 gene and cDNA was cloned and analyzed in the present study. Major B cell epitopes of deduced CyHV-3 pORF131 was also predicted. Then the complete CDS of CyHV-3 ORF131 was inserted into pEGFP-N1 vector and a modified pYD1/EBY100 system to construct the DNA and subunit vaccine, respectively. Subsequently, carp were immunized with homologous and heterologous prime-boost regimens relying on the constructed DNA and oral subunit vaccines. Then the protective immunity generated from different vaccines and regimens as well as the capacity of yeast (Saccharomyces cerevisiae) as an oral vaccine vehicle was evaluated. Our study confirmed that CyHV-3 ORF131 gene consisted of 2 introns and 3 exons encoding a 428 amino acids peptide. Further analysis indicated that four fragments of CyHV-3 pORF131 contained the major B cell epitopes (Cys20~Val140, Ser169~Tyr245, Thr258~Pro390, Phe414~Gln428), which could be linked and expressed in E. coli (BL21) as a truncated pORF131. The expression of full-length CyHV-3 pORF131 by pEGFP-N1 and yeast surface display was verified by In vitro assays before vaccination. Immunization of carp with CyHV-3 ORF131 DNA and subunit vaccines could evoke the activation of immune-related genes such as CXCa, CXCR1, IL-1β, TNF-α, INF-a1, Mx-1, IgM, IgT1 and production of specific serum IgM measured by ELISA. RPS (relative percent of survival) ranging from 53.33% to 66.67% was acquired post challenge test. Moreover, flow cytometry analysis illustrated the delivery of surface-displayed CyHV-3 pORF131 to midgut after oral gavage. Thus, our findings suggest that CyHV-3 ORF131 can serve as DNA/subunit vaccines candidate and the yeast as an ideal oral vaccine vehicle.

Effectiveness of formalin-killed vaccines containing CpG oligodeoxynucleotide 1668 adjuvants against Vibrio harveyi in orange-spotted grouper

Vibrio harveyi is a major bacterial pathogen that causes serious vibriosis in cultured groupers, leading to massive deaths. In this study, we evaluated the immune responses and protective efficacy of vaccines containing V. harveyi formalin-killed cells (FKC) formulated with CpG ODN 1668-enriched plasmids (p30CpG and p60CpG) in the orange-spotted grouper. Results indicated that antibody titres were remarkably increased in vaccinated fish 2 weeks post-immunisation. Expression level of major histocompatibility complex (MHC) class II, CD 8, and toll-like receptor 9 was significantly upregulated in the spleen of fish immunised with CpG ODN 1668-adjuvanted vaccines, as recorded at 6 weeks after immunisation. Additionally, the FKC + p60CpG-vaccinated fish displayed greater mRNA levels of MHC I and tumor necrosis factor-alpha. Of note, the relative percent survival after V. harveyi challenge was significantly higher in FKC + p60CpG-vaccinated fish (96.2%) than in FKC + p30CpG-vaccinated (79.8%) and FKC-vaccinated fish (59.9%). These results demonstrate that the FKC + CpG ODN 1668 vaccines are promising candidates that could enhance both innate and adaptive immune responses, conferred remarkable protection, and CpG ODN 1668 is a potential adjuvant for vaccines against V. harveyi.

CpG ODN mimicking CpG rich region of myxosporean Myxobolus supamattayai stimulates innate immunity in Asian sea bass (Lates calcarifer) and defense against Streptococcus iniae

Oligodeoxynucleotides (ODNs) containing unmethylated cytosine-phosphate-guanine CpG dinucleotides within specific sequence contexts (CpG motifs) have been reported as pathogen-associated molecular patterns (PAMPs). Its immunostimulatory effects have been demonstrated in diverse vertebrate models. CpG ODN is typically found in bacterial or viral genome and recognized by a non-self recognition receptor Toll-like receptor9 (TLR9). Here, a new CpG ODN 1013 which mimics sequence of SSU rDNA of early eukaryotic organism myxosporidia, Myxobolus supamattayai, was employed to stimulate the immune responses of Asian sea bass Lates calcarifer. Its immunostimulant potentiality was comparatively compared with that of CpG ODN 1668, a widely used as functional immunostimulant. Both unmethylated CpG ODNs with some modified phosphorothioated positions were intraperitoneally injection (5 μg/fish). Hematological examination, immunological assays and immune-related genes expression were evaluated 12 h, 1, 3 and 5 d after post CpG ODN challenge. The immunosimulatory effect of these CpG ODNs on fish immunity to protect the bacterial pathogen Streptococcus iniae was also determined. The results demonstrated that these two CpG ODNs could induce immune responses in Asian sea bass including the significant (P < 0.05) increase level of WBC, peroxidase activity and oxidative radicals in head kidney (HK) leukocyte, serum innate immune parameters and up-regulation of four immune responsive genes compared with the control group. Most of immune responses induced by ODN 1668 were strong within 1 d but lesser extended while ODN 1013 prolonged the stimulatory effects during the whole experimental period. After challenge with S. iniae, the survival proportion in ODN 1013-treated fish was apparently higher than that treated with ODN 1668 and PBS, respectively. The results together suggested that CpG ODN 1013 enhanced innate immune responses, including humoral and cellular responses, through TLR9 mediated signaling pathway which is mainly contribute to the protective immunity in Asian sea bass against S. iniae infection. These findings can lead to a new approach in immunostimulant development by using the novel CpG ODN originating from the parasite M. supamattayai, besides those from bacterial and viral genomes, for disease control in fish host.