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Abstract Infectious pancreatic necrosis virus (IPNV) infects wild and cultured salmonid fish causing high mortality with serious economic losses to salmonid aquaculture. Ideally, the method of oral immunization should prevent the infection of rainbow trout juveniles with IPNV. In the present study, genetically engineered Lactobacillus casei 393 pPG-612-VP2/ L. casei 393 and pPG-612-CK6-VP2/ L. casei 393 constitutively expressing VP2 protein of IPNV were constructed. The recombinant strains pPG-612-CK6-VP2/ L. casei 393 and pPG-612-VP2/ L. casei 393 were orally administrated to juvenile rainbow trouts, and significant titers of IgM and IgT of pPG-612-CK6-VP2/ L. casei 393 were observed. The results demonstrate that the recombinants could elicit both local mucosal and systemic immune responses. The proliferation of spleen lymphocytes in trouts immunized with pPG-612-CK6-VP2/ L. casei 393 showed that the recombinant strain could induce a strong cellular immune response. The IL-1β, IL-8, CK6, MHC-II, Mx, β-defensin, and TNF-1α levels in the spleen and gut suggest that the target molecular chemokine has the ability to attract relevant immune cells to participate in the inflammatory response and enhance the function of the innate immune response. Additionally, the pPG-612-CK6-VP2/ L. casei 393 induced the expression of cytokines, which have the effect of promoting inflammation to drive the differentiation of macrophages and clear target cells. After challenging with IPNV, the reduction in viral load caused by pPG-612-CK6-VP2/ L. casei 393 was significantly higher than that of the other groups. Thus, the recombinant pPG-612-CK6-VP2/ L. casei 393 is a promising candidate for the development of an oral vaccine against IPNV. Highlights • We engineered Lactobacillus casei 393 expressing VP2 protein of IPNV modified by targeted molecules. • The recombinant strain modified by CK6 could lead to a stronger and quicker immune response. • The chemokine has the ability to attract immune cells to enhance the function of the innate immune response. • The pPG-612-CK6-VP2/ L. casei 393 is a promising candidate for the development of an oral vaccine against IPNV. [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis virus (IPNV) primarily infects larvae and young salmonid with serious economic losses, which causes haemorrhage and putrescence of hepatopancreas. To develop a more effective oral vaccine against IPNV infection, the aeromonas hydrophila adhesion (AHA1) gene was used as a targeting molecule for intestinal epithelial cells. A genetically engineered Lactobacillus casei (pPG-612-AHA1-CK6-VP2/ L. casei 393) was constructed to express the AHA1-CK6-VP2 fusion protein. The expression of interest protein was confirmed by western blotting and the immunogenicity of pPG-612-AHA1-CK6-VP2/ L. casei 393 was evaluated. And the results showed that more pPG-612-AHA1-CK6-VP2/ L. casei 393 were found in the intestinal mucosal surface of the immunized group. The Lactobacillus -derived AHA1-CK6-VP2 fusion protein could induce the production of serum IgM and skin mucus IgT specific for IPNV with neutralizing activity in rainbow trouts. The levels of IL-1β , IL-8 and TNF-α isolated from the lymphocytes stimulated by AHA1-CK6-EGFP produced were significantly higher than EGFP group. For transcription levels of IL-1β , IL-8, CK6 , MHC-II , Mx and TNF-1α in the spleen, the result indicated that the adhesion and target chemokine recruit more immune cells to induce cellular immunity. The level of IPNV in the immunized group of pPG-612-AHA1-CK6-VP2/ L. casei 393 was significantly lower than that in the control groups. These data indicated that the adhesion and target chemokine could enhance antigen delivery efficiency, which provides a valuable strategy for the development of IPNV recombination Lactobacillus casei oral vaccine in the future. • The AHA1 and CK6 were co-expressed with VP2 of IPNV in expression system of Lactobacillus casei to prepare oral lactobacillus vaccine. • The L. casei 393 delivering the VP2 in combination with AHA1-CK6 can prolong the time of antigen in intestine and promote immune responses in rainbow trouts. • The genetically engineered pPG-612-AHA1-CK6-VP2/ L.casei 393 was able to effectively induce immune responses at both the systemic and mucosal levels. • The recombinant pPG-612-AHA1-CK6-VP2/ L.casei 393 is a promising candidate for the development of an oral vaccine against IPNV. [ABSTRACT FROM AUTHOR]

Viral infections frequently lead to the activation of host innate immune signaling pathways involved in the defense against invading pathogens. To ensure their survival, viruses have evolved sophisticated mechanisms to overcome the host immune responses. The present study demonstrated for the first time that infectious hematopoietic necrosis virus (IHNV) activated NF-κB pathway in fish cells. We further identified that the IHNV L protein could activate the NF-κB signaling pathway and that IHNV NV functioned as an inhibitor of NF-κB activation. Further results demonstrated that the NV protein blocked the degradation of the inhibitor of NF-κB (IκBα) and suppressed the SeV-induced NF-κB nuclear translocation. In conclusion, our study explored the functions of different IHNV proteins on NF-κB activation, and revealed a potential mechanism by which IHNV evades innate immune responses. [ABSTRACT FROM AUTHOR]

Infectious pancreatic necrosis (IPN) is a disease caused by the infectious pancreatic necrosis virus (IPNV). The condition is associated with highly fatal hemorrhage and putrescence of hepatopancreas in fry and juvenile salmonids, resulting in significant economic losses. The conventionally developed recombinant Lactobacillus casei oral vaccines against IPNV use antibiotic resistance as a selectable marker, which is linked to the development of antibiotic resistance, and this poses serious threats to biosafety. Herein, we developed a safe and effective oral vaccine against IPNV by replacing the chloramphenicol resistance (Cmr) marker in the L. casei expression system with an enhanced green fluorescent protein (eGFP) as a reporter gene. The rainbow trout chemokine (CK6) was used as a target molecule for antigen-presenting cells co-expressed with IPNV VP2. We constructed and evaluated the immunogenicity of the antibiotic-free selection marker pPGF-612-CK6-VP2-eGFP/ L. casei 393. The levels of anti-IPNV-specific IgM and IgT of rainbow trouts immunized with pPGF-612-CK6-VP2-eGFP/ L. casei 393 were significantly higher than those of phosphate-buffered saline (PBS) or pPG-612/ L. casei 393 groups. Also, the candidate vaccine exhibited neutralizing effects against IPNV. The viral loads of IPNV in the pPGF-612-CK6-VP2-eGFP/ L. casei 393 group were significantly lower than those in the control groups. These results indicate that the antibiotic-free resistance genetically engineered L. casei oral vaccine can provide a safe and promising strategy for the development of recombinant L. casei vaccine against IPNV. • eGFP was used to construct an oral Lactobacillus casei vaccine without resistance expressing the IPNV VP2 and CK6 of rainbow trout. • The antibiotic-free resistance pPGF-612-CK6-VP2-eGFP/L.casei 393 could efficiently induce immune responses against IPNV. • The pPGF-612-CK6-VP2-eGFP/L.casei 393 provides a safe and promising strategy for the oral vaccines against IPNV infection. [ABSTRACT FROM AUTHOR]

• Genome and transcriptome of D. flagrans was studied by comparative analysis. • Virulence and pathogenicity genes are expanded in D. flagrans genome. • The secretory proteins coding genes play crucial role in nematode-trapping. • Proteases are required for D. flagrans to catch and feed on nematodes. Duddingtonia flagrans is a nematode-trapping fungus that is widely used to control parasitic nematodes in livestock. To investigate the features and advantages of D. flagrans for nematode control at the molecular level, the genome and transcriptome of D. flagrans were sequenced and studied through a comparative analysis. The genome of D. flagrans had a size of 36.3 Mb and contained a higher ratio of repetitive sequences, which revealed its slow evolution. Comparative genomics analysis revealed the genome of D. flagrans to be relatively conserved compared to eight sequenced fungal genomes. Genes related to nematode trapping, virulence and pathogenicity were expanded in the D. flagrans genome, such as PHI genes, cytochrome P450 genes and various secretory protein genes. Remarkably, D. flagrans possessed a significant variety and abundance of putative proteases, while carbohydrate degradation-related genes were rare. Based on transcriptional profiling of different nematode trapping stages (0 h, 12 h and 48 h), the genes for some crucial secreted enzymes were up-regulated during nematode trapping process, including Zn(2)-C6-type transcription factor, chitinases, serine proteases and lectin-coding genes. The draft genome and transcriptome of D. flagrans provide evidence for the high pathogenicity and weaker saprophytic capability of this organism and constitute a theoretical foundation for the clinical use of D. flagrans as a biocontrol agent against parasitic nematodes. [ABSTRACT FROM AUTHOR]