Surface display of hirame novirhabdovirus (HIRRV) G protein in Lactococcus lactis and its immune protection in flounder (Paralichthys olivaceus)

The molecular characterization of Rab11 and its immune roles in red swamp crayfish (Procambarus clarkii)

The Rab proteins primarily regulate vesicular transport between membrane-bound organelles and are important for innate immune. However, there is currently a lack of studies on crustaceans regarding Rab proteins, particularly core Rabs. We identified a Rab11 gene from Procambarus clarkii (PcRab11) and evaluated its potential involvement in immune response. The results showed PcRab11 was 1789 bp long, with an open reading frame of 645 bp encoding 211 amino acids and an estimated molecular weight of 23.8 kDa. Sequence analysis revealed its remarkable evolutionary conservation. The PcRab11 was widely expressed in various tissues, with highest levels in hepatopancreas, and localized within the cell cytoplasm. Upon infection with white spot syndrome virus (WSSV) or Aeromonas veronii, the expression of PcRab11 in immune organs was significantly induced. Furthermore, silencing PcRab11 reduced phagocytosis-related genes expression and haemocytes' phagocytic activity to FITC-labeled A. veronii, as well as decreased mortality and death time in WSSV or A. veronii infected P. clarkii. Additionally, the potential protein interaction between PcRab11 and 14-3-3ε was identified in haemocytes. Overall, our findings provided evidence for the involvement of Rab11 in P. clarkii's immune response, establishing a foundation to explore the immune role of core Rab proteins in crustaceans' innate immune system.

Lactococcus lactis, a bacterium with probiotic functions and pathogenicity

Lactococcus lactis (L. lactis) is the primary organism for lactic acid bacteria (LAB) and is a globally recognized safe microorganism for the regulation of the intestinal micro-ecological balance of animals and improving the immune performance of the host. L. lactis is known to play a commercially important role in feed fortification, milk fermentation, and vaccine production, but pathogenic L. lactis has been isolated from many clinical cases in recent years, such as the brain of silver carp with Lactococcosis, the liver and spleen of diseased waterfowl, milk samples and padding materials with cow mastitis, and blood and urine from human patients with endocarditis. In dairy farming, where L. lactis has been used as a probiotic in the past, however, some studies have found that L. lactis can cause mastitis in cows, but the lack of understanding of the pathogenesis of mastitis in cows caused by L. lactis has become a new problem. The main objective of this review is to analyze the increasingly serious clinical mastitis caused by L. lactis and combined with the wide application of L. lactis as probiotics, to comprehensively discuss the characteristics and diversity of L. lactis.

Untargeted LC-MS metabolomics reveals the metabolic responses in olive flounder subjected to hirame rhabdovirus infection

Hirame novirhabdovirus (HIRRV), which mainly infects the olive flounder (Paralichthys olivaceus), is considered to be one of the most serious viral pathogens threatening the global fish culture industry. However, little is known about the mechanism of host-pathogen interactions at the metabolomic level. In this study, in order to explore the metabolic response of olive flounder to HIRRV infection, liquid chromatography mass spectrometry (LC-MS) was used to detect the changes of endogenous compounds of the olive flounder after HIRRV infection. A total of 954 unique masses were obtained, including 495 metabolites and 459 lipids. Among them, 7 and 173 qualified differential metabolites were identified at 2 days and 7 days post-infection, respectively. Distinct metabolic profiles were observed along with viral infection. At the early stage of infection, only a few metabolites were perturbed. Among them, the level of inosine and carnosine were increased and the potential antiviral ability of these two metabolites was further confirmed by exogenous addition experiment. At the late stage of HIRRV infection, the metabolic profiles changed remarkably. The changes in amino acids and nucleotides especially the 7-methylguanine also accelerated the amplification of viral particles. And the down-regulation of glutathione (GSH) implied an elevated level of ROS (reactive oxygen species) that attenuated the immune system of flounders. HIRRV also induced the accumulation of purine and reduction of pyrimidine, and elevated LPC and LPE levels. The unbalanced purine/pyrimidine and altered lipid profile may be beneficial for the replication and infection of HIRRV at the late stage of infection. These findings provide new insights into the pathogenic mechanism of HIRRV infection in olive flounder.

Proteomic and Phosphoproteomic Analysis Reveals Differential Immune Response to Hirame Novirhabdovirus (HIRRV) Infection in the Flounder (Paralichthys olivaceus) under Different Temperature

Hirame novirhabdovirus (HIRRV) is one of most serious viral pathogens causing significant economic losses to the flounder (Paralichthys olivaceus)-farming industry. Previous studies have shown that the outbreak of HIRRV is highly temperature-dependent, and revealed the viral replication was significantly affected by the antiviral response of flounders under different temperatures. In the present study, the proteome and phosphoproteome was used to analyze the different antiviral responses in the HIRRV-infected flounder under 10 °C and 20 °C. Post viral infection, 472 differentially expressed proteins (DEPs) were identified in the spleen of flounder under 10 °C, which related to NOD-like receptor signaling pathway, RIG-I-like receptor signaling pathway, RNA transport and so on. Under 20 °C, 652 DEPs were identified and involved in focal adhesion, regulation of actin cytoskeleton, phagosome, NOD-like receptor signaling pathway and RIG-I-like receptor signaling pathway. Phosphoproteome analysis showed that 675 differentially expressed phosphoproteins (DEPPs) were identified in the viral infected spleen under 10 °C and significantly enriched in Spliceosome, signaling pathway, necroptosis and RNA transport. Under 20 °C, 1304 DEPPs were identified and significantly enriched to Proteasome, VEGF signaling pathway, apoptosis, Spliceosome, mTOR signaling pathway, mRNA surveillance pathway, and RNA transport. To be noted, the proteins and phosphoproteins involved in interferon production and signaling showed significant upregulations in the viral infected flounder under 20 °C compared with that under 10 °C. Furthermore, the temporal expression profiles of eight selected antiviral-related mRNA including IRF3, IRF7, IKKβ, TBK1, IFIT1, IFI44, MX1 and ISG15 were detected by qRT-PCR, which showed a significantly stronger response at early infection under 20 °C. These results provided fundamental resources for subsequent in-depth research on the HIRRV infection mechanism and the antiviral immunity of flounder, and also gives evidences for the high mortality of HIRRV-infected flounder under low temperature.

Recombinant vaccines in 2022: a perspective from the cell factory

The last big outbreaks of Ebola fever in Africa, the thousands of avian influenza outbreaks across Europe, Asia, North America and Africa, the emergence of monkeypox virus in Europe and specially the COVID-19 pandemics have globally stressed the need for efficient, cost-effective vaccines against infectious diseases. Ideally, they should be based on transversal technologies of wide applicability. In this context, and pushed by the above-mentioned epidemiological needs, new and highly sophisticated DNA-or RNA-based vaccination strategies have been recently developed and applied at large-scale. Being very promising and effective, they still need to be assessed regarding the level of conferred long-term protection. Despite these fast-developing approaches, subunit vaccines, based on recombinant proteins obtained by conventional genetic engineering, still show a wide spectrum of interesting potentialities and an important margin for further development. In the 80’s, the first vaccination attempts with recombinant vaccines consisted in single structural proteins from viral pathogens, administered as soluble plain versions. In contrast, more complex formulations of recombinant antigens with particular geometries are progressively generated and explored in an attempt to mimic the multifaceted set of stimuli offered to the immune system by replicating pathogens. The diversity of recombinant antimicrobial vaccines and vaccine prototypes is revised here considering the cell factory types, through relevant examples of prototypes under development as well as already approved products.

Gut Immune System and the Implications of Oral-Administered Immunoprophylaxis in Finfish Aquaculture

The gastrointestinal immune system plays an important role in immune homeostasis regulation. It regulates the symbiotic host-microbiome interactions by training and developing the host's innate and adaptive immunity. This interaction plays a vital role in host defence mechanisms and at the same time, balancing the endogenous perturbations of the host immune homeostasis. The fish gastrointestinal immune system is armed with intricate diffused gut-associated lymphoid tissues (GALTs) that establish tolerance toward the enormous commensal gut microbiome while preserving immune responses against the intrusion of enteric pathogens. A comprehensive understanding of the intestinal immune system is a prerequisite for developing an oral vaccine and immunostimulants in aquaculture, particularly in cultured fish species. In this review, we outline the remarkable features of gut immunity and the essential components of gut-associated lymphoid tissue. The mechanistic principles underlying the antigen absorption and uptake through the intestinal epithelial, and the subsequent immune activation through a series of molecular events are reviewed. The emphasis is on the significance of gut immunity in oral administration of immunoprophylactics, and the different potential adjuvants that circumvent intestinal immune tolerance. Comprehension of the intestinal immune system is pivotal for developing effective fish vaccines that can be delivered orally, which is less labour-intensive and could improve fish health and facilitate disease management in the aquaculture industry.

Lactococcus lactis Expressing Type I Interferon From Atlantic Salmon Enhances the Innate Antiviral Immune Response In Vivo and In Vitro

In salmon farming, viruses are responsible for outbreaks that produce significant economic losses for which there is a lack of control tools other than vaccines. Type I interferon has been successfully used for treating some chronic viral infections in humans. However, its application in salmonids depends on the proper design of a vehicle that allows its massive administration, ideally orally. In mammals, administration of recombinant probiotics capable of expressing cytokines has shown local and systemic therapeutic effects. In this work, we evaluate the use of Lactococcus lactis as a type I Interferon expression system in Atlantic salmon, and we analyze its ability to stimulate the antiviral immune response against IPNV, in vivo and in vitro. The interferon expressed in L. lactis, even though it was located mainly in the bacterial cytoplasm, was functional, stimulating Mx and PKR expression in CHSE-214 cells, and reducing the IPNV viral load in SHK-1 cells. In vivo, the oral administration of this L. lactis producer of Interferon I increases Mx and PKR expression, mainly in the spleen, and to a lesser extent, in the head kidney. The oral administration of this strain also reduces the IPNV viral load in Atlantic salmon specimens challenged with this pathogen. Our results show that oral administration of L. lactis producing Interferon I induces systemic effects in Atlantic salmon, allowing to stimulate the antiviral immune response. This probiotic could have effects against a wide variety of viruses that infect Atlantic salmon and also be effective in other salmonids due to the high identity among their type I interferons.

Vaccination with live Hirame novirhabdovirus (HIRRV) at temperature-controlled condition induced protective immunity in flounder (Paralichthys olivaceus)

Hirame novirhabdovirus (HIRRV) is a severe viral pathogen of flounder resulting in significant losses to the aquaculture industry. However, the mortality due to the disease would be significantly reduced when the water temperature was increased from 10 to 20 °C. In this study, we examined the potentiality of vaccination with live HIRRV under a temperature-controlled culture condition for development of protective immunity in flounder. Flounders were infected with HIRRV at 10 °C and maintained for 2 days, and then the temperature was shift up to 20 °C. When the temperature was further shift down to 10 °C at 7 (S-7 group), 14 (S-14 group) or 21 (S-21 group) days post infection (dpi), mortality rates of 60%, 13.33% and 0 were observed, respectively. To investigate the development of protective immunity of survived flounder, a re-challenge was performed and a highest survival rate of 80% was found in S-21 group, which was significantly higher than S-14 group (65%) and S-7 group (45%). Moreover, it was found that a lower viral load was detected in the flounder maintained at 20 °C for a longer time, and a longer maintaining of survived flounder at 20 °C would also elicit higher percentages of IgM + B lymphocytes and specific antibodies levels. Notably, a significantly higher levels of specific antibodies were detected post re-challenge compared with the first peak level after initial infection. Therefore, these demonstrated that the initial infection with live HIRRV under a temperature-controlled condition elicited an effective protective immune response against HIRRV, and maintaining at 20 °C for a long enough time would allow the HIRRV-infected flounder to eliminate the virus completely and acquired a protective immunity against HIRRV infection. This is the first study showing the possibility of developing an effective preventive measure against HIRRV by vaccination with live virus under controlled water temperature.

Development of monoclonal antibody against glycoprotein of hirame novirhabdovirus (HIRRV) with virus neutralizing activity

Hirame rhabdovirus (HIRRV) is one of the most important viruses of fish, posing a great threat to the fish industry in Asia and Europe. The glycoprotein (G) of HIRRV is known to play important roles in virus attachment and entry, making it an ideal target for both diagnosis and therapy. In this study, a truncated G of HIRRV was expressed as a fusion protein in Escherichia coli. Using the recombinant G protein (rG), monoclonal antibodies (mAbs) were prepared by the hybridoma technology. Subsequently, positive clones were screened by indirect enzyme-linked immunosorbent assay (ELISA) and further characterized by Western blot and immunofluorescence assay (IFA). ELISA results showed that two mAbs (3E5 and 4D10) could react with the rG, as well as the purified HIRRV. Western blot analysis showed that the mAbs belong to the IgG isotype and could recognize a 60 kDa viral protein, which is consistent with the molecular weight of G protein and determined to be the G protein of HIRRV by mass spectrometry. The virions in HIRRV-infected EPC could also be recognized by two mAbs in IFA. Moreover, neutralization assay showed that mAb 4D10 could significantly inhibit the proliferation of HIRRV and delay the development of cytopathic effect in viral-infected EPC cells, and in vivo neutralization assay also showed that mAb 4D10 could significantly reduce the mortality of HIRRV-infected flounder, indicating that mAb 4D10 can partially neutralize the HIRRV infection. Western blot analysis showed that mAb 4D10 could specifically bind the C-terminal domain of HIRRV-G protein. These results demonstrated that the produced mAbs could specifically recognize the G protein of HIRRV and displayed virus-neutralizing activity in vitro and in vivo, which could serve as effective detection probes and potential neutralizing antibodies for HIRRV.

Plasmid Replicons for the Production of Pharmaceutical-Grade pDNA, Proteins and Antigens by Lactococcus lactis Cell Factories

The Lactococcus lactis bacterium found in different natural environments is traditionally associated with the fermented food industry. But recently, its applications have been spreading to the pharmaceutical industry, which has exploited its probiotic characteristics and is moving towards its use as cell factories for the production of added-value recombinant proteins and plasmid DNA (pDNA) for DNA vaccination, as a safer and industrially profitable alternative to the traditional Escherichia coli host. Additionally, due to its food-grade and generally recognized safe status, there have been an increasing number of studies about its use in live mucosal vaccination. In this review, we critically systematize the plasmid replicons available for the production of pharmaceutical-grade pDNA and recombinant proteins by L. lactis. A plasmid vector is an easily customized component when the goal is to engineer bacteria in order to produce a heterologous compound in industrially significant amounts, as an alternative to genomic DNA modifications. The additional burden to the cell depends on plasmid copy number and on the expression level, targeting location and type of protein expressed. For live mucosal vaccination applications, besides the presence of the necessary regulatory sequences, it is imperative that cells produce the antigen of interest in sufficient yields. The cell wall anchored antigens had shown more promising results in live mucosal vaccination studies, when compared with intracellular or secreted antigens. On the other side, engineering L. lactis to express membrane proteins, especially if they have a eukaryotic background, increases the overall cellular burden. The different alternative replicons for live mucosal vaccination, using L. lactis as the DNA vaccine carrier or the antigen producer, are critically reviewed, as a starting platform to choose or engineer the best vector for each application.

Different immune responses of flounder (Paralichthys olivaceus) towards the full-length and N-terminal or C-terminal portion of hirame novirhabdovirus glycoprotein

Glycoprotein is an important immunogenic protein of Hirame novirhabdovirus (HIRRV). In this study, the full-length and N-/C-terminal portions of glycoprotein were recombinantly expressed (rG, rGn and rGc protein), and the induced immune responses were investigated in flounder (Paralichthys olivaceus) model. The results showed that compared to PBS control, rG, rGn and rGc proteins and inactivated HIRRV suspension (iVS) could all stimulate significant increases of flounder CD4-1⁺, CD4-2⁺ T lymphocytes and surface IgM positive (sIgM⁺) B lymphocytes in peripheral blood, spleen and head kidney (p < 0.05). However, no significant differences of the percentages of CD4-1⁺ or CD4-2⁺ T lymphocytes were observed among three protein vaccination groups (p > 0.05). iVS could induce the highest mean levels of CD4⁺ T lymphocytes in peripheral blood and spleen. For sIgM⁺ B lymphocytes, the average peak percentages in rG and rGc groups were higher than rGn group. Moreover, significant increases of specific serum IgM against HIRRV or rG protein were observed in iVS, rG, rGn and rGc groups, but rG group exhibited the highest mean level. Furthermore, rG protein induced the highest titer of neutralizing antibodies against HIRRV, followed by iVS. Meanwhile, the challenge test showed that the relative percent survival (RPS) of rG, rGn, rGc and iVS groups were 75.0%, 35.7%, 53.6% and 60.7%, respectively. These results revealed that the full-length G protein would be a more effective subunit vaccine candidate against HIRRV infection.

A Lactococcus lactis-vectored oral vaccine induces protective immunity of mice against enterotoxigenic Escherichia coli lethal challenge

Enterotoxigenic Escherichia coli (ETEC) is a global primary pathogenic bacterium causing diarrhoea in human and a wide variety of neonatal animals. Lactococcus lactis as non-pathogenic and food-grade lactic acid bacteria has already been explored as a vector for mucosal vaccine. Here, the current study was undertaken to evaluate the live recombinant L. lactis (rL. lactis) vaccine expressing the trivalent enterotoxin protein STa-LTB-STb and the F5 fimbrial antigen (SLS-F5) with OmpH of Yersinia enterocolitica in protection against ETEC. Western blot confirmed the expression of fusion protein SLS-F5-OmpH in nisin-controlled expression (NICE) system. Mice orally immunized with rL. lactis-SLS-F5-OmpH were observed to produce high levels of mucosal SIgA and serum IgG antibodies, while also inducing increases in the production of CD4⁺ and CD8⁺ T cells, lymphocyte proliferation, and secretion of cytokines. Moreover, orally immunized mice produced complete protection after ETEC challenge. The above results suggested that rL. lactis-SLS-F5-OmpH has the potential as a candidate for oral vaccine against ETEC.