Fusion of flagellin 2 with bivalent white spot syndrome virus vaccine increases survival in freshwater shrimp

Navigating Fish Immunity: Focus on Mucosal Immunity and the Evolving Landscape of Mucosal Vaccines

The growing role of aquaculture in global food security has underscored the need for advanced immunological insights to protect fish health and boost productivity. As aquaculture's importance rises, understanding fish immunity is crucial for developing effective vaccination strategies. Fish possess a specialized immune system with unique mucosal structures that enable resilience in aquatic environments. This review examines critical advances in fish mucosal immunity, particularly focusing on mucosal vaccines that target infection at primary entry points, such as the gills, skin, and gastrointestinal tract. Mucosal vaccination has demonstrated a compelling capacity to stimulate localized and systemic immune responses, offering enhanced protection against waterborne pathogens. Additionally, this review addresses knowledge gaps from previous research on the global aquaculture vaccines market by offering a regional perspective on industry developments, recent trends, and innovative vaccine formulations. In doing so, it highlights the role of mucosal vaccines in overcoming the specific challenges of fish farming and supporting sustainable aquaculture. This synthesis of current methodologies, industry practices, and future directions contributes to a deeper understanding of fish immunology, ultimately informing strategies to achieve optimal disease management and bolster global aquaculture resilience.

Transforming Aquaculture through Vaccination: A Review on Recent Developments and Milestones

Aquaculture has rapidly emerged as one of the fastest growing industries, expanding both on global and on national fronts. With the ever-increasing demand for proteins with a high biological value, the aquaculture industry has established itself as one of the most efficient forms of animal production, proving to be a vital component of global food production by supplying nearly half of aquatic food products intended for human consumption. As in classic animal production, the prevention of diseases constitutes an enduring challenge associated with severe economic and environmental repercussions. Nevertheless, remarkable strides in the development of aquaculture vaccines have been recently witnessed, offering sustainable solutions to persistent health-related issues challenging resilient aquaculture production. These advancements are characterized by breakthroughs in increased species-specific precision, improved vaccine-delivery systems, and innovations in vaccine development, following the recent advent of nanotechnology, biotechnology, and artificial intelligence in the -omics era. The objective of this paper was to assess recent developments and milestones revolving around aquaculture vaccinology and provide an updated overview of strengths, weaknesses, opportunities, and threats of the sector, by incorporating and comparatively discussing various diffuse advances that span across a wide range of topics, including emerging vaccine technologies, innovative delivery methods, insights on novel adjuvants, and parasite vaccine development for the aquaculture sector.

Effects of dietary supplementation of Anabaena sp. PCC7120 expressing VP28 protein on survival and histopathology after WSSV infection in Macrobrachium nipponense

Shrimp are especially susceptible to the White Spot Syndrome Virus (WSSV). Oral administration of the WSSV envelop protein VP28 is a promising approach to protect shrimp against WSSV. In this study, Macrobrachium nipponense (M. nipponense) were fed for 7 days with food supplemented with Anabaena sp. PCC 7120 (Ana7120) expressing VP28 and then challenged with WSSV. The survival rates of M. nipponense in three groups, including control, WSSV-challenged, and VP28-vaccinated, were subsequently determined. We also determined the WSSV content of different tissues and the tissue morphology in the absence of and after viral challenge. The survival rate of the positive control group (no vaccination and challenge, 10%) and empty vector group (fed with Ana7120 pRL-489 algae and challenged, 13.3%) was much lower than the survival rate of M. nipponense in wild type group (fed with Ana7120 and challenged, 18.9%), immunity group 1 (fed with 3.33% Ana7120 pRL-489-vp28 and challenged, 45.6%) or immunity group 2 (fed with 6.66% Ana7120 pRL-489-vp28 and challenged, 62.2%). RT-qPCR showed that WSSV content of the gill, hepatopancreas and muscle of immunity groups 1 and 2 were substantially lower than the positive control. Microscopic examination revealed that WSSV-challenged positive control exhibited large number of cell rupture, necrosis, nuclear exfoliation in gills and hepatopancreatic tissues. The gill and hepatopancreas of immunity group 1 showed partial symptoms of infection, yet the tissue was visibly healthier than that of the positive control group. No symptoms were visible in the gills and hepatopancreatic tissue of immunity group 2. The results demonstrate that the probability of M. nipponense infected by WSSV can be diminished by oral administration of cyanobacteria-expressed VP28. Such an approach could improve the disease resistance and delay the death of M. nipponense in the commercial production of this shrimp.

Shoc2 recognizes bacterial flagellin and mediates antibacterial Erk/Stat signaling in an invertebrate

Flagellin is a key bacterial virulence factor that can stimulate molecular immune signaling in both animals and plants. The detailed mechanisms of recognizing flagellin and mounting an efficient immune response have been uncovered in vertebrates; however, whether invertebrates can discriminate flagellin remains largely unknown. In the present study, the homolog of human SHOC2 leucine rich repeat scaffold protein in kuruma shrimp (Marsupenaeus japonicus), designated MjShoc2, was found to interact with Vibrio anguillarum flagellin A (FlaA) using yeast two-hybrid and pull-down assays. MjShoc2 plays a role in antibacterial response by mediating the FlaA-induced expression of certain antibacterial effectors, including lectin and antimicrobial peptide. FlaA challenge, via MjShoc2, led to phosphorylation of extracellular regulated kinase (Erk), and the subsequent activation of signal transducer and activator of transcription (Stat), ultimately inducing the expression of effectors. Therefore, by establishing the FlaA/MjShoc2/Erk/Stat signaling axis, this study revealed a new antibacterial strategy in shrimp, and provides insights into the flagellin sensing mechanism in invertebrates.

Flagellin sensing has been proven as a general antibacterial strategy. Recognition of bacterial flagellin by the transmembrane receptor toll like receptor 5 (TLR5) leads to the activation of nuclear factor kappa B (NF-κB) pathway and induction of proinflammatory cytokines, while recognition by the intracellular nucleotide-binding leucine-rich (NLR) receptor leads to caspase-activation and cytokines-expression. Although flagellin is an effective immune stimulator that induces antimicrobial peptides in Drosophila and in crustaceans, how an invertebrate host senses flagellin and mounts an immune response is poorly understood. Here, we used the flagellin (FlaA) from Vibrio anguillarum, a pathogen of shrimp, as a bait protein to screen a yeast two-hybrid library derived from kuruma shrimp (Marsupenaeus japonicus). We found a scaffold protein, MjShoc2, able to interact with FlaA. We also found that FlaA could effectively induce the expression of certain recognized antibacterial effectors in shrimp depending on MjShoc2. We revealed that extracellular regulated kinase (Erk) phosphorylation occurred downstream of FlaA/MjShoc2, and led to signal transducer and activator of transcription (Stat) activation, resulting in transcription of certain effectors. Therefore our study provides new insights into the FlaA-induced molecular immunity in invertebrates.

Identification and characterization of a Toll-like receptor gene from Macrobrachium nipponense

Outbreaks of infectious disease in shrimp pose a serious threat to shrimp agriculture worldwide. Shrimp lack adaptive immunity and depend only on innate immunity as a defense system against infectious disease. Toll-like receptors (TLR) are reported to play a critical role in the innate immune system. In this study, we identified a Toll-like receptor gene of a species of freshwater shrimp, Macrobrachium nipponense, designated MnToll, for the first time. The sequence of MnToll encoded 935 residues arranged as 10 leucine-rich repeat (LRR) domains, a leucine-rich repeat C-terminal (LRR CT) domain and a Toll/interleukin-1 receptor (TIR) domain and displayed 90% amino acid similarity to previously identified TLRs (Toll 1 and 2) of Macrobrachium rosenbergii. We additionally evaluated mRNA expression of MnToll in various tissues, including heart, gills, stomach, digestive gland, ventral nerve cord, antennal gland and muscle. Following infection with a viral pathogen, white spot syndrome virus (WSSV), MnToll expression was significantly upregulated between 12 and 72 h. Our data collectively suggest that the newly identified MnToll gene belongs to the TLR family in shrimp and is potentially involved in innate host defense, especially against WSSV.

Effects of Synechococcus sp. PCC 7942 harboring vp19, vp28, and vp (19 + 28) on the survival and immune response of Litopenaeus vannamei infected WSSV

This study aimed to assess the effect of oral administration of Synechococcus sp. PCC 7942 harboring vp19, vp28, and vp(19 + 28)against infection by white spot syndrome virus (WSSV) on juveniles of Litopenaeus vannamei. L. vannamei was orally administrated by feeding with different mutants of Synechococcus for 10 days, and then challenged with WSSV. The cumulative mortality of vp19, vp28, vp (19 + 28) groups was lower than that of the positive control group (57.8%, 62.2%, 71.1%, respectively); vp (19 + 28) group had a better protection rate than vp19 and vp28 groups. The analysis of shrimp immunological parameters showed that, after WSSV injection, the activity of superoxide dismutase, phenol oxidase, catalase, and lysozyme in the hepatopancreas of vp19, vp28, and vp (19 + 28) groups was higher than in the positive group; at the same time, growth performances of L. vannamei of experimental groups were better than control groups. Results showed that the Synechococcus mutants harboring vp19, vp28, and vp (19 + 28) could be used both as drug and feed to also enhance the defensive ability of juvenile shrimp against WSSV infection by increasing the activity of immune related enzymes.

An attenuated Vibrio harveyi surface display of envelope protein VP28 to be protective against WSSV and vibriosis as an immunoactivator for Litopenaeus vannamei

Surface display can expose foreign antigenic protein on the surface of the vaccine vector, which is promising choice to elicit better immune responses. In this study, we apply this strategy to develop an immunoactivator by using a live attenuated Vibrio harveyi as an antigenic protein carrier with surface displayed VP28, a major envelope protein of white spot syndrome virus (WSSV), for two major pathogens of Litopenaeus vannamei. As a result, the immunoactivator showed self-limited growth and attenuation of virulence in shrimp via different inoculation routes either with single-repetitive dose or high dose. Moreover, either intramuscular injection or oral administration of the immunoactivator did not affect growth of shrimp body weight or cause pathologic changes. Additionally, the rapid immunoprotection was induced by the immunoactivator after administration for one week with highly relative percent survival (RPS) more than 90% against both V. harveyi and WSSV. Until 4 weeks post administration, the immunoactivator still possessed efficient immune effect with no less than 60% RPS for both pathogens. Totally, the attenuated V. harveyi surface displaying VP28 could be a potential immunoactivator for WSSV and vibriosis control in L. vannamei.

PED subunit vaccine based on COE domain replacement of flagellin domain D3 improved specific humoral and mucosal immunity in mice

Porcine epidemic diarrhea (PED) is an important re-emergent infectious disease and inflicts huge economic losses to the swine industry worldwide. To meet the pressing need of developing a safe and cost-efficient PED maternal vaccine, we generated three PED subunit vaccine candidates, using recombined Salmonella flagellin (rSF) as a mucosal molecular adjuvant. Domain D3 in rSF was replaced with COE domain of PEDV to generate rSF-COE-3D. COE fused to the flanking C'/N' terminal of rSF yielded rSF-COE-C and rSF-COE-N. As a result, rSF-COE-3D could significantly improve COE specific antibody production including serum IgG, serum IgA, mucosal IgA and PEDV neutralizing antibody. Furthermore, rSF-COE-3D elicited more CD3⁺CD8⁺ T cell and cytokine production of IFN-γ and IL-4 in mouse splenocytes. In summary, our data showed that rSF-COE-3D could improve specific humoral and mucosal immunity in mice, thus suggesting that rSF-COE-3D could be applied as a novel efficient maternal PED vaccine.