Recombinant Vibrio parahaemolyticus ghosts protect zebrafish against infection by Vibrio species

Identification of a potential antigen stimulating immune response against Vibrio parahaemolyticus infection in hybrid tilapia (Oreochromis aureus♂ × Oreochromis niloticus♀)

Vibrio parahaemolyticus (V. parahaemolyticus) is a major pathogen that causes substantial losses in the marine fishery. With the emergence of antibiotic resistance, vaccines have become the most effective approach against V. parahaemolyticus infection. Adhesion factors on the cell surface are pivotal in the colonization and pathogenesis of V. parahaemolyticus within the host, highlighting their potential as vaccine candidates. This study aims to assess the immunogenicity and potential of recombinant V. parahaemolyticus MAM7 (rMAM7) as a vaccine candidate. Initially, we cloned and purified the MAM7 protein of V. parahaemolyticus. Moreover, after 4 weeks of vaccination, the fish were challenged with V. parahaemolyticus. rMAM7 demonstrated a certain protective effect. Immunological analysis revealed that rMAM7 immunization-induced antibody production and significantly increased acid phosphatase (ACP) and alkaline phosphatase (AKP) activity in hybrid tilapia. Furthermore, serum bactericidal tests demonstrated a lower bacterial survival rate in the rMAM7 group compared to PBS and rTrxa. qRT-PCR results indicated that rMAM7 significantly upregulated CD4, CD8 and IgM gene expression, suggesting the induction of Th1 and Th2 responses in hybrid tilapia. Overall, these findings highlight the potential application of MAM7 from V. parahaemolyticus in the development of protein vaccines.

Construction of the flagellin F mutant of Vibrio parahaemolyticus and its toxic effects on silver pomfret (Pampus argenteus) cells

Vibrio parahaemolyticus causes diseases in aquatic organisms, leading to substantial financial losses to the aquaculture industry; its flagellin F (flaF) protein triggers severe inflammation in host cells. To enhance the understanding of the function of flaF in V. parahaemolyticus infection, in this study, a flaF-deficient mutant was constructed by employing two-step homologous recombination. The flaF-deficient mutant induced a significantly lower toll-like receptor 5 (TLR5) expression and apoptosis in fish intestinal epithelial cells than the wild-type V. parahaemolyticus. Furthermore, fluorescence labelling and microscopy analysis of TLR5 showed that V. parahaemolyticus and its mutant strain significantly enhanced TLR5 expression. Additionally, the findings suggest that flaF deletion did not significantly affect the expression of myeloid differentiation factor 88 (MyD88) and interleukin-8 (IL-8) induced by V.parahaemolyticus. In summary, V. parahaemolyticus induced a TLR5-dependent inflammatory response and apoptosis through MyD88, which was observed to be influenced by flaF deletion. In this study, we obtained stable mutants of V. parahaemolyticus via target gene deletion-which is a rapid and effective approach-and compared the induction of inflammatory response and apoptosis by V. parahaemolyticus and its mutant strain, providing novel perspectives for functional gene research in V. parahaemolyticus.

The role of flagellin F in Vibrio Parahaemolyticus-induced intestinal immunity and functional domain identification

The marine pathogen Vibrio parahaemolyticus has caused huge economic losses to aquaculture. Flagellin is a key bacterial virulence factor that induces an inflammatory response via activation of Toll-like receptor 5 (TLR5) signaling. Herein, to explore the inflammatory activity of V. parahaemolyticus flagellins (flaA, flaB, flaC, flaD, flaE, and flaF), we investigated their ability to induce apoptosis in a fish cell line. All six flagellins induced severe apoptosis. Moreover, treatment with V. parahaemolyticus flagellins increased TLR5 and myeloid differentiation factor 88 (MyD88) expression and the production of TNF-α and IL-8 significantly. This indicated that flagellins might induce a TLR5-meditated immune response via an MyD88-dependent pathway. FlaF exhibited the strongest immunostimulatory effect; therefore, the interaction between TLR5 and flaF was screened using the yeast two-hybrid system. A significant interaction between the two proteins was observed, indicating that flaF binds directly to TLR5. Finally, the amino acids that participate in the TLR5-flaF interaction were identified using molecular simulation, which indicated three binding sites. These results deepen our understanding of the immunogenic properties of flagellins from V. parahaemolyticus, which could be used for vaccine development in the future.

Bacterial Ghosts-Based Vaccine and Drug Delivery Systems

Bacterial ghosts (BGs) are empty bacterial envelopes of Gram-negative bacteria produced by controlled expressions of cloned gene E, forming a lysis tunnel structure within the envelope of the living bacteria. Globally, BGs have been used as vaccine delivery systems and vaccine adjuvants. There is an increasing interest in the development of novel delivery systems that are based on BGs for biomedical applications. Due to intact reservation of bacterial cell membranes, BGs have an inherent immunogenicity, which enables targeted drug delivery and controlled release. As carrier vehicles, BGs protect drugs from interference by external factors. In recent years, there has been an increasing interest in BG-based delivery systems against tumors, inflammation, and infection, among others. Herein, we reviewed the preparation methods for BGs, interactions between BGs and the host, and further highlighted research progress in BG development.

Immune response and protective efficacy of two new adjuvants, Montanide™ ISA 763B VG and Montanide™ GEL02, administered with a Streptococcus agalactiae ghost vaccine in Nile tilapia (Oreochromis niloticus)

Streptococcus agalactiae is one of the most important pathogens infecting tilapia worldwide and causes meningoencephalitis, septicemia and high mortalities with considerable losses. Various types of vaccines have been developed against S. agalactiae infection, such as inactivated vaccines, live attenuated vaccines and subunit vaccines. Bacterial ghosts (BGs) are nonliving, empty cell envelopes and have been reported as novel vaccine candidates. Therefore, the main aims of this study were to develop an S. agalactiae ghost vaccine (SAGV) and to evaluate the immune response and protective effect of SAGV against S. agalactiae with two novel adjuvants, Montanide™ ISA 763B VG and Montanide™ GEL02. Nile tilapia, mean weight 50 g, were divided into four groups as follows; 1) fish injected with PBS as control, 2) fish injected with the SAGV alone; 3) fish injected with the SAGV+Montanide™ ISA 763B VG; and 4) fish injected with SAGV+Montanide™ GEL02. Following vaccination, innate immunity parameters including serum lysozyme, myeloperoxidase, catalase, and bactericidal activity were all significantly enhanced. Moreover, specific serum IgM antibodies were induced and reached their highest level 2-8 weeks post vaccination. Importantly, the relative percent survival of tilapia vaccinated against the SAGV formulated with both adjuvants was 80-93%. Furthermore, the transcription of immune-related genes (IgM, TCRβ, IL-1β, IL-8 and TNFα) were up-regulated in tilapia after vaccination, indicating that both cellular and humoral immune responses were induced by these adjuvanted vaccines. In summary, Montanide™ ISA 763B VG and Montanide™ GEL02 can enhance immunoprotection induced by the SAGV vaccine against streptococcosis, demonstrating that both have value as potential adjuvants of fish vaccines.

Identification and functional analysis of the perforin-1 like gene in disease resistance in half smooth tongue sole (Cynoglossus semilaevis)

The pore-forming protein perforin is one of the effectors of cell-mediated killing via the granule exocytosis pathway. In this study, a genome-wide association study was conducted in Vibrio harveyi disease-resistant and disease-susceptible families of half smooth tongue sole (Cynoglossus semilaevis) to determine the genes accounting for host resistance, and a perforin homologue was identified, designated perforin-1 like (CsPRF1l). The full-length cDNA of CsPRF1l is 1835 bp, and encodes 514 amino acids. The CsPRF1l gene consists of 10 exons and 9 introns, spanning approximately 7 kb. The amino acid sequence of CsPRF1l shows 60.35, 54.03, 41.92, and 34.17% identities to Morone saxatilis PRF1l, Oryzias melastigma PRF1l, Danio rerio PRF1.5 and Homo sapiens PRF, respectively. Sequence analysis revealed the presence of membrane attack complex/perforin (MACPF) and C2 domains in CsPRF1l. Quantitative real-time PCR showed that CsPRF1l presented a higher intestinal expression level in disease-resistant families than in susceptible families. Tissue expression pattern analysis showed that CsPRF1l is present in most of the tested tissues and highly expressed in the intestine, brain, stomach and gills. After challenge with V. harveyi, CsPRF1l mRNA was markedly upregulated in the liver, spleen, kidney, intestine, gills and skin. In addition, the recombinant CsPRF1l protein exhibited obvious antimicrobial activity against V. harveyi in vitro and in a zebrafish model. Collectively, these data indicate that CsPRF1l modulates host immune defense against V. harveyi invasion and provide clues about the efficacy of rCsPRF1l in fish that will give rise to useful therapeutic applications for V. harveyi infection in C. semilaevis.