Subunit vaccines are being developed as a potential therapy for preventing microbial pathogen infection. In this study, the immunogenicity of recombinant Brucella (B.) abortus Fe/Mn superoxide dismutase (rFe/Mn SOD) protein as a subunit vaccine against B. abortus was investigated in BALB/c mice model. Brucella Fe/Mn SOD gene was cloned into a pcold-TF DNA vector. The bacterial recombinant protein was expressed using the Escherichia coli DH5α strain with a size of 82.50 kDa. The western blotting assay showed that rFe/Mn SOD reacted with Brucella-positive serum, indicating the potential immunoreactivity of this recombinant protein. After the second and third vaccinations, the peripheral CD4+ T cell population was increased significantly in the rFe/Mn SOD-immunized mice group compared to the PBS control group. Moreover, immunization of this recombinant protein increased the CD4+ T cell population from the first vaccination to the third vaccination. Meanwhile, the CD8+ T cells were slightly enhanced after the second vaccination compared to the first vaccination and compared to control groups. Fourteen days after the bacterial infection, the splenomegaly and the number of bacteria in the spleen were evaluated. The result showed that both rFe/Mn SOD and positive control RB51 decreased the bacterial replication in the spleen and the splenomegaly compared to control groups. Altogether, these results suggested that rFe/Mn SOD could induce host immunity against B. abortus infection.

This study aimed to investigate whether bacterial ghosts (BGs), empty cell envelopes of a gram-negative bacterium, delivering envelope protein domain III (EDIII) of dengue virus (DENV) serotype 2 could induce protective immune responses against dengue infection. In this study, we constructed Salmonella Typhimurium BGs expressing and delivering EDIII (BG-EDIII) and evaluated these ghosts for their immunogenicity studies in C57BL/6 mice. Our results demonstrated that the mice vaccinated once orally with BG-EDIII followed by an intramuscular boosting with a recombinant EDIII protein elicited significantly higher humoral and cell-mediated immune responses compared to the BGs alone vaccinated group (p<0.001). Upon challenge with DENV2, significantly lower viral load and liver damage was observed in BG-EDIII vaccinated group than BGs alone control group (p<0.05). The outcomes of this study revealed the ability of BG- EDIII to stimulate immune response with no observable damage to the vital organs.

This study aims to investigate the effects of exogenous succinic acid (SCA) on Brucella (B.) abortus infection in macrophage RAW 264.7 cells and ICR mice. Firstly, the in vitro experiment was conducted by MTT cytotoxicity and bacterial internalization assay to evaluate the uptake of B. abortus into macrophage cells. Two non-cytotoxic concentrations of SCA demonstrated attenuated invasion of Brucella into macrophages at 30 and 45 min post- infection (pi). Secondly, ICR mice were treated with SCA and infected with B. abortus. On day-14 pi, spleen and blood serum were collected to evaluate the bacterial burden and total spleen weight as well as the production of cytokine/chemokine, respectively. The results showed that SCA treatment promoted bacterial growth and reduced the total spleen weight in mice. Furthermore, SCA treatment increased the level of IL-10 cytokine in the sera, while dampening the production of MCP-1 chemokine compared to the control. The results of bacterial load in spleen and spleen weight together with cytokine/chemokine production profile in the sera indicated that SCA induced the host anti-inflammatory response which is beneficial for the survival of Brucella. Therefore, these findings suggest that SCA contributed to host immunity against Brucella infection and the emerging potential topic-immunometabolism should be invested for further investigations.

Salmonella Enteritidis (SE) infection, one of a major foodborne disease remains considerable public health concerns globally. In this study, we have constructed that the genetically inactivated SE ghost vaccine candidate, JOL2220 (Δlon ΔcpxR Δasd), which express the immunogenic hemagglutinin portion (HA1) of H1N1 virus on the Salmonella surface. The lysis gene cassette, holin-endolysin system originated from double DNA bacteriophage λ was cloned into the ghost vector plasmid pJHL464, which activated under the control of the convergent promoter system. Scanning electronic microscopic examination revealed that transmembrane tunnels of JOL2220 was formed following the 48 hr of the lysis mediated by the holin-endolysin system. In vitro expression of HA1 antigenic protein was also determined by Western blot analysis. The Chickens immunized with JOL2220 ghost via intramuscular and oral routes showed significant increase in IgG level against both SE and HA1 antigen. Further, we observed markedly enhancement of lymphocyte proliferation and T-cell differentiation in the primed PBMC of the immunized chicken, compared to those in the control group. Collectively, the results indicated that the SE ghosts expressing HA1 antigen may have immunostimulatory properties against Salmonella and influenza infection where the chicken is the predominant reservoir.

This study investigated the efficacy of four Brucella (B.) abortus recombinant proteins, namely adenylate kinase (Adk), nucleoside diphosphate kinase (Ndk), 50S ribosomal protein (L7/L12) and preprotein translocase subunit (SecB), as a combined subunit vaccine (CSV) against B. abortus infection in BALB/c mice. Immunoblotting assay showed that these four recombinant proteins as well as pcold-TF vector reacted individually with Brucella-positive serum, but not with Brucella-negative serum. The peripheral blood CD4+ T cell population was increased in CSV-immunized mice compared to PBS and pcold-TF vector groups. In addition, CSV and pcold-TF groups displayed induced IgG1 and IgG2a antibodies production compared to PBS and RB51 group, whereas IgG2a titer was higher than IgG1 titer in CSV group. The secretion profiles of IgG1 and IgG2a production together with an enhancement of CD4+ T cell population suggested that CSV did not only induce T helper 1 (Th1) T cell immunity but also humoral immunity. Therein, Th1 T cell immunity is more predominant in eliminating intracellular bacteria B. abortus. Furthermore, CSV immunization significantly reduced the bacterial burden in the spleen as well as the spleen weight in comparison to PBS and pcold-TF groups. Altogether, combination of these antigens could be potential to induce protective immunity against B. abortus infection in animals.

Shiga toxin 2e (Stx2e) has a pivotal role in the colonization and enterotoxicity of F18+Shiga toxin-producing Escherichia coli (STEC), which causes porcine edema disease (ED). In this study, a Stx2eA mutant, which has a Glu167Gln mutation in Stx2eA that inactivates N-glycosidase activity, was genetically engineered to evaluate its potential immunogenicity and protective efficacy. A significant increase in serum IgG1 (a Th2 indicator) was shown in mice immunized with the mutated Stx2eA. However, only 56% of the mice immunized with the toxoid (5 μg) survived following a challenge with a lethal dose 50 (LD50) of a virulent F18+STEC strain (JOL654), while mice immunized with Salmonella ghosts delivering selected antigens of F18+STEC showed an 86% survival rate. The results suggest that sole use of the mutated Stx2eA toxoid may not be an effective preventive strategy for the control of porcine ED.

We previously developed a novel attenuated Salmonella Typhimurium (S.Typhimurium) △lon△cpxR vaccine. This study was conducted in order to examine whether this vaccine could effectively protect growing piglets against Salmonella infection. Pregnant sows in group A were primed and boosted with the vaccine, whereas pregnant sows in group B received sterile PBS-sucrose. After farrowing, newborn piglets in groups A and B were challenged with a wild type virulent S. Typhimurium at three weeks of age. During the study, serum IgG titers of piglets in group A were significantly higher than those of piglets in group B (P<0.001). In addition, clinical signs were observed in 5.9% of piglets in group A during the entire experimental period after the challenge, while diarrhea was observed in 81.6% of piglets in group B. These results indicate that vaccination of the pregnant sows resulted in effective protection in piglets against Salmonella infection.