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.

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe respiratory disease in humans, with a case fatality rate of approximately 35%, thus posing a considerable threat to public health. A lack of approved vaccines or antivirals currently constitutes a barrier for controlling disease outbreaks and spread. In this study, we generated a replication-defective recombinant vesicular stomatitis virus expressing the MERS-CoV spike (S) protein (VSV/MERS). Uncleaved and cleaved S proteins were detected in VSV/MERS by western blotting. And VSV/MERS specifically transduced cells expressing human dipeptidyl peptidase 4, a receptor for MERS-CoV. To investigate the immunogenicity of VSV/MERS, mice were immunized intramuscularly with VSV/MERS and alum adjuvant. MERS-CoV S-specific IgG was detected in serum samples from immunized mice. These antibodies inhibited MERS entry in vitro, suggesting a protective efficacy of VSV/MERS immunity. The data demonstrate that VSV/MERS has potent immunogenicity and could serve as a novel potential vaccine platform for MERS in dromedary camels and human.

Riptortus pedestris possesses Burkholderia as gut symbiont in a symbiotic organ M4 midgut. To answer why Burkholderia symbionts are not eliminated by Riptortu s immune responses, we developed two hypotheses: (i) Burkholderia symbionts do not activate host innate immunity, or (ii) Burkholderia symbionts are resistant to th e host immune responses. For the first hypothesis, we compared the antimicrobial activities of the cultured Burkholderia-injected hemolymph and symbiotic Burkhol deria-injected hemolymphs. As a result, the symbiotic Burkholderia induced antim icrobial activity like the cultured Burkholderia, indicating the symbiotic cells are st ill immunogentic to host. However, when the activated hemolymph was treated to the Burkholderia cells, the symbiotic Burkholderia showed much higher susceptibi lity than the cultured Burkholderia. To understand molecular basis of these results, we purified antimicrobial peptides (AMPs) from Riptortus hemolymph. Similarly, the symbiotic Burkholderia exhibited the high susceptibility to the purified AMPs, riptocin and rip-defensin. To understand how symbiotic Burkholderia can survive in host in spite of their immuno-susceptibility, we examined the AMP expression i n the M4 midgut. Interestingly, the expression of AMPs is suppressed in the M4 mi dgut in comparison to that of the fat body. Finally, we proposed that the immuno-su sceptibility of Burkholderia symbiont helps them to retain in the symbiotic organ. Our in vivo data showing the rapid clearance of the symbiotic Burkholderia after inj ection to host Riptortus supports our proposal.

Canine parvovirus (CPV2) is one of the most virulent virus causing acute hemorrhagic enteritis and myocarditis in dogs. Infection mainly caused by the ingestion of virus through the mucosal route. Therefore, induction of mucosal immunity is essential in prevention of Canine Parvovirus (CPV2) infection. For safe and effective delivery of viral antigens to the mucosal immune system, a novel surface antigen display system for lactic acid bacteria using the poly-γ-glutamic acid synthetase A protein (pgsA) of Bacillus subtilis as an anchoring matrix was applied in order to display CPV2 antigen on the surface of the recombinant L. casei. Recombinant fusion proteins comprised of pgsA and the capsid protein (VP2-S1) showed stable expression in Lactobacillus casei. Surface localization of the fusion protein was verified by cellular fractionation analyses. Oral and nasal inoculations of recombinant L. casei into mice resulted in high levels of serum immunoglobulin G (IgG) and mucosal IgA, as demonstrated by ELISA using recombinant VP2-S1 proteins. Mice receiving intranasal immunization mounted higher antibody response than those receiving oral immunization. These results indicate that mucosal immunization with recombinant L. casei expressing CPV2 VP2-S1 protein on its surface provides an effective means for elicitation of strong antibody responses against CPV 2 VP2-S1.

Mycoplasma hyopneumoniae (M. hyopneumoniae) is one of the causative bacteria that can induce chronic enzootic pneumonia, resulting in low production in the swine industry. Potentiation of porcine reproductive and respiratory syndrome virus-induced pneumonia by M. hyopneumoniae has also been recognized. Although some available vaccines have been developed for prevention of M. hyopneumoniae infection, protective immunity is still poor. In this study, in order to provide valuable information on vaccine antigen, we investigated the immunogenicity of M. hyopneumoniae on mouse spleen cells. Concanavalin A (ConA) and lipopolysaccharide (LPS) were used for generation of activated T and B lymphocytes. M. hyopneumoniae made clusters of spleen cells and also affected the cellular activity and viability of spleen cells by alone or with mitogens. Of particular interest, it induced a significant increase in production of TNF-alpha in ConA- treated spleen cells, meaning T helper 1 response. In addition, cell size and mitochondrial membrane potential of M. hyopneumoniae–treated spleen cells were measured by flow cytometric analysis. M. hyopneumoniae did not affect the cell size by alone, whereas ConA or LPS profoundly increased the cell size. Taken together, M. hyopneumoniae significantly affect the cellular activity and cytokine production of spleen cells by alone or in a combination of ConA. This study provides valuable information for production of the vaccine against M. hyopneumoniae.

The silkworm-baculovirus expression system has distinct advantages, such as a high yield and safe usage in vertebrates. Here, we report a novel strategy for the large-scale production of a classical swine fever virus (CSFV) envelope glycoprotein E2 in the larvae of a baculovirus-infected silkworm, Bombyx mori. We constructed a recombinant B. mori nucleopolyhedrovirus (BmNPV) that expressed recombinant polyhedra together with the N-terminal 179 amino acids of CSFV E2 (E2ΔC). BmNPV-E2ΔC-infected silkworm larvae expressed native polyhedrin and approximately 44-kDa fusion protein that was detected using both anti-polyhedrin and anti-CSFV E2 antibodies. Electron and confocal microscopy both demonstrated that the recombinant polyhedra contained both the fusion protein and native polyhedrin were morphologically normal and contained CSFV E2ΔC. The CSFV E2ΔC antigen produced in BmNPV-E2ΔC-infected silkworm larvae reached 0.68 mg per ml of hemolymph and 0.53 mg per larva at 6 days post-infection. Six-week-old female BALB/c mice that were immunized with the E2ΔC protein purified from solubilized recombinant polyhedraelicited CSFV E2 antibodies, which indicated that the CSFV E2ΔC protein from recombinant polyhedra was immunogenic. The virus neutralization test showed that the serum from mice that were treated with E2ΔC protein from recombinant polyhedra contained significant levels of virus neutralization activity. These results demonstrate that the present strategy can be used for the large-scale production of CSFV E2 antigen.