Passive Immunization Experiments Research Articles

Novel virulence factor Cba induces antibody-dependent enhancement (ADE) of Streptococcus suis Serotype 9 infection in a mouse model.

Streptococcus suis (SS) is a zoonotic pathogen that affects the health of humans and the development of the pig industry. The SS Cba protein is a collagen adhesin, and a few of its homologs are related to the enhancement of bacterial adhesion. We compared the phenotypes of SS9-P10, SS9-P10 cba knockout strains and its complementary strains in vitro and in vivo and found that knocking out the cba gene did not affect the growth characteristics of the strain, but it significantly reduced the ability of SS to form biofilms, adhesion to host cells, phagocytic resistance to macrophages and attenuated virulence in a mouse infection model. These results indicated that Cba was a virulence related factor of SS9. In addition, Mice immunized with the Cba protein had higher mortality and more serious organ lesions after challenge, and the same was observed in passive immunization experiments. This phenomenon is similar to the antibody-dependent enhancement of infection by bacteria such as Acinetobacter baumannii and Streptococcus pneumoniae. To our knowledge, this is the first demonstration of antibody-dependent enhancement of SS, and these observations highlight the complexity of antibody-based therapy for SS infection.

Immunogenicity of loop 3 of Omp34 from A. Baumannii in loopless C-lobe of TbpB of N. meningitidis

Acinetobacter baumannii is a common causative agent of nosocomial infections, with a mortality rate of 43% in infected patients. Due to the emergence of multidrug-resistant (MDR) strains, vaccine development has become necessary. Since the 34 kDa outer membrane protein Omp34 has been identified as a potential vaccine target, we implemented a hybrid antigen approach to target its extracellular loops. Using bioinformatic and structural analyses, we selected Loop 3 from Omp34 and displayed it on the loopless C-lobe (LCL) of TbpB of Neisseria meningitidis. The hybrid antigen and the LCL were produced and used to immunize mice for passive and active immunization and challenge experiments in which the reactivity of the sera was assessed by ELISAs, the bacterial load in the tissues measured and the survival of immunized mice compared. LCL was ineffective in immunization against A. baumannii thus the resulting immunity was due to the presence of Omp34 loop 3. It resulted in increased survival and a reduced bacterial load in the tissues compared to the control groups. The findings indicate that the immunogenicity of Omp34 loops can induce protection against A. baumannii infection, and it could probably be used as a vaccine candidate to control the pathogenesis of A. baumannii.

Development of a Novel Alzheimer's Disease Model Based on the Theory of the Toxic-conformer of Amyloid β

Development of therapeutics for Alzheimer's disease (AD) is an urgent research task. Amyloid β (Aβ) is one of the causative proteins of AD. Irie et al. identified a toxic conformer among the various structures of 42-mer Aβ (Aβ42). This conformer, which possesses a turn structure at the positions Glu22-Asp23, exhibits rapid oligomerization and potent neurotoxicity. By the generation of conformationally-specific antibodies against this toxic conformer of Aβ, elevation of the toxic conformer in the AD brain was strongly suggested. To investigate the pathogenic role of the toxic conformer in AD, passive immunization experiments against conventional AD model mice were conducted. Specific antibody administration improved the behavioral abnormalities observed in AD model mice without affecting senile plaque pathology. Next, knock-in mice exclusively producing the toxic conformer of Aβ were generated. These mice exhibited cognitive dysfunction and oligomerization of Aβ, which preceded the onset of the plaque deposition. Taken together, the toxic conformer of Aβ is confirmed to be involved in the pathogenesis of AD, and our knock-in mice could be useful in analyzing the Aβ oligomer-related pathology of AD.

Revisiting the Correlate of Reduced HIV Infection Risk in the Rv144 Vaccine Trial.

The RV144 vaccine trial is the only clinical study to have shown a modest but statistically significant decrease in HIV infection risk. RV144 and the subsequent studies identifying the level of V1V2-specific antibodies as a correlate of reduced infection risk are still controversial despite many papers supporting and expanding the initial study. We address these controversies and summarize active-immunization and passive-immunization experiments in nonhuman primates that support the initial finding.

Evaluating the efficacy of an attenuated Streptococcus equi ssp. zooepidemicus vaccine produced by multi-gene deletion in pathogenicity island SeseCisland_4

Streptococcus equi ssp. zooepidemicus (SEZ) is a pathogen associated with a wild range of animal species. Frequent outbreaks have occurred in recent years in pigs, horses, goats and dogs which is liable to infect humans. There is a lack of efficient vaccines against this disease and the occurrence of antibiotic resistance may render drug therapies ineffective. In this study, gene deletion mutant (ΔSEZ) in pathogenicity islands SeseCisland_4 was constructed. The mutant ΔSEZ had a 52-fold decrease in 50% lethal dose (LD50) and had less capacity to adhere epithelial cells. Importantly, immunization of mice with attenuated vaccine ΔSEZ at the dose of 102 colony-forming units (CFU) mL−1 elicited a significant humoral antibody response, with an antibody titer of 1:12 800. Therefore, 102 CFU mL−1 might be used as the appropriate immune dose for the attenuated vaccine ΔSEZ, which provided mice with efficient protection against virulent SEZ. In addition, the hyperimmune sera against 102 CFU mL−1 attenuated vaccine ΔSEZ could confer significant protection against virulent SEZ infection in the passive immunization experiment and exhibited efficient bactericidal activity in the whole blood assay. Meanwhile, no viable bacteria was detected in blood when mice were immunized with ΔSEZ at the dose of 102 CFU mL−1via hypodermic injection. Thereafter, the mutant ΔSEZ at the dose of 102 CFU mL−1 could confer significant protection in mice and had less negative effects on host, which could be an effective attenuated vaccine candidate for the prevention of SEZ.

Identification of a surface protective antigen, MAP of Streptococcus equi subspecies zooepidemicus

Streptococcus equi subspecies zooepidemicus (SEZ) is a zoonotic pathogen with adhesive and invasive properties. Due to the shortcomings of antibiotics and traditional inactivated vaccine, identifying protective antigens against SEZ would be helpful to the development of novel vaccines. MAP has been identified as a membrane anchored protein with a typical LPXTG-like cell wall-anchored motif. In present study, the objective was to evaluate the effects of MAP as a subunit vaccine with mouse model. The Western blot analysis shown that the purified recombinant MAP presented good immunoreactive to convalescent porcine sera against SEZ. The protein could elicit a remarkable humoral antibody response and protect 80% of mice against lethal dose challenge of SEZ in mouse model. Moreover, the hyperimmune sera against MAP could efficiently kill the bacteria in whole blood killing assay and conferred significant protection against SEZ in passive immunization experiments. This study suggests with good reasons that MAP could be a novel and effective vaccine candidate for SEZ.

Immunogenicity of anthrax recombinant peptides and killed spores in goats and protective efficacy of immune sera in A/J mouse model

Anthrax is primarily recognized as an affliction of herbivores with incubation period ranging from three to five days post-infection. Currently, the Sterne live-spore vaccine is the only vaccine approved for control of the disease in susceptible animals. While largely effective, the Sterne vaccine has several problems including adverse reactions in sensitive species, ineffectiveness in active outbreaks and incompatibility with antibiotics. These can be surmounted with the advent of recombinant peptides (non-living) next generation vaccines. The candidate vaccine antigens comprised of recombinant protective antigen (PA), spore-specific antigen (bacillus collagen-like protein of anthracis, BclA) and formaldehyde inactivated spores (FIS). Presently, little information exists on the protectivity of these novel vaccine candidates in susceptible ruminants. Thus, this study sought to assess the immunogenicity of these vaccine candidates in goats and evaluate their protectivity using an in vivo mouse model. Goats receiving a combination of PA, BclA and FIS yielded the highest antibody and toxin neutralizing titres compared to recombinant peptides alone. This was also reflected in the passive immunization experiment whereby mice receiving immune sera from goats vaccinated with the antigen combination had higher survival post-challenge. In conclusion, the current data indicate promising potential for further development of non-living anthrax vaccines in ruminants.

Anti-tau conformational scFv MC1 antibody efficiently reduces pathological tau species in adult JNPL3 mice

Tau, the main component of the neurofibrillary tangles (NFTs), is an attractive target for immunotherapy in Alzheimer’s disease (AD) and other tauopathies. MC1/Alz50 are currently the only antibodies targeting a disease-specific conformational modification of tau. Passive immunization experiments using intra-peritoneal injections have previously shown that MC1 is effective at reducing tau pathology in the forebrain of tau transgenic JNPL3 mice. In order to reach a long-term and sustained brain delivery, and avoid multiple injection protocols, we tested the efficacy of the single-chain variable fragment of MC1 (scFv-MC1) to reduce tau pathology in the same animal model, with focus on brain regional differences. ScFv-MC1 was cloned into an AAV delivery system and was directly injected into the hippocampus of adult JNPL3 mice. Specific promoters were employed to selectively target neurons or astrocytes for scFv-MC1 expression. ScFv-MC1 was able to decrease soluble, oligomeric and insoluble tau species, in our model. The effect was evident in the cortex, hippocampus and hindbrain. The astrocytic machinery appeared more efficient than the neuronal, with significant reduction of pathology in areas distant from the site of injection. To our knowledge, this is the first evidence that an anti-tau conformational scFv antibody, delivered directly into the mouse adult brain, is able to reduce pathological tau, providing further insight into the nature of immunotherapy strategies.

Protective humoral and CD4+ T cellular immune responses of Staphylococcus aureus vaccine MntC in a murine peritonitis model

Staphylococcus aureus can cause different types of diseases from mild skin infections to life-threatening sepsis worldwide. Owing to the emergence and transmission of multidrug-resistant strains, developing an impactful immunotherapy especially vaccine control approach against S. aureus infections is increasingly encouraged and supported. S. aureus manganese transport protein C (MntC), which is a highly-conserved cell surface protein, can elicit protective immunity against S. aureus and Staphylococcus epidermidis. In this study, we evaluated the humoral immune response and CD4+ T cell-mediated immune responses in a mouse peritonitis model. The results showed that MntC-specific antibodies conferred an essential protection for mice to reduce invasion of S. aureus, which was corroborated via the opsonophagocytic killing assay and passive immunization experiment in mice, and moreover MntC-induced Th17 played a remarkable part in preventing S. aureus infection since the MntC-induced protective immunity decreased after neutralization of IL-17 by antibody in vivo and the Th17 adoptive transferred-mice could partly resist S. aureus challenge. In conclusion, we considered that the MntC-specific antibodies and MntC-specific Th17 cells play cooperative roles in the prevention of S. aureus infection.

Passive Immunization of Farmed Fish.

The fast growth and potential of global aquaculture has necessitated the adoption of sustainable and welfare-oriented therapeutics and prophylactic strategies. Knowledge gathered from studies about maternal passive immunity in fish and fish-to-fish passive immunization experiments supports the concept of using therapeutic Abs (of piscine and other vertebrate origin) in aquaculture. Traditional Ab formats (IgG, IgM) are expensive and laborious to produce; however, the introduction of new rAb fragments and single-domain Abs have reinvigorated the concept of passive immunization. This review will focus primarily on farmed salmonids (salmon and trout) within a comparative context and will give an overview of the basic principles and scientific premises for the passive immunization strategy, including existing and emerging Ab therapeutics.

Streptococcus pneumoniae Transmission Is Blocked by Type-Specific Immunity in an Infant Mouse Model.

ABSTRACTEpidemiological studies on Streptococcus pneumoniae show that rates of carriage are highest in early childhood and that the major benefit of the pneumococcal conjugate vaccine (PCV) is a reduction in the incidence of nasopharyngeal colonization through decreased transmission within a population. In this study, we sought to understand how anti-S. pneumoniae immunity affects nasal shedding of bacteria, the limiting step in experimental pneumococcal transmission. Using an infant mouse model, we examined the role of immunity (passed from mother to pup) on shedding and within-litter transmission of S. pneumoniae by pups infected at 4 days of life. Pups from both previously colonized immune and PCV-vaccinated mothers had higher levels of anti-S. pneumoniae IgG than pups from non-immune or non-vaccinated mothers and shed significantly fewer S. pneumoniae over the first 5 days of infection. By setting up cross-foster experiments, we demonstrated that maternal passage of antibody to pups either in utero or post-natally decreases S. pneumoniae shedding. Passive immunization experiments showed that type-specific antibody to capsular polysaccharide is sufficient to decrease shedding and that the agglutinating function of immunoglobulin is required for this effect. Finally, we established that anti-pneumococcal immunity and anti-PCV vaccination block host-to-host transmission of S. pneumoniae. Moreover, immunity in either the donor or recipient pups alone was sufficient to reduce rates of transmission, indicating that decreased shedding and protection from acquisition of colonization are both contributing factors. Our findings provide a mechanistic explanation for the reduced levels of S. pneumoniae transmission between hosts immune from prior exposure and among vaccinated children.

Reproducing SIVΔnef vaccine correlates of protection: trimeric gp41 antibody concentrated at mucosal front lines.

Vaccination with SIVmac239Δnef provides robust protection against subsequent challenge with wild-type simian immunodeficiency virus (SIV), but safety issues have precluded designing an HIV-1 vaccine based on a live-attenuated virus concept. Safe immunogens and adjuvants that could reproduce identified immune correlates of SIVmac239Δnef protection therefore offer an alternative path for development of an HIV vaccine. Here we describe SIV envelope trimeric gp41 (gp41t) immunogens based on a protective correlate of antibodies to gp41t concentrated on the path of virus entry by the neonatal Fc receptor (FcRn) in cervical vaginal epithelium. We developed a gp41t immunogen-monophosphoryl lipid A adjuvant liposomal nanoparticle for intramuscular (i.m.) immunization and a gp41t-Fc immunogen for intranasal immunization for pilot studies in mice, rabbits, and rhesus macaques. Repeated immunizations to mimic persistent antigen exposure in infection elicited gp41t antibodies in rhesus macaques that were detectable in FcRn+ cervical vaginal epithelium, thus recapitulating one key feature of SIVmac239Δnef vaccinated and protected animals. Although this strategy did not reproduce the system of local production of antibody in SIVmac239Δnef-vaccinated animals, passive immunization experiments supported the concept that sufficiently high levels of antibody can be concentrated by the FcRn at mucosal frontlines, thus setting the stage for assessing protection against vaginal challenge by gp41t immunization.

Generation of Plasmodium falciparum parasite-inhibitory antibodies by immunization with recombinantly-expressed CyRPA.

BackgroundThe pathogenesis of malaria is primarily associated with blood-stage infection and there is strong evidence that antibodies specific for parasite blood-stage antigens can control parasitaemia. This provides a strong rationale for incorporation of asexual blood-stage antigen components into an effective multivalent malaria subunit vaccine. On the basis of available genome-wide transcriptomic and proteomic data, previously uncharacterized Plasmodium falciparum open reading frames were screened for new blood stage vaccine candidates. This has led to the identification of the cysteine-rich protective antigen (PfCyRPA), which forms together with PfRH5 and PfRipr a multiprotein complex that is crucial for erythrocyte invasion.MethodsGlycosylated and non-glycosylated variants of recombinant PfCyRPA were expressed and produced as secreted protein in mammalian cells. Adjuvanted formulations of purified PfCyRPA were tested to assess whether they can effectively elicit parasite inhibitory antibodies, and to investigate whether or not the glycosylation status affects antibody binding. For this purpose, two sets of PfCyRPA-specific mouse monoclonal antibodies (mAbs) have been raised and evaluated for functional activity.ResultsGenerated PfCyRPA-specific mAbs, irrespective of the immunogen’s glycosylation status, showed substantial parasite in vitro growth-inhibitory activity due to inhibition of erythrocyte invasion by merozoites. Furthermore, passive immunization experiments in P. falciparum infected NOD-scid IL2Rγnull mice engrafted with human erythrocytes demonstrated potent in vivo growth-inhibitory activity of generated mAbs.ConclusionsRecombinantly expressed PfCyRPA tested as adjuvanted vaccine formulations in mice elicited antibodies that significantly inhibit P. falciparum asexual blood stage parasite growth both in vitro and in vivo. These findings render PfCyRPA a promising blood-stage candidate antigen for inclusion into a multicomponent malaria subunit vaccine.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1213-x) contains supplementary material, which is available to authorized users.

Production of anti-LPS IgM by B1a B cells depends on IL-1β and is protective against lung infection with Francisella tularensis LVS.

The role of IL-1β and IL-18 during lung infection with the gram-negative bacterium Francisella tularensis LVS has not been characterized in detail. Here, using a mouse model of pneumonic tularemia, we show that both cytokines are protective, but through different mechanisms. Il-18-/- mice quickly succumb to the infection and showed higher bacterial burden in organs and lower level of IFNγ in BALF and serum compared to wild type C57BL/6J mice. Administration of IFNγ rescued the survival of Il-18-/- mice, suggesting that their decreased resistance to tularemia is due to inability to produce IFNγ. In contrast, mice lacking IL-1 receptor or IL-1β, but not IL-1α, appeared to control the infection in its early stages, but eventually succumbed. IFNγ administration had no effect on Il-1r1-/- mice survival. Rather, Il-1r1-/- mice were found to have significantly reduced titer of Ft LPS-specific IgM. The anti-Ft LPS IgM was generated in a IL-1β-, TLR2-, and ASC-dependent fashion, promoted bacteria agglutination and phagocytosis, and was protective in passive immunization experiments. B1a B cells produced the anti-Ft LPS IgM and these cells were significantly decreased in the spleen and peritoneal cavity of infected Il-1b-/- mice, compared to C57BL/6J mice. Collectively, our results show that IL-1β and IL-18 activate non-redundant protective responses against tularemia and identify an essential role for IL-1β in the rapid generation of pathogen-specific IgM by B1a B cells.

Passive transfer of serum from tilapia vaccinated with a Vibrio vulnificus vaccine provides protection from specific pathogen challenge

Vibrio vulnificus is a Gram-negative bacterium that has been associated with disease losses in some aquaculture reared fish species. Vaccination has proven effective for reducing the impact of this disease and research has suggested that specific antibodies are important for protective immunity. The present study determined the role of antibodies specific for V. vulnificus in protection by passive immunization and identified components of the bacterium the antibodies specifically recognize. Antiserum was generated by vaccinating hybrid tilapia with a formalin killed V. vulnificus ARS-1-Br-09 bacterin. Two passive immunization experiments were conducted, with and without heat inactivation of the antiserum. In both experiments, hybrid tilapia (mean weight, 6.5 g) were passively immunized by intraperitoneal injection of antiserum or control serum and then challenged with homologous V. vulnificus 24 h post-immunization. Following the challenge, relative percent survival values of 86 and 90 were obtained for tilapia passively immunized with non-heated and heat inactivated antiserum, respectively. Cell lysates and lipopolysaccharide preparations from V. vulnificus ARS-1-Br-09 and a heterologous isolate (CECT 4601) were probed with the antiserum and control serum by western blot analyses to determine the specificity of the antibodies. The antibodies exhibited specificity to proteins of both isolates and to the lipopolysaccharide of only the homologous isolate. The results supported a role of specific antibodies in the protection of tilapia against V. vulnificus, and suggested that shared immunogenic antigens were involved in protection previously described against heterologous isolates.

Immunization against a merozoite sheddase promotes multiple invasion of red blood cells and attenuates Plasmodium infection in mice.

BackgroundSubtilisin-like protease 2 (SUB2) is a conserved serine protease utilized by Plasmodium parasites as a surface sheddase required for successful merozoite invasion of host red blood cells and has been implicated in ookinete invasion of the mosquito midgut. To determine if SUB2 is a suitable vaccine target to interfere with malaria parasite development, the effects of SUB2-immunization on the Plasmodium life cycle were examined in its vertebrate and invertebrate hosts.MethodsSwiss Webster mice were immunized with SUB2 peptides conjugated to Keyhole limpet hemocyanin (KLH) or KLH alone, and then challenged with Plasmodium berghei. To determine the effects of immunization on parasite development, infected mice were evaluated by blood film and Giemsa staining. In addition, collected immune sera were used to perform passive immunization experiments in non-immunized, P. berghei-infected mice to determine the potential role of SUB2 in parasite development in the mosquito.ResultsFollowing P. berghei challenge, SUB2-immunized mice develop a lower parasitaemia and show improved survival when compared to control immunized mice. Moreover, SUB2 immunization results in an increase in the number of multiply invaded red blood cells, suggesting that SUB2 antibodies interfere with merozoite invasion. Passive immunization experiments imply that SUB2 may not have a major role in ookinete invasion, but this requires further investigation.ConclusionBy interfering with red blood cell invasion, immunization against SUB2 limits malaria parasite development and confers protection from severe malaria. Together, these results provide proof-of-principle evidence for future investigation into the use of SUB2 as a vaccine or drug target to interrupt parasite development in more relevant human malaria models.Electronic supplementary materialThe online version of this article (doi:10.1186/1475-2875-13-313) contains supplementary material, which is available to authorized users.

Is an HIV vaccine achievable? - Pros

The development of an HIV/ AIDS vaccine has been a long and difficult endeavor, which so far was met with a great many failures. New, recent advances may however change the deal. The RV144 clinical trial in Thailand showed that a canarypox-gp120 prime-boost vaccination regimen had a modest 31% efficacy at 42 months after vaccination, but protection was as high as 60% at 6 months after vaccination. A series of new trials is expected to take place in the near future to try to improve these numbers using a more potent vector than canarypox, gp140 rather than gp120, a water-in-oil adjuvant rather than aluminium salts, and increasing the number of booster immunizations. Protection in the RV144 trial correlated with the induction of antibodies (Ab) to the V2 region of gp120, not with neutralizing Abs. A major difficulty met in the development of an efficacious HIV vaccine has indeed been to design proper immunogens able to elicit broadly neutralizing Abs (bnAbs) that can neutralize a wide range of circulating virus strains. BnAbs are highly protective, as demonstrated by passive immunization experiments and by vectored immunoprophylaxis experiments using AAV as a vector in animal models such as macaques or humanized mice. Their efficacy in humans should be tested soon in upcoming clinical trials. On another hand, the report that monkeys immunized with a simian CMV-SIV vaccine can clear SIV infection following viral challenge has emphasized the importance of self-renewing, long-lasting memory TEM cells that can differentiate into specific effector T cells and control provirus activation, eventually resulting in the clearance of infection. A HIV vaccine that could elicit both a bnAb response and the formation of specific TEM cells would obviously be an ideal vaccine. It might even offer hopes for a cure of HIV infection when used therapeutically in HIV-infected persons. The development of such a vaccine is still long and difficult but may not to be an unrealistic goal.

Development of Leptospira in vitro potency assays: EU/industry experience and perspectives

Nobivac® Lepto (MSD Animal Health) is a non-adjuvanted canine leptospirosis vaccine containing inactivated whole cells of Leptospira interrogans serogroup Canicola serovar Portlandvere and L. interrogans serogroup Icterohaemorrhagiae serovar Copenhageni. The current standard in vivo potency test is a hamster challenge test associated with major drawbacks such as animal suffering and poor reproducibility. Here, the quantification of antigenic mass by ELISA as a new in vitro potency test is described, supporting the 3Rs concept (replacement, reduction, and refinement of animal tests) and in accordance with European Pharmacopoeia Monograph 0447 (Canine Leptospirosis Vaccine [Inactivated]). The two corresponding sandwich ELISAs are based on monoclonal antibodies specific for immunodominant leptospiral lipopolysaccharide epitopes. Protection in passive immunization experiments demonstrate that these monoclonal antibodies recognize key protective antigens in currently licensed human and veterinary whole cell Leptospira vaccines. The high precision and robustness renders the two ELISAs much more reliable correlates of potency in dogs than the hamster potency test. The recent approval of these assays for a new canine leptospirosis vaccine is an important contribution to the 3Rs in quality control testing of Leptospira vaccines.

Protective Efficacy of Neutralizing Monoclonal Antibodies in a Nonhuman Primate Model of Ebola Hemorrhagic Fever

Ebola virus (EBOV) is the causative agent of severe hemorrhagic fever in primates, with human case fatality rates up to 90%. Today, there is neither a licensed vaccine nor a treatment available for Ebola hemorrhagic fever (EHF). Single monoclonal antibodies (MAbs) specific for Zaire ebolavirus (ZEBOV) have been successfully used in passive immunization experiments in rodent models, but have failed to protect nonhuman primates from lethal disease. In this study, we used two clones of human-mouse chimeric MAbs (ch133 and ch226) with strong neutralizing activity against ZEBOV and evaluated their protective potential in a rhesus macaque model of EHF. Reduced viral loads and partial protection were observed in animals given MAbs ch133 and ch226 combined intravenously at 24 hours before and 24 and 72 hours after challenge. MAbs circulated in the blood of a surviving animal until virus-induced IgG responses were detected. In contrast, serum MAb concentrations decreased to undetectable levels at terminal stages of disease in animals that succumbed to infection, indicating substantial consumption of these antibodies due to virus replication. Accordingly, the rapid decrease of serum MAbs was clearly associated with increased viremia in non-survivors. Our results indicate that EBOV neutralizing antibodies, particularly in combination with other therapeutic strategies, might be beneficial in reducing viral loads and prolonging disease progression during EHF.

Evaluation of the immunogenicity and the protective efficacy of a novel identified immunogenic protein, SsPepO, of Streptococcus suis serotype 2

Streptococcus suis serotype 2 (S. suis 2) is an important porcine and human pathogen. Some proteins secreted by S. suis 2 are thought to play important roles in the pathogenesis of this organism and in its induced immune response. SsPepO has been previously identified as a secretary immunogenic protein using immunoproteomic techniques. In this study, we confirmed that the sequence of this protein is highly conserved in S. suis 2 and compared it with its homologues in other pathogens. To test the protective efficacy of SsPepO in animal models, the recombinant SsPepO protein was used to immunize mice and pigs. The results demonstrated that it could elicit a strong humoral antibody response and confer significant protection against challenge with a lethal dose of S. suis 2 in mice and pig models. In addition, the antisera against rSsPepO could efficiently inhibit bacterial growth in a whole blood assay and conferred significant protection against S. suis 2 infection in passive immunization experiments. Our findings suggest that SsPepO plays an important role in the pathogenesis of S. suis 2 and would be a promising subunit vaccine candidate.