Characterization of in vitro viral neutralization targets of highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) in alveolar macrophage and evaluation of protection potential against HP-PRRSV challenged based on combination of HP-PRRSV-structure proteins in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant threat to the global pork industry, resulting in substantial economic losses. Current control measures rely on modified live virus (MLV) vaccines with safety concerns. However, the lack of consensus on protective PRRSV antigens is impeding the development of effective and safety subunit vaccines. In this study, we conducted in vitro virus neutralization (VN) assays in MARC-145 and CRL-2843CD163/CD169 cell lines and primary porcine alveolar macrophages (PAMs) to systemically identify PRRSV structural proteins (SPs) recognized by virus-neutralizing antibodies in hyperimmune serum collected from piglets infected with highly pathogenic PRRSV (HP-PRRSV). Additionally, piglets immunized with different combinations of recombinant PRRSV-SPs were challenged with HP-PRRSV to evaluate their in vivo protection potential. Intriguingly, different in vitro VN activities of serum antibodies elicited by each PRRSV SP were observed depending on the cell type used in the VN assay. Notably, antibodies specific for GP3, GP4, and M exhibited highest in vitro VN activities in PAMs, correlating with complete protection (100% survival) against HP-PRRSV challenge in vivo after immunization of piglets with combination of GP3, GP4, M and N (GP3/GP4/M/N). Further analysis of lung pathology, weight gain, and viremia post-challenge revealed that the combination of GP3/GP4/M/N provided superior protective efficacy against severe infection. These findings underscore the potential of this SP combination to serve as an effective PRRSV subunit vaccine, marking a significant advancement in pork industry disease management.

A Poly Aptamer Encoded DNA Nanocatcher Informs Efficient Virus Trapping

Broad-spectrum antiviral platforms are always desired but still lack the ability to cope with the threats to global public health. Herein, we develop a poly aptamer encoded DNA nanocatcher platform that can trap entire virus particles to inhibit infection with a broad antiviral spectrum. Ultralong single-stranded DNA (ssDNA) containing repeated aptamers was synthesized as the scaffold of a nanocatcher via a biocatalytic process, wherein mineralization of magnesium pyrophosphate on the ssDNA could occur and consequently lead to the formation of nanocatcher with interfacial nanocaves decorated with virus-binding aptamers. Once the viruses were recognized by the apatmers, they would be captured and trapped in the nanocaves via multisite synergistic interactions. Meanwhile, the size of nanocatchers was optimized to prevent their cellular uptake, which further guaranteed inhibition of virus infection. By taking SARS-CoV-2 variants as a model target, we demonstrated the broad virus-trapping capability of a DNA nanocatcher in engulfing the variants and blocking the infection to host cells.

Identification of neutralizing epitopes on the D/A domain of the E2 glycoprotein of classical swine fever virus

Classical swine fever virus (CSFV) shares high antigenic homology with other members of the genus Pestivirus. Because several pestivirus species can also infect swine, eliciting cross-reactive antibodies, it is important to define CSFV-specific epitopes for the differential diagnosis of classical swine fever (CSF) by serology. For this purpose, epitope mapping of seven monoclonal antibodies (mAbs), recognizing sites on the D/A domain of glycoprotein E2, was performed using recombinant expressed antigenic domains and mutants of E2, as well as an overlapping peptide library. Three CSFV-specific epitopes, i.e., 780-IEEMGDDFGFGLCPF-794, 810-NGSAFYLVCPIGWTG-824, and 846-REKPF-850, were identified within the D/A domain of E2. Site-directed mutagenesis further confirmed that residues 783-MGD-785, 789-FGLCPF-794, 813-AFYLVCPIGWTG-824, and 846-REK-848 were critical residues in these regions. In addition, a F789S difference within the epitope 780-IEEMGDDFGFGLCPF-794 was responsible for the absence of binding of two mAbs to the E2 protein of the live attenuated CSFV vaccine strain Riems. Structural modeling revealed that, the three epitopes are located near each other, suggesting that they may form a more complex conformational epitope on the D/A domain in vivo. Six of the mAbs neutralized viruses of diverse genotypes, indicating that the target epitopes are involved in virus interaction with cells. The binding of CSFV to cells was significantly reduced after pre-incubation with either truncated E2 proteins comprising the D/A domain or with the CSFV-specific mAbs targeting the domain D/A. These epitopes identified on the D/A domain are important targets for virus neutralization that might be involved in the early steps of CSFV infection. These findings reveal potential candidates for improving the differential diagnosis of pestiviruses by serology.

Multivariate analysis reveals that BVDV field isolates do not show a close VN-based antigenic relationship to US vaccine strains

OBJECTIVE

Evaluate bovine viral diarrhea virus (BVDV) antigenicity by using virus neutralization titers (VNT) analyzed using the principal component analysis (PCA) from antisera generated against US-based vaccine strains against both US-origin field isolates and non-US-origin field isolates.

RESULTS

Data from both independent analyses demonstrated that several US-origin and non-US-origin BVDV field isolates appear to be antigenically divergent from the US-based vaccine strains. Results from the combined analysis provided greater insight into the antigenic diversity observed among BVDV isolates. Data from this study further support genetic assignment into BVDV subgenotypes, as well as strains within subgenotypes is not representative of antigenic relatedness. PCA highlights isolates that are antigenically divergent from members of the same species and subgenotype and conversely isolates that belong to different subgenotypes have similar antigenic characteristics when using antisera from US-based vaccine isolates.

Antigenic diversity of type 1 polioviruses and its implications for the efficacy of polio vaccines

Inactivated Polio Vaccines (IPV) and live Oral Polio Vaccine (OPV) were introduced in the mid-20th century, and their coordinated worldwide use led to almost complete elimination of the disease, with only one serotype of poliovirus remaining endemic in just two countries. Polio eradication will lead to discontinuation of OPV use and its replacement with IPV or other vaccines that are currently under development that will need to be tested in clinical trials. Despite decades of research, questions remain about the serological correlates of polio vaccine efficacy, specifically whether the vaccines are equally protective against immunologically different strains of the same serotype. The absence of significant morbidity does not allow use of a protection endpoint in clinical trials, so the answer could be obtained only by using surrogate markers such as immunogenicity. In this study, a panel of wild and vaccine-derived polioviruses of serotype 1 were tested in neutralization assays with sera from vaccine-immunized individuals. The results demonstrated that there was a significant difference in titers of neutralizing antibodies in human sera when measured against different strains. When measured with a homologous strain used for vaccine manufacture all subjects had detectable levels of antibodies, while neutralization tests with some heterologous strains failed to detect neutralizing antibodies in a number of subjects. Administration of a booster dose of IPV led to a significant increase in neutralizing titers against all strains. Results of the experiments using animal sera, performed to obtain more information on protectivity of neutralizing antibodies against heterologous strains, were consistent with the results obtained in the assays using human sera. These results are discussed in the context of serological biomarkers of protection against poliomyelitis, suggesting that potency of vaccines made from serologically different strains should be determined against both homologous and heterologous challenge viruses.

Influenza subtype-specific maternal antibodies protect offspring against infection but inhibit vaccine-induced immunity and protection in mice

Following influenza A virus (IAV) infection or vaccination during pregnancy, maternal antibodies are transferred to offspring in utero and during lactation. The age and sex of offspring may differentially impact the transfer and effects of maternal immunity on offspring. To evaluate the effects of maternal IAV infection on immunity in offspring, we intranasally inoculated pregnant mice with sublethal doses of mouse-adapted (ma) H1N1, maH3N2, or media (mock) at embryonic day 10. In offspring of IAV-infected dams, maternal subtype-specific antibodies peaked at postnatal day (PND) 23, remained detectable through PND 50, and were undetectable by PND 105 in both sexes. When offspring were challenged with homologous IAV at PND 23, both male and female offspring had greater clearance of pulmonary virus and less morbidity and mortality than offspring from mock-inoculated dams. Inactivated influenza vaccination (IIV) against homologous IAV at PND 23 caused lower vaccine-induced antibody responses and protection following live virus challenge in offspring from IAV than mock-infected dams, with this effect being more pronounced among female than male offspring. At PND 105, there was no impact of maternal infection status, but vaccination induced greater antibody responses and protection against challenge in female than male offspring of both IAV-infected and mock-inoculated dams. To determine if maternal antibody or infection interfered with vaccine-induced immunity and protection in early life, offspring were vaccinated and challenged against a heterosubtypic IAV (i.e., different IAV group than dam) at PND 23 or 105. Heterosubtypic IAV maternal immunity did not affect antibody responses after IIV or protection after live IAV challenge of vaccinated offspring at either age. Subtype-specific maternal IAV antibodies, therefore, provide protection independent of offspring sex but interfere with vaccine-induced immunity and protection in offspring with more pronounced effects among females than males.

Receptor-binding domain recombinant protein on alum-CpG induces broad protection against SARS-CoV-2 variants of concern

We conducted preclinical studies in mice using a yeast-produced SARS-CoV-2 RBD subunit vaccine candidate formulated with aluminum hydroxide (alum) and CpG deoxynucleotides. This formulation is equivalent to the Corbevax^TM vaccine that recently received emergency use authorization by the Drugs Controller General ofIndia. We compared the immune response of mice vaccinated with RBD/alum to mice vaccinated with RBD/alum + CpG. We also evaluated mice immunized with RBD/alum + CpG and boosted with RBD/alum. Mice were immunized twice intramuscularly at a 21-day interval. Compared to two doses of the /alum formulation, the RBD/alum + CpG vaccine induced a stronger and more balanced Th1/Th2 cellular immune response, with high levels of neutralizing antibodies against the original Wuhan isolate of SARS-CoV-2 as well as the B.1.1.7 (Alpha), B.1.351 (Beta), B.1.617.2 and (Delta) variants. Neutralizing antibody titers against the B.1.1.529 (BA.1, Omicron) variant exceeded those in human convalescent plasma after Wuhan infection but were lower than against the other variants. Interestingly, the second dose did not benefit from the addition of CpG, possibly allowing dose-sparing of the adjuvant in the future. The data reported here reinforces that the RBD/alum + CpG vaccine formulation is suitable for inducing broadly neutralizing antibodies against SARS-CoV-2, including variants of concern.

Equine immunoglobulin fragment F(ab')2 displays high neutralizing capability against multiple SARS-CoV-2 variants

Neutralizing antibody-based passive immunotherapy could be an important therapeutic option against COVID-19. Herein, we demonstrate that equines hyper-immunized with chemically inactivated SARS-CoV-2 elicited high antibody titers with a strong virus-neutralizing potential, and F(ab')₂ fragments purified from them displayed strong neutralization potential against five different SARS-CoV-2 variants. F(ab')₂ fragments purified from the plasma of hyperimmunized horses showed high antigen-specific affinity. Experiments in rabbits suggested that the F(ab')₂ displays a linear pharmacokinetics with approximate plasma half-life of 47 h. In vitro microneutralization assays using the purified F(ab')₂ displayed high neutralization titers against five different variants of SARS-CoV-2 including the Delta variant, demonstrating its potential efficacy against the emerging viral variants. In conclusion, this study demonstrates that F(ab')₂ generated against SARS-CoV-2 in equines have high neutralization titers and have broad target-range against the evolving variants, making passive immunotherapy a potential regimen against the existing and evolving SARS-CoV-2 variants in combating COVID-19.

Human serum from SARS-CoV-2-vaccinated and COVID-19 patients shows reduced binding to the RBD of SARS-CoV-2 Omicron variant

BACKGROUND

The COVID-19 pandemic is caused by the betacoronavirus SARS-CoV-2. In November 2021, the Omicron variant was discovered and immediately classified as a variant of concern (VOC), since it shows substantially more mutations in the spike protein than any previous variant, especially in the receptor-binding domain (RBD). We analyzed the binding of the Omicron RBD to the human angiotensin-converting enzyme-2 receptor (ACE2) and the ability of human sera from COVID-19 patients or vaccinees in comparison to Wuhan, Beta, or Delta RBD variants.

METHODS

All RBDs were produced in insect cells. RBD binding to ACE2 was analyzed by ELISA and microscale thermophoresis (MST). Similarly, sera from 27 COVID-19 patients, 81 vaccinated individuals, and 34 booster recipients were titrated by ELISA on RBDs from the original Wuhan strain, Beta, Delta, and Omicron VOCs. In addition, the neutralization efficacy of authentic SARS-CoV-2 wild type (D614G), Delta, and Omicron by sera from 2× or 3× BNT162b2-vaccinated persons was analyzed.

RESULTS

Surprisingly, the Omicron RBD showed a somewhat weaker binding to ACE2 compared to Beta and Delta, arguing that improved ACE2 binding is not a likely driver of Omicron evolution. Serum antibody titers were significantly lower against Omicron RBD compared to the original Wuhan strain. A 2.6× reduction in Omicron RBD binding was observed for serum of 2× BNT162b2-vaccinated persons. Neutralization of Omicron SARS-CoV-2 was completely diminished in our setup.

CONCLUSION

These results indicate an immune escape focused on neutralizing antibodies. Nevertheless, a boost vaccination increased the level of anti-RBD antibodies against Omicron, and neutralization of authentic Omicron SARS-CoV-2 was at least partially restored. This study adds evidence that current vaccination protocols may be less efficient against the Omicron variant.

Antibody affinity maturation and cross-variant activity following SARS-CoV-2 mRNA vaccination: Impact of prior exposure and sex

BACKGROUND

Limited knowledge exists regarding antibody affinity maturation following mRNA vaccination in naïve vs. COVID-19 recovered individuals and potential sex differences.

METHODS

We elucidated post-vaccination antibody profiles of 69 naïve and 17 COVID-19 convalescent adults using pseudovirus neutralization assay (PsVNA) covering SARS-CoV-2 WA-1, variants of concern (VOCs) and variants of interest (VOIs). Surface Plasmon Resonance (SPR) was used to measure antibody affinity against prefusion spike and receptor binding domain (RBD) and RBD mutants.

FINDINGS

Higher neutralizing antibodies were observed in convalescent vs. naïve adults against, WA-1, VOCs, and VOIs. Antibody binding to RBD and RBD mutants showed lower binding of post-vaccination sera from naïve compared with convalescent individuals. Moreover, we observed early antibody affinity maturation in convalescent individuals after one vaccine dose and higher antibody affinity after two doses compared with the naïve group. Among the naïve participants, antibody affinity against the SARS-CoV-2 prefusion spike was significantly higher for males than females even though there were no difference in neutralization titers between sexes.

INTERPRETATION

This study demonstrates the impact of prior infection on vaccine-induced antibody affinity maturation and difference in antibody affinity between males and females. Further studies are needed to determine whether antibody affinity may contribute to correlates of protection against SARS-CoV-2 and its variants.

FUNDING

The antibody characterization work described in this manuscript was supported by FDA's Medical Countermeasures Initiative (MCMi) grant #OCET 2021-1565 to S.K and intramural FDA-CBER COVID-19 supplemental funds. The SPARTA program was supported by the National Institute of Allergy and Infectious Diseases (NIAID), U.S. National Institutes of Health (NIH), Department of Health and Human Services contract 75N93019C00052, and the University of Georgia (US) grant UGA-001. T.M.R is also supported by the Georgia Research Alliance (US) grant GRA-001. The CTRU was supported by the National Center for Advancing Translational Sciences of the National Institutes of Health under Award Number UL1TR002378.

Use of multivariate analysis to evaluate antigenic relationships between US BVDV vaccine strains and non-US genetically divergent isolates

Bovine viral diarrhea virus (BVDV) comprises two species, BVDV-1 and BVDV-2. But given the genetic diversity among pestiviruses, at least 22 subgenotypes are described for BVDV-1 and 3-4 for BVDV-2. Genetic characterization is generally accomplished through complete or partial sequencing and phylogeny, but it is not a reliable method to define antigenic relationships. The traditional method for evaluating antigenic relationships between pestivirus isolates is the virus neutralization (VN) assay, but interpretation of the data to define antigenic relatedness can be difficult to discern for BVDV isolates within the same BVDV species. Data from this study utilized a multivariate analysis for visualization of VN results to analyze the antigenic relationships between US vaccine strains and field isolates from Switzerland, Italy, Brazil, and the UK. Polyclonal sera were generated against six BVDV strains currently contained in vaccine formulations, and each serum was used in VNs to measure the titers against seven vaccine strains (including the six homologous strains) and 23 BVDV field isolates. Principal component analysis (PCA) was performed using VN titers, and results were interpreted from PCA clustering within the PCA dendrogram and scatter plot. The results demonstrated clustering patterns among various isolates suggesting antigenic relatedness. As expected, the BVDV-1 and BVDV-2 isolates did not cluster together and had the greatest spatial distribution. Notably, a number of clusters representing antigenically related BVDV-1 subgroups contain isolates of different subgenotypes. The multivariate analysis may be a method to better characterize antigenic relationships among BVDV isolates that belong to the same BVDV species and do not have distinct antigenic differences. This might be an invaluable tool to ameliorate the composition of current vaccines, which might well be important for the success of any BVDV control program that includes vaccination in its scheme.

COVID-19 antibody donation using immunoadsorption: Report of two cases

For more than a year the whole world is suffering from the COVID-19 pandemic with no treatment option in sight. Administration of plasma from convalescent donors containing anti-SARS-CoV-2 antibodies, though promising according to case reports, failed to show a clear benefit in a greater number of trials. One reason could be varying and low antibody contents in a majority of plasma units hampering standardization and clinical efficacy. Besides, other plasma components unnecessarily transfused like coagulation factors might promote hypercoagulation seen in severe COVID-19 etiopathology. We therefore hypothesized that instead of collecting whole plasma units, convalescent donors could donate solely immunoglobulins by undergoing immunoadsorption, a mode of therapy regularly applied in autoimmune diseases. Here, we report the results of the first two antibody donations performed at the University Hospital Düsseldorf. In both cases, immunoadsorptions were very well tolerated with no side effects. Collected and neutralized eluates were concentrated using tangential flow filtration increasing the concentration of immunoglobulins 10fold as compared to peripheral blood and leading to probably eight times more neutralizing antibodies than in one plasma unit. Therefore, immunoadsorption can be used as a method of antibody donation. Whether these donated antibodies can be used as passive immunization in acutely infected patients remains to be elucidated.

Diverse contributions of avidity to the broad neutralization of Dengue virus by antibodies targeting the E dimer epitope

Antibodies (Abs) recognizing the Dengue virus (DENV) E dimer epitope (EDE) that potently neutralize all DENV serotypes are promising templates for vaccine design. As an important feature for some Abs is their bivalency, we sought to define the role avidity plays in neutralization by EDE Abs. We compared neutralization activity between bivalent IgGs and monovalent Ab fragments (Fabs) for two EDE Abs, A11 and C10. IgG forms of both Abs exhibited more potent neutralization activity than their counterpart Fabs, yet only for C10 was this enhanced activity associated with bivalent binding. A11 and C10 also exhibited differential binding profiles to DENV virus-like particles under acidic conditions mimicking the environment that triggers viral membrane fusion, suggesting that EDE Abs employ diverse neutralization mechanisms despite sharing an epitope. Delineating the full range of Ab binding modes and neutralization mechanisms against a single epitope may inform therapeutic approaches and refine vaccine design.

A highly specific and sensitive serological assay detects SARS-CoV-2 antibody levels in COVID-19 patients that correlate with neutralization

OBJECTIVE

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic challenges national health systems and the global economy. Monitoring of infection rates and seroprevalence can guide public health measures to combat the pandemic. This depends on reliable tests on active and former infections. Here, we set out to develop and validate a specific and sensitive enzyme linked immunosorbent assay (ELISA) for detection of anti-SARS-CoV-2 antibody levels.

METHODS

In our ELISA, we used SARS-CoV-2 receptor-binding domain (RBD) and a stabilized version of the spike (S) ectodomain as antigens. We assessed sera from patients infected with seasonal coronaviruses, SARS-CoV-2 and controls. We determined and monitored IgM-, IgA- and IgG-antibody responses towards these antigens. In addition, for a panel of 22 sera, virus neutralization and ELISA parameters were measured and correlated.

RESULTS

The RBD-based ELISA detected SARS-CoV-2-directed antibodies, did not cross-react with seasonal coronavirus antibodies and correlated with virus neutralization (R2 = 0.89). Seroconversion started at 5 days after symptom onset and led to robust antibody levels at 10 days after symptom onset. We demonstrate high specificity (99.3%; N = 1000) and sensitivity (92% for IgA, 96% for IgG and 98% for IgM; > 10 days after PCR-proven infection; N = 53) in serum.

CONCLUSIONS

With the described RBD-based ELISA protocol, we provide a reliable test for seroepidemiological surveys. Due to high specificity and strong correlation with virus neutralization, the RBD ELISA holds great potential to become a preferred tool to assess thresholds of protective immunity after infection and vaccination.

Avian anti-NS1 IgY antibodies neutralize dengue virus infection and protect against lethal dengue virus challenge

Dengue is the most prevalent arboviral disease in humans and a continually increasing global public health burden. To date, there are no approved antiviral therapies against dengue virus (DENV) and the only licensed vaccine, Dengvaxia, is exclusively indicated for individuals with prior DENV infection. Endothelial hyperpermeability and vascular leak, pathogenic hallmarks of severe dengue disease, can be directly triggered by DENV non-structural protein 1 (NS1). As such, anti-NS1 antibodies can prevent NS1-triggered endothelial dysfunction in vitro and pathogenesis in vivo. Recently, goose-derived anti-DENV immunoglobulin Y (IgY) antibodies were shown to neutralize DENV and Zika virus (ZIKV) infection without adverse effects, such as antibody-dependent enhancement (ADE). In this study, we used egg yolks from DENV-immunized geese to purify IgY antibodies specific to DENV NS1 epitopes. We determined that 2 anti-NS1 IgY antibodies, NS1-1 and NS1-8, were capable of neutralizing DENV infection in vitro. In addition, these antibodies did not cross-react with the DENV Envelope (E) protein nor enhance DENV or ZIKV infection in vitro. Intriguingly, NS1-8, but not NS1-1, partially blocked NS1-induced endothelial dysfunction in vitro while neither antibody blocked binding of soluble NS1 to cells. Finally, prophylactic treatment of mice with NS1-8 conferred significant protection against lethal DENV challenge. Although further research is needed to define the mechanism of action of these antibodies, our findings highlight the potential of anti-NS1 IgY as a promising prophylactic approach against DENV infection.

Multivariate analysis as a method to evaluate antigenic relationships between BVDV vaccine and field strains

Bovine viral diarrhea virus (BVDV) is comprised of two species, BVDV-1 and BVDV-2, but given the genetic diversity among pestiviruses, at least 21 subgenotypes are described for BVDV-1 and 4 for BVDV-2. Genetic characterization can be achieved through complete or partial sequencing and phylogeny, but antigenic characterization can be difficult to determine due to the antigenic diversity and cross-neutralization that exists among isolates. The traditional method for evaluating antigenic relationships between pestivirus isolates is the virus neutralization (VN) assay, but interpretation of the data to determine antigenic difference can be unclear. Data from this study utilized a multivariate analysis for visualization of VN results to analyze the antigenic relationships between vaccine strains and multiple field isolates. Polyclonal sera were generated against 6 BVDV strains currently contained in vaccine formulations, and each serum was used in VN's to measure the neutralizing antibody titers against 15 BVDV field isolates characterized as prevalent and divergent subgenotypes in the USA. Principal component analysis (PCA) were performed on the VN assay datasets, and results were interpreted from PCA clustering within the PCA dendrogram and scatter plot. The results demonstrated clustering patterns among isolates suggestive of antigenic differences. While expected, the BVDV-1 and BVDV-2 isolates did not cluster together and had the greatest spatial distribution. In addition, other BVDV isolates had distinct spatial patterns suggesting antigenically divergent isolates. This analysis provides an alternative and more efficient means to analyze large VN datasets to visualize antigenic relationships between pestivirus isolates. This analysis could be beneficial for vaccine development and evaluation of efficacy, since most vaccines cannot fully protect animals from the broad range diversity of BVDV viruses.

Hepatitis C virus vaccine design: focus on the humoral immune response

Despite the recent development of safe and highly effective direct-acting antivirals, hepatitis C virus (HCV) infection remains a significant health problem. In 2016, the World Health Organization set out to reduce the rate of new HCV infections by 90% by 2030. Still, global control of the virus does not seem to be achievable in the absence of an effective vaccine. Current approaches to the development of a vaccine against HCV include the production of recombinant proteins, synthetic peptides, DNA vaccines, virus-like particles, and viral vectors expressing various antigens. In this review, we focus on the development of vaccines targeting the humoral immune response against HCV based on the cumulative evidence supporting the important role of neutralizing antibodies in protection against HCV infection. The main targets of HCV-specific neutralizing antibodies are the glycoproteins E1 and E2. Recent advances in the knowledge of HCV glycoprotein structure and their epitopes, as well as the possibility of getting detailed information on the human antibody repertoire generated by the infection, will allow rational structure-based antigen design to target specific germline antibodies. Although obtaining a vaccine capable of inducing sterilizing immunity will be a difficult task, a vaccine that prevents chronic hepatitis C infections, a more realistic goal in the short term, would have a considerable health impact.

Serum Virus Neutralization Assay for Detection and Quantitation of Serum Neutralizing Antibodies to Influenza A Virus in Swine

The serum virus neutralization (SVN) assay is a serological test used to detect the presence and magnitude of functional systemic antibodies that prevent infectivity of a virus. The SVN assay is a highly sensitive and specific test that may be applied to influenza A viruses (IAV) in swine to measure the titer of neutralizing antibodies postexposure, postvaccination, or after passive transfer of maternally derived antibody (MDA). Conventional SVN methods performed in vitro are based on inhibition of virus infectivity in cell culture in the presence of neutralizing antibodies in serum. Titer determination may be based on the presence or absence of cytopathic effect or evidence of viral infection using an immunoreactive technique. The SVN assay is relatively inexpensive using standard laboratory equipment, although it requires cell culture, more time and labor, and technical skill to conduct the assay compared to other serological methods. The SVN test may be used to evaluate the level of serological cross-reactivity between IAV exposure or vaccine antisera and heterologous influenza viruses that may correlate with cross-protection in the host.

Development and Validation of a S1 Protein-Based ELISA for the Specific Detection of Antibodies against Equine Coronavirus

Equine coronavirus (ECoV) is considered to be involved in enteric diseases in foals. Recently, several outbreaks of ECoV infection have also been reported in adult horses from the USA, France and Japan. Epidemiological studies of ECoV infection are still limited, and the seroprevalence of ECoV infection in Europe is unknown. In this study, an indirect enzyme-linked immunosorbent assay (ELISA) method utilizing ECoV spike S1 protein was developed in two formats, and further validated by analyzing 27 paired serum samples (acute and convalescent sera) from horses involved in an ECoV outbreak and 1084 sera of horses with unknown ECoV exposure. Both formats showed high diagnostic accuracy compared to virus neutralization (VN) assay. Receiver-operating characteristic (ROC) analyses were performed to determine the best cut-off values for both ELISA formats, assuming a test specificity of 99%. Employing the developed ELISA method, we detected seroconversion in 70.4% of horses from an ECoV outbreak. Among the 1084 horse sera, seropositivity varied from 25.9% (young horses) to 82.8% (adult horses) in Dutch horse populations. Further, sera of Icelandic horses were included in this study and a significant number of sera (62%) were found to be positive. Overall, the results demonstrated that the ECoV S1-based ELISA has reliable diagnostic performance compared to the VN assay and is a useful assay to support seroconversion in horses involved with ECoV outbreaks and to estimate ECoV seroprevalence in populations of horses.

Effect of simultaneous administration of foot-and-mouth disease (FMD) and anthrax vaccines on antibody response to FMD in sheep

Purpose

Foot-and-mouth disease (FMD) and anthrax are important diseases in sheep. Vaccination is a favorable strategy against both infections. Simultaneous administration of vaccines does generally not impede the immune responses of each other, although there are some exceptions, and it may help reduce the labor and costs of vaccination as well as distress on animals. Although oil adjuvant FMD vaccine has been tried with live anthrax vaccine in cattle, there are no reports on the simultaneous use of both vaccines in sheep.

Materials and Methods

In this study, FMD seronegative sheep were used to investigate the impact of the simultaneous vaccination of FMD and anthrax on FMD antibody titers of sheep. Virus neutralization test and liquid phase blocking enzyme-linked immunosorbent assay were used to determine the antibody response to the FMD vaccine.

Results

The results demonstrated that both vaccines can be used simultaneously without any interference with the FMD response. Moreover, the simultaneous administration with anthrax vaccine had a stimulating effect on the early (day 7 post-vaccination) virus neutralization antibody response to the FMD vaccine.

Conclusion

The simultaneous use of the FMD and anthrax vaccines did not hinder the response to the FMD vaccine in sheep.

Isolation of HCV Neutralizing Antibodies by Yeast Display

Yeast surface display (YSD) enables efficient screening and selection of single chain variable fragments (scFvs) of heavy (V_H) and light (V_L) chains that bind to target antigen with different affinities. Assembly of a scFv library from cDNA usually involves adding different primers and linkers (Gly₄/Ser)₃ through multiple rounds of PCR amplification and purification. We describe here a simplified scFv assembly method by creating a modified YSD vector with a built-in linker that reduces the time of assembly and decreases accumulated base exchanges due to PCR errors. In addition, we describe a bias screening strategy toward maximizing novel antibodies of interest by a combination of memory B cell selection and depletion by binding to mutant antigens that do not bind to previously identified monoclonal antibodies.

Overview of diagnostic tools for Capripox virus infections

Capripox viruses are the causative agents of important animal diseases in cattle (Lumpy Skin Disease), sheep (Sheeppox) and goats (Goatpox) with severe socio-economic impact in case of wide scale outbreaks. Therefore there is a constant need for adequate diagnostic tools. The assays must be fit-for-purpose to identify the virus quickly and correctly and to be useful for surveillance and monitoring at different stages of an epidemic. Different diagnostic performance characteristics are required depending on the situation and the test purpose. The need for high throughput, high specificity/sensitivity and the capability for differentiating field virus strains from vaccine strains drives the development of new and better assays preferably with an advantageous cost-benefit balance. This review aims to look at existing and new virological and serological diagnostic tools used in the control against diseases caused by Capripox viruses.

Characterization of a PCV2d-2 isolate by experimental infection of pigs

Porcine circovirus type 2 (PCV2), a highly prevalent, economically important swine pathogen is classified into different genotypes (PCV2a-f) based on phylogenetic analysis. Since the introduction of extensive vaccination programs, at least two major shifts have been observed in the prevalence of PCV2 genotypes. The first genotype shift from 2a towards 2b occurred around 2003, while in recent years, we are witnessing the second change in genotype prevalence from the predominant 2b towards 2d.In this study, a PCV2d-2 isolate was characterized as a potential challenge virus for the evaluation of PCV2 vaccine efficacy. Ten-week-old pigs carrying low to moderate levels of maternally derived antibodies to PCV2 were infected with the isolate by the nasal route. Over the next 4 weeks post-infection, the pigs were monitored for the presence of viremia, fecal virus excretion, and humoral immune responses. At the end of the post-infection observation period, samples were taken from the mediastinal and mesenteric lymph nodes of the animals and tested for viral load. The gradual depletion of maternally derived antibodies in the sera of piglets was demonstrated by ELISA and virus neutralization tests. Following experimental infection by PCV2d-2, specific IgM antibodies were first detected at 14 days post challenge (dpch), while IgG class antibodies were first detected at 21 dpch. Both viremia and virus shedding could be detected at 7 dpch, in 36 and 50% of the pigs, respectively. The proportion of shedders reached 100% by 14 dpch and remained at this level, while viremia was demonstrated in 86, 100, and 100% of the pigs at 14, 21, and 28 dpch, respectively. Both the mediastinal and mesenteric lymph nodes contained high levels of virus (7.6 and 8.5 log₁₀ copies/mg tissue, respectively).

A convenient colorimetric assay for the quantification of porcine epidemic diarrhea virus and neutralizing antibodies

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PEDV is an economically important, enteric coronavirus of swine.

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Visual reading of 96 well plates for virus neutralization (V/N) or TCID₅₀ assays is time consuming.

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The newly developed colorimetric PEDV V/N and TCID₅₀ assays are reliable and convenient.

Neonatal enteritis caused by the porcine epidemic diarrhea virus (PEDV) is an important cause of high mortality and economic losses to the swine industry. Virus neutralization (V/N) assays are commonly requested in diagnostic laboratories for the assessment of protective antibodies. However, the visual assessment of viral cytopathic effects by operators to determine antibody titers or for viral quantification is a tedious, subjective and time-consuming process, especially when high volume testing is involved. To improve the ease of testing, a colorimetric virus neutralization and TCID₅₀ assays were developed and validated in this study using (3-(4,5-dimethylthiazol-2-yl) Tr-2,5-diphenyltetrazolium- bromide) (MTT), a colorimetric agent which measures cell viability. The respective conventional assays were used as the gold standards. An OD cut off value of ≤0.53, selected by receiver operating characteristics analysis, could distinguish between wells with and without CPE accurately. Performance and reproducibility parameters of the colorimetric assays were comparable to the conventional assays. The described methods can reduce testing time in diagnostic laboratories, while significantly improving current protocols.

Development of Human Monoclonal Antibodies Against Respiratory Syncytial Virus Using a High Efficiency Human Hybridoma Technique

Human monoclonal antibodies against RSV have high potential for use as prophylaxis or therapeutic molecules, and they also can be used to define the structure of protective epitopes for rational vaccine design. In the past, however, isolation of human monoclonal antibodies was difficult and inefficient. Here, we describe contemporary methods for activation and proliferation of primary human memory B cells followed by cytofusion to non-secreting myeloma cells by dielectrophoresis to generate human hybridomas secreting RSV-specific monoclonal antibodies. We also provide experimental methods for screening human B cell lines to obtain RSV-specific lines, especially lines secreting neutralizing antibodies.

Bovine single chain Fv antibody inhibits bovine herpesvirus-1 infectivity by targeting viral glycoprotein D

Glycoprotein D (gD) of bovine herpesvirus-1 (BoHV-1) is essential for attachment and penetration of cells during infection and is a major target for neutralizing antibodies during an adaptive immune response. Currently there are no recombinant antibodies capable of binding gD epitopes for use in treating BoHV-1 infection. In this study, a bovine scFv gene derived from a hybridoma secreting monoclonal antibodies (McAbs) against the amino acid motif MEESKGYEPP of gD was expressed in E. coli. Molecular modeling, western blot and ELISA analysis showed that this scFv had a high affinity for BoHV-1 gD, with a Kd of 161.2 ± 37.58 nM and for whole BoHV-1 virus, with a Kd of 67.44 ± 16.99 nM. In addition, this scFv displayed a high affinity for BoHV-1 antigen in an ELISA and competed with BoHV-1 anti-serum in a competitive ELISA. Immunofluorescence assay (IFA) and laser confocal microscopy showed that this scFv could efficiently bind to and be internalized by BoHV-1 infected Madin-Darby bovine kidney (MDBK) cells. Importantly, this scFv was shown to inhibit BoHV-1 infectivity and to reduce the number of viral plaques by blocking viral attachment to MDBK cells. Our study suggests that this bovine single-chain antibody could be developed for use as a diagnostic and therapeutic agent against BoHV-1 infection in cattle.

Development of a novel Newcastle disease virus (NDV) neutralization test based on recombinant NDV expressing enhanced green fluorescent protein

BACKGROUND

Newcastle disease is one of the most important infectious diseases of poultry, caused by Newcastle disease virus (NDV). This virus is distributed worldwide and it can cause severe economic losses in the poultry industry due to recurring outbreaks in vaccinated and unvaccinated flocks. Protection against NDV in chickens has been associated with development of humoral response. Although hemagglutination inhibition (HI) assay and ELISA do not corroborate the presence of neutralizing antibodies (nAbs); they are used to measure protection and immune response against NDV.

METHODS

In this study, we established a system to recover a recombinant NDV (rLS1) from a cloned cDNA, which is able to accept exogenous genes in desired positions. An enhanced green fluorescent protein (eGFP) gene was engineered in the first position of the NDV genome and we generated a recombinant NDV carrying eGFP. This NDV- eGFP reporter virus was used to develop an eGFP-based neutralization test (eGFP-NT), in which nAbs titers were expressed as the reciprocal of the highest dilution that expressed the eGFP.

RESULTS

The eGFP-NT gave conclusive results in 24 h without using any additional staining procedure. A total of 57 serum samples were assayed by conventional neutralization (NT) and eGFP-NT. Additionally, HI and a commercial ELISA kit were evaluated with the same set of samples. Although HI (R ² = 0.816) and ELISA (R ² = 0.791) showed substantial correlation with conventional NT, eGFP-NT showed higher correlation (R ² = 0.994), indicating that eGFP-NT is more accurate method to quantify nAbs.

CONCLUSIONS

Overall, the neutralization test developed here is a simple, rapid and reliable method for quantitation of NDV specific nAbs. It is suitable for vaccine studies and diagnostics.

Binding and neutralizing anti-cytomegalovirus activities in immune globulin products

Congenital infection as well as infection of immunocompromised individuals by cytomegalovirus (CMV) can be associated with significant morbidity, mortality, and long-term adverse health outcomes. Assessment of anti-viral activity using appropriate assays is essential for ensuring safe and efficacious use of therapeutic CMV immune globulin (IG) products. In this study, we used commercial ELISA kits to compare anti-CMV antibody binding activity and avidity for lots of CMV-specific and normal IG products available in the US market. Additionally, neutralizing activity of IG products was measured against CMV strains (AD169^wt131 or TB40E-GFP) in MRC-5 human fibroblasts and ARPE-19 human epithelial cells. Our data revealed that, regardless of the method, anti-CMV activity was higher in CMV IG lots we tested compared with normal IG lots; CMV binding activity was at least 4-fold higher, and neutralizing activity at least 2- and 3-fold higher for epithelial and fibroblast cells, respectively, in CMV IG lots compared with normal IG lots. Furthermore, anti-CMV activity values from all three methods (ELISA, neutralization in MRC-5 cells, and neutralization in ARPE-19 cells) were highly correlated, whereas avidity, although higher in CMV IG lots, did not correlate well with either binding or neutralizing activities.

An Optimized Method for the Production Using PEI, Titration and Neutralizationof SARS-CoV Spike Luciferase Pseudotypes

The protocol outlined represents a cost-effective, rapid and reliable method for the generation of high-titre viral pseudotype particles with the wild-type SARS-CoV spike protein on a lentiviral vector core using the widely available transfection reagent PEI. This protocol is optimized for transfection in 6-well plates; however it can be readily scaled to different production volumes according to application. This protocol has multiple benefits including the use of readily available reagents, consistent, high pseudotype virus production Relative Luminescence Units (RLU) titres and rapid generation of novel coronavirus pseudotypes for research into strain variation, tropism and immunogenicity/sero-prevalence.

Chimeric influenza haemagglutinins: Generation and use in pseudotype neutralization assays

Recently chimeric influenza haemagglutinins (cHAs) have been generated as potential ‘universal’ vaccination antigens and as tools to identify HA stalk-directed antibodies via their use as antigens in ELISA, and virus or pseudotype-based neutralization assays. The original methods [1], [2] used for their generation require the amplification of regions of interest (head and stalk) using primers containing SapI sites and subsequent cloning into pDZ plasmid. This requires precise primer design, checking for the absence of SapI sites in the sequence of interest, and multi‐segment ligation. As an alternative strategy we have developed and optimized a new protocol for assembling the cHA by exploiting Gibson Assembly.

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This method also requires precise primer design, but it is rapid and methodologically simple to perform. We have evaluated that using this method it is possible to construct a cHA encoding DNA in less than a week.

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Additional weeks are however necessary to optimize the production of pseudotyped lentiviral particles and to perform neutralization assays using them as surrogate antigens.

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In comparison to the original protocols, we have also observed that performing parallel neutralization assays using pseudotypes harbouring the two parental HAs, permits effective delineation between stalk and head antibody responses in the samples tested.

Immunotherapy With the PreS-based Grass Pollen Allergy Vaccine BM32 Induces Antibody Responses Protecting Against Hepatitis B Infection

Background

We have constructed and clinically evaluated a hypoallergenic vaccine for grass pollen allergy, BM32, which is based on fusion proteins consisting of peptides from the IgE binding sites of the major grass pollen allergens fused to preS (preS1 + preS2), a domain of the hepatitis B virus (HBV) large envelope protein which mediates the viral attachment and entry. Aim of this study was the characterization of the HBV-specific immune response induced by vaccination of allergic patients with BM32 and the investigation of the vaccines' potential to protect against infection with HBV.

Methods

Hepatitis B-specific antibody and T cell responses of patients vaccinated with BM32 were studied using recombinant preS and synthetic overlapping peptides spanning the preS sequence. The specificities of the antibody responses were compared with those of patients with chronic HBV infection. Furthermore, the capacity of BM32-induced antibodies, to inhibit HBV infection was investigated using HepG2-hNTCP cell-based in vitro virus neutralization assays.

Findings

IgG antibodies from BM32-vaccinated but not of HBV-infected individuals recognized the sequence motif implicated in NTCP (sodium-taurocholate co-transporting polypeptide)-receptor interaction of the hepatitis B virus and inhibited HBV infection.

Interpretation

Our study demonstrates that the recombinant hypoallergenic grass pollen allergy vaccine BM32 induces hepatitis B-specific immune responses which protect against hepatitis B virus infection in vitro.

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BM32 is a recombinant allergy vaccine consisting of the preS domain of the large envelope protein of hepatitis B virus (HBV) and allergen-derived peptides.

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Vaccination of allergic patients with BM32 induced preS-specific antibodies which inhibit hepatitis B infection in vitro.

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BM32 may be useful as therapeutic vaccine in HBV-infected patients.

Infection with HBV remains a major cause of morbidity and mortality worldwide. Conventional HBV vaccines, consisting of SHBs particles solely, do not elicit adequate antibody production in 5–10% of vaccines and there is a need for therapeutic HBV vaccines. We have engineered an allergy vaccine which consists of allergen-derived peptides fused to the preS domain of the large envelope protein of HBV. Here we show that vaccination of allergic patients with this vaccine induces antibodies which protect against HBV infection in vitro. The preS-containing allergy vaccine may thus be also useful for therapeutic vaccination of HBV-infected patients.

Evaluation of serological cross-reactivity and cross-neutralization between the United States porcine epidemic diarrhea virus prototype and S-INDEL-variant strains

Background

At least two genetically different porcine epidemic diarrhea virus (PEDV) strains have been identified in the United States (U.S. PEDV prototype and S-INDEL-variant strains). The current serological assays offered at veterinary diagnostic laboratories for detection of PEDV-specific antibody are based on the U.S. PEDV prototype strain. The objectives of this study were: 1) isolate the U.S. PEDV S-INDEL-variant strain in cell culture; 2) generate antisera against the U.S. PEDV prototype and S-INDEL-variant strains by experimentally infecting weaned pigs; 3) determine if the various PEDV serological assays could detect antibodies against the U.S. PEDV S-INDEL-variant strain and vice versa.

Results

A U.S. PEDV S-INDEL-variant strain was isolated in cell culture in this study. Three groups of PEDV-negative, 3-week-old pigs (five pigs per group) were inoculated orally with a U.S. PEDV prototype isolate (previously isolated in our lab), an S-INDEL-variant isolate or virus-negative culture medium. Serum samples collected at 0, 7, 14, 21 and 28 days post inoculation were evaluated by the following PEDV serological assays: 1) indirect fluorescent antibody (IFA) assays using the prototype and S-INDEL-variant strains as indicator viruses; 2) virus neutralization (VN) tests against the prototype and S-INDEL-variant viruses; 3) PEDV prototype strain whole virus based ELISA; 4) PEDV prototype strain S1-based ELISA; and 5) PEDV S-INDEL-variant strain S1-based ELISA. The positive antisera against the prototype strain reacted to and neutralized both prototype and S-INDEL-variant viruses, and the positive antisera against the S-INDEL-variant strain also reacted to and neutralized both prototype and S-INDEL-variant viruses, as examined by IFA antibody assays and VN tests. Antibodies against the two PEDV strains could be detected by all three ELISAs although detection rates varied to some degree.

Conclusions

These data indicate that the antibodies against U.S. PEDV prototype and S-INDEL-variant strains cross-reacted and cross-neutralized both strains in vitro. The current serological assays based on U.S. PEDV prototype strain can detect antibodies against both U.S. PEDV strains.

MmuPV1 infection and tumor development of T cell-deficient mice is prevented by passively transferred hyperimmune sera from normal congenic mice immunized with MmuPV1 virus-like particles (VLPs)

Infection by mouse papillomavirus (PV), MmuPV1, of T cell-deficient, B6.Cg-Foxn1(nu)/J nude mice revealed that four, distinct squamous papilloma phenotypes developed simultaneously after infection of experimental mice. Papillomas appeared on the muzzle, vagina, and tail at or about day 42days post-inoculation. The dorsal skin developed papillomas and hair follicle tumors (trichoblastomas) as early as 26days after infection. Passive transfer of hyperimmune sera from normal congenic mice immunized with MmuPV1 virus-like particles (VLPs) to T cell-deficient strains of mice prevented infection by virions of experimental mice. This study provides further evidence that T cell deficiency is critical for tumor formation by MmuPV1 infection.

Diverse antigenic site targeting of influenza hemagglutinin in the murine antibody recall response to A(H1N1)pdm09 virus

Here we define the epitopes on HA that are targeted by a group of 9 recombinant monoclonal antibodies (rmAbs) isolated from memory B cells of mice, immunized by infection with A(H1N1)pdm09 virus followed by a seasonal TIV boost. These rmAbs were all reactive against the HA1 region of HA, but display 7 distinct binding footprints, targeting each of the 4 known antigenic sites. Although the rmAbs were not broadly cross-reactive, a group showed subtype-specific cross-reactivity with the HA of A/South Carolina/1/18. Screening these rmAbs with a panel of human A(H1N1)pdm09 virus isolates indicated that naturally-occurring changes in HA could reduce rmAb binding, HI activity, and/or virus neutralization activity by rmAb, without showing changes in recognition by polyclonal antiserum. In some instances, virus neutralization was lost while both ELISA binding and HI activity were retained, demonstrating a discordance between the two serological assays traditionally used to detect antigenic drift.

Systemic immune responses to an inactivated, whole H9N2 avian influenza virus vaccine using class B CpG oligonucleotides in chickens

Commercial vaccines against avian influenza viruses (AIV) in chickens consist mainly of inactivated AIV, requiring parenteral administration and co-delivery of an adjuvant. Limitations in T helper 1 or T helper 2 biased responses generated by these vaccines emphasize the need for alternative, more efficacious adjuvants. The Toll-like receptor (TLR) 21 ligand, CpG oligodeoxynucleotides (ODN), has been established as immunomodulatory in chickens. Therefore, the objective of this study was to investigate the adjuvant potential of high (20μg) and low (2μg) doses of CpG ODN 2007 (CpG 2007) and CpG ODN 1826 (CpG 1826) when administered to chickens with a formalin-inactivated H9N2 AIV. Antibody responses in sera were evaluated in 90 specific pathogen free (SPF) chickens after intramuscular administration of vaccine formulations at 7 and 21 days post-hatch. Antibody responses were assessed based on haemagglutination inhibition (HI) and virus neutralization (VN) assays; virus-specific IgM and IgY antibody responses were evaluated by ELISA. The results suggest that the vaccine formulation containing low dose CpG 2007 was significantly more effective at generating neutralizing (both HI and VN) responses than formulations with high or low doses of CpG 1826 or high dose CpG 2007. Neutralizing responses elicited by low dose CpG 2007 significantly exceeded those generated by a squalene-based adjuvanted vaccine formulation during peak responses. A significantly higher IgM response was elicited by the formulation containing low dose CpG 2007 compared to high and low doses of 1826. Although the low dose of CpG 2007 elicited a higher IgY response than CpG 1826, the difference was not statistically significant. In conclusion, 2μg of CpG 2007 is potentially promising as a vaccine adjuvant when delivered intramuscularly with inactivated H9N2 virus to chickens. Future studies may be directed at determining the mucosal antibody responses to the same vaccine formulations.

Enhanced humanization and affinity maturation of neutralizing anti-hepatitis B virus preS1 antibody based on antigen-antibody complex structure

To improve a previously constructed broadly neutralizing hepatitis B virus (HBV)-specific preS1 humanized antibody (HzKR127), we further humanized it through specificity-determining residue (SDR) grafting. Moreover, we improved affinity by mutating two residues in heavy-chain complementarity-determining regions (CDR), on the basis of the crystal structure of the antigen-antibody complex. HzKR127-3.2 exhibited 2.5-fold higher affinity and enhanced virus-neutralizing activity compared to the original KR127 antibody and showed less immunogenic potential than HzKR127. Enhanced virus-neutralizing activity was achieved by the increased association rate, providing insights into engineering potent antibody therapeutics for HBV immunoprophylaxis. HzKR127-3.2 may be a good candidate for HBV immunoprophylaxis.

A structural view of coronavirus-receptor interactions

In the coronavirus (CoV), the envelope spike (S) glycoprotein is responsible for CoV cell entry and host-to-host transmission. The S is a multifunctional glycoprotein that mediates both attachment of CoV particles to cell surface receptor molecules as well as membrane penetration by fusion. Receptor-binding domains (RBD) have been identified in the S of diverse CoV; they usually contain antigenic determinants targeted by antibodies that neutralize CoV infections. To penetrate host cells, the CoV can use various cell surface molecules, although they preferentially bind to ectoenzymes. Several crystal structures have determined the folding of CoV RBD and the mode by which they recognize cell entry receptors. Here we review the CoV-receptor complex structures reported to date, and highlight the distinct receptor recognition modes, common features, and key determinants of the binding specificity. Structural studies have established the basis for understanding receptor recognition diversity in CoV, its evolution and the adaptation of this virus family to different hosts. CoV responsible for recent outbreaks have extraordinary potential for cross-species transmission; their RBD bear large platforms specialized in recognition of receptors from different species, which facilitates host-to-host circulation and adaptation to man.

Neutralizing antibody responses to foot-and-mouth disease quadrivalent (type O, A, C and Asia 1) vaccines in growing calves with pre-existing maternal antibodies

The presence of maternal antibodies is a major obstacle for eliciting protective immune responses to foot-and-mouth disease (FMD) vaccines in young, growing animals. In this report, we analyzed the ability of inactivated quadrivalent oil emulsified and aluminium hydroxide adjuvanted FMD vaccines to elicit neutralizing antibody responses in growing calves that had maternal antibodies. Our results demonstrate that oil emulsified vaccines but not aluminium hydroxide adjuvanted FMD vaccines could surmount maternal antibodies to elicit strong and significant levels of neutralizing antibody responses in growing claves.