Development and comparison of enzyme-linked immunosorbent assays based on recombinant trimeric full-length and truncated spike proteins for detecting antibodies against porcine epidemic diarrhea virus

High-affinity monoclonal antibodies against the porcine epidemic diarrhea virus S1 protein

The porcine epidemic diarrhea virus (PEDV) infection inflicted substantial economic losses upon the global pig-breeding industry. This pathogen can infect all pigs and poses a particularly high fatality risk for suckling piglets. The S1 subunit of spike protein is a crucial target protein for inducing the particularly neutralizing antibodies that can intercept the virus-host interaction and neutralize virus infectivity. In the present study, the HEK293F eukaryotic expression system was successfully utilized to express and produce recombinant S1 protein. Through quantitative analysis, five monoclonal antibodies (mAbs) specifically targeting the recombinant S1 protein of PEDV were developed and subsequently evaluated using enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence assay (IFA), and flow cytometry assay (FCA). The results indicate that all five mAbs belong to the IgG1 isotype, and their half-maximal effective concentration (EC50) values measured at 84.77, 7.42, 0.89, 14.64, and 7.86 pM. All these five mAbs can be utilized in ELISA, FCA, and IFA for the detection of PEDV infection. MAb 5-F9 exhibits the highest sensitivity to detect as low as 0.3125 ng/mL of recombinant PEDV-S1 protein in ELISA, while only 0.096 ng/mL of mAb 5-F9 is required to detect PEDV in FCA. The results from antigen epitope analysis indicated that mAb 8-G2 is the sole antibody capable of recognizing linear epitopes. In conclusion, this study has yielded a highly immunogenic S1 protein and five high-affinity mAbs specifically targeting the S1 protein. These findings have significant implications for early detection of PEDV infection and provide a solid foundation for further investigation into studying virus-host interactions.

Establishment of an Indirect ELISA Method for the Detection of the Bovine Rotavirus VP6 Protein

The objective of this study was to develop an indirect ELISA utilizing a polyclonal antibody against bovine rotavirus (BRV) VP6 protein. To achieve this, pcDNA3.1-VP6, a recombinant eukaryotic expression plasmid, was constructed based on the sequence of the conserved BRV gene VP6 and was transfected into CHO-K1 cells using the transient transfection method. The VP6 protein was purified as the coating antigen using nickel ion affinity chromatography, and an indirect ELISA was subsequently established. The study found that the optimal concentration of coating for the VP6 protein was 1 μg/mL. The optimal blocking solution was 3% skim milk, and the blocking time was 120 min. The secondary antibody was diluted to 1:4000, and the incubation time for the secondary antibody was 30 min. A positive result was indicated when the serum OD450 was greater than or equal to 0.357. The coefficients of variation were less than 10% both within and between batches, indicating the good reproducibility of the method. The study found that the test result was positive when the serum dilution was 217, indicating the high sensitivity of the method. A total of 24 positive sera and 40 negative sera were tested using the well-established ELISA. The study also established an indirect ELISA assay with good specificity and sensitivity for the detection of antibodies to bovine rotavirus. Overall, the results suggest that the indirect ELISA method developed in this study is an effective test for detecting such antibodies.

Development of an Indirect Enzyme-Linked Immunosorbent Assay Based on the Yeast-Expressed CO-26K-Equivalent Epitope-Containing Antigen for Detection of Serum Antibodies against Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea (PED) is a severe contagious intestinal disease caused by the porcine epidemic diarrhea virus (PEDV), which leads to high mortality in piglets. In this study, by analyzing a total of 53 full-length spike genes and COE domain regions of PEDVs, the conserved COE fragment of the spike protein from the dominant strain SC1402 was chosen as the target protein and expressed successfully in Pichia pastoris (P. pastoris). Furthermore, an indirect enzyme-linked immunosorbent assay (iELISA) based on the recombinant COE protein was developed for the detection of anti-PEDV antibodies in pig sera. The results showed that under the optimized conditions, the cut-off value of COE-based indirect ELISA (COE-iELISA) was determined to be 0.12. Taking the serum neutralization test as standard, the relative sensitivity of the COE-iELISA was 94.4% and specificity 92.6%. Meanwhile, no cross-reactivity to other porcine pathogens was noted with this assay. The intra-assay and inter-assay coefficients of variation were less than 7%. Moreover, 164 vaccinated serum samples test showed that overall agreement between COE-iELISA and the actual diagnosis result was up to 99.4%. More importantly, the developed iELISA exhibited a 95.08% agreement rate with the commercial ELISA kit (Kappa value = 0.88), which suggested that the expressed COE protein was an effective antigen in serologic tests and the established COE-iELISA is reliable for monitoring PEDV infection in pigs or vaccine effectiveness.

Development of an enzyme-linked immunosorbent assay based on viral antigen capture by anti-spike glycoprotein monoclonal antibody for detecting immunoglobulin A antibodies against porcine epidemic diarrhea virus in milk

BACKGROUND

Porcine epidemic diarrhea (PED), caused by PED virus (PEDV), is a severe enteric disease burdening the global swine industry in recent years. Especially, the mortality of PED in neonatal piglets approaches 100%. Maternal antibodies in milk, particularly immunoglobulin A (IgA) antibodies, are of great importance for protection neonatal suckling piglets against PEDV infection as passive lactogenic immunity. Therefore, appropriate detection methods are required for detecting PEDV IgA antibodies in milk. In the current study, we prepared monoclonal antibodies (mAbs) against PEDV spike (S) glycoprotein. An enzyme-linked immunosorbent assay (ELISA) was subsequently developed based on PEDV antigen capture by a specific anti-S mAb.

RESULTS

The developed ELISA showed high sensitivity (the maximum dilution of milk samples up to 1:1280) and repeatability (coefficient of variation values < 10%) in detecting PEDV IgA antibody positive and negative milk samples. More importantly, the developed ELISA showed a high coincidence rate with a commercial ELISA kit for PEDV IgA antibody detection in clinical milk samples.

CONCLUSIONS

The developed ELISA in the current study is applicable for PEDV IgA antibody detection in milk samples, which is beneficial for evaluating vaccination efficacies and neonate immune status against the virus.

Seroprevalence of Getah virus in Pigs in Eastern China Determined with a Recombinant E2 Protein-Based Indirect ELISA

Getah virus (GETV), in the genus Alphavirus and the family Togaviridae, has been detected throughout the world. GETV causes high morbidity and mortality in newborn piglets, entailing serious economic losses. Therefore, the experimental work on GETV detection is necessary. However, due to the influence of a variety of unavoidable factors, the ELISA test for the primary screening of animal diseases has low accuracy in detection results. Therefore, we optimized a recombinant E2 (rE2) protein-based enzyme-linked immunosorbent assay (ELISA) for the detection of GETV antibodies in pig serum. The E2 protein was successfully expressed and purified with SDS-PAGE. A Western blotting analysis of sera from infected pigs showed strong reaction with a viral antigen of ~46 KDa corresponding to the E2 glycoproteins. By using chessboard titration and comparing the P/N values, we found that the optimal concentration of coated antigen was found to be 24.5 μg/mL, and the optimal dilution of serum specimens was 1:100. The best working dilution of the horseradish peroxidase (HRP)-conjugated goat anti-pig immunoglobulin (IgG) was 1:5000. The optimal coating conditions were 12 h at 4 °C. The optimal incubation conditions for serum specimens, blocking, and reaction with the secondary antibody were all 1 h at 37 °C. We also investigated the seroprevalence of GETV in 133 serum specimens collected in Eastern China, and 37.59% of the samples tested positive for anti-GETV IgG antibodies, indicating that the seroprevalence of GETV is high in pig populations in China. The seroprevalence was significantly lower in spring (April; 24.24%, 16/66) than in autumn (October; 50.75%, 34/67), which suggested that the presence of anti-GETV antibodies in pigs was seasonal. In conclusion, we improved an rE2 ELISA that detected pig antibodies against GETV after experimental and natural infections. This should be useful in the diagnosis and surveillance of GETV infections.

Characterisation of ORF3, M, N and E gene sequences of porcine epidemic diarrhoea virus from domestic pigs in Poland

Introduction

Porcine epidemic diarrhoea virus (PEDV) is an enteric pathogen causing porcine epidemic diarrhoea and acute gastroenteritis in pigs of all ages. Previous analysis of the viral genome of PEDV in Poland was only based on the spike protein (S) gene sequences and no analysis of other genes has been performed. The aim of this study was to analyse the envelope (E), membrane (M) and nucleocapsid (N) protein and open reading frame 3 (ORF3) gene sequences.

Material and Methods

Viral RNA from 18 Polish pig faecal samples that were quantitative reverse transcription PCR-positive for PEDV was analysed in four genomic regions (E, M, N and ORF3).

Results

Phylogenetic analysis based on these regions’ sequences revealed that Polish PEDV isolates were highly related and were clustered into group G2a across the four genes compared. Moreover, the Polish strains were located in distinct subclusters on the phylogenetic trees, which suggests the presence of at least three independently evolving PEDV genetic lines circulating in Poland. The occurrence of unique mutations in the sequences of Polish PEDV strains suggests that PEDV continues to undergo evolutionary processes, accumulating the mutations necessary for viral fitness in its natural hosts. The Polish PEDV strains differed genetically from the CV777 vaccine strain, suggesting the risk of relatively low vaccine efficacy if this strain is used.

Conclusion

Our results promote a better understanding of the genetic diversity of PEDV field isolates in Poland and highlight the importance of molecular characterisation of PEDV field strains for the development of an effective vaccine against PEDV.

Current State of Molecular and Serological Methods for Detection of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV), a member of the Coronaviridae family, is the etiological agent of an acute and devastating enteric disease that causes moderate-to-high mortality in suckling piglets. The accurate and early detection of PEDV infection is essential for the prevention and control of the spread of the disease. Many molecular assays have been developed for the detection of PEDV, including reverse-transcription polymerase chain reaction (RT-PCR), real-time RT-PCR (qRT-PCR) and loop-mediated isothermal amplification assays. Additionally, several serological methods have been developed and are widely used for the detection of antibodies against PEDV. Some of them, such as the immunochromatography assay, can generate results very quickly and in field conditions. Molecular assays detect viral RNA in clinical samples rapidly, and with high sensitivity and specificity. Serological assays can determine prior immune exposure to PEDV, can be used to monitor the efficacy of vaccination strategies and may help to predict the duration of immunity in piglets. However, they are less sensitive than nucleic acid-based detection methods. Sanger and next-generation sequencing (NGS) allow the analysis of PEDV cDNA or RNA sequences, and thus, provide highly specific results. Furthermore, NGS based on nonspecific DNA cleavage in clustered regularly interspaced short palindromic repeats (CRISPR)–Cas systems promise major advances in the diagnosis of PEDV infection. The objective of this paper was to summarize the current serological and molecular PEDV assays, highlight their diagnostic performance and emphasize the advantages and drawbacks of the application of individual tests.

In situ structure and dynamics of an alphacoronavirus spike protein by cryo-ET and cryo-EM

Porcine epidemic diarrhea (PED) is a highly contagious swine disease caused by porcine epidemic diarrhea virus (PEDV). PED causes enteric disorders with an exceptionally high fatality in neonates, bringing substantial economic losses in the pork industry. The trimeric spike (S) glycoprotein of PEDV is responsible for virus-host recognition, membrane fusion, and is the main target for vaccine development and antigenic analysis. The atomic structures of the recombinant PEDV S proteins of two different strains have been reported, but they reveal distinct N-terminal domain 0 (D0) architectures that may correspond to different functional states. The existence of the D0 is a unique feature of alphacoronavirus. Here we combined cryo-electron tomography (cryo-ET) and cryo-electron microscopy (cryo-EM) to demonstrate in situ the asynchronous S protein D0 motions on intact viral particles of a highly virulent PEDV Pintung 52 strain. We further determined the cryo-EM structure of the recombinant S protein derived from a porcine cell line, which revealed additional domain motions likely associated with receptor binding. By integrating mass spectrometry and cryo-EM, we delineated the complex compositions and spatial distribution of the PEDV S protein N-glycans, and demonstrated the functional role of a key N-glycan in modulating the D0 conformation.

Hsu and co-workers integrate cryo-electron tomography, cryo-electron microscopy and mass spectrometry to reveal the structural polymorphism of a pig coronavirus spike protein within intact viral particles, and how glycosylation modulates the conformational changes pertinent to host recognition.

Systems of conductive skin for power transfer in clinical applications

The primary aim of this article is to review the clinical challenges related to the supply of power in implanted left ventricular assist devices (LVADs) by means of transcutaneous drivelines. In effect of that, we present the preventive measures and post-operative protocols that are regularly employed to address the leading problem of driveline infections. Due to the lack of reliable wireless solutions for power transfer in LVADs, the development of new driveline configurations remains at the forefront of different strategies that aim to power LVADs in a less destructive manner. To this end, skin damage and breach formation around transcutaneous LVAD drivelines represent key challenges before improving the current standard of care. For this reason, we assess recent strategies on the surface functionalization of LVAD drivelines, which aim to limit the incidence of driveline infection by directing the responses of the skin tissue. Moreover, we propose a class of power transfer systems that could leverage the ability of skin tissue to effectively heal short diameter wounds. In this direction, we employed a novel method to generate thin conductive wires of controllable surface topography with the potential to minimize skin disruption and eliminate the problem of driveline infections. Our initial results suggest the viability of the small diameter wires for the investigation of new power transfer systems for LVADs. Overall, this review uniquely compiles a diverse number of topics with the aim to instigate new research ventures on the design of power transfer systems for IMDs, and specifically LVADs.

PEDV Infection Generates Conformation-Specific Antibodies That Can Be Effectively Detected by a Cell-Based ELISA

Porcine epidemic diarrhea virus (PEDV) is a coronavirus that causes serious and highly contagious enteric disease in swine worldwide. In this study, we constructed a recombinant baculovirus (S-Bac) expressing full-length spike protein of the virulent epidemic genotype 2b (G2b) PEDV strain for serological studies of infected pigs. We found that most spike-specific antibodies produced upon PEDV infection in pigs are conformation-specific and they could be detected on S-Bac-infected insect cells by immunofluorescent assay, but they were insensitive to Western blot analysis, the typical method for antiserum analysis. These results indicated that spike conformation is crucial for serum recognition. Since it is difficult to purify trimeric spike membrane protein for conventional enzyme-linked immunosorbent assay (ELISA), we used S-Bac to generate a novel cell-based ELISA for convenient PEDV detection. We analyzed 100 pig serum samples, and our cell-based ELISA exhibited a sensitivity of 100%, a specificity of 97%, and almost perfect agreement [Cohen’s kappa coefficient value (κ) = 0.98] with immunocytochemical staining results. Our cell-based ELISA rapidly presented antigen for proper detection of conformation-specific antibodies, making PEDV detection more convenient, and it will be useful for detecting many viral diseases in the future.

Porcine enteric coronaviruses: an updated overview of the pathogenesis, prevalence, and diagnosis

The recent prevalence of coronavirus (CoV) poses a serious threat to animal and human health. Currently, porcine enteric coronaviruses (PECs), including the transmissible gastroenteritis virus (TGEV), the novel emerging swine acute diarrhoea syndrome coronavirus (SADS-CoV), porcine delta coronavirus (PDCoV), and re-emerging porcine epidemic diarrhoea virus (PEDV), which infect pigs of different ages, have caused more frequent occurrences of diarrhoea, vomiting, and dehydration with high morbidity and mortality in piglets. PECs have the potential for cross-species transmission and are causing huge economic losses in the pig industry in China and the world, which therefore needs to be urgently addressed. Accordingly, this article summarises the pathogenicity, prevalence, and diagnostic methods of PECs and provides an important reference for their improved diagnosis, prevention, and control.

Parenterally Administered Porcine Epidemic Diarrhea Virus-Like Particle-Based Vaccine Formulated with CCL25/28 Chemokines Induces Systemic and Mucosal Immune Protectivity in Pigs

Generation of a safe, economical, and effective vaccine capable of inducing mucosal immunity is critical for the development of vaccines against enteric viral diseases. In the current study, virus-like particles (VLPs) containing the spike (S), membrane (M), and envelope (E) structural proteins of porcine epidemic diarrhea virus (PEDV) expressed by the novel polycistronic baculovirus expression vector were generated. The immunogenicity and protective efficacy of the PEDV VLPs formulated with or without mucosal adjuvants of CCL25 and CCL28 (CCL25/28) were evaluated in post-weaning pigs. While pigs intramuscularly immunized with VLPs alone were capable of eliciting systemic anti-PEDV S-specific IgG and cellular immunity, co-administration of PEDV VLPs with CCL25/28 could further modulate the immune responses by enhancing systemic anti-PEDV S-specific IgG, mucosal IgA, and cellular immunity. Upon challenge with PEDV, both VLP-immunized groups showed milder clinical signs with reduced fecal viral shedding as compared to the control group. Furthermore, pigs immunized with VLPs adjuvanted with CCL25/28 showed superior immune protection against PEDV. Our results suggest that VLPs formulated with CCL25/28 may serve as a potential PEDV vaccine candidate and the same strategy may serve as a platform for the development of other enteric viral vaccines.

Molecular Characterization of Porcine Epidemic Diarrhea Virus and Its New Genetic Classification Based on the Nucleocapsid Gene

Porcine epidemic diarrhea virus (PEDV) causes continuous, significant damage to the swine industry worldwide. By RT-PCR-based methods, this study demonstrated the ongoing presence of PEDV in pigs of all ages in Korea at the average detection rate of 9.92%. By the application of Bayesian phylogenetic analysis, it was found that the nucleocapsid (N) gene of PEDV could evolve at similar rates to the spike (S) gene at the order of 10^-4 substitutions/site/year. Based on branching patterns of PEDV strains, three main N gene-base genogroups (N1, N2, and N3) and two sub-genogroups (N3a, N3b) were proposed in this study. By analyzing the antigenic index, possible antigenic differences also emerged in both the spike and nucleocapsid proteins between the three genogroups. The antigenic indexes of genogroup N3 strains were significantly lower compared with those of genogroups N1 and N2 strains in the B-cell epitope of the nucleocapsid protein. Similarly, significantly lower antigenic indexes in some parts of the B-cell epitope sequences of the spike protein (COE, S1D, and 2C10) were also identified. PEDV mutants derived from genetic mutations of the S and N genes may cause severe damage to swine farms by evading established host immunities.