Epitope mapping and characterization of a novel Nsp10-specific monoclonal antibody that differentiates genotype 2 PRRSV from genotype 1 PRRSV

ZNF283, a Krüppel-associated box zinc finger protein, inhibits RNA synthesis of porcine reproductive and respiratory syndrome virus by interacting with Nsp9 and Nsp10

Porcine reproductive and respiratory syndrome virus (PRRSV) is a viral pathogen with substantial economic implications for the global swine industry. The existing vaccination strategies and antiviral drugs offer limited protection. Replication of the viral RNA genome encompasses a complex series of steps, wherein a replication complex is assembled from various components derived from both viral and cellular sources, as well as from the viral genomic RNA template. In this study, we found that ZNF283, a Krüppel-associated box (KRAB) containing zinc finger protein, was upregulated in PRRSV-infected Marc-145 cells and porcine alveolar macrophages and that ZNF283 inhibited PRRSV replication and RNA synthesis. We also found that ZNF283 interacts with the viral proteins Nsp9, an RNA-dependent RNA polymerase, and Nsp10, a helicase. The main regions involved in the interaction between ZNF283 and Nsp9 were determined to be the KRAB domain of ZNF283 and amino acids 178-449 of Nsp9. The KRAB domain of ZNF283 plays a role in facilitating Nsp10 binding. In addition, ZNF283 may have an affinity for the 3' untranslated region of PRRSV. These findings suggest that ZNF283 is an antiviral factor that inhibits PRRSV infection and extend our understanding of the interactions between KRAB-containing zinc finger proteins and viruses.

Research Progress on the detection methods of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes clinical syndromes typified as reproductive disorders in sows and respiratory diseases in piglets. PRRSV remains one of the most prevalent pathogens affecting the pig industry, because of its complex infection profile and highly heterogeneous genetic and recombination characteristics. Therefore, a rapid and effective PRRSV detection method is important for the prevention and control of PRRS. With extensive in-depth research on PRRSV detection methods, many detection methods have been improved and promoted. Laboratory methods include techniques based on virus isolation (VI), enzyme-linked immunosorbent assays (ELISA), indirect immunofluorescence assays (IFA), immunoperoxidase monolayer assays (IPMA), polymerase chain reaction (PCR), quantitative real-time PCR (qPCR), digital PCR (dPCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), clustered regularly interspaced short palindromic repeats (CRISPR), metagenomic next-generation sequencing (mNGS), and other methods. This study reviews the latest research on improving the main PRRSV detection methods and discusses their advantages and disadvantages.

Identificationof a novel linear epitope on the porcine reproductive and respiratory syndrome virus nucleocapsid protein, as recognized by a specific monoclonal antibody

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) remains one of the most threatening pathogens of swine. The nucleocapsid (N) protein is the major structural protein of the virus and has been used as a PRRSV diagnostic antigen due to its high level of inherent immunogenicity.

Methods

The recombinant PRRSV N protein was generated by the prokaryotic expressing system and used to immunized mice. Monoclonal antibodies against PRRSV were produced and validated by western blot analysis and indirect immunofluorescence analysis. In this study, the linear epitope of a specific monoclonal antibody mAb (N06) was subsequently identified by enzyme-linked immunosorbent assays (ELISA) using the synthesized overlapping peptides as antigens.

Results

According to the results of western blot analysis and indirect immunofluorescence analysis, mAb (N06) was capable of recognizing the native form as well as the denatured form of PRRSV N protein. The results of ELISA showed that mAb N06 recognized the epitope NRKKNPEKPHFPLATE, which was consistent with BCPREDS predictions of antigenicity.

Conclusion

All the data suggested that the mAb (N06) can be used as diagnostic reagents for PRRSV detection, while the recognized linear epitope can be useful in epitope-based vaccines development, which is helpful for the control of local PRRSV infections in swine.

Research Progress in Porcine Reproductive and Respiratory Syndrome Virus–Host Protein Interactions

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), which has been regarded as a persistent challenge for the pig industry in many countries. PRRSV is internalized into host cells by the interaction between PRRSV proteins and cellular receptors. When the virus invades the cells, the host antiviral immune system is quickly activated to suppress the replication of the viruses. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate the host machine and circumvent against the host antiviral responses. Therefore, identification of virus–host interactions is critical for understanding the host defense against viral infections and the pathogenesis of the viral infectious diseases. Most viruses, including PRRSV, interact with host proteins during infection. On the one hand, such interaction promotes the virus from escaping the host immune system to complete its replication. On the other hand, the interactions regulate the host cell immune response to inhibit viral infections. As common antiviral drugs become increasingly inefficient under the pressure of viral selectivity, therapeutic agents targeting the intrinsic immune factors of the host protein are more promising because the host protein has a lower probability of mutation under drug-mediated selective pressure. This review elaborates on the virus–host interactions during PRRSV infection to summarize the pathogenic mechanisms of PRRSV, and we hope this can provide insights for designing effective vaccines or drugs to prevent and control the spread of PRRS.

Development of a potential diagnostic monoclonal antibody against capsid spike protein VP27 of the novel goose astrovirus

Goose astrovirus (GAstVs) is an emerging pathogen of goslings that causes fatal gout, kidney hemorrhages, renomegaly, and high mortality. The GAstVs VP27 protein is an important capsid protein and a candidate for the development of diagnostic reagents. The aim of this study was to clone and express the VP27 gene for preparation of a specific monoclonal antibody (mAb). The VP27 protein was expressed and purified in the supernatant of Escherichia coli BL21. Then, the mAb was obtained with the hybridoma technique and named 2AF11. It was differentiated as IgG1 with the help of immunoglobulin subclass tests. This mAb can specifically recognize the VP27 protein in GAstVs-infected cells, as evidenced by western blot analysis and immunofluorescent assay. Furthermore, this mAb could also detect the VP27 protein in GAstVs-infected tissues, as demonstrated by immunohistochemistry. These findings indicate that this mAb has high diagnostic potential. Therefore, the newly produced anti-VP27 mAb, 2AF11, could be a useful tool as a specific diagnostic marker for GAstVs.

Mapping the Nonstructural Protein Interaction Network of Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a positive-stranded RNA virus belonging to the family Arteriviridae Synthesis of the viral RNA is directed by replication/transcription complexes (RTC) that are mainly composed of a network of PRRSV nonstructural proteins (nsps) and likely cellular proteins. Here, we mapped the interaction network among PRRSV nsps by using yeast two-hybrid screening in conjunction with coimmunoprecipitation (co-IP) and cotransfection assays. We identified a total of 24 novel interactions and found that the interactions were centered on open reading frame 1b (ORF1b)-encoded nsps that were mainly connected by the transmembrane proteins nsp2, nsp3, and nsp5. Interestingly, the interactions of the core enzymes nsp9 and nsp10 with transmembrane proteins did not occur in a straightforward manner, as they worked in the co-IP assay but were poorly capable of finding each other within intact mammalian cells. Further proof that they can interact within cells required the engineering of N-terminal truncations of both nsp9 and nsp10. However, despite the poor colocalization relationship in cotransfected cells, both nsp9 and nsp10 came together with membrane proteins (e.g., nsp2) at the viral replication and transcription complexes (RTC) in PRRSV-infected cells. Thus, our results indicate the existence of a complex interaction network among PRRSV nsps and raise the possibility that the recruitment of key replicase proteins to membrane-associated nsps may involve some regulatory mechanisms during infection.IMPORTANCE Synthesis of PRRSV RNAs within host cells depends on the efficient and correct assembly of RTC that takes places on modified intracellular membranes. As an important step toward dissecting this poorly understood event, we investigated the interaction network among PRRSV nsps. Our studies established a comprehensive interaction map for PRRSV nsps and revealed important players within the network. The results also highlight the likely existence of a regulated recruitment of the PRRSV core enzymes nsp9 and nsp10 to viral membrane nsps during PRRSV RTC assembly.

Identification of Nonstructural Protein 8 as the N-Terminus of the RNA-Dependent RNA Polymerase of Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a member within the family Arteriviridae of the order Nidovirales. Replication of this positive-stranded RNA virus within the host cell involves expression of viral replicase proteins encoded by two ORFs, namely ORF1a and ORF1b. In particular, translation of ORF1b depends on a -1-ribosomal frameshift strategy. Thus, nonstructural protein 9 (nsp9), the first protein within ORF1b that specifies the function of the viral RNA-dependent RNA polymerase, is expressed as the C-terminal extension of nsp8, a small nsp that is encoded by ORF1a. However, it has remained unclear whether the mature form of nsp9 in virus-infected cells still retains nsp8, addressing which is clearly critical to understand the biological function of nsp9. By taking advantage of specific antibodies to both nsp8 and nsp9, we report the following findings. (1) In infected cells, PRRSV nsp9 was identified as a major product with a size between 72 and 95 kDa (72-95 KDa form), which exhibited the similar mobility on the gel to the in vitro expressed nsp8-9ORF1b, but not the ORF1b-coded portion (nsp9ORF1b). (2) The antibodies to nsp8, but not to nsp7 or nsp10, could detect a major product that had the similar mobility to the 72-95 KDa form of nsp9. Moreover, nsp9 could be co-immunoprecipitated by antibodies to nsp8, and vice versa. (3) Neither nsp4 nor nsp2 PLP2 was able to cleave nsp8-nsp9 in vitro. Together, our studies provide experimental evidence to suggest that nsp8 is an N-terminal extension of nsp9. Our findings here paves way for further charactering the biological function of PRRSV nsp9.

Identification of the strain-specifically truncated nonstructural protein 10 of porcine reproductive and respiratory syndrome virus in infected cells

The nonstructural protein 10 (nsp10) of porcine reproductive and respiratory syndrome virus (PRRSV) encodes for helicase which plays a vital role in viral replication. In the present study, a truncated form of nsp10, termed nsp10a, was found in PRRSV-infected cells and the production of nsp10a was strain-specific. Mass spectrometric analysis and deletion mutagenesis indicated that nsp10a may be short of about 70 amino acids in the N terminus of nsp10. Further studies by rescuing recombinant viruses showed that the Glu-69 in nsp10 was the key amino acid for nsp10a production. Finally, we demonstrated that nsp10a exerted little influence on the growth kinetics of PRRSV in vitro.

Identification of a novel linear B-cell epitope in nonstructural protein 11 of porcine reproductive and respiratory syndrome virus that are conserved in both genotypes

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important pathogens, that hinder the development of global pork industry. Its nonstructural protein 11 (nsp11), with the nidoviral uridylate-specific endoribonuclease (NendoU) domain, is essential for PRRSV genome replication and it also contributes to host innate immunity suppression. However, the immunogenicity and immune structure of PRRSV nsp11 have not been well investigated yet. In this study, a monoclonal antibody (mAb), designated 3F9, that against nsp11 was generated. Subsequently, a series of partially overlapped fragments, covered the nsp11_40-223aa, were expressed to test the reactivity with mAb 3F9, and the ¹¹¹DCREY¹¹⁵ was found to be the core unit of the B-cell epitope recognized by mAb 3F9. Further investigation indicated that both genotype 1 and genotype 2 PRRSV can be recognized by mAb 3F9, due to the ¹¹¹DCREY¹¹⁵ is conserved in both genotype virus. Meanwhile, this epitope, localized at the surface of nsp11 in 3D structure, is confirmed to be able to induce humoral immune response in PRRSV infected pigs. These findings do not only provide an mAb tool to further investigate the function of nsp11, they also indicate the diagnostic potential for this epitope.