An attenuated herpesvirus vectored vaccine candidate induces T-cell responses against highly conserved porcine reproductive and respiratory syndrome virus M and NSP5 proteins that are unable to control infection.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a leading cause of economic loss in pig farming worldwide. Existing commercial vaccines, all based on modified live or inactivated PRRSV, fail to provide effective immunity against the highly diverse circulating strains of both PRRSV-1 and PRRSV-2. Therefore, there is an urgent need to develop more effective and broadly active PRRSV vaccines. In the absence of neutralizing antibodies, T cells are thought to play a central role in controlling PRRSV infection. Herpesvirus-based vectors are novel vaccine platforms capable of inducing high levels of T cells against encoded heterologous antigens. Therefore, the aim of this study was to assess the immunogenicity and efficacy of an attenuated herpesvirus-based vector (bovine herpesvirus-4; BoHV-4) expressing a fusion protein comprising two well-characterized PRRSV-1 T-cell antigens (M and NSP5). Prime-boost immunization of pigs with BoHV-4 expressing the M and NSP5 fusion protein (vector designated BoHV-4-M-NSP5) induced strong IFN-γ responses, as assessed by ELISpot assays of peripheral blood mononuclear cells (PBMC) stimulated with a pool of peptides representing PRRSV-1 M and NSP5. The responses were closely mirrored by spontaneous IFN-γ release from unstimulated cells, albeit at lower levels. A lower frequency of M and NSP5 specific IFN-γ responding cells was induced following a single dose of BoHV-4-M-NSP5 vector. Restimulation using M and NSP5 peptides from PRRSV-2 demonstrated a high level of cross-reactivity. Vaccination with BoHV-4-M-NSP5 did not affect viral loads in either the blood or lungs following challenge with the two heterologous PRRSV-1 strains. However, the BoHV-4-M-NSP5 prime-boost vaccination showed a marked trend toward reduced lung pathology following PRRSV-1 challenge. The limited effect of T cells on PRRSV-1 viral load was further examined by analyzing local and circulating T-cell responses using intracellular cytokine staining and proliferation assays. The results from this study suggest that vaccine-primed T-cell responses may have helped in the control of PRRSV-1 associated tissue damage, but had a minimal, if any, effect on controlling PRRSV-1 viral loads. Together, these results indicate that future efforts to develop effective PRRSV vaccines should focus on achieving a balanced T-cell and antibody response.

A New Long Noncoding RNA, MAHAT, Inhibits Replication of Porcine Reproductive and Respiratory Syndrome Virus by Recruiting DDX6 To Bind to ZNF34 and Promote an Innate Immune Response.

Long noncoding RNAs (lncRNAs) have increasingly been recognized as being integral to cellular processes, including the antiviral immune response. Porcine reproductive and respiratory syndrome virus (PRRSV) is costly to the global swine industry. To identify PRRSV-related lncRNAs, we performed RNA deep sequencing and compared the profiles of lncRNAs in PRRSV-infected and uninfected Marc-145 cells. We identified a novel lncRNA called MAHAT (maintaining cell morphology-associated and highly conserved antiviral transcript; LTCON_00080558) that inhibits PRRSV replication. MAHAT binds and negatively regulates ZNF34 expression by recruiting and binding DDX6, an RNA helicase forming a complex with ZNF34. Inhibition of ZNF34 expression results in increased type I interferon expression and decreased PRRSV replication. This finding reveals a novel mechanism by which PRRSV evades the host antiviral innate immune response by downregulating the MAHAT-DDX6-ZNF34 pathway. MAHAT could be a host factor target for antiviral therapies against PRRSV infection. IMPORTANCE Long noncoding RNAs (lncRNAs) play important roles in viral infection by regulating the transcription and expression of host genes, and interferon signaling pathways. Porcine reproductive and respiratory syndrome virus (PRRSV) causes huge economic losses in the swine industry worldwide, but the mechanisms of its pathogenesis and immunology are not fully understood. Here, a new lncRNA, designated MAHAT, was identified as a regulator of host innate immune responses. MAHAT negatively regulates the expression of its target gene, ZNF34, by recruiting and binding DDX6, an RNA helicase, forming a complex with ZNF34. Inhibition of ZNF34 expression increases type I interferon expression and decreases PRRSV replication. This finding suggests that MAHAT has potential as a new target for developing antiviral drugs against PRRSV infection.

Host Cells Actively Resist Porcine Reproductive and Respiratory Syndrome Virus Infection via the IRF8-MicroRNA-10a-SRP14 Regulatory Pathway.

MicroRNAs (miRNAs) play an important role in the virus-host interaction. Our previous work has indicated that the expression level of miR-10a increased in porcine alveolar macrophages (PAMs) during porcine reproductive and respiratory syndrome virus (PRRSV) infection and further inhibited viral replication through downregulates the expression of host molecule signal-recognition particle 14 (SRP14) protein. However, the molecular mechanism of miR-10a increased after PRRSV infection remains unknown. In the present study, transcription factor interferon regulatory factor 8 (IRF8) was identified as a negative regulator of miR-10a. PRRSV infection decreases the expression level of IRF8 in PAMs, leading to upregulating miR-10a expression to play an anti-PRRSV role. Meanwhile, this work first proved that IRF8 promoted PRRSV replication in an miR-10a-dependent manner. Further, we explained that SRP14, the target gene of miR-10a, promotes the synthesis of the PRRSV genome by interacting with the viral components Nsp2, thus facilitating PRRSV replication. In conclusion, we identified a novel IRF8-miR-10a-SRP14 regulatory pathway against PRRSV infection, which provides new insights into virus-host interactions and suggests potential new antiviral strategies to control PRRSV. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) has rapidly spread to the global pig industry and caused incalculable economic damage since first discovered in the 1980s. However, conventional vaccines do not provide satisfactory protection. Understanding the molecular mechanisms of host resistance to PRRSV infection is necessary to develop safe and effective strategies to control PRRSV. During viral infection, miRNAs play vital roles in regulating the expression of viral or host genes at the posttranscriptional level. The significance of our study is that we revealed the transcriptional regulation mechanism of the antiviral molecule miR-10a after PRRSV infection. Moreover, our research also explained the mechanism of host molecule SRP14, the target gene of miR-10a regulating PRRSV replication. Thus, we report a novel regulatory pathway of IRF8-miR-10a-SRP14 against PRRSV infection, which provides new insights into virus-host interactions and suggests potential new control measures for future PRRSV outbreaks.

Modeling suggests gene editing combined with vaccination could eliminate a persistent disease in livestock.

Recent breakthroughs in gene-editing technologies that can render individual animals fully resistant to infections may offer unprecedented opportunities for controlling future epidemics in farm animals. Yet, their potential for reducing disease spread is poorly understood as the necessary theoretical framework for estimating epidemiological effects arising from gene-editing applications is currently lacking. Here, we develop semistochastic modeling approaches to investigate how the adoption of gene editing may affect infectious disease prevalence in farmed animal populations and the prospects and time scale for disease elimination. We apply our models to the porcine reproductive and respiratory syndrome (PRRS), one of the most persistent global livestock diseases to date. Whereas extensive control efforts have shown limited success, recent production of gene-edited pigs that are fully resistant to the PRRS virus have raised expectations for eliminating this deadly disease. Our models predict that disease elimination on a national scale would be difficult to achieve if gene editing was used as the only disease control. However, from a purely epidemiological perspective, disease elimination may be achievable within 3 to 6 y, if gene editing were complemented with widespread and sufficiently effective vaccination. Besides strategic distribution of genetically resistant animals, several other key determinants underpinning the epidemiological impact of gene editing were identified.

Impact of Cryopreservation on Viability, Phenotype, and Functionality of Porcine PBMC.

The use of frozen peripheral blood mononuclear cells (PBMC) is common in immunological studies. The impact of freezing PBMC has been assessed using human and mice cells, but little information is available regarding domestic animals. In the present study, the phenotype and functionality of frozen porcine PBMC were examined. In a preliminary experiment, three freezing media: fetal bovine serum plus 10% dimethyl sulfoxide, PSC cryopreservation kit, and Cryostor CS10, were compared regarding the preservation of cell viability and the response of PBMC to mitogens after thawing. After being stored one month in liquid nitrogen, cell viability was above 89% for all freezing media. The ELISPOT IFN-gamma (IFN-γ) results in response to PHA and of IgG ELISPOT in response to R848+IL-2 were similar to those obtained using fresh PBMC. In the second set of experiments, PBMC were obtained from five pigs vaccinated against Porcine reproductive and respiratory syndrome virus (PRRSV) and then frozen using Cryostor CS10. Recovered cells were phenotyped by flow cytometry using anti-CD3, CD4, CD8, and CD21 antibodies and were used to assess the PRRSV-specific responses in a proliferation experiment, an IFN-γ ELISPOT, and an IgG ELISPOT, and compared to the results obtained with fresh cells. The antigen-specific responses of frozen cells were significantly (p<0.05) impaired in the proliferation assay, particularly for CD4/CD8 double-positive T-cells and for CD21+ cells. Freezing resulted in decreased proliferation when Con A, but not PHA, was used. In ELISPOT, cryopreservation resulted in a decreased frequency of IFN-γ-secreting cells in response to PRRSV (p<0.05) but the response to PHA was not affected. No differences were observed in the IgG ELISPOT after polyclonal activation. Taken together, cryopreservation of porcine PBMC had a significant impact on the magnitude of recall antigen responses and therefore, it may affect the response of effector/memory cells but seems not to have a major impact on naïve T-cells. These results may help to the better use of frozen porcine PBMC, and to the interpretation of the results obtained from them.

Simultaneous Infection With Porcine Reproductive and Respiratory Syndrome and Influenza Viruses Abrogates Clinical Protection Induced by Live Attenuated Porcine Reproductive and Respiratory Syndrome Vaccination.

The porcine respiratory disease complex (PRDC) is responsible for significant economic losses in the pig industry worldwide. Porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus are major viral contributors to PRDC. Vaccines are cost-effective measures for controlling PRRS, however, their efficacy in the context of co-infections has been poorly investigated. In this study, we aimed to determine the effect of PRRSV-2 and swine influenza H3N2 virus co-infection on the efficacy of PRRSV modified live virus (MLV) vaccination, which is widely used in the field. Following simultaneous challenge with contemporary PRRSV-2 and H3N2 field isolates, we found that the protective effect of PRRS MLV vaccination on clinical disease and pathology was abrogated, although viral load was unaffected and antibody responses were enhanced. In contrast, co-infection in non-immunized animals reduced PRRSV-2 viremia and H3N2 virus load in the upper respiratory tract and potentiated T cell responses against both PRRSV-2 and H3N2 in the lung. Further analysis suggested that an upregulation of inhibitory cytokines gene expression in the lungs of vaccinated pigs may have influenced responses to H3N2 and PRRSV-2. These findings provide important insights into the effect of viral co-infections on PRRS vaccine efficacy that may help identify more effective vaccination strategies against PRDC in the field.

Establishment of a peptide-based enzyme-linked immunosorbent assay for detecting antibodies against PRRSV M protein.

BACKGROUND: Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating diseases affecting the swine industry globally. Evaluation of antibody responses and neutralizing antibody titers is the most effective method for vaccine evaluation. In this study, the B cell line epitopes of PRRSV M protein were predicted, and two peptide ELISA assays were established (M-A110-129 ELISA, M-A148-174 ELISA) to detect antibodies against PRRSV M protein. Field serum samples collected from pig farms were used to validate the peptide ELISA and compare it with an indirect immunofluorescence assay. RESULTS: The sensitivity and specificity of M-A110-129 ELISA and M-A148-174 ELISA were (111/125) 88.80%, (69/70) 98.57% and (122/125) 97.60%, (70/70) 100%, relative to indirect immunofluorescence assay. This peptide ELISA could detect antibodies against different genotypes of PRRSV including type 1 PRRSV, classical PRRSV, HP-PRRSV, and NADC30 like PRRSV, but not antibodies against other common swine viruses. The results of ROC analysis showed that the area under the curve (AUC) of the M-A110-129 ELISA and M-A148-174 ELISA were 0.967 and 0.996, respectively. Compared the concordance of results using two peptide ELISA assays, the IDEXX PRRSV X3 Ab ELISA and a virus neutralization test, were assessed using a series of 147 sera from pigs vaccinated with the NADC30-like PRRSV inactivated vaccine. The M-A148-174 ELISA had the best consistency, with a Cohen's kappa coefficient of 0.8772. The concordance rates of the Hipra PRRSV ELISA kit, M-A110-129 ELISA and M-A148-174 ELISA in the field seropositive detection results were 91.08, 86.32 and 95.35%, relative to indirect immunofluorescence assay. CONCLUSIONS: In summary, compared with M-A110-129 ELISA, the PRRSV M-A148-174 ELISA is of value for detecting antibodies against PRRSV and the evaluation of the NADC30-like PRRSV inactivated vaccine, but the advantage is insufficient in serological early diagnosis.

Successive Inoculations of Pigs with Porcine Reproductive and Respiratory Syndrome Virus 1 (PRRSV-1) and Swine H1N2 Influenza Virus Suggest a Mutual Interference between the Two Viral Infections.

Porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza A virus (swIAV) are major pathogens of the porcine respiratory disease complex, but little is known on their interaction in super-infected pigs. In this study, we investigated clinical, virological and immunological outcomes of successive infections with PRRSV-1 and H1N2 swIAV. Twenty-four specific pathogen-free piglets were distributed into four groups and inoculated either with PRRSV at study day (SD) 0, or with swIAV at SD8, or with PRRSV and swIAV one week apart at SD0 and SD8, respectively, or mock-inoculated. In PRRSV/swIAV group, the clinical signs usually observed after swIAV infection were attenuated while higher levels of anti-swIAV antibodies were measured in lungs. Concurrently, PRRSV multiplication in lungs was significantly affected by swIAV infection, whereas the cell-mediated immune response specific to PRRSV was detected earlier in blood, as compared to PRRSV group. Moreover, levels of interferon (IFN)-α measured from SD9 in the blood of super-infected pigs were lower than those measured in the swIAV group, but higher than in the PRRSV group at the same time. Correlation analyses suggested an important role of IFN-α in the two-way interference highlighted between both viral infections.

Porcine Reproductive and Respiratory Syndrome Virus nsp11 Antagonizes Broad Antiviral Effects of MCPIP1 by Inducing Interleukin-17 Expression.

Monocyte chemotactic protein-induced protein 1 (MCPIP1) is an inflammatory regulator in immune response and has broad antiviral effects by targeting viral RNA. Porcine reproductive and respiratory syndrome virus (PRRSV), a major viral pathogen in pigs, causes immune suppression leading to coinfection of swine pathogens, but the mechanisms are not fully clarified. In this study, MCPIP1 expression was found to be significantly upregulated in lungs of PRRSV-infected piglets, as well as in Marc-145 and porcine pulmonary alveolar macrophage (PAM) cells upon PRRSV stimulation. MCPIP1 overexpression significantly inhibited PRRSV replication, while MCPIP1 knockdown increased the virus titer. Various mutations in RNase functional domains of MCPIP1 impaired the inhibitory activity against PRRSV, while those in deubiquitinase domains failed to do so. MCPIP1 expression started to decrease from 60 h after PRRSV infection in PAMs. Meanwhile, infection with higher dose of PRRSV further downregulated MCPIP1, indicating the antagonizing effects from PRRSV against MCPIP1. Moreover, it was confirmed that MCPIP1 expression was downregulated in 3D4 cells with either interleukin-17 (IL-17) or nsp11 overexpression, while IL-17 inhibitor abolished the decrease of MCPIP1 caused by nsp11, indicating nsp11 employs IL-17 induction to inhibit MCPIP1. Furthermore, the PRRSV nsp11 mutant with a deficiency in IL-17 induction showed the recovered expression of MCPIP1 in infected cells, inspiring a strategy for virus attenuation. This is the first report about the role of MCPIP1 against PRRSV and the function of PRRSV nsp11 against innate immunity to facilitate virus replication via IL-17. The study not only illuminates PRRSV infection machinery but also enlightens alternative antiviral strategies, such as vaccine candidates. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the innate immunity and leads to coinfection of swine pathogens. Monocyte chemotactic protein-induced protein 1 (MCPIP1) is a broad-spectrum host antiviral protein. Therefore, to further clarify the mechanism of PRRSV against innate immunity, we explored the relationship between MCPIP1 and PRRSV infection. The results showed that MCPIP1 inhibited PRRSV infection in the early stage of virus infection. Importantly, PRRSV nsp11 subsequently employed IL-17 induction to suppress MCPIP1 expression and antagonized anti-PRRSV effects. Furthermore, PRRSV with mutation of nsp11 S74A failed to induce MCPIP1 reduction. These findings confirmed the function of MCPIP1 against PRRSV and revealed that PRRSV nsp11 plays an important role in virus against innate immunity. This study enlightens a new strategy to develop safer attenuated vaccines against PRRSV by nsp11 mutation.

The Innate Immune DNA Sensing cGAS-STING Signaling Pathway Mediates Anti-PRRSV Function.

Porcine reproductive and respiratory syndrome virus (PRRSV) modulates host innate immunity which plays a key role against PRRSV infection. As a RNA virus, PRRSV is mainly sensed by innate immune RNA receptors, whereas the role of innate immune DNA sensors in the PRRSV infection has not been elucidated. Here, we investigated the roles of DNA sensing cGAS-STING pathway in both PRRSV infected Marc-145 cells and porcine macrophages. The results show that in Marc-145 cells, the stable expression of STING with or without stimulations exhibited anti-PRRSV activity, and STING knockout heightened PRRSV infection. In CD163-3D4/21 porcine macrophages, either expression of STING or stimulation of cGAS-STING signaling obviously suppressed PRRSV infection, whereas in STING knockdown macrophages, the PRRSV infection was upregulated. Our results clearly demonstrate that the host cGAS-STING signal exerts an important antiviral role in PRRSV infection.

MicroRNA ssc-miR-124a exhibits antiviral activity against porcine reproductive and respiratory syndrome virus via suppression of host genes CD163.

Porcine reproductive and respiratory syndrome (PRRS) is a serious infectious disease in the swine industry, which causes severe economic losses to current swine production worldwide. There are no effective antiviral strategies for preventing this disease. Previous studies showed that microRNAs (miRNAs) play important role in virus-host interactions. In this study, we demonstrated that the expression level of ssc-miR-124a was significantly downregulated during both high and low pathogenic PRRSV infection. Overexpression of ssc-miR-124a markedly inhibits PRRSV replication in PAMs. Luciferase reporter experiments and RISC immunoprecipitation assay were used to identify the ssc-miR-124a could directly target the 3'UTR of pig CD163 mRNA in a sequence-specific manner and that CD163 mRNA and protein levels were reduced in PAMs overexpressing ssc-miR-124a. These data not only provide new insights into virus-host interactions during PRRSV infection, but also suggest potential new antiviral strategies against PRRSV infection in the future.

Efficacy of a live attenuated highly pathogenic PRRSV vaccine against a NADC30-like strain challenge: implications for ADE of PRRSV.

BACKGROUND: Porcine reproductive and respiratory syndrome virus (PRRSV) infection can cause severe reproductive failure in sows and respiratory distress in pigs of all ages, leading to major economic losses. To date, there are still no effective strategies to prevent and control PRRSV. Antibody-dependent enhancement (ADE), a phenomenon in which preexisting non-neutralizing antibodies or sub-neutralizing antibodies facilitate virus entry and replication, may be a significant obstacle in the development of effective vaccines for many viruses, including PRRSV. However, the contribution of ADE to PRRSV infection remains controversial, especially in vivo. Whether attenuated PRRSV vaccines prevent or worsen subsequent disease in pigs infected by novel PRRSV strains requires more research. In the present study, in vivo experiments were conducted to evaluate ADE under different immune statuses, which were produced by waiting different lengths of time after vaccination with a commercially available attenuated highly pathogenic PRRSV (HP-PRRSV) vaccine (JXA1-R) before challenging the pigs with a novel heterologous NADC30-like strain. RESULTS: Piglets that were vaccinated before being challenged with PRRSV exhibited lower mortality rates, lower body temperatures, higher bodyweight gain, and lower viremia. These results demonstrate that vaccination with JXA1-R alleviated the clinical signs of PRRSV infection in all vaccinated groups. CONCLUSIONS: The obtained data indicate that the attenuated vaccine test here provided partial protection against the NADC30-like strain HNhx. No signs of enhanced PRRSV infection were observed under the applied experimental conditions. Our results provide some insight into the molecular mechanisms underlying vaccine-induced protection or enhancement in PRRSV.

Development of a monoclonal antibody against PRRSV glycoprotein 3 using an immuodominant peptide as immunogen.

Glycoprotein 3 (GP3), a highly glycosylated membrane protein, is a protective antigen and minor structural protein of porcine reproductive and respiratory syndrome virus (PRRSV), and plays a crucial role in virus assembly and infection. In the present study, we synthesized 23 overlapping peptides span GP3 protein sequence and used pig anti-PRRSV serums to identify immunodominant peptides by indirect ELISA. Five immunodominant peptides GP3-P3, P4, P5, P6 and P7 were identified and GP3-P4 (P55LCPTRQAAAEILEPGKS72) was conjugated to carrier protein BSA. One mAb 1E5 against GP3 was generated from BALB/c mice immunized with the conjugates BSA-P4. The Characterization of mAb was identified by Western blot, Dot-ELISA, IPMA and IFA. We found that mAb 1E5 can specifically react with HP-PRRSV strains but not C-PRRSV or NADC30-like PRRSV strains tested in this study. Site-directed alanine substitution analysis revealed that 8 amino acid residues were involved in antibody binding, among them E65, L67 and P69 were critical residue recognized by mAb 1E5. Taken together, this study provided a novel strategy for generating specific mAbs against virus proteins by using immunodominant peptides as targets, and the mAb 1E5 may be useful for development of rapid differential detection method differentiating HP-PRRSV from C-PRRSV and NADC30-like PRRSV.

Swine Dendritic Cell Response to Porcine Reproductive and Respiratory Syndrome Virus: An Update.

Dendritic cells (DCs) are the most potent antigen-presenting cells, unique to initiate and coordinate the adaptive immune response. In pigs, conventional DCs (cDCs), plasmacytoid DCs (pDCs), and monocyte-derived DCs (moDCs) have been described in blood and tissues. Different pathogens, such as viruses, could infect these cells, and in some cases, compromise their response. The understanding of the interaction between DCs and viruses is critical to comprehend viral immunopathological responses. Porcine reproductive and respiratory syndrome virus (PRRSV) is the most important respiratory pathogen in the global pig population. Different reports support the notion that PRRSV modulates pig immune response in addition to their genetic and antigenic variability. The interaction of PRRSV with DCs is a mostly unexplored area with conflicting results and lots of uncertainties. Among the scarce certainties, cDCs and pDCs are refractory to PRRSV infection in contrast to moDCs. Additionally, response of DCs to PRRSV can be different depending on the type of DCs and maybe is related to the virulence of the viral isolate. The precise impact of this virus-DC interaction upon the development of the specific immune response is not fully elucidated. The present review briefly summarizes and discusses the previous studies on the interaction of in vitro derived bone marrow (bm)- and moDCs, and in vivo isolated cDCs, pDCs, and moDCs with PRRSV1 and 2.

The Ability of Porcine Reproductive and Respiratory Syndrome Virus Isolates to Induce Broadly Reactive Neutralizing Antibodies Correlates With In Vivo Protection.

Porcine reproductive and respiratory syndrome (PRRS) is considered one of the most relevant diseases of swine. The condition is caused by PRRS virus (PRRSV), an extremely variable virus of the Arteriviridae family. Its heterogeneity can be responsible, at least partially, of the poor cross-protection observed between PRRSV isolates. Neutralizing antibodies (NAs), known to play a role in protection, usually poorly recognize heterologous PRRSV isolates, indicating that most NAs are strain-specific. However, some pigs develop broadly reactive NAs able to recognize a wide range of heterologous isolates. The aim of this study was to determine whether PRRSV isolates that induce broadly reactive NAs as determined in vitro are able to confer a better protection in vivo. For this purpose two in vivo experiments were performed. Initially, 40 pigs were immunized with a PRRSV-1 isolate known to induce broadly reactive NAs and 24 additional pigs were used as controls. On day 70 after immunization, the pigs were divided into eight groups composed by five immunized and three control pigs and exposed to one of the eight different heterologous PRRSV isolates used for the challenge. In the second experiment, the same experimental design was followed but the pigs were immunized with a PRRSV-1 isolate, which is known to generate mostly strain-specific NAs. Virological parameters, specifically viremia and the presence of challenge virus in tonsils, were used to determine protection. In the first experiment, sterilizing immunity was obtained in three groups, prevention of viremia was observed in two additional groups, although the challenge virus was detected occasionally in the tonsils of immunized pigs, and partial protection, understood as a reduction in the frequency of viremia compared with controls, was recorded in the remaining three groups. On the contrary, only partial protection was observed in all groups in the second experiment. The results obtained in this study confirm that PRRSV-1 isolates differ in their ability to induce cross-reactive NAs and, although other components of the immune response might have contributed to protection, pigs with cross-reactive NAs at the time of challenge exhibited better protection, indicating that broadly reactive NAs might play a role in protection against heterologous reinfections.

Porcine Reproductive and Respiratory Syndrome Virus Infection Upregulates Negative Immune Regulators and T-Cell Exhaustion Markers.

Porcine alveolar macrophage (PAM) is one of the primary cellular targets for porcine reproductive and respiratory syndrome virus (PRRSV), but less than 2% of PAMs are infected with the virus during the acute stage of infection. To comparatively analyze the host transcriptional response between PRRSV-infected PAMs and bystander PAMs that remained uninfected but were exposed to the inflammatory milieu of an infected lung, pigs were infected with a PRRSV strain expressing green fluorescent protein (PRRSV-GFP), and GFP+ (PRRSV infected) and GFP- (bystander) cells were sorted for RNA sequencing (RNA-seq). Approximately 4.2% of RNA reads from GFP+ and 0.06% reads from GFP- PAMs mapped to the PRRSV genome, indicating that PRRSV-infected PAMs were effectively separated from bystander PAMs. Further analysis revealed that inflammatory cytokines, interferon-stimulated genes, and antiviral genes were highly upregulated in GFP+ compared to GFP- PAMs. Importantly, negative immune regulators, including NF-κB inhibitors (NFKBIA, NFKBID, NFKBIZ, and TNFAIP3) and T-cell exhaustion markers (programmed death ligand-1 [PD-L1], PD-L2, interleukin-10 [IL-10], IDO1, and transforming growth factor ß2 [TGFB2]) were highly upregulated in GFP+ cells compared to GFP- cells. By using an in situ hybridization assay, RNA transcripts of tumor necrosis factor (TNF) and NF-κB inhibitors were detected in PRRSV-infected PAMs cultured ex vivo and lung sections of PRRSV-infected pigs during the acute stage of infection. Collectively, the results suggest that PRRSV infection upregulates expression of negative immune regulators and T-cell exhaustion markers in PAMs to modulate the host immune response. Our findings provide further insight into PRRSV immunopathogenesis. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is widespread in many swine-producing countries, causing substantial economic losses to the swine industry. Porcine alveolar macrophage (PAM) is considered the primary target for PRRSV replication in pigs. However, less than 2% of PAMs from acutely infected pigs are infected with the virus. In the present study, we utilized a PRRSV strain expressing green fluorescent protein to infect pigs and sorted infected and bystander PAMs from the pigs during the acute stage of infection for transcriptome analysis. PRRSV-infected PAMs showed a distinctive gene expression profile and contained many uniquely activated pathways compared to bystander PAMs. Interestingly, upregulated expression of NF-κB signaling inhibitors and T-cell exhaustion molecules were observed in PRRSV-infected PAMs. Our findings provide additional knowledge on the mechanisms that PRRSV employs to modulate the host immune system.

Abundance of Lactobacillus in porcine gut microbiota is closely related to immune response following PRRSV immunization.

Increasing evidence shows that gut microbiota plays a critical role in host immune system development and immune regulation, thus the composition of gut microbiota may affect how individuals respond to immunizations. Currently, little evidence is available on the correlation between porcine gut microbiota and vaccine immune response. Here, we investigated the influence of gut microbiota on immune response in pigs to porcine reproductive and respiratory syndrome virus (PRRSV) vaccine. Based on the antibody levels for PRRSV, the immunized pigs were divided into three groups (high, low, and others), and followed by virulent PRRSV challenge. The comprehensive analysis of microbial composition revealed that gut microbiota was similar in the richness and diversity among different groups before immunization. After immunization, the richness and diversity of gut microbial community in the high group were still similar to the low group, although there was a decrease in community diversity overtime. Interestingly, the antibody titer was positively correlated with the abundance of Lactobacillus in gut microbiota in immunized pigs. Further analysis indicated that gut microbial composition might be correlated to the clinical parameters such as body weight and rectal temperature after virus challenge. Taken together, our findings suggest that certain specific members of gut microbiota, such as Lactobacillus may serve as a mechanism for regulating the immune response following immunization in pigs.

Interaction of Type 1 Porcine Reproductive and Respiratory Syndrome Virus With In Vitro Derived Conventional Dendritic Cells.

The present study delineates the interaction of a typical PRRSV1.1 isolate 3267 (moderate virulence) with in vitro derived pig conventional dendritic cells, cDC1, cDC2, and a CD14+ population (designated as CD14+ DCs). cDC1 and cDC2 were not susceptible to 3267 infection, but a fraction of CD14+ DCs were infected. After exposure to the virus, all three DC types remained immature as determined by no increase of maturation molecules (MHC-I, MHC-II, CD80/86, CCR7), no release of cytokines, no modification of antigen presentation abilities, and no alteration of endocytic/phagocytic capabilities. However, when infected MARC-145 cells were used as a source of viral antigens, cDC2 and CD14+ DCs showed a significant increase in the expression of maturation molecules and substantial release of cytokines, notably IL-12/IL-23p40 (by both DC types) and IL-10 (by CD14+ DCs). To address the impact of PRRSV1 3267 on TLR3- and TLR7-mediated activation, cDC1, cDC2, and CD14+ DCs were inoculated by the virus (live or UV-inactivated) for 6 h prior to or simultaneously with the addition of poly I:C (TLR3 ligand) or gardiquimod (TLR7 ligand; not used for cDC1). Compared with using TLR ligand alone, combination with the virus did not result in any alteration to the maturation markers on all DC types but changed the cytokine response to either TLR3 or TLR7 ligand. Pre-exposure of cDC2 or CD14+ DCs to the live virus resulted in an increased production of IFN-α upon poly I:C stimulation, while pre-exposure to UV-inactivated virus tended to enhance the release of IL-10 upon gardiquimod stimulation. Simultaneous addition of the live virus and the TLR ligand either had no effect (mainly in cDC2) or impaired most of the cytokine release after gardiquimod stimulation (in CD14+ DCs). When used as antigen presenting cells, cDC2 pre-inoculated by the live virus before addition of gardiquimod impaired the proliferation of CD4-CD8- T cells. In the case of CD14+ DCs, pre-exposure to the live virus or simultaneously added with TLR3 or TLR7 ligand largely decreased the proliferation of CD4-CD8+ and CD4-CD8+ T-cell subsets. For cDC1, no significant changes were observed in cytokine responses or T-cell proliferation after poly I:C stimulation. Of note, cDC1 had a short life during in vitro culturing, for which the results obtained might be biased. Overall, exposure to PRRSV1 did not induce maturation of cDC1, cDC2, or CD14+ DCs, but modified TLR3 and TLR7-associated responses (except for cDC1), which may affect the development of adaptive immunity during PRRSV1 infection. Moreover, the sensing of infected cells was different from that of the free virus.

The superposition anti-viral activity of porcine tri-subtype interferon expressed by Saccharomyces cerevisiae.

Interferon (IFN)-mediated antiviral responses are central to host defense against viral infection. Porcine viral infection has emerged as a serious hazard for the pig industry. The construction of an engineered Saccharomyces cerevisiae strain that efficiently produces porcine IFN has demonstrated several advantages. It can be easily fed to pigs, which helps in reducing antibiotic residues in pork and improve meat quality. In this study, the stable expression of several porcine IFN molecules (pIFN-α1, pIFN-ß, pIFN-λ1, pIFN-λ1-ß, pIFN-λ1-ß-α1) were determined using an engineered S. cerevisiae system. With the YeastFab assembly method, the complete transcriptional units containing promoter (GPD), secretory peptide (α-mating factor), target gene (IFN) and terminator (ADH1) were successfully constructed using the characteristics of type II restriction endonuclease, and then integrated into the chromosomes Ⅳ and XVI of ST1814 yeast host strain, respectively. The expression kinetics of recombinant pIFNs were further analyzed. Synergism in the expression level of IFN receptor, antiviral protein, and viral loading was observed in viral-cell infection model treated with different porcine IFN subtypes. The porcine reproductive and respiratory syndrome viral load and antibody titer in serum decreased significantly after oral administration of IFN expression yeast fermentation broth. These findings indicate the potential efficacy of multi-valent pIFNs expressing S. cerevisiae as a potent feed material to prevent viral infections of pigs.

Identification of potential SLA-I-restricted CTL epitopes within the M protein of porcine reproductive and respiratory syndrome virus.

CD8+ cytotoxic T lymphocytes (CTLs), are essential for clearance of porcine reproductive and respiratory syndrome virus (PRRSV) infection and regulation of host immune responses. Identification of SLA I-restricted CD8+ CTL epitopes would facilitate PRRSV vaccine development. Here, cells isolated from peripheral blood mononuclear cells (PBMCs) of PRRSV-immunized Large White pigs (JXA1-R strain) were screened for immunodominant PRRSV-2 M protein T cell epitopes via ELISPOT assay. Of nine immunodominant epitopes detected, eight elicited significant IFN-γ secretion responses that varied among individual pigs and according to epitope. To predict which epitopes harbored potential CTL epitopes, swine leukocyte antigen (SLA) class I genes of Large White pigs were cloned and sequenced, yielding fourteen distinct SLA class I gene sequences. Based on ELISPOT and SLA genotyping results, SLA-restricted binding of the fourteen predicted class I proteins to peptides derived from the eight immunodominant epitopes were predicted in-silico. After evaluation of 42 pET-peptide-SLA-I-ß2m complexes containing predicted restricted peptides, extracellular SLA class I domains and ß2m, ELISA testing of 33 peptide-SLA-I-ß2m complexes detected four complexed peptides. These four peptides were evaluated using in vitro complex refolding assays that confirmed that M2-5 and M6-1 peptides each formed complexes with SLA-2*0502 and sß2m, while M9-1 formed a complex with SLA-2*1201 and sß2m. ELISPOT results confirmed these three 9-mer potential CTL epitopes efficiently stimulated IFN-γ secretion when presented by SLA class I molecules specified here. This study describes effective CTL epitope identification methods for use in future investigations of swine cellular immunity toward T cell-based vaccine development.