Validation of a phenotyping method to identify PRRSV-resilient sows and its impact on sow stayability.

Endemic and epidemic outbreaks of porcine reproductive and respiratory syndrome virus (PRRSV) are causing large economic losses in commercial pig production worldwide. Given the complexity of controlling this disease with vaccines or other biosecurity measures, the selection for pigs with a natural resilience to this infection has been proposed as an alternative approach. In this context, we previously reported a vaccine-based protocol to classify 6-week-old female piglets from one farm into resilient and susceptible phenotypes. Subsequent analysis showed that resilient sows had fewer lost piglets during a PRRSV epidemic. In the present study, we validated the results in four additional farms by showing a robust effect on the percentage of piglets lost (P<0.05). We were able to associate the resilient phenotype with a 2-4% reduction in piglet losses on sow farms in both endemic and endemic/epidemic situations. Also consistent with previous results, susceptible sows delivered on average, almost 0.5 more piglets born per parity (P<0.05). However, we show here that resilient sows have a longer stayability in the farm (+57 d; P<0.05) and +0.3 more successful parities (P<0.05), which balances the total number of piglets born and born alive in the full productive life of the sow between the two groups. Resilient sows thus contribute towards to a more sustainable production system, reducing sow replacement and piglet mortality. The validation of this protocol on four independent production farms paves the way for the study of the genetic variation underlying the resilient/susceptible classification, with a view to incorporating this information into selection programs in the future.

Enhancing the understanding of coinfection outcomes: Impact of natural atypical porcine pestivirus infection on porcine reproductive and respiratory syndrome in pigs.

Atypical porcine pestivirus (APPV) is a novel member of the Pestivirus genus detected in association with congenital tremor (CT) type A-II outbreaks and from apparently healthy pigs, both as singular infection and as part of multi-pathogen infections. 'Classical' pestiviruses are known to cause immunosuppression of their host, which can increase susceptibility to secondary infections, severely impacting health, welfare, and production. To investigate APPV's effect on the host's immune system and characterise disease outcomes, 12 piglets from a natural APPV CT type A-II outbreak were experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV), a significant porcine pathogen. Rectal temperatures indicating febrile responses, viremia and viral-specific humoral and cellular responses were assessed throughout the study. Pathological assessment of the lungs and APPV-PRRSV co-localisation within the lungs was performed at necropsy. Viral co-localisation and pathological assessment of the lungs (Immunohistochemistry, BaseScope in situ hybridisation) were performed post-mortem. APPV status did not impact virological or immunological differences in PRRSV-infected groups. However, significantly higher rectal temperatures were observed in the APPV+ve/PRRSV+ve group over four days, indicating APPV increased the febrile response. Significant differences in the lung consolidation of the apical and intermediate lobes were also present, suggesting that APPV co-infection may augment lung pathology.

Knock down of transforming growth factor beta improves expressions of co-stimulatory molecules, type I interferon-regulated genes, and pro-inflammatory cytokine in PRRSV-inoculated monocyte-derived macrophages.

Porcine reproductive and respiratory syndrome virus (PRRSV) induces a poor innate immune response following infection. This study evaluates the effects of transforming growth factor beta 1 (TGFß1) up-regulated by PRRSV on gene expressions of co-stimulatory molecules, type I interferon (IFN), type I IFN-regulated genes (IRGs), pattern recognition receptors, and pro-inflammatory cytokines in PRRSV-inoculated monocyte-derived macrophages (MDMs). Phosphorothioate-modified antisense oligodeoxynucleotides (AS ODNs) specific to various regions of porcine TGFß1 mRNA were synthesized, and those specific to the AUG region efficiently knockdown TGFß1 mRNA expression and protein translation. Transfection of TGFßAS ODNs in MDMs inoculated with either classical PRRSV-2 (cPRRSV-2) or highly pathogenic PRRSV-2 (HP-PRRSV-2) significantly reduced TGFß1 mRNA expression and significantly increased mRNA expressions of CD80, CD86, IFNß, IRGs (i.e. IFN regulatory factor 3 (IRF3), IRF7, myxovirus resistance 1, osteopontin, and stimulator of IFN genes), Toll-like receptor 3, and tumor necrosis factor-alpha. Transfection of TGFßAS ODNs in MDMs inoculated with HP-PRRSV-2 also significantly increased mRNA expressions of IFNα, IFNγ, and 2'-5'-oligoadenylate synthetase 1. The quantity of PRRSV-2 RNA copy numbers was significantly reduced in MDMs transfected with TGFßAS ODNs as compared to untransfected MDMs. Recombinant porcine TGFß1 (rTGFß1) and recombinant porcine IFNα (rIFNα) sustained and reduced the yields of PRRSV-2 RNA copy numbers in PRRSV-2 inoculated MDMs, respectively. These findings demonstrate a strategy of PRRSV for innate immune suppression via an induction of TGFß expression. These findings also suggest TGFß as a potential parameter that future PRRSV vaccine and vaccine adjuvant candidates should take into consideration.

Exploratory application of a cannulation model in recently weaned pigs to monitor longitudinal changes in the enteric microbiome across varied porcine reproductive and respiratory syndrome virus (PRRSV) infection statuses.

Introduction: The enteric microbiome and its possible modulation to improve feed conversion or vaccine efficacy is gaining more attention in pigs. Weaning pigs from their dam, along with many routine procedures, is stressful. A better understanding of the impact of this process on the microbiome may be important for improving pig production. The objective of this study was to develop a weaner pig cannulation model, thus allowing ileum content collection from the same pig over time for 16S rRNA sequencing under different porcine reproductive and respiratory syndrome virus (PRRSV) infection statuses. Methods: A total of 15 3-week-old pigs underwent abdominal surgery and were fitted with an ileum cannula, with ileum contents collected over time. In this pilot study, treatment groups included a NEG-CONTROL group (no vaccination, no PRRSV challenge), a POS-CONTROL group (no vaccination, challenged with PRRSV), a VAC-PRRSV group (vaccinated, challenged with PRRSV), a VAC-PRO-PRRSV group (vaccinated, supplemented with a probiotic, challenged with PRRSV), and a VAC-ANTI-PRRSV group (vaccinated, administered an antibiotic, challenged with PRRSV). We assessed the microbiome over time and measured anti-PRRSV serum antibodies, PRRSV load in serum and nasal samples, and the severity of lung lesions. Results: Vaccination was protective against PRRSV challenge, irrespective of other treatments. All vaccinated pigs mounted an immune response to PRRSV within 1 week after vaccination. A discernible impact of treatment on the diversity, structure, and taxonomic abundance of the enteric microbiome among the groups was not observed. Instead, significant influences on the ileum microbiome were observed in relation to time and treatment. Discussion: The cannulation model described in this pilot study has the potential to be useful in studying the impact of weaning, vaccination, disease challenge, and antimicrobial administration on the enteric microbiome and its impact on pig health and production. Remarkably, despite the cannulation procedures, all vaccinated pigs exhibited robust immune responses and remained protected against PRRSV challenge, as evidenced by the development of anti-PRRSV serum antibodies and viral shedding data.

Multi-Omics Analysis by Machine Learning Identified Lysophosphatidic Acid as a Biomarker and Therapeutic Target for Porcine Reproductive and Respiratory Syndrome.

As a significant infectious disease in livestock, porcine reproductive and respiratory syndrome (PRRS) imposes substantial economic losses on the swine industry. Identification of diagnostic markers and therapeutic targets has been a focal challenge in PPRS prevention and control. By integrating metabolomic and lipidomic serum analyses of clinical pig cohorts through a machine learning approach with in vivo and in vitro infection models, lysophosphatidic acid (LPA) is discovered as a serum metabolic biomarker for PRRS virus (PRRSV) clinical diagnosis. PRRSV promoted LPA synthesis by upregulating the autotaxin expression, which causes innate immunosuppression by dampening the retinoic acid-inducible gene I (RIG-I) and type I interferon responses, leading to enhanced virus replication. Targeting LPA demonstrated protection against virus infection and associated disease outcomes in infected pigs, indicating that LPA is a novel antiviral target against PRRSV. This study lays a foundation for clinical prevention and control of PRRSV infections.

Determination of the frequency of individuals with broadly cross-reactive neutralizing antibodies against PRRSV in the sow population under field conditions.

BACKGROUND: Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a significant swine pathogen, yet the immune response components contributing to protection remain incompletely understood. Broadly reactive neutralizing antibodies (bNAs) may play a crucial role in preventing reinfections by heterologous viruses, although their occurrence is considered low under both field and experimental conditions. This study aimed to assess the frequency of sows exhibiting bNAs against PRRSV under field conditions and to analyze the epidemiological factors influencing the occurrence of these elite neutralizers. Blood samples were collected from breeding sows across eleven unrelated pig farms, with samples categorized by parity. Serum obtained was utilized in virus neutralization assays (VNs) against six PRRSV field isolates and two MLV strains. RESULTS: Approximately 7% of the sows exhibited neutralization activity against all viruses in the panel, with a geometric mean of the titer (GMT) of NAs at or exceeding 4 log2. Exclusion of the PRRSV-2 isolate from the panel increased the proportion of elite neutralizers to around 15%. Farm-specific analysis revealed significant variations in both GMT of NAs and proportion of elite neutralizers. PRRSV unstable farms and those with a PRRS outbreak in the last 12 months displayed higher GMT of NAs compared to stable farms without recent outbreaks. The GMT of NAs showed a gradual, albeit moderate, increase with the parity of the sows. Parity's impact on bNA response was consistently observed in stable farms but not necessarily in unstable farms or those with recent outbreaks. Finally, the results indicated that vaccinated animals had higher NA titers against the vaccine virus used in the farm than against field viruses. CONCLUSION: bNAs against heterologous isolates induced by PRRSV infection under field conditions are generally low, often falling below titers necessary for protection against reproductive failure. However, a subset of sows (approximately 15%) can be considered elite neutralizers, efficiently recognizing various PRRSV strains. Repeated exposures to PRRSV play a crucial role in eliciting these bNAs, with a higher frequency observed in unstable farms and those with recent outbreaks. In stable farms, parity only marginally influences bNA titers, highlighting its limited role compared to the impact of PRRSV exposure history.

The effect of matrine and glycyrrhizic acid on porcine reproductive and respiratory syndrome virus in Vitro and in vivo.

Porcine reproductive and respiratory syndrome (PRRS) is endemic worldwide, seriously affecting the development of the pig industry, but vaccines have limited protective effects against PRRSV transmission. The aim of this study was to identify potential anti-PRRSV drugs. We examined the cytotoxicity of seven compounds formulated based on the mass ratio of glycyrrhizic acid to matrine and calculated their inhibition rates against PRRSV in vitro. The results showed that the seven compounds all had direct killing and therapeutic effects on PRRSV, and the compounds inhibited PRRSV replication in a time- and dose-dependent manner. The compound with the strongest anti-PRRSV effect was selected for subsequent in vivo experiments. Pigs were divided into a control group and a medication group for the in vivo evaluation. The results showed that pigs treated with the 4:1 compound had 100% morbidity after PRRSV challenge, and the mortality rate reached 75% on the 8th day of the virus challenge. These results suggest that this compound has no practical anti-PRRSV effect in vivo and can actually accelerate the death of infected pigs. Next, we further analyzed the pigs that exhibited semiprotective effects following vaccination with the compound to determine whether the compound can synergize with the vaccine in vivo. The results indicated that pigs treated with the compound had higher mortality rates and more severe clinical reactions after PRRSV infection (p < 0.05). The levels of proinflammatory cytokines (IL-6, IL-8, IL-1ß, IFN-γ, and TNF-α) were significantly greater in the compound-treated pigs than in the positive control-treated pigs (p < 0.05), and there was no synergistic enhancement with the live attenuated PRRSV vaccine (p < 0.05). The compound enhanced the inflammatory response, prompted the body to produce excessive levels of inflammatory cytokines and caused body damage, preventing a therapeutic effect. In conclusion, the present study revealed that the in vitro effectiveness of these agents does not indicate that they are effective in vivo or useful for developing anti-PRRSV drugs. Our findings also showed that, to identify effective anti-PRRSV drugs, comprehensive drug screening is needed, for compounds with solid anti-inflammatory effects both in vitro and in vivo. Our study may aid in the development of new anti-PRRSV drugs.

Field efficacy of a novel porcine reproductive and respiratory syndrome modified-live virus vaccine with an emphasis on growth performance.

BACKGROUND: This field evaluation was designed to evaluate the efficacy of a new porcine reproductive and respiratory syndrome virus-2 (PRRSV-2) modified live virus vaccine at three independent pig farms. METHODS: Three farms were selected for this study based on their respiratory disease status caused by PRRSV-2 infection in post-weaning and growing pigs. Each farm housed a total of 40, 18-day-old pigs that were randomly allocated to one of two treatment groups. Pigs were administered a 1.0 mL dose of the bivalent vaccine intramuscularly at 21 days of age in accordance with the manufacturer's recommendations, whereas unvaccinated pigs were administered a single dose of phosphate buffered saline at the same age. RESULTS: Vaccinated groups were measured and calculated significantly (p < 0.05) higher in body weight and average daily weight gain on all three farms compared with unvaccinated groups. Vaccinated groups elicited PRRS antibodies and PRRSV-2-specific interferon-γ secreting cells, which reduced the amount of PRRSV-2 genomic copies in the blood and reduced macroscopic and microscopic lung lesions severity when compared with unvaccinated groups. CONCLUSIONS: The field evaluation data demonstrated that a new PRRSV-2 modified live virus vaccine was efficacious in swine herds suffering from respiratory diseases caused by PRRSV-2 infection.

Porcine reproductive and respiratory syndrome virus infects the reproductive system of male piglets and impairs development of the blood-testis barrier.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly contagious disease that threatens the global swine industry. Recent studies have focused on the damage that PRRSV causes to the reproductive system of male pigs, although pathological research is lacking. Therefore, we examined the pathogenic mechanisms in male piglets infected with PRRSV. Gross and histopathological changes indicated that PRRSV affected the entire reproductive system, as confirmed via immunohistochemical analysis. PRRSV infected Sertoli cells and spermatogonia. To test the new hypothesis that PRRSV infection in piglets impairs blood - testis barrier (BTB) development, we investigated the pathology of PRRSV damage in the BTB. PRRSV infection significantly decreased the quantity and proliferative capacity of Sertoli cells constituting the BTB. Zonula occludens-1 and ß-catenin were downregulated in cell - cell junctions. Transcriptome analysis revealed that several crucial genes and signalling pathways involved in the growth and development of Leydig cells, Sertoli cells, and tight junctions in the testes were downregulated. Apoptosis, necroptosis, inflammatory, and oxidative stress-related pathways were activated, whereas hormone secretion-related pathways were inhibited. Many Sertoli cells and spermatogonia underwent apoptosis during early differentiation. Infected piglets exhibited disrupted androgen secretion, leading to significantly reduced testosterone and anti-Müllerian hormone levels. A cytokine storm occurred, notably upregulating cytokines such as tumour necrosis factor-α and interleukin-6. Markers of oxidative-stress damage (i.e. H2O2, malondialdehyde, and glutathione) were upregulated, whereas antioxidant-enzyme activities (i.e. superoxide dismutase, total antioxidant capacity, and catalase) were downregulated. Our results demonstrated that PRRSV infected multiple organs in the male reproductive system, which impaired growth in the BTB.

Multiplex Assay to Determine Acute Phase Proteins in Modified Live PRRSV Vaccinated Pigs.

Acute phase protein (APP) response to vaccine challenges is an attractive alternative to natural infection for identifying pigs with increased disease resilience and monitoring the productive performance. Currently, the methods used for APP quantification are diverse and often based on techniques that use antibodies that are not necessarily pig specific. The objective of this work is the development of a method based on a UPLC-SRM/MS system for simultaneous determination of haptoglobin, apolipoprotein A1, C-reactive protein, pig-major acute protein, and serum amyloid A and its application in pigs to monitor the effect of a vaccine administered against porcine reproductive and respiratory syndrome virus (PRRSV). With the aim of tracing the complete analytical process for each proteotypic peptide, a synthetic QconCat polypeptide construct was designed. It was possible to develop an SRM method including haptoglobin, apolipoprotein A1, pig-MAP, and serum amyloid A1. The PRRSV vaccine only affected haptoglobin. The pigs with positive viremia tended to show higher values than negative pigs, reaching significant differences in the three haptoglobin SRM-detected peptides but not with the data acquired by immunoenzymatic and spectrophotometric assays. These results open the door to the use of SRM to accurately monitor APP changes in experimental pigs.

Host cells reprogram lipid droplet synthesis through YY1 to resist PRRSV infection.

Metabolism in host cells can be modulated after viral infection, favoring viral survival or clearance. Here, we report that lipid droplet (LD) synthesis in host cells can be modulated by yin yang 1 (YY1) after porcine reproductive and respiratory syndrome virus (PRRSV) infection, resulting in active antiviral activity. As a ubiquitously distributed transcription factor, there was increased expression of YY1 upon PRRSV infection both in vitro and in vivo. YY1 silencing promoted the replication of PRRSV, whereas YY1 overexpression inhibited PRRSV replication. PRRSV infection led to a marked increase in LDs, while YY1 knockout inhibited LD synthesis, and YY1 overexpression enhanced LD accumulation, indicating that YY1 reprograms PRRSV infection-induced intracellular LD synthesis. We also showed that the viral components do not colocalize with LDs during PRRSV infection, and the effect of exogenously induced LD synthesis on PRRSV replication is nearly lethal. Moreover, we demonstrated that YY1 affects the synthesis of LDs by regulating the expression of lipid metabolism genes. YY1 negatively regulates the expression of fatty acid synthase (FASN) to weaken the fatty acid synthesis pathway and positively regulates the expression of peroxisome proliferator-activated receptor gamma (PPARγ) to promote the synthesis of LDs, thus inhibiting PRRSV replication. These novel findings indicate that YY1 plays a crucial role in regulating PRRSV replication by reprogramming LD synthesis. Therefore, our study provides a novel mechanism of host resistance to PRRSV and suggests potential new antiviral strategies against PRRSV infection.IMPORTANCEPorcine reproductive and respiratory virus (PRRSV) has caused incalculable economic damage to the global pig industry since it was first discovered in the 1980s. However, conventional vaccines do not provide satisfactory protection. It is well known that viruses are parasitic pathogens, and the completion of their replication life cycle is highly dependent on host cells. A better understanding of host resistance to PRRSV infection is essential for developing safe and effective strategies to control PRRSV. Here, we report a crucial host antiviral molecule, yin yang 1 (YY1), which is induced to be expressed upon PRRSV infection and subsequently inhibits virus replication by reprogramming lipid droplet (LD) synthesis through transcriptional regulation. Our work provides a novel antiviral mechanism against PRRSV infection and suggests that targeting YY1 could be a new strategy for controlling PRRSV.

PRRSV infection facilitates the shedding of soluble CD163 to induce inflammatory responses.

Porcine reproductive and respiratory syndrome (PRRS), which poses substantial threats to the global pig industry, is primarily characterized by interstitial pneumonia. Cluster of differentiation 163 (CD163) is the essential receptor for PRRSV infection. Metalloproteinase-mediated cleavage of CD163 leads to the shedding of soluble CD163 (sCD163), thereby inhibiting PRRSV proliferation. However, the exact cleavage site in CD163 and the potential role of sCD163 in inflammatory responses during PRRSV infection remain unclear. Herein, we found that PRRSV infection increased sCD163 levels, as demonstrated in primary alveolar macrophages (PAMs), immortalized PAM (IPAM) cell lines, and sera from PRRSV-infected piglets. With LC-MS/MS, Arg-1041/Ser-1042 was identified as the cleavage site in porcine CD163, and an IPAM cell line with precise mutation at the cleavage site was constructed. Using the precisely mutated IPAM cells, we found that exogenous addition of sCD163 protein promoted inflammatory responses, while mutation at the CD163 cleavage site suppressed inflammatory responses. Consistently, inhibition of sCD163 using its neutralizing antibodies reduced PRRSV infection-triggered inflammatory responses. Importantly, sCD163 promoted cell polarization from M2 to M1 phenotype, which in turn facilitated inflammatory responses. Taken together, our findings identify sCD163 as a novel proinflammatory mediator and provide valuable insights into the mechanisms underlying the induction of inflammatory responses by PRRSV infection.

Quercetin alleviates inflammation induced by porcine reproductive and respiratory syndrome virus in MARC-145 cells through the regulation of arachidonic acid and glutamine metabolism.

BACKGROUND: Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes severe inflammatory response, respiratory disease and sow reproductive failure. Quercetin is among the widely occurring polypheno found abundantly in nature. Quercetin has anti-inflammatory, anti-oxidative and anti-viral properties. OBJECTIVES: This study aimed to explore the effect and mechanism of quercetin on PRRSV-induced inflammation in MARC-145 cells. METHODS: Observing the cytopathic effect and measurements of inflammatory markers in MARC-145 cells collectively demonstrate that quercetin elicits a curative effect on PRRSV-induced inflammation. Liquid chromatography-mass spectrometry was further used for a non-targeted metabolic analysis of the role of quercetin in the metabolic regulation of PRRSV inflammation in MARC-145 cells. RESULTS: It was shown that quercetin attenuated PRRSV-induced cytopathy in MARC-145 cells. Quercetin treatment inhibited PRRSV replication in MARC-145 cells in a dose-dependent manner. We also found that quercetin inhibited PRRSV-induced mRNA expression and secretion levels of tumour necrosis factor-α, interleukin 1ß and interleukin 6. Metabolomics analysis revealed that quercetin ameliorated PRRSV-induced inflammation. Pathway analysis results revealed that PRRSV-induced pathways including arachidonic acid metabolism, linoleic acid, glycerophospholipid and alanine, aspartate and glutamate metabolism were suppressed by quercetin. Moreover, we confirmed that quercetin inhibited the activation of NF-κB/p65 pathway, probably by attenuating PLA2, ALOX and COX mRNA expression. CONCLUSIONS: These results provide a crucial insight into the molecular mechanism of quercetin in alleviating PRRSV-induced inflammation.

Importance of sequential infection order of porcine circovirus type 2 and porcine reproductive and respiratory syndrome virus to divergent clinical outcomes.

This study was designed to investigate the different sequential order of infection for porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV). Thirty-six pigs were randomly assigned to six different treatment groups. The first (hereafter referred to as PRRSV-PCV2) group was inoculated with PRRSV first followed by PCV2d. The second (hereafter referred to as PCV2+PRRSV) group was co-infected with both viruses at the same timepoint (42 days of age). The third (hereafter referred to as PCV2-PRRSV) group was inoculated with PCV2d first followed by PRRSV. A fourth group was only inoculated with PCV2d at 42 days of age, while a fifth group was only inoculated with PRRSV at the same timepoint. The sixth group served as a negative control group. The most important observation discovered that PRRSV only had a potentiation effect on PCV2 in both PRRS-PCV2 and PCV2+PRRSV groups. Both PRRSV-PCV2 and PCV2+PRRSV groups experienced a significant reduction in growth performance compared with control pigs. In addition, PRRSV-PCV2 and PCV2+PRRSV groups exhibited a greater severity in their clinical signs, and/or had higher PCV2 blood and lymphoid viral loads that resulted in a stronger severity of lymphoid lesions compared with PCV2-PRRSV group. Serum TNF-α levels were significantly higher in both PRRS-PCV2 and PCV2+PRRSV groups compared with those in PCV2-PRRS, PCV2, and PRRSV groups. The results of this study demonstrated that divergent clinical outcomes are dependent on the sequential infection order of PCV2 and PRRSV.

Antiviral activity and underlying mechanisms of baicalin against porcine reproductive and respiratory syndrome virus in vitro.

Porcine reproductive and respiratory syndrome (PRRS) is a major challenge for the global swine industry, causing huge economic losses worldwide. To date, there are no effective measures to prevent and control the spread of PRRS virus (PRRSV). Baicalin (BA) is a natural flavonoid with various pharmacological effects, including antiviral, anti-inflammatory, antioxidant and immunomodulatory. Here, we demonstrate that BA exhibits potent anti-PRRSV activity in vitro, BA concentrations in the range of 5-20 µg/mL significantly inhibited PRRSV infection in a dose-dependent manner and were independent of PRRSV strain. Mechanistically, BA inhibited PRRSV replication by directly interacting with virions, thereby affecting multiple stages of the virus life cycle. Meanwhile, the preventive effect of BA on PRRSV could be realized by inhibiting CD151 and CD163 expression. Furthermore, BA reduced the PRRSV-induced expression of PAMs cytokines (IFN-α, IL-6, IL-8, and TNF-α), suggesting that BA-induced antiviral cytokines may help BA inhibit PRRSV infection. Taken together, BA can be used as an inhibitor of PRRSV infection in vitro, which provides a theoretical basis for the clinical application of BA and the prevention and control of PRRSV infection, which is worthy of further in vivo studies in swine.

Current Status of Vaccines for Porcine Reproductive and Respiratory Syndrome: Interferon Response, Immunological Overview, and Future Prospects.

Porcine reproductive and respiratory syndrome (PRRS) remains a formidable challenge for the global pig industry. Caused by PRRS virus (PRRSV), this disease primarily affects porcine reproductive and respiratory systems, undermining effective host interferon and other immune responses, resulting in vaccine ineffectiveness. In the absence of specific antiviral treatments for PRRSV, vaccines play a crucial role in managing the disease. The current market features a range of vaccine technologies, including live, inactivated, subunit, DNA, and vector vaccines, but only modified live virus (MLV) and killed virus (KV) vaccines are commercially available for PRRS control. Live vaccines are promoted for their enhanced protective effectiveness, although their ability to provide cross-protection is modest. On the other hand, inactivated vaccines are emphasized for their safety profile but are limited in their protective efficacy. This review updates the current knowledge on PRRS vaccines' interactions with the host interferon system, and other immunological aspects, to assess their current status and evaluate advents in PRRSV vaccine development. It presents the strengths and weaknesses of both live attenuated and inactivated vaccines in the prevention and management of PRRS, aiming to inspire the development of innovative strategies and technologies for the next generation of PRRS vaccines.

Boosting PRRSV-Specific Cellular Immunity: The Immunological Profiling of an Fc-Fused Multi-CTL Epitope Vaccine in Mice.

The continuously evolving PRRSV has been plaguing pig farms worldwide for over 30 years, with conventional vaccines suffering from insufficient protection and biosecurity risks. To address these challenges, we identified 10 PRRSV-specific CTL epitopes through enzyme-linked immunospot assay (ELISPOT) and constructed a multi-epitope peptide (PTE) by linking them in tandem. This PTE was then fused with a modified porcine Fc molecule to create the recombinant protein pFc-PTE. Our findings indicate that pFc-PTE effectively stimulates PRRSV-infected specific splenic lymphocytes to secrete high levels of interferon-gamma (IFN-γ) and is predicted to be non-toxic and non-allergenic. Compared to PTE alone, pFc-PTE not only induced a comparable cellular immune response in mice but also extended the duration of the immune response to at least 10 weeks post-immunization. Additionally, pFc-PTE predominantly induced a Th1 immune response, suggesting its potential advantage in enhancing cellular immunity. Consequently, pFc-PTE holds promise as a novel, safe, and potent candidate vaccine for PRRSV and may also provide new perspectives for vaccine design against other viral diseases.

Enhancement of systemic virus-specific T lymphocyte responses in pigs supplemented with algae-derived ß-glucan.

Algae-derived ß-glucan has been widely used as a feed additive in the swine industry. The supplementation of ß-glucan aims to improve growth performance and modulate the immunity of pigs. However, the potential effects of supplementing ß-glucan from algae on immune responses in pigs-specifically antigen-specific immunity-must be determined. In this study, the effects of algae-derived ß-glucan supplementation on growth performance, virus neutralising antibody and virus-specific T lymphocytes responses were investigated in pigs. Piglets (n=112 per treatment) were assigned to three treatments including non-supplemented group (control), ß-glucan 100 g/ton supplemented group (BG100), and ß-glucan 200 g/ton supplemented group (BG200). In this study, production performance of pigs was not found to be different between the experimental groups. Pigs supplemented with ß-glucan exhibited high levels of classical swine fever virus (CSFV)-specific producing T lymphocytes and neutralising antibody titer, compared to the control group. Interestingly, supplementation of ß-glucan significantly enhanced porcine reproductive and respiratory syndrome virus (PRRSV)-specific interferon-gamma (IFN-γ) producing T lymphocytes, including CD4+, CD8+, and CD4+CD8+ T lymphocyte subpopulations. Moreover, PRRS modified live vaccine (MLV) viremia was reduced in earlier for ß-glucan-supplemented pigs compared to the control group. The findings indicate that the algae-derived ß-glucan possesses biological potential as an immunomodulatory substance to enhance antiviral immunity, which may contribute to disease resistance in pigs.

Investigation of PRRS Virus Infection in Hungarian Wild Boar Populations during Its Eradication from Domestic Pig Herds.

Porcine Reproductive and Respiratory Syndrome (PRRS) significantly impacts the pig farming industry globally, leading to economic losses due to reduced productivity. This study focuses on assessing the presence and impact of PRRS within Hungarian wild boar populations amidst efforts to eradicate the virus from domestic pig herds. We used a combination of serological and virological tests on samples collected from wild boars across Hungary to evaluate the prevalence of PRRS virus and its potential transmission risks to domestic pigs. Our findings reveal a low seropositivity rate in wild boars, suggesting a minimal role of wild boars in the transmission of PRRS to domestic pig populations. Moreover, no relationship was found between domestic pig and wild boar densities, emphasizing the limited interaction and consequent risk of disease spread between these populations. We confirm the effectiveness of Hungary's PRRS eradication measures among domestic herds and highlight the negligible risk posed by wild boars in re-introducing the PRRS virus.

NSP4 promotes replication of porcine reproductive and respiratory syndrome virus-2.

Porcine reproductive and respiratory syndrome (PRRS) is one of the most detrimental contagious swine ailments worldwide. Currently, no effective drugs are available for its treatment. Targeting the structural and non-structural proteins (NSP) of the type 2 PRRS virus (PRRSV-2) with small interfering RNA (siRNA) is an effective approach to inhibit PRRSV replication. NSP4, which is highly conserved and possesses 3 C-like serine protease activity (3CLSP), can cleave PRRSV self-proteins, thereby contributing to viral replication. To investigate the mechanism by which NSP4 regulates PRRSV-2 replication and screen for effective siRNA inhibitors of PRRSV-2 replication, the recombinant plasmid pEGFP-C1-NSP4 was constructed, and a control siRNA pair and two siRNA pairs targeting the PRRSV-2 NSP4 gene (shRNA-ctr, shRNA-150, and shRNA-536) were synthesized and cloned into the pSilencer4.1-CMV vector. After 24 h of incubation, Marc-145 cells were transfected with recombinant plasmids, and subsequently infected with different PRRSV-2 (XH-GD, ZQ-GD, GDr180, and JXA1-R). Subsequently, the effects of NSP4 overexpression, shRNA on PRRSV-2 replication were evaluated by assessing cytopathic effects (CPE), TCID50, quantitative real-time PCR (qPCR), immunofluorescence assays (IFA), and Western blotting. The data from these CPE, TCID50, qPCR, and IFA experiments revealed that NSP4 overexpression significantly enhanced PRRSV-2 replication and shRNA targeting NSP4 can inhibit PRRSV-2 replication in Marc-145 cells, indicating that shRNA could serve as candidate molecules for fundamental research on PRRSV-2.