Porcine reproductive and respiratory syndrome virus modifies innate immunity and alters disease outcome in pigs subsequently infected with porcine respiratory coronavirus: implications for respiratory viral co-infections

The rules in co-infection of multiple viruses across diverse lineages in a fungal host

Viruses, ubiquitous non-cellular organisms, pose significant threats to human health and to the agricultural productivity of both livestock and crops. Emerging evidence indicates that multiple viruses can infect a single host, and viral co-infection can exert a profound influence on host physiology. However, our understanding of the prevalence of co-infection and the compatibility of phylogenetically distant viruses is still limited. In this study, we surveyed 406 field strains of the plant fungal pathogen Botrytis cinerea and identified 76 mycoviruses. Strikingly, 404 strains were co-infected with two or more viruses, with some harboring up to 25 viruses simultaneously. We discerned significant preference patterns among viruses in their host. Specifically, we identified "one-to-one" and "two-to-one" rules, wherein one or two viruses could be used to reliably predict the presence or absence of other viruses in the same host, and validated these predicted rules by using five B. cinerea strains. Furthermore, through the RNA-sequencing approach, we uncovered B. cinerea genes associated with the differences caused by different sets of co-infecting viruses. These are implicated in integral components of membrane, transmembrane transporter activity, autophagy pathways, mitophagy pathway, fatty acid biosynthetic process, sphingolipid metabolism, and glycosphingolipid biosynthesis. Our findings underscore the high prevalence of co-infection by multiple viruses in a fungal host within a population and highlight compatibility dynamics among phylogenetically diverse viruses. These insights contribute to our understanding of viral ecology and hold promise for informing strategies to manage viral diseases effectively.

IMPORTANCE

Viruses, pervasive threats to both humans and agriculture, often infect hosts concurrently, profoundly impacting physiology. Despite this, the prevalence and compatibility of co-infecting viruses remain poorly understood. In the study of 406 Botrytis cinerea strains, we discovered a striking phenomenon: 404 out of the 406 strains hosted multiple viruses, some with up to 25 at once. Through rigorous analysis, we unveiled distinct preference patterns among these viruses within hosts, identifying predictive co-infection rules validated by experimentation. Furthermore, we identified genes linked to these dynamics, shedding light on critical cellular processes involved in the regulation of the co-infection rules. These findings highlight the widespread nature of viral co-infection and offer insights crucial for effectively managing viral diseases.

Coinfection with bacterial pathogens and genetic modification of PRRSV-2 for suppression of NF-κB and attenuation of proinflammatory responses

Porcine reproductive and respiratory syndrome virus (PRRSV) infects pulmonary alveolar macrophages and induces inflammation in the respiratory system. In swine farms, coinfection with PRRSV and bacterial pathogens is common and can result in clinically complicated outcomes, including porcine respiratory disease complex. Coinfection can cause excessive expressions of proinflammatory mediators and may lead to cytokine-storm-like syndrome. An immunological hallmark of PRRSV-2 is the bidirectional regulation of NF-κB with the nucleocapsid (N) protein identified as the NF-κB activator. We generated an NF-κB-silencing mutant PRRSV-2 by mutating the N gene to block its binding to PIAS1 [protein inhibitor of activated STAT-1 (signal transducer and activator of transcription 1)]. PIAS1 functions as an NF-κB repressor, and thus, the PIAS1-binding modified N-mutant PRRSV-2 became NF-κB activation-resistant in its phenotype. During coinfection of pigs with PRRSV-2 and Streptococcus suis, the N-mutant PRRSV-2 decreased the expression of proinflammatory cytokines and showed clinical attenuation. This review describes the coinfection of pigs with various pathogens, the generation of mutant PRRSV for NF-κB suppression, inflammatory profiles during bacterial coinfection, and the potential application of these findings to designing a new vaccine candidate for PRRSV-2.

Neferine inhibits PRRSV infection by disrupting p65 nuclear translocation

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), imposes substantial economic losses on the global swine industry due to its profound impact on pig health and production efficiency. The main clinical manifestations are reproductive disorders such as miscarriage, stillbirth or weak foetuses in sows, as well as severe respiratory diseases in pigs of all ages. Currently, due to the high genomic diversity, antigen heterogeneity, and antibody-dependent enhancement effects of PRRSV, vaccination strategies cannot effectively control PRRSV infection. It is also difficult to control these viral infectious diseases with antiviral drugs. In this study, we demonstrate that neferine (Nef), a natural compound derived from lotus seeds, inhibits NF-κB activation during PRRSV infection. Consequently, Nef effectively suppresses PRRSV gene expression and virion replication in the PRRSV-infected Marc-145 cell line. Further studies demonstrated that Nef attenuates the nuclear translocation of p65 triggered by PRRSV infection, consequently mitigating the excessive production of inflammatory cytokines in infected cells. This anti-inflammatory mechanism may contribute to its observed antiviral efficacy against PRRSV. As a result, we conclude that Nef may be an effective clinical treatment for the acute occurrence and transmission of PRRSV infections. Furthermore, PRRSV is thought to be responsible for an increase in proinflammatory cytokines.

Development of a triplex crystal digital PCR for the detection of PRCoV, PRRSV, and SIV

Porcine respiratory coronavirus (PRCoV), porcine reproductive and respiratory syndrome virus (PRRSV), and swine influenza virus (SIV) are important pathogens of significant infectious diseases. They cause similar clinical respiratory symptoms, including fever, cough, runny nose, and respiratory distress, which makes these diseases difficult to distinguish from each other. In this study, three pairs of specific primers and TaqMan probes were designed for the conserved regions of the PRCoV S gene, PRRSV N gene, and SIV M gene, respectively. The annealing temperature, primer and probe concentrations, and reaction cycle were optimized, and a triplex crystal digital PCR (cdPCR) assay was established for the detection of PRCoV, PRRSV, and SIV. According to the test results, the assay was capable of specifically detecting PRCoV, PRRSV, and SIV, and there was no cross-reaction with other control swine viruses. Based on the Poisson distribution analysis, the limits of detection (LODs) for PRCoV, PRRSV, and SIV were 6.00, 5.75 and 6.00 copies/reaction, respectively, and the sensitivity was 26 times higher than those of the corresponding multiplex RT-qPCR. The coefficients of variation (CVs) of the intra-assay and inter-assay ranged from 0.19 to 1.84%. The assay was used to test 1,657 clinical samples, and the positivity rates of PRCoV, PRRSV, and SIV were 1.15, 12.79, and 2.05%, respectively. It showed diagnostic sensitivity and specificity of 100 and 99.82% for PRCoV, 100 and 99.24% for PRRSV, and 100 and 99.69% for SIV, respectively. These results indicated that the triplex cdPCR assay has strong specificity, high sensitivity, and excellent repeatability, which provides a valuable tool for the detection and differentiation of PRCoV, PRRSV, and SIV.

Transmissible Gastroenteritis Virus (TGEV) and Porcine Respiratory Coronavirus (PRCV): Epidemiology and Molecular Characteristics-An Updated Overview

Transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV) are enveloped, single-stranded RNA viruses belonging to the genus Alphacoronavirus in the family Coronaviridae. PRCV, a TGEV mutant with a spike(S) gene deletion, exhibits altered tissue tropism. TGEV replicates mainly in the intestines and causes severe diarrhea and high mortality in piglets, whereas PRCV replicates mainly in the respiratory tract. PRCV causes mild or subclinical respiratory infections but may contribute to respiratory disease syndrome in pigs infected with other respiratory pathogens. As PRCV and TGEV continuously evolve, monitoring these viruses is important for disease prevention and control. In this review, we provide updated information on the prevalence and genetic characteristics of TGEV/PRCV and their phylogenetic relationships. We also discuss the impact of mutations, deletions and recombination on the virulence and tissue tropism of TGEV/PRCV and highlight the possible zoonotic potential of these viruses.

A Passion for Small Things and Staying Primed: My Career in Virology and Immunology

A love of science and animals, perseverance, and happenstance propelled my career in veterinary virology and immunology. I have focused on deadly enteric and respiratory viral infections in neonatal livestock and humans with an aim to understand their prevalence, pathogenesis, interspecies transmission, and immunity and develop vaccines. Research on animal coronaviruses (CoVs), including their broad interspecies transmission, provided a foundation to understand emerging zoonotic fatal human respiratory CoVs [severe acute respiratory syndrome, Middle East respiratory syndrome, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)] and reverse zoonosis of SARS-CoV-2 to animals. A highlight of my early research was the discovery of the gut-mammary gland-sIgA axis, documenting a common mucosal immune system. The latter remains pivotal to designing maternal vaccines for passive immunity in neonates. Our discovery and innovative cell propagation of fastidious human and animal rotaviruses and caliciviruses and their infectivity in germ-free animals has provided cell-adapted and animal disease models for ongoing virologic and immunologic investigations and vaccines. Nevertheless, besides the research discoveries, my lasting legacy remains the outstanding mentees who have enriched my science and my life.

Alveolar Macrophages in Viral Respiratory Infections: Sentinels and Saboteurs of Lung Defense

Respiratory viral infections continue to cause pandemic and epidemic outbreaks in humans and animals. Under steady-state conditions, alveolar macrophages (AlvMϕ) fulfill a multitude of tasks in order to maintain tissue homeostasis. Due to their anatomic localization within the deep lung, AlvMϕ are prone to detect and react to inhaled viruses and thus play a role in the early pathogenesis of several respiratory viral infections. Here, detection of viral pathogens causes diverse antiviral and proinflammatory reactions. This fact not only makes them promising research targets, but also suggests them as potential targets for therapeutic and prophylactic approaches. This review aims to give a comprehensive overview of the current knowledge about the role of AlvMϕ in respiratory viral infections of humans and animals.

High-throughput screening for respiratory pathogens within pigs in Denmark; analysis of circulating porcine respiratory coronaviruses and their association with other pathogens

Porcine respiratory coronavirus (PRCV) typically causes subclinical or mild respiratory infections in pigs, but may lead to more severe disease with other factors. PRCV infection in Denmark was initially detected in 1984, but data are lacking about its current prevalence and diversity. Antibodies against PRCV were detected in about 75 % of recent pig sera from Denmark. In addition, pig nasal swab samples were screened for PRCV and 12 other respiratory pathogens using a high-throughput RT-qPCR system. All targeted pathogens were detected but at different prevalences. Significant associations were found between the presence of PRCV and certain other pathogens. From PRCV positive samples, partial spike gene sequences and complete nucleocapsid coding sequences were determined. In phylogenetic analyses, these PRCVs clustered with earlier European PRCVs and were distinct from transmissible gastroenteritis virus. We conclude that PRCV is widespread within the pig population in Denmark. Further studies on the significance of PRCV are warranted.

A Comprehensive Review on Porcine Reproductive and Respiratory Syndrome Virus with Emphasis on Immunity

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in pig production worldwide and responsible for enormous production and economic losses. PRRSV infection in gestating gilts and sows induces important reproductive failure. Additionally, respiratory distress is observed in infected piglets and fattening pigs, resulting in growth retardation and increased mortality. Importantly, PRRSV infection interferes with immunity in the respiratory tract, making PRRSV-infected pigs more susceptible to opportunistic secondary pathogens. Despite the availability of commercial PRRSV vaccines for more than three decades, control of the disease remains a frustrating and challenging task. This paper provides a comprehensive overview of PRRSV, covering its history, economic and scientific importance, and description of the viral structure and genetic diversity. It explores the virus's pathogenesis, including cell tropism, viral entry, replication, stages of infection and epidemiology. It reviews the porcine innate and adaptative immune responses to comprehend the modulation mechanisms employed by PRRS for immune evasion.

Porcine lung tissue slices: a culture model for PRCV infection and innate immune response investigations

Respiratory coronaviruses (RCoVs) significantly threaten human health, necessitating the development of an ex vivo respiratory culture system for investigating RCoVs infection. Here, we successfully generated a porcine precision-cut lung slices (PCLSs) culture system, containing all resident lung cell types in their natural arrangement. Next, this culture system was inoculated with a porcine respiratory coronavirus (PRCV), exhibiting clinical features akin to humans who were infected by SARS-CoV-2. The results demonstrated that PRCV efficiently infected and replicated within PCLSs, targeting ciliated cells in the bronchioles, terminal bronchioles, respiratory bronchioles, and pulmonary alveoli. Additionally, through RNA-Seq analysis of the innate immune response in PCLSs following PRCV infection, expression levels of interferons, inflammatory cytokines and IFN stimulated genes were significantly upregulated. This ex vivo model may not only offer new insights into PRCV infection in the porcine respiratory tract but also serve as a valuable tool for studying human respiratory CoVs infection.

Simultaneous Detection of Porcine Respiratory Coronavirus, Porcine Reproductive and Respiratory Syndrome Virus, Swine Influenza Virus, and Pseudorabies Virus via Quadruplex One-Step RT-qPCR

Porcine respiratory coronavirus (PRCoV), porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), and pseudorabies virus (PRV) are significant viruses causing respiratory diseases in pigs. Sick pigs exhibit similar clinical symptoms such as fever, cough, runny nose, and dyspnea, making it very difficult to accurately differentially diagnose these diseases on site. In this study, a quadruplex one-step reverse-transcription real-time quantitative PCR (RT-qPCR) for the detection of PRCoV, PRRSV, SIV, and PRV was established. The assay showed strong specificity, high sensitivity, and good repeatability. It could detect only PRCoV, PRRSV, SIV, and PRV, without cross-reactions with TGEV, PEDV, PRoV, ASFV, FMDV, PCV2, PDCoV, and CSFV. The limits of detection (LODs) for PRCoV, PRRSV, SIV, and PRV were 129.594, 133.205, 139.791, and 136.600 copies/reaction, respectively. The intra-assay and inter-assay coefficients of variation (CVs) ranged from 0.29% to 1.89%. The established quadruplex RT-qPCR was used to test 4909 clinical specimens, which were collected in Guangxi Province, China, from July 2022 to September 2023. PRCoV, PRRSV, SIV, and PRV showed positivity rates of 1.36%, 10.17%, 4.87%, and 0.84%, respectively. In addition, the previously reported RT-qPCR was also used to test these specimens, and the agreement between these methods was higher than 99.43%. The established quadruplex RT-qPCR can accurately detect these four porcine respiratory viruses simultaneously, providing an accurate and reliable detection technique for clinical diagnosis.

A clinically attenuated double-mutant of porcine reproductive and respiratory syndrome virus-2 that does not prompt overexpression of proinflammatory cytokines during co-infection with a secondary pathogen

Porcine reproductive and respiratory syndrome virus (PRRSV) is known to suppress the type I interferon (IFNs-α/β) response during infection. PRRSV also activates the NF-κB signaling pathway, leading to the production of proinflammatory cytokines during infection. In swine farms, co-infections of PRRSV and other secondary bacterial pathogens are common and exacerbate the production of proinflammatory cytokines, contributing to the porcine respiratory disease complex (PRDC) which is clinically a severe disease. Previous studies identified the non-structural protein 1β (nsp1β) of PRRSV-2 as an IFN antagonist and the nucleocapsid (N) protein as the NF-κB activator. Further studies showed the leucine at position 126 (L126) of nsp1β as the essential residue for IFN suppression and the region spanning the nuclear localization signal (NLS) of N as the NF-κB activation domain. In the present study, we generated a double-mutant PRRSV-2 that contained the L126A mutation in the nsp1β gene and the NLS mutation (ΔNLS) in the N gene using reverse genetics. The immunological phenotype of this mutant PRRSV-2 was examined in porcine alveolar macrophages (PAMs) in vitro and in young pigs in vivo. In PAMs, the double-mutant virus did not suppress IFN-β expression but decreased the NF-κB-dependent inflammatory cytokine productions compared to those for wild-type PRRSV-2. Co-infection of PAMs with the mutant PRRSV-2 and Streptococcus suis (S. suis) also reduced the production of NF-κB-directed inflammatory cytokines. To further examine the cytokine profiles and the disease severity by the mutant virus in natural host animals, 6 groups of pigs, 7 animals per group, were used for co-infection with the mutant PRRSV-2 and S. suis. The double-mutant PRRSV-2 was clinically attenuated, and the expressions of proinflammatory cytokines and chemokines were significantly reduced in pigs after bacterial co-infection. Compared to the wild-type PRRSV-2 and S. suis co-infection control, pigs coinfected with the double-mutant PRRSV-2 exhibited milder clinical signs, lower titers and shorter duration of viremia, and lower expression of proinflammatory cytokines. In conclusion, our study demonstrates that genetic modification of the type I IFN suppression and NF-κB activation functions of PRRSV-2 may allow us to design a novel vaccine candidate to alleviate the clinical severity of PRRS-2 and PRDC during bacterial co-infection.

Experimental Infection of Pigs with a Traditional or a Variant Porcine Respiratory Coronavirus (PRCV) Strain and Impact on Subsequent Influenza A Infection

Porcine respiratory coronavirus (PRCV) pathogenicity in pigs has been characterized using traditional PRCV isolates; however, information is lacking on pathogenicity of currently circulating PRCV isolates. Recently, a contemporary US PRCV variant was isolated. The infection dynamics of that strain (PRCV-var) and a traditional PRCV strain (PRCV-trad) were compared. In brief, 4-week-old pigs were divided into three groups with five pigs each. The pigs were inoculated with PRCV-trad or PRCV-var, or left uninfected. Nasal swabs were collected daily, and all pigs were necropsied at day (D) 3. PRCV nasal shedding was significantly higher in PRCV-var pigs compared to PRCV-trad pigs. To investigate the impact of trad and var PRCVs on subsequent infection with influenza A virus (IAV), four additional groups of five pigs were used: PRCV-trad-IAV (PRCV-trad at D0, co-infected with IAV at D5), PRCV-var-IAV, and IAV positive and negative controls. Significantly higher mean PRCV antibody titers and a significantly higher area under the curve (AUC) for PRCV shedding were observed in PRCV-var compared to PRCV-trad-pigs at D10. There was no impact on IAV infection. In conclusion, a 2020 PRCV variant isolate was similar in pathogenicity but more transmissible compared to a traditional 1989 isolate. These findings raise concerns about virus evolution towards more highly pathogenic and transmissible strains and the need to monitor such viruses.

Gene expression of peripheral blood mononuclear cells and CD8+ T cells from gilts after PRRSV infection

Porcine reproductive and respiratory syndrome virus (PRRSV) is a positive-stranded RNA virus, which emerged in Europe and U.S.A. in the late 1980s and has since caused huge economic losses. Infection with PRRSV causes mild to severe respiratory and reproductive clinical symptoms in pigs. Alteration of the host immune response by PRRSV is associated with the increased susceptibility to secondary viral and bacterial infections resulting in more serious and chronic disease. However, the expression profiles underlying innate and adaptive immune responses to PRRSV infection are yet to be further elucidated. In this study, we investigated gene expression profiles of PBMCs and CD8⁺ T cells after PRRSV AUT15-33 infection. We identified the highest number of differentially expressed genes in PBMCs and CD8⁺ T cells at 7 dpi and 21 dpi, respectively. The gene expression profile of PBMCs from infected animals was dominated by a strong innate immune response at 7 dpi which persisted through 14 dpi and 21 dpi and was accompanied by involvement of adaptive immunity. The gene expression pattern of CD8⁺ T cells showed a strong adaptive immune response to PRRSV, leading to the formation of highly differentiated CD8⁺ T cells starting from 14 dpi. The hallmark of the CD8⁺ T-cell response was the increased expression of effector and cytolytic genes (PRF1, GZMA, GZMB, GZMK, KLRK1, KLRD1, FASL, NKG7), with the highest levels observed at 21 dpi. Temporal clustering analysis of DEGs of PBMCs and CD8⁺ T cells from PRRSV-infected animals revealed three and four clusters, respectively, suggesting tight transcriptional regulation of both the innate and the adaptive immune response to PRRSV. The main cluster of PBMCs was related to the innate immune response to PRRSV, while the main clusters of CD8⁺ T cells represented the initial transformation and differentiation of these cells in response to the PRRSV infection. Together, we provided extensive transcriptomics data explaining gene signatures of the immune response of PBMCs and CD8⁺ T cells after PRRSV infection. Additionally, our study provides potential biomarker targets useful for vaccine and therapeutics development.

Streptococcus suis contributes to inguinal lymph node lesions in piglets after highly pathogenic porcine reproductive and respiratory syndrome virus infection

The swine pathogens porcine reproductive and respiratory syndrome virus (PRRSV) and Streptococcus suis have both been reported to cause damage to the immune organs. Inguinal lymph node (ILN) injury has been reported in PRRSV-infected pigs with secondary S. suis infection, but not much is known about the mechanism. In this study, secondary S. suis infection after highly pathogenic (HP)-PRRSV infection caused more severe clinical symptoms, mortality, and ILN lesions. Histopathological lesions were seen in ILNs with a marked decrease in lymphocyte numbers. Terminal deoxynucleotidyl transferase (TdT)-mediated de-oxyuridine triphosphate (dUTP)-biotin nick end-labeling (TUNEL) assays revealed that HP-PRRSV strain HuN4 alone induced ILN apoptosis, but dual-infection with S. suis strain BM0806 induced greater levels of apoptosis. Besides, we found that some HP-PRRSV-infected cells underwent apoptosis. Furthermore, anti-caspase-3 antibody staining confirmed that ILN apoptosis was mainly induced by a caspase-dependent pathway. Pyroptosis was also observed in HP-PRRSV-infected cells, and there was more pyroptosis in piglets infected with HP-PRRSV alone compared with those with secondary S. suis infection, and HP-PRRSV-infected cells underwent pyroptosis. Altogether, this is the first report to identify pyroptosis in ILNs and which signaling pathway is related to ILN apoptosis in single or dual-infected piglets. These results contribute to a better understanding of the pathogenic mechanisms during secondary S. suis infection.

Ferret acute lung injury model induced by repeated nebulized lipopolysaccharide administration

Inflammatory lung diseases affect millions of people worldwide. These diseases are caused by a number of factors such as pneumonia, sepsis, trauma, and inhalation of toxins. Pulmonary function testing (PFT) is a valuable functional methodology for better understanding mechanisms of lung disease, measuring disease progression, clinical diagnosis, and evaluating therapeutic interventions. Animal models of inflammatory lung diseases are needed that accurately recapitulate disease manifestations observed in human patients and provide an accurate prediction of clinical outcomes using clinically relevant pulmonary disease parameters. In this study, we evaluated a ferret lung inflammation model that closely represents multiple clinical manifestations of acute lung inflammation and injury observed in human patients. Lipopolysaccharide (LPS) from Pseudomonas aeruginosa was nebulized into ferrets for 7 repeated daily doses. Repeated exposure to nebulized LPS resulted in a restrictive pulmonary injury characterized using Buxco forced maneuver PFT system custom developed for ferrets. This is the first study to report repeated forced maneuver PFT in ferrets, establishing lung function measurements pre- and post-injury in live animals. Bronchoalveolar lavage and histological analysis confirmed that LPS exposure elicited pulmonary neutrophilic inflammation and structural damage to the alveoli. We believe this ferret model of lung inflammation, with clinically relevant disease manifestations and parameters for functional evaluation, is a useful pre-clinical model for understanding human inflammatory lung disease and for the evaluation of potential therapies.

A total infectome approach to understand the etiology of infectious disease in pigs

BACKGROUND

The global pork industry is continuously affected by infectious diseases that can result in large-scale mortality, trade restrictions, and major reductions in production. Nevertheless, the cause of many infectious diseases in pigs remains unclear, largely because commonly used diagnostic tools fail to capture the full diversity of potential pathogens and because pathogen co-infection is common.

RESULTS

We used a meta-transcriptomic approach to systematically characterize the pathogens in 136 clinical cases representing different disease syndromes in pigs, as well as in 12 non-diseased controls. This enabled us to simultaneously determine the diversity, abundance, genomic information, and detailed epidemiological history of a wide range of potential pathogens. We identified 34 species of RNA viruses, nine species of DNA viruses, seven species of bacteria, and three species of fungi, including two novel divergent members of the genus Pneumocystis. While most of these pathogens were only apparent in diseased animals or were at higher abundance in diseased animals than in healthy animals, others were present in healthy controls, suggesting opportunistic infections. Importantly, most of the cases examined here were characterized by co-infection with more than two species of viral, bacterial, or fungal pathogens, some with highly correlated occurrence and abundance levels. Examination of clinical signs and necropsy results in the context of relevant pathogens revealed that a multiple-pathogen model was better associated with the data than a single-pathogen model was.

CONCLUSIONS

Our data demonstrate that most of the pig diseases examined were better explained by the presence of multiple rather than single pathogens and that infection with one pathogen can facilitate infection or increase the prevalence/abundance of another. Consequently, it is generally preferable to consider the cause of a disease based on a panel of co-infecting pathogens rather than on individual infectious agents. Video abstract.

Mapping the Key Residues within the Porcine Reproductive and Respiratory Syndrome Virus nsp1α Replicase Protein Required for Degradation of Swine Leukocyte Antigen Class I Molecules

The nonstructural protein 1α (nsp1α) of the porcine reproductive and respiratory syndrome virus (PRRSV) has been shown to target swine leukocyte antigen class I (SLA-I) for degradation, but the molecular details remain unclear. In this report, we further mapped the critical residues within nsp1α by site-directed mutagenesis. We identified a cluster of residues (i.e., Phe17, Ile81, Phe82, Arg86, Thr88, Gly90, Asn91, Phe94, Arg97, Thr160, and Asn161) necessary for this function. Interestingly, they are all located in a structurally relatively concentrated region. Further analysis by reverse genetics led to the generation of two viable viral mutants, namely, nsp1α-G90A and nsp1α-T160A. Compared to WT, nsp1α-G90A failed to co-localize with either chain of SLA-I within infected cells, whereas nsp1α-T160A exhibited a partial co-localization relationship. Consequently, the mutant nsp1α-G90A exhibited an impaired ability to downregulate SLA-I in infected macrophages as demonstrated by Western blot, indirect immunofluorescence, and flow cytometry analysis. Consistently, the ubiquitination level of SLA-I was significantly reduced in the conditions of both infection and transfection. Together, our results provide further insights into the mechanism underlying PRRSV subversion of host immunity and have important implications in vaccine development.

The Swine IFN System in Viral Infections: Major Advances and Translational Prospects

Interferons (IFNs) are a family of cytokines that play a pivotal role in orchestrating the innate immune response during viral infections, thus representing the first line of defense in the host. After binding to their respective receptors, they are able to elicit a plethora of biological activities, by initiating signaling cascades which lead to the transcription of genes involved in antiviral, anti-inflammatory, immunomodulatory and antitumoral effector mechanisms. In hindsight, it is not surprising that viruses have evolved multiple IFN escape strategies toward efficient replication in the host. Hence, in order to achieve insight into preventive and treatment strategies, it is essential to explore the mechanisms underlying the IFN response to viral infections and the constraints thereof. Accordingly, this review is focused on three RNA and three DNA viruses of major importance in the swine farming sector, aiming to provide essential data as to how the IFN system modulates the antiviral immune response, and is affected by diverse, virus-driven, immune escape mechanisms.

Porcine Respiratory Coronavirus as a Model for Acute Respiratory Coronavirus Disease

In the light of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, we have developed a porcine respiratory coronavirus (PRCV) model for in depth mechanistic evaluation of the pathogenesis, virology and immune responses of this important family of viruses. Pigs are a large animal with similar physiology and immunology to humans and are a natural host for PRCV. Four PRCV strains were investigated and shown to induce different degrees of lung pathology. Importantly, although all four strains replicated equally well in porcine cell lines in vitro and in the upper respiratory tract in vivo, PRCV strains causing more severe lung pathology were also able to replicate in ex vivo tracheal organ cultures as well as in vivo in the trachea and lung. The time course of infection of PRCV 135, which caused the most severe pulmonary pathology, was investigated. Virus was shed from the upper respiratory tract until day 10 post infection, with infection of the respiratory mucosa, as well as olfactory and sustentacular cells, providing an excellent model to study upper respiratory tract disease in addition to the commonly known lower respiratory tract disease from PRCV. Infected animals made antibody and T cell responses that cross reacted with the four PRCV strains and Transmissible Gastroenteritis Virus. The antibody response was reproduced in vitro in organ cultures. Comparison of mechanisms of infection and immune control in pigs infected with PRCVs of differing pathogenicity with human data from SARS-CoV-2 infection and from our in vitro organ cultures, will enable key events in coronavirus infection and disease pathogenesis to be identified.

The Role of Pathology in the Diagnosis of Swine Respiratory Disease

The definition “porcine respiratory disease complex” (PRDC) is used to indicate the current approach for presenting respiratory pathology in modern pig farming. PRDC includes pneumonias with variable pictures, mixed with both aerogenous and hematogenous forms with variable etiology, often multimicrobial, and influenced by environmental and management factors. The notion that many etiological agents of swine respiratory pathology are ubiquitous in the airways is commonly understood; however, their isolation or identification is not always associable with the current pathology. In this complex context, lung lesions registered at slaughterhouse or during necropsy, and supplemented by histological investigations, must be considered as powerful tools for assigning a prominent role to etiologic agents. In recent years, the goal of colocalizing causative agents with the lesions they produce has been frequently applied, and valid examples in routine diagnostics are those that indicate pulmonary involvement during porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) infections.

Porcine Coronaviruses: Overview of the State of the Art

Like RNA viruses in general, coronaviruses (CoV) exhibit high mutation rates which, in combination with their strong tendency to recombine, enable them to overcome the host species barrier and adapt to new hosts. It is currently known that six CoV are able to infect pigs. Four of them belong to the genus Alphacoronavirus [transmissible gastroenteritis coronavirus (TEGV), porcine respiratory coronavirus (PRCV), porcine epidemic diarrhea virus (PEDV), swine acute diarrhea syndrome coronavirus (SADS-CoV)], one of them to the genus Betacoronavirus [porcine hemagglutinating encephalomyelitis virus (PHEV)] and the last one to the genus Deltacoronavirus (PDCoV). PHEV was one of the first identified swine CoV and is still widespread, causing subclinical infections in pigs in several countries. PRCV, a spike deletion mutant of TGEV associated with respiratory tract infection, appeared in the 1980s. PRCV is considered non-pathogenic since its infection course is mild or subclinical. Since its appearance, pig populations have become immune to both PRCV and TGEV, leading to a significant reduction in the clinical and economic importance of TGEV. TGEV, PEDV and PDCoV are enteropathogenic CoV and cause clinically indistinguishable acute gastroenteritis in all age groups of pigs. PDCoV and SADS-CoV have emerged in 2014 (US) and in 2017 (China), respectively. Rapid diagnosis is crucial for controlling CoV infections and preventing them from spreading. Since vaccines are available only for some porcine CoV, prevention should focus mainly on a high level of biosecurity. In view of the diversity of CoV and the potential risk factors associated with zoonotic emergence, updating the knowledge concerning this area is essential.

A network pharmacology based approach for predicting active ingredients and potential mechanism of Lianhuaqingwen capsule in treating COVID-19

The outbreak of severe respiratory disease caused by SARS-CoV-2 has led to millions of infections and raised global health concerns. Lianhuaqingwen capsule (LHQW-C), a traditional Chinese medicine (TCM) formula widely used for respiratory diseases, shows therapeutic efficacy in the application of coronavirus disease 2019 (COVID-19). However, the active ingredients, drug targets, and the therapeutic mechanisms of LHQW-C in treating COVID-19 are poorly understood. In this study, an integrating network pharmacology approach including pharmacokinetic screening, target prediction (targets of the host and targets from the SARS-CoV-2), network analysis, GO enrichment analysis, KEGG pathway enrichment analysis, and virtual docking were conducted. Finally, 158 active ingredients in LHQW-C were screen out, and 49 targets were predicted. GO function analysis revealed that these targets were associated with inflammatory response, oxidative stress reaction, and other biological processes. KEGG enrichment analysis indicated that the targets of LHQW-C were highly enriched to several immune response-related and inflammation-related pathways, including the IL-17 signaling pathway, TNF signaling pathway, NF-kappa B signaling pathway, and Th17 cell differentiation. Moreover, four key components (quercetin, luteolin, wogonin, and kaempferol) showed a high binding affinity with SARS-CoV-2 3-chymotrypsin-like protease (3CL pro). The study indicates that some anti-inflammatory ingredients in LHQW-C probably modulate the inflammatory response in severely ill patients with COVID-19.

Indoor PM2.5 removal efficiency of two different non-thermal plasma systems

The use of non-thermal plasma (NTP) generators in air processing systems and their duct networks to improve indoor air quality (IAQ) has grown considerably in recent years. This paper reviews the advantages and disadvantages of NTP generators for IAQ improvement in biological, chemical and particulate pollutant terms. Also, it assesses and compares the ability of a multipin corona discharge (MPCD) and a dielectric barrier discharge (DBD) generator to reduce the concentration of fine particulate matter (PM2.5) in recycled, unfiltered air in a refrigeration chamber. The MPCD generator was found to have a higher PM2.5 removal efficiency; also, it was faster in removing pollutants, used less energy, and produced much less ozone. The fact that the MPCD generator performed better was seemingly the result of its increased ion production mainly. NTP generators, however, cannot match air filtration media purifiers in this respect as the latter are much more effective in removing particles. Besides, NTP-based air purifying technology continues to be subject to a major drawback, namely: the formation of ozone as a by-product. In any case, the ozone generation was uncorrelated to ion emission when using different technologies.

Respiratory viral infections drive different lung cytokine profiles in pigs

Background

Swine influenza A virus (IAV) and porcine reproductive and respiratory syndrome virus (PRRSV) are considered key viral pathogens involved in the porcine respiratory disease complex. Concerning the effect of one virus on another with respect to local immune response is still very limited. Determination of presence and quantity of cytokines in the lung tissue and its relation to the lung pathology can lead to a better understanding of the host inflammatory response and its influence on the lung pathology during single or multi-virus infection. The aim of the present study was to explore and compare the patterns of lung cytokine protein response in pigs after single or dual infection with swine IAV and/or PRRSV.

Results

Inoculation with IAV alone causes an increase in lung concentration of IFN-α, IFN-ɣ, TNF-α, IL-6, IL-8 and IL-10, especially at 2 and 4 DPI. In PRRSV group, beyond early IFN-α, IFN-ɣ, IL-6, IL-8 and IL-10 induction, elevated levels of cytokines at 10 and 21 DPI have been found. In IAV+PRRSV inoculated pigs the lung concentrations of all cytokines were higher than in control pigs.

Conclusions

Current results indicate that experimental infection of pigs with IAV or PRRSV alone and co-infection with both pathogens induce different kinetics of local cytokine response. Due to strong positive correlation between local TNF-α and IL-10 concentration and lung pathology, we hypothesize that these cytokines are involved in the induction of lung lesions during investigates infection. Nevertheless, no apparent increase in lung cytokine response was seen in pigs co-inoculated simultaneously with both pathogens compared to single inoculated groups. It may also explain no significant effect of co-infection on the lung pathology and pathogen load, compared to single infections. Strong correlation between local concentration of TNF-α, IFN-ɣ, IL-8 and SwH1N1 load in the lung, as well as TNF-α, IL-8 and PRRSV lung titres suggested that local replication of both viruses also influenced the local cytokine response during infection.

Naturally Occurring Animal Coronaviruses as Models for Studying Highly Pathogenic Human Coronaviral Disease

Coronaviruses (CoVs) comprise a large group of positive stranded RNA viruses that infect a diverse host range including birds and mammals. Infection with CoVs typically presents as mild to severe respiratory or enteric disease, but CoVs have the potential to cause significant morbidity or mortality in highly susceptible age groups. CoVs have exhibited a penchant for jumping species barriers throughout history with devastating effects. The emergence of highly pathogenic or infectious CoVs in humans over the past 20 years, including severe acute respiratory syndrome CoV (SARS-CoV), Middle East respiratory syndrome CoV (MERS-CoV), and most recently severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), underscores the significant threat that CoV spillovers pose to humans. Similar to the emergence of SARS-CoV-2, CoVs have been devastating to commercial animal production over the past century, including infectious bronchitis virus in poultry and bovine CoV, as well as the emergence and reemergence of multiple CoVs in swine including transmissible gastroenteritis virus, porcine epidemic diarrhea virus, and porcine deltacoronavirus. These naturally occurring animal CoV infections provide important examples for understanding CoV disease as many animal CoVs have complex pathogenesis similar to SARS-CoV-2 and can shed light on the ongoing SARS-CoV-2 outbreak. We provide an overview and update regarding selected existing animal CoVs and their primary host species, diseases caused by CoVs, how CoVs jump species, whether these CoVs pose an outbreak risk or risk to humans, and how we can mitigate these risks.

Intranasal Delivery of Inactivated Influenza Virus and Poly(I:C) Adsorbed Corn-Based Nanoparticle Vaccine Elicited Robust Antigen-Specific Cell-Mediated Immune Responses in Maternal Antibody Positive Nursery Pigs

We designed the killed swine influenza A virus (SwIAV) H1N2 antigen (KAg) with polyriboinosinic:polyribocytidylic acid [(Poly(I:C)] adsorbed corn-derived Nano-11 particle based nanovaccine called Nano-11-KAg+Poly(I:C), and evaluated its immune correlates in maternally derived antibody (MDA)-positive pigs against a heterologous H1N1 SwIAV infection. Immunologically, in tracheobronchial lymph nodes (TBLN) detected enhanced H1N2-specific cytotoxic T-lymphocytes (CTLs) in Nano-11-KAg+Poly(I:C) vaccinates, and in commercial vaccinates detected CTLs with mainly IL-17A⁺ and early effector phenotypes specific to both H1N2 and H1N1 SwAIV. In commercial vaccinates, activated H1N2- and H1N1-specific IFNγ⁺&TNFα⁺, IL-17A⁺ and central memory T-helper/Memory cells, and in Nano-11-KAg+Poly(I:C) vaccinates H1N2-specific central memory, IFNγ⁺ and IFNγ⁺&TNFα⁺, and H1N1-specific IL-17A⁺ T-helper/Memory cells were observed. Systemically, Nano-11-KAg+Poly(I:C) vaccine augmented H1N2-specific IFNγ⁺ CTLs and H1N1-specific IFNγ⁺ T-helper/Memory cells, and commercial vaccine boosted H1N2- specific early effector CTLs and H1N1-specific IFNγ⁺&TNFα⁺ CTLs, as well as H1N2- and H1N1-specific T-helper/Memory cells with central memory, IFNγ⁺&TNFα⁺, and IL-17A⁺ phenotypes. Remarkably, commercial vaccine induced an increase in H1N1-specific T-helper cells in TBLN and naive T-helper cells in both TBLN and peripheral blood mononuclear cells (PBMCs), while H1N1- and H1N2-specific only T-helper cells were augmented in Nano-11-KAg+Poly(I:C) vaccinates in both TBLN and PBMCs. Furthermore, the Nano-11-KAg+Poly(I:C) vaccine stimulated robust cross-reactive IgG and secretory IgA (SIgA) responses in lungs, while the commercial vaccine elicited high levels of serum and lung IgG and serum hemagglutination inhibition (HI) titers. In conclusion, despite vast genetic difference (77% in HA gene identity) between the vaccine H1N2 and H1N1 challenge viruses in Nano-11-KAg+Poly(I:C) vaccinates, compared to over 95% identity between H1N1 of commercial vaccine and challenge viruses, the virus load and macroscopic lesions in the lungs of both types of vaccinates were comparable, but the Nano-11-KAg+Poly(I:C) vaccine cleared the virus from the nasal passage better. These data suggested the important role played by Nano-11 and Poly(I:C) in the induction of polyfunctional, cross-protective cell-mediated immunity against SwIAV in MDA-positive pigs.

Comparative Pathogenesis of Bovine and Porcine Respiratory Coronaviruses in the Animal Host Species and SARS-CoV-2 in Humans

Discovery of bats with severe acute respiratory syndrome (SARS)-related coronaviruses (CoVs) raised the specter of potential future outbreaks of zoonotic SARS-CoV-like disease in humans, which largely went unheeded. Nevertheless, the novel SARS-CoV-2 of bat ancestral origin emerged to infect humans in Wuhan, China, in late 2019 and then became a global pandemic. Less than 5 months after its emergence, millions of people worldwide have been infected asymptomatically or symptomatically and at least 360,000 have died. Coronavirus disease 2019 (COVID-19) in severely affected patients includes atypical pneumonia characterized by a dry cough, persistent fever, and progressive dyspnea and hypoxia, sometimes accompanied by diarrhea and often followed by multiple organ failure, especially of the respiratory and cardiovascular systems. In this minireview, we focus on two endemic respiratory CoV infections of livestock: bovine coronavirus (BCoV) and porcine respiratory coronavirus (PRCV). Both animal respiratory CoVs share some common features with SARS-CoV and SARS-CoV-2. BCoV has a broad host range including wild ruminants and a zoonotic potential. BCoV also has a dual tropism for the respiratory and gastrointestinal tracts. These aspects, their interspecies transmission, and certain factors that impact disease severity in cattle parallel related facets of SARS-CoV or SARS-CoV-2 in humans. PRCV has a tissue tropism for the upper and lower respiratory tracts and a cellular tropism for type 1 and 2 pneumocytes in lung but is generally a mild infection unless complicated by other exacerbating factors, such as bacterial or viral coinfections and immunosuppression (corticosteroids).

Kinetics of single and dual simultaneous infection of pigs with swine influenza A virus and porcine reproductive and respiratory syndrome virus

Background

Simultaneous viral infections exhibit the phenomenon of viral interference, but understanding of the effect of one virus on another is limited.

Objective

Evaluate and compare clinical characteristics, immune and acute phase response, viral shedding and viral load in pigs singly and doubly inoculated with swine influenza A virus (swIAV) and porcine reproductive and respiratory syndrome virus (PRRSV).

Animals

Fifty‐four 7‐week‐old piglets.

Methods

Clinical status and gross lung lesions were scored. Titration of swIAV was carried out in Madin‐Darby canine kidney cells. The PRRSV RNA was quantified using a commercial qPCR kit. Antibodies were detected by hemagglutination inhibition assay and commercial ELISA. A lymphocyte proliferation assay was used to measure antigen‐specific T‐cell responses. Acute phase proteins were determined using ELISA.

Results

No differences were found between mean clinical scores, swIAV and PRRSV shedding, and magnitude of the humoral and T‐cell response between single‐inoculated and dual‐inoculated groups. Concentrations of C‐reactive protein and haptoglobin increased in PRRSV‐inoculated and coinoculated groups, whereas serum amyloid A concentration was increased in groups inoculated or coinoculated with swIAV. Mean swIAV TCID₅₀ titers in the lungs did not differ significantly between coinoculated and swIAV single‐inoculated pigs. A significantly higher mean copy number of PRRSV was found in the lungs of PRRSV only‐inoculated pigs at 2 day postinoculation (DPI). From 4 DPI, no significant differences in PRRSV load were identified.

Conclusions and Clinical Importance

Coinfection of pigs with swIAV and PRRSV did not potentiate clinical signs, lung lesions, immune response, and replication of the viruses in the respiratory tract.

An Escherichia coli-Expressed Porcine Reproductive and Respiratory Syndrome Virus Chimeric Protein Induces a Specific Immunoglobulin G Response in Immunized Piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) still poses a threat to the swine industry worldwide. Currently, commercial vaccines against PRRSV, which consist of modified live or inactivated virus, reduce symptoms and viremia in immunized pigs, but efficacy against heterologous strains is variable. This has led to the development of subunit vaccines that contain viral antigens that show the highest variability. In this work, a chimeric protein comprising short amino acid sequences from glycoprotein 3 (GP3), glycoprotein 4 (GP4), glycoprotein 5 (GP5), and M (matrix protein) proteins of PRRSV was designed and expressed in Escherichia coli. This protein, designated as PRRSVchim, was purified by immobilized metal affinity chromatography and evaluated. PRRSVchim was identified by immunoglobulin G (IgG) presence in serum samples from PRRSV-positive pigs. Also, the protein probed to be antigenic in immunized mice and piglets and provided some degree of protection against challenge with a PRRSV field isolate. These results show the potential of PRRSVchim protein for both PRRSV diagnostic and immunoprophylaxis.

Multiday maintenance of extracorporeal lungs using cross-circulation with conscious swine

Objectives

Lung remains the least-utilized solid organ for transplantation. Efforts to recover donor lungs with reversible injuries using ex vivo perfusion systems are limited to <24 hours of support. Here, we demonstrate the feasibility of extending normothermic extracorporeal lung support to 4 days using cross-circulation with conscious swine.

Methods

A swine behavioral training program and custom enclosure were developed to enable multiday cross-circulation between extracorporeal lungs and recipient swine. Lungs were ventilated and perfused in a normothermic chamber for 4 days. Longitudinal analyses of extracorporeal lungs (ie, functional assessments, multiscale imaging, cytokine quantification, and cellular assays) and recipient swine (eg, vital signs and blood and tissue analyses) were performed.

Results

Throughout 4 days of normothermic support, extracorporeal lung function was maintained (arterial oxygen tension/inspired oxygen fraction >400 mm Hg; compliance >20 mL/cm H₂O), and recipient swine were hemodynamically stable (lactate <3 mmol/L; pH, 7.42 ± 0.05). Radiography revealed well-aerated lower lobes and consolidation in upper lobes of extracorporeal lungs, and bronchoscopy showed healthy airways without edema or secretions. In bronchoalveolar lavage fluid, granulocyte-macrophage colony-stimulating factor, interleukin (IL) 4, IL-6, and IL-10 levels increased less than 6-fold, whereas interferon gamma, IL-1α, IL-1β, IL-1ra, IL-2, IL-8, IL-12, IL-18, and tumor necrosis factor alpha levels decreased from baseline to day 4. Histologic evaluations confirmed an intact blood–gas barrier and outstanding preservation of airway and alveolar architecture. Cellular viability and metabolism in extracorporeal lungs were confirmed after 4 days.

Conclusions

We demonstrate feasibility of normothermic maintenance of extracorporeal lungs for 4 days by cross-circulation with conscious swine. Cross-circulation approaches could support the recovery of damaged lungs and enable organ bioengineering to improve transplant outcomes.

TNF-α induced by porcine reproductive and respiratory syndrome virus inhibits the replication of classical swine fever virus C-strain

Porcine productive and respiratory syndrome virus (PRRSV) and classical swine fever virus (CSFV) both are major pathogens of swine that pose a great threat to the Chinese pig industry. It has been found that PRRSV infection can lead to vaccination failure of CSFV C strain-derived modified live vaccine (CSFV-C) by interfering with the immune responses to the latter. To investigate whether PRRSV can suppress CSFV-C replication, we created a 3D4/21-based cell line PAM39 that is susceptible to both viruses by expressing PRRSV receptors CD163 and CD169, and then investigated their interplay under the condition of either sequential or simultaneous co-infection. The most significant suppressive effect came from the sequential infection when the cells were first infected by PRRSV and then followed by CSFV-C at an interval of 6 h. In addition, this effect was independent of PRRSV strains. Mechanistically, PRRSV induced an elevated level of a subset of pro-inflammatory cytokines, especially tumor necrosis factor (TNF-α), through the nuclear factor κB (NF-κB) signaling pathway to inhibit the replication of CSFV-C in vitro. Thus, our studies provide an alternative explanation on PRRSV-induced CSFV vaccination failure, and this has an important implication in CSF vaccination and control.

Negative Immunomodulatory Effects of Type 2 Porcine Reproductive and Respiratory Syndrome Virus-Induced Interleukin-1 Receptor Antagonist on Porcine Innate and Adaptive Immune Functions

Impaired innate and adaptive immune responses are evidenced throughout the course of PRRSV infection. We previously reported that interleukin-1 receptor antagonist (IL-1Ra) was involved in PRRSV-induced immunosuppression during an early phase of infection. However, the exact mechanism associated with PRRSV-induced IL-1Ra immunomodulation remains unknown. To explore the immunomodulatory properties of PRRSV-induced IL-1Ra on porcine immune functions, monocyte-derived dendritic cells (MoDC) and leukocytes were cultured with type 2 PRRSV, and the immunological role of IL-1Ra was assessed by addition of anti-porcine IL-1Ra Ab. The results demonstrated that PRRSV-induced IL-1Ra reduced phagocytosis, surface expression of MHC II (SLA-DR) and CD86, as well as downregulation of IFNA and IL1 gene expression in the MoDC culture system. Interestingly, IL-1Ra secreted by the PRRSV-infected MoDC also inhibited T lymphocyte differentiation and proliferation, but not IFN-γ production. Although PRRSV-induced IL-1Ra was not directly linked to IL-10 production, it contributed to the differentiation of regulatory T lymphocytes (Treg) within the culture system. Taken together, our results demonstrated that PRRSV-induced IL-1Ra downregulates innate immune functions, T lymphocyte differentiation and proliferation, and influences collectively with IL-10 in the Treg induction. The immunomodulatory roles of IL-1Ra elucidated in this study increase our understanding of the immunobiology of PRRSV.

Attenuation of Influenza A Virus Disease Severity by Viral Coinfection in a Mouse Model

Influenza viruses and rhinoviruses are responsible for a large number of acute respiratory viral infections in human populations and are detected as copathogens within hosts. Clinical and epidemiological studies suggest that coinfection by rhinovirus and influenza virus may reduce disease severity and that they may also interfere with each other's spread within a host population. To determine how coinfection by these two unrelated respiratory viruses affects pathogenesis, we established a mouse model using a minor serogroup rhinovirus (rhinovirus strain 1B [RV1B]) and mouse-adapted influenza A virus (A/Puerto Rico/8/1934 [PR8]). Infection of mice with RV1B 2 days before PR8 reduced the severity of infection by a low or medium, but not high, dose of PR8. Disease attenuation was associated with an early inflammatory response in the lungs and enhanced clearance of PR8. However, coinfection by RV1B did not reduce PR8 viral loads early in infection or inhibit replication of PR8 within respiratory epithelia or in vitro Inflammation in coinfected mice remained focal compared to diffuse inflammation and damage in the lungs of mice infected by PR8. The timing of RV1B coinfection was a critical determinant of protection, suggesting that sufficient time is needed to induce this response. Finally, disease attenuation was not unique to RV1B: dose-dependent coinfection by a murine coronavirus (mouse hepatitis virus strain 1 [MHV-1]) also reduced the severity of PR8 infection. Unlike RV1B, coinfection with MHV-1 reduced early PR8 replication, which was associated with upregulation of beta interferon (IFN-β) expression. This model is critical for understanding the mechanisms responsible for influenza disease attenuation during coinfection by unrelated respiratory viruses.IMPORTANCE Viral infections in the respiratory tract can cause severe disease and are responsible for a majority of pediatric hospitalizations. Molecular diagnostics have revealed that approximately 20% of these patients are infected by more than one unrelated viral pathogen. To understand how viral coinfection affects disease severity, we inoculated mice with a mild viral pathogen (rhinovirus or murine coronavirus), followed 2 days later by a virulent viral pathogen (influenza A virus). This model demonstrated that rhinovirus can reduce the severity of influenza A virus, which corresponded with an early but controlled inflammatory response in the lungs and early clearance of influenza A virus. We further determined the dose and timing parameters that were important for effective disease attenuation and showed that influenza disease is also reduced by coinfection with a murine coronavirus. These findings demonstrate that coinfecting viruses can alter immune responses and pathogenesis in the respiratory tract.

Characterisation of the Virome of Tonsils from Conventional Pigs and from Specific Pathogen-Free Pigs

Porcine respiratory disease is a multifactorial disease that can be influenced by a number of different microorganisms, as well as by non-infectious factors such as the management and environment of the animals. It is generally believed that the interaction between different infectious agents plays an important role in regard to respiratory diseases. Therefore, we used high-throughput sequencing combined with viral metagenomics to characterise the viral community of tonsil samples from pigs coming from a conventional herd with lesions in the respiratory tract at slaughter. In parallel, samples from specific pathogen-free pigs were also analysed. This study showed a variable co-infection rate in the different pigs. The differences were not seen at the group level but in individual pigs. Some viruses such as adenoviruses and certain picornaviruses could be found in most pigs, while others such as different parvoviruses and anelloviruses were only identified in a few pigs. In addition, the complete coding region of porcine parvovirus 7 was obtained, as were the complete genomes of two teschoviruses. The results from this study will aid in elucidating which viruses are circulating in both healthy pigs and in pigs associated with respiratory illness. This knowledge is needed for future investigations into the role of viral-viral interactions in relation to disease development.

Nasal delivery of chitosan/alginate nanoparticle encapsulated bee (Apis mellifera) venom promotes antibody production and viral clearance during porcine reproductive and respiratory syndrome virus infection by modulating T cell related responses

In this study, we administered specially developed chitosan/alginate nanoparticle encapsulated BV (CH/AL-BV) which has slow-releasing properties and mucosal adhesiveness to pig via nasal route and evaluate whether it can facilitate systemic immune response and improve clearance of porcine reproductive and respiratory syndrome virus (PRRSV). The CH/AL-BV-administered group with PRRSV vaccination showed significantly enhanced Th1-related responses including a high population of CD4⁺ T lymphocyte and cytokine mRNA levels including interferon-gamma (IFN-γ) and interleukin (IL)-12 and increased PRRSV-specific IgG levels. In the PRRSV challenge experiment, the CH/AL-BV group showed a significant decrease of viral burden in the sera and tissues (lung and bronchial lymph node) and mild interstitial pneumonia signs on both lung gross examination and microscopic evaluation with high levels of PRRSV-specific IgG and viral neutralizing antibody. CH/AL-BV also effectively induced not only Th1-related immune responses including increase in portion of CD4⁺ T lymphocyte, cytokines (IFN-γ and IL-12), and transcriptional factors (STAT4 and T-bet), but also stimulated IFN-γ-secreting cell families such as CD4⁺ T lymphocytes and Th/memory cells. Interestingly, the CH/AL-BV group showed decrease in PRRSV-specific immune-suppressive actions, including the T regulatory cell population and its related cytokines (IL-10 and TGF-β) and transcriptional factors (STAT5 and Foxp3). Therefore, nasal-delivered CH/AL-BV may effectively induce non-specific immune stimulating actions, particularly those related to Th1 responses and viral clearance activities against PRRSV infection. Based on these results, CH/AL-BV could be a promising strategy for overcoming the disadvantages of classical PRRSV vaccination and can be applied as a preventive agent against PRRSV and other viral diseases, particularly those with immune-suppressive characteristics.

Mesenchymal stem cell-derived extracellular vesicles attenuate influenza virus-induced acute lung injury in a pig model

BACKGROUND

Mesenchymal stem (stromal) cells (MSCs) mediate their immunoregulatory and tissue repair functions by secreting paracrine factors, including extracellular vesicles (EVs). In several animal models of human diseases, MSC-EVs mimic the beneficial effects of MSCs. Influenza viruses cause annual outbreaks of acute respiratory illness resulting in significant mortality and morbidity. Influenza viruses constantly evolve, thus generating drug-resistant strains and rendering current vaccines less effective against the newly generated strains. Therefore, new therapies that can control virus replication and the inflammatory response of the host are needed. The objective of this study was to examine if MSC-EV treatment can attenuate influenza virus-induced acute lung injury in a preclinical model.

METHODS

We isolated EVs from swine bone marrow-derived MSCs. Morphology of MSC-EVs was determined by electron microscopy and expression of mesenchymal markers was examined by flow cytometry. Next, we examined the anti-influenza activity of MSC-EVs in vitro in lung epithelial cells and anti-viral and immunomodulatory properties in vivo in a pig model of influenza virus.

RESULTS

MSC-EVs were isolated from MSC-conditioned medium by ultracentrifugation. MSC-EVs were round-shaped and, similarly to MSCs, expressed mesenchymal markers and lacked the expression of swine leukocyte antigens I and II. Incubation of PKH-26-labeled EVs with lung epithelial cells revealed that MSC-EVs incorporated into the epithelial cells. Next, we examined the anti-influenza and anti-inflammatory properties of MSC-EVs. MSC-EVs inhibited the hemagglutination activity of avian, swine, and human influenza viruses at concentrations of 1.25-5 μg/ml. MSC-EVs inhibited influenza virus replication and virus-induced apoptosis in lung epithelial cells. The anti-influenza activity of MSC-EVs was due to transfer of RNAs from EVs to epithelial cells since pre-incubation of MSC-EVs with RNase enzyme abrogated the anti-influenza activity of MSC-EVs. In a pig model of influenza virus, intratracheal administration of MSC-EVs 12 h after influenza virus infection significantly reduced virus shedding in the nasal swabs, influenza virus replication in the lungs, and virus-induced production of proinflammatory cytokines in the lungs of influenza-infected pigs. The histopathological findings revealed that MSC-EVs alleviated influenza virus-induced lung lesions in pigs.

CONCLUSIONS

Our data demonstrated in a relevant preclinical large animal model of influenza virus that MSC-EVs possessed anti-influenza and anti-inflammatory properties and that EVs may be used as cell-free therapy for influenza in humans.

Therapeutic potential of porcine bronchoalveolar fluid-derived mesenchymal stromal cells in a pig model of LPS-induced ALI

In this study, we isolated mesenchymal stromal (stem) cells (MSCs) from broncho-alveolar lavage fluid (BAL) of 2-6-week-old commercial pigs. BAL-MSCs displayed fibroblastic morphology and possessed self-renewal properties. Similar to bone-marrow MSCs, BAL-MSCs expressed mesenchymal markers and both cell types lacked the expression of hematopoetic markers. BAL-MSCs, when cultured in differentiation induction media, differentiated into adipocytes, osteocytes, and chondrocytes. Next, we examined if BAL-MSCs have the ability to treat lipopolysaccharide (LPS)-induced acute lung injury (ALI) in a pig model. Five-week-old commercial pigs were inoculated intra-tracheally with E. coli LPS (1 mg/kg body weight [b.wt.]). Twelve hours after the LPS inoculation, groups of pigs were inoculated intra-tracheally with BM-MSCs or BAL-MSCs (2 × 10⁶  cells/kg b.wt.). Forty eight hours after the cells administration pigs were euthanized and neutrophils in BAL, lung lesions, and cytokines in lung lysates, and engraftment of MSCs in lungs were examined. Engraftment of BAL-MSCs in injured lungs was significantly higher than the BM-MSCs, however, both cell types were equally effective in attenuating LPS-induced ALI as evidenced by decreased inflammation, lung lesions, and proinflammatory cytokines in the lungs of pigs treated with BAL- or BM-MSCs. These data in a preclinical large animal model suggest that BAL-MSCs may be used in clinical settings to treat ALI in humans.

Comparison of mono- and co-infection by swine influenza A viruses and porcine respiratory coronavirus in porcine precision-cut lung slices

Coronaviruses as well as influenza A viruses are widely spread in pig fattening and can cause high economical loss. Here we infected porcine precision-cut lung slices with porcine respiratory coronavirus and two Influenza A viruses to analyze if co-infection with these viruses may enhance disease outcome in swine. Ciliary activity of the epithelial cells in the bronchus of precision-cut lung slices was measured. Co-infection of PCLS reduced virulence of both virus species compared to mono-infection. Similar results were obtained by mono- and co-infection experiments on a porcine respiratory cell line. Again lower titers in co-infection groups indicated an interference of the two RNA viruses. This is in accordance with in vivo experiments, revealing cell innate immune answers to both PRCoV and SIV that are able to restrict the virulence and pathogenicity of the viruses.

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PCLS can be used to analyze porcine respiratory coronavirus infection.

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Co-infection of PCLS with PRCoV and SIV reduces viral replication efficiency.

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SIV replication is reduced after co-infection of NPTr cells with PRCoV.

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Porcine influenza and coronaviruses interfere during infection.

Mechanisms of Adaptive Immunity to Porcine Reproductive and Respiratory Syndrome Virus

The adaptive immune response is necessary for the development of protective immunity against infectious diseases. Porcine reproductive and respiratory syndrome virus (PRRSV), a genetically heterogeneous and rapidly evolving RNA virus, is the most burdensome pathogen of swine health and wellbeing worldwide. Viral infection induces antigen-specific immunity that ultimately clears the infection. However, the resulting immune memory, induced by virulent or attenuated vaccine viruses, is inconsistently protective against diverse viral strains. The immunological mechanisms by which primary and memory protection are generated and used are not well understood. Here, we summarize current knowledge regarding cellular and humoral components of the adaptive immune response to PRRSV infection that mediate primary and memory immune protection against viruses.

UK Pigs at the Time of Slaughter: Investigation into the Correlation of Infection with PRRSV and HEV

Hepatitis E virus (HEV) and porcine reproductive and respiratory syndrome virus (PRRSV) and are both globally prevalent in the pig population. While HEV does not cause clinical disease in pigs, its zoonotic potential has raised concerns in the food safety sector. PRRS has become endemic in the United Kingdom (UK) since its introduction in 1991, and continues to cause considerable economic losses to the swine industry. A better understanding of the current prevalence and diversity of PRRSV and HEV in the UK, and their potential association, is needed to assess risks and target control measures appropriately. This study used plasma, tonsil, and cecal content samples previously collected from pigs in 14 abattoirs in England and Northern Ireland to study the prevalence of several pathogens including PRRSV and HEV. The diversity of PRRSV strains detected in these samples was analyzed by sequencing open reading frame 5 (ORF5), revealing no substantial difference in PRRSV strains from these clinically unaffected pigs relative to those from clinical cases of disease in the UK. Despite the potential immuno-modulatory effect of PRRSV infection, previously demonstrated to affect Salmonella and HEV shedding profiles, no significant association was found between positive PRRSV status and positive HEV status.

Vaccines for porcine epidemic diarrhea virus and other swine coronaviruses

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Swine coronaviruses responsible for significant economic losses to the swine industry.

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Vaccines available only for TGEV and PEDV.

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Types of vaccines include inactivated, live attenuated, recombinant, vectored and DNA vaccines.

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Most vaccines aim to induce lactogenic immunity by immunizing sows at the end of gestation.

The recent introduction of the porcine epidemic diarrhea virus (PEDV) into the North American swine herd has highlighted again the need for effective vaccines for swine coronaviruses. While vaccines for transmissible gastroenteritis virus (TGEV) have been available to producers around the world for a long time, effective vaccines for PEDV and deltacoronaviruses were only recently developed or are still in development. Here, we review existing vaccine technologies for swine coronaviruses and highlight promising technologies which may help to control these important viruses in the future.

Experimental Piscine orthoreovirus infection mediates protection against pancreas disease in Atlantic salmon (Salmo salar)

Viral diseases are among the main challenges in farming of Atlantic salmon (Salmo salar). The most prevalent viral diseases in Norwegian salmon aquaculture are heart and skeletal muscle inflammation (HSMI) caused by Piscine orthoreovirus (PRV), and pancreas disease (PD) caused by Salmonid alphavirus (SAV). Both PRV and SAV target heart and skeletal muscles, but SAV additionally targets exocrine pancreas. PRV and SAV are often present in the same locations and co-infections occur, but the effect of this crosstalk on disease development has not been investigated. In the present experiment, the effect of a primary PRV infection on subsequent SAV infection was studied. Atlantic salmon were infected with PRV by cohabitation, followed by addition of SAV shedder fish 4 or 10 weeks after the initial PRV infection. Histopathological evaluation, monitoring of viral RNA levels and host gene expression analysis were used to assess disease development. Significant reduction of SAV RNA levels and of PD specific histopathological changes were observed in the co-infected groups compared to fish infected by SAV only. A strong correlation was found between histopathological development and expression of disease related genes in heart. In conclusion, experimentally PRV infected salmon are less susceptible to secondary SAV infection and development of PD.

Porcine reproductive and respiratory syndrome virus (PRRSV) up-regulates IL-15 through PKCβ1-TAK1-NF-κB signaling pathway

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is one of the most important infectious diseases in swine industry. IL-15 is a pleiotropic cytokine and has been shown to be essential to transform NKs, CD8 T cells, and other cells of the immune systems into functional effectors. Here, we demonstrated that the broad-spectrum or conventional PKC inhibitors repressed PRRSV-induced IL-15 expression and NF-κB activation. Subsequently, we found that the PKCβ specific inhibitor inhibited PRRSV-induced IL-15 production, which was also confirmed by knock-down of PKCβ1, suggesting that PKCβ1 is involved in the PRRSV-induced IL-15 expression. In addition, we demonstrated that PRRSV activated NF-κB through PKCβ1-induced TAK1 activation. Finally, we demonstrated that PRRSV activated PKCβ1 dependent on the participation of TRIF and MAVS. These data indicate that PRRSV up-regulates IL-15 through TRIF/MAVS-PKCβ1-TAK1-NF-κB signaling pathway. These findings will provide new insights into the molecular mechanisms of IL-15 production induced by PRRSV.