Dynamic changes in inflammatory cytokines in pigs infected with highly pathogenic porcine reproductive and respiratory syndrome virus

Comparison of pathogenicity and host responses of emerging porcine reproductive and respiratory syndrome virus variants in piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly variable virus with genetic diversity. This study comparatively examines the pathogenicity and immunological impact of two emergent PRRSV strains, SD53 and HuN4, in piglets. Our results indicate that SD53 strain induces milder clinical syndromes and less severe tissue damage than HuN4, despite similar replication rates. Hematological tests showed less perturbations in peripheral blood cell profiles after SD53 infection, suggesting a less systemic impact. The neutrophil-to-lymphocyte ratio was notably lower in SD53-infected piglets, suggesting a less intense inflammatory reaction. Moreover, SD53 infection led to lower levels of pro-inflammatory cytokines, further supporting a less pronounced inflammatory profile. Both strains induced the production of PRRSV-specific antibodies. However, transcriptomic analysis of lung and lymph node tissues from infected piglets disclosed a more moderate up-regulation of core genes, including ISGs, in the SD53 group. Further analysis indicated that SD53 primarily enhanced immune-related signaling, particularly in T cell response modules, while HuN4 caused a more robust pro-inflammatory reaction and a dampening of T cell functionality. Flow cytometry analyses confirmed these findings, showing higher CD4/CD8 ratios and increased CD4+ T cell percentages in SD53-infected piglets, implying a more robust T cell response. Collectively, these findings broaden our comprehension of PRRSV pathogenesis and may inform the development of future therapeutic or prophylactic strategies for controlling PRRSV infections more effectively.

IMPORTANCE

The high mutation rate of porcine reproductive and respiratory syndrome virus (PRRSV) poses significant challenges to its accurate diagnosis and the implementation of effective control measures. This research explores the pathogenic profiles of two emerging PRRSV stains: the NADC30-like strain SD53 and the highly pathogenic strain HuN4. Our investigation reveals that SD53 initiates distinct immunopathological responses in vivo compared with those provoked by HuN4. By conducting a transcriptome analysis of differential gene expression in the lungs and lymph nodes of infected piglets, we unveil the intricate molecular mechanisms underlying the contrasting pathogenicity of these two strains. The comprehensive insights yielded by this study are instrumental in advancing our understanding of the dominant NADC30-like PRRSV strain, which has become increasingly prevalent in China's swine industry.

Plasma microRNAs as non-invasive biomarkers in bovine endometritis caused by Gram-negative and Gram-positive bacteria

The purpose was to identify differentially expressed plasma microRNAs (miRNAs) in cows with clinical and subclinical endometritis. In this study clinical endometritis (CE; n = 23) based on vaginal discharge score (VDS), subclinical endometritis (SCE; n = 17) based on VDS (0), and endometrial cytology (the presence of 8.00% polymorphonuclear neutrophils (PMN) on days 21-31 and 5.00% on days 41-51 days in milk (DIM) and healthy cows (n = 21) based on vaginal discharge score (0), and endometrial cytology (< 5.00% PMN on days 21 - 31 and < 5.00% on days 41 - 51 DIM) were selected. The results showed that the expression level of miR-146a was significantly higher in the CE (19.17-fold), and SCE (6.22-fold) groups than those of healthy cows. The relative transcript abundance of miR-223 was considerably down-regulated in the CE (0.26-fold) and SCE (0.06-fold) compared to the healthy cows. The expression levels of miR-146a and miR-223 were significantly higher in the CE group which could be caused by Gram-negative bacterial infection. Our results showed that the expression level of plasma miRNAs postpartum could be used as a reliable marker to distinguish between SCE, CE and healthy cows.

PRRSV infection activates NLRP3 inflammasome through inducing cytosolic mitochondrial DNA stress

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes severe interstitial pneumonia and inflammatory response in piglets and growing pigs. IL-1β is implicated in PRRSV-mediated inflammatory response and the pathogenesis of PRRSV infection. Mitochondria are critical intracellular organelles which is served as signaling platform for antiviral immunity response to participate in immune response of virus infection. The role of mitochondria in PRRSV-mediated inflammatory response and the pathogenesis of PRRSV infection has not been elucidated. Here, our data suggested that PRRSV infection facilitates mitochondrial dysfunction, which induces cytosolic mitochondrial DNA (mtDNA) stress and ROS accumulation, severally activates the NLRP3 inflammasome and NF-κB signaling pathway, and consequently stimulates IL-1β production in PAMs. Furthermore, mtDNA degradation by DNase I abrogates the activation of NLRP3 inflammasome and IL-1β secretion during PRRSV infection. Scavenging ROS significantly inhibits NF-κB signaling activation and the subsequently transcription and secretion of IL-1β. In conclusion, our results indicate that cytosolic mtDNA stress and ROS accumulation after PRRSV infection-induced mitochondrial dysfunction activate NLRP3 inflammasome and NF-κB signaling pathway to promote IL-1β production, revealing a new strategy for vaccine and drug development to PRRSV.

Effects of a water-soluble formulation of tylvalosin on disease caused by porcine reproductive and respiratory syndrome virus alone in sows or in combination with Mycoplasma hyopneumoniae in piglets

BACKGROUND

The effect of a water-soluble formulation of tylvalosin (Aivlosin® 625 mg/g granules) on disease caused by porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (Mhyop) was investigated in two animal studies. In a PRRSV challenge model in pregnant sows (n = 18), six sows received water medicated at target dose of 5 mg tylvalosin/kg body weight/day from 3 days prior to challenge until the end of gestation. Six sows were left untreated, with a third group remaining untreated and unchallenged. Sows were challenged with PRRSV-2 at approximately 85 days of gestation. Cytokines, viremia, viral shedding, sow reproductive parameters and piglet performance to weaning were evaluated. In a dual infection study (n = 16), piglets were challenged with Mhyop on days 0, 1 and 2, and with PRRSV-1 on day 14 and euthanized on day 24. From day 10 to 20, eight piglets received water medicated at target dose of 20 mg tylvalosin/kg body weight/day and eight piglets were left untreated. Cytokines, viremia, bacteriology and lung lesions were evaluated.

RESULTS

In the PRRSV challenge study in pregnant sows, tylvalosin significantly reduced the levels of serum IL-8 (P < 0.001), IL-12 (P = 0.032), TNFα (P < 0.001) and GM-CSF (P = 0.001). IL-8 (P = 0.100) tended to be lower in uterus of tylvalosin sows. All piglets from tylvalosin sows surviving to weaning were PRRSV negative in faecal swabs at weaning compared to 33.3% PRRSV positive piglets from untreated sows (P = 0.08). In the dual challenge study in piglet, tylvalosin reduced serum IL1β, IL-4, IL-6, IL-8, IL-10, IL-12, IL-1α, IL-13, IL-17A, IL-18, GM-CSF, TGFβ1, TNFα, CCL3L1, MIG, PEPCAM-1 (P < 0.001) and increased serum IFNα, IL-1ra and MIP-1b (P < 0.001). In the lungs, tylvalosin reduced IL-8, IL-10 and IL-12 compared to untreated pigs (P < 0.001) and tended to reduce TNFα (P = 0.082). Lung lavage samples from all tylvalosin treated piglets were negative for Mhyop (0 cfu/mL) compared to the untreated piglets which had mean Mhyop counts of 2.68 × 10⁴ cfu/mL (P = 0.023).

CONCLUSION

Overall, tylvalosin reduced both local and systemic proinflammatory cytokines after challenge with respiratory pathogens in sows and in piglets. Tylvalosin was effective in reducing Mhyop recovery from the lungs and may reduce virus shedding in piglets following transplacental PRRSV infection in sows.

Evaluation of porcine GM-CSF during PRRSV infection in vitro and in vivo indicating a protective role of GM-CSF related with M1 biased activation in alveolar macrophage during PRRSV infection

Granulocyte-macrophage colony stimulating factor (GM-CSF), participates in diverse biological processes associated with innate and adaptive immunity, has unknown effects during PRRSV infection. Here, a double-antibody sandwich ELISA for pGM-CSF was developed in-house for evaluation of pGM-CSF level during PRRSV infection both in vitro and in vivo. In in vitro assay, it was notable that PRRSV-infected porcine alveolar macrophages (PAMs) yielded inconsistent pGM-CSF protein- and mRNA-level, suggesting a post-transcriptional inhibition of pGM-CSF mRNA was employed by PRRSV. Meanwhile, concurrent analysis of pGM-CSF levels in serum samples from PRRSV-infected piglets suggested that effect of PRRSV infection demonstrated minimum effect on pGM-CSF levels regardless of PRRSV virulence phenotypes. Moreover, in vitro treatment of PAMs with pGM-CSF prior PRRSV inoculation did not inhibit PRRSV replication in PAMs although genes downstream of pGM-CSF in PAMs could be upregulated by pGM-CSF treatment. Meanwhile, knockdown of pGM-CSF using siRNA did not enhance PRRSV replication as well. Intriguingly, therapeutic antibody treatment of HP-PRRSV-infected piglets led to significantly increased serum pGM-CSF levels, thus aligning with low pneumonia incidence and low intracellular PRRSV-RNA levels in PAMs of therapeutic antibody treated piglets. Furthermore, transcriptome analysis of PAMs from infected piglets revealed increased serum pGM-CSF levels correlated with activation of downstream signal of pGM-CSF in PAMs as evidenced by a M1-like phenotypes of gene expression pattern, implying a potential host-protective role played by pGM-CSF for PRRSV infection in vivo. In conclusion, our results demonstrated developments of a highly sensitive and specific ELISA for pGM-CSF and revealed a potential protective role conferred by pGM-CSF during PRRSV infection.

Maternal Immune Activation and Dietary Soy Isoflavone Supplementation Influence Pig Immune Function but not Muscle Fiber Formation

The goals of this study were to determine the impact of maternal PRRSV infection on offspring muscle and immune development and the potential of dietary soy isoflavones to mitigate those effects. Thirteen first-parity gilts (“gilts”) were randomly allotted into one of three treatments: not infected and fed a diet devoid of isoflavones (CON), infected with porcine reproductive and respiratory syndrome virus (PRRSV) and fed the control diet (POS) or that supplemented with 1,500 mg/kg soy-derived isoflavones (ISF). Gilts were inoculated with PRRSV intranasally on gestational day (GD) 70. After farrowing (GD 114 ± 2), 1-2 offspring (“pigs”) closest to the average litter weight were selected either at birth (3 ± 2 d of age) or weaning (21 ±2 d of age) to determine body, muscle, and organ weights as well as muscle cell number and size. Four weaned pigs of average body weight within each litter were selected for postnatal immune challenge. At PND 52, pigs were injected with 5 µg/kg BW lipopolysaccharide (LPS) intraperitoneally. Serum was collected at 0, 4, and 8 h following LPS administration to analyze tumor necrosis factor alpha (TNF-α). At PND 59, pigs were administered a novel vaccine to elicit an adaptive immune response. At PND 59, 66, and 73, peripheral blood mononuclear cells were isolated and T-cell populations determined by flow cytometry. Both POS and ISF pigs exhibited persistent PRRSV infections throughout the study (PND 1-73). At PND 3, whole body, muscle, and organ weights were not different (P &gt; 0.22) between groups, with the exception of relative liver weight, which was increased (P &lt; 0.05) in POS compared with CON pigs. At PND 21, ISF pigs had reduced (P ≤ 0.05) whole body and muscle weights, but greater (P &lt; 0.05) kidney weight compared with CON, and greater (P &lt; 0.05) relative liver weight compared with CON and POS. Muscle fiber number and size were not different (P &gt; 0.39) between groups at birth or weaning. After LPS administration, TNF-α was greatest in ISF pigs (P &lt; 0.05) at both 0 and 8 h post-challenge. At the peak time-point of 4 h post-challenge, ISF pigs had the greatest concentration of TNF-α and CON pigs had the lowest, with POS pigs being intermediate (P = 0.01). After vaccination, ISF offspring had shifts in T-cell populations indicating an impaired immune response. These data indicate that maternal PRRSV infection may impact offspring organ growth and immune function, particularly when the dam is supplemented with isoflavones.

Alterations in the expression level of visfatin in the lungs of piglets infected with PRRSV and its effect on PRRSV replication

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by PRRS virus (PRRSV), characterized by sow reproductive failure and respiratory symptoms in pigs of all ages. PRRSV mainly causes severe lung damage by invading alveolar macrophages. Visfatin is closely related to acute lung injury, immune response and inflammation along with virus invasion to the host. Therefore, the current study was performed to clarify the relationship between visfatin and PRRSV infection. We used ternary piglets to construct a piglet model to explore the expression of visfatin and tight junction protein in lung injury induced by PRRSV infection, and then further studied the inhibition effect of visfatin on PRRSV replication by PRRSV infection of Marc-145 cells. Our results indicated that both PRRSV attenuated and virulent infections could damage the lung tissues, which could not only lead to severe inflammatory reaction (such as increased expression of TNF-α, TGF-β, IL-8 and IL-10) in lung tissues of piglets, but also brought about the sharp decrease of ZO-1 and Tricellulin expressions resulting in impaired alveolar epithelial barrier. Meanwhile, we found significantly up-regulated expression of visfatin in lungs and serum of pigs after PRRSV infection that were related to both the degree of lung injury and the virulence of PRRSV strain. Moreover, visfatin might inhibit the PRRSV infection to Marc-145 cells in time dependent fashion. Hence, the current investigation provides the novel information about the effect of visfatin and PRRSV co-culture on Marc-145 cells and the effect of visfatin on PRRSV proliferation at different time points.

Andrographolide and Its Derivative Potassium Dehydrographolide Succinate Suppress PRRSV Replication in Primary and Established Cells via Differential Mechanisms of Action

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause significant economic loss worldwide and remains a serious threat to the pork industry. Currently, vaccination strategies provide limited protection against PRRSV infection, and consequently, new antiviral strategies are urgently required. Andrographolide (Andro) and its derivative potassium dehydrographolide succinate (PDS) have been used clinically in China and other Asian countries as therapies for inflammation-related diseases, including bacterial and viral infections, for decades. Here, we demonstrate that Andro and PDS exhibit robust activity against PRRSV replication in Marc-145 cells and primary porcine alveolar macrophages (PAMs). The two compounds exhibited broad-spectrum inhibitory activities in vitro against clinically circulating type 2 PRRSV GD-HD, XH-GD, and NADC30-like HNhx strains in China. The EC₅₀ values of Andro against three tested PRRSV strain infections in Marc-145 cells ranged from 11.7 to 15.3 μmol/L, with selectivity indexes ranging from 8.3 to 10.8, while the EC₅₀ values of PDS ranged from 57.1 to 85.4 μmol/L, with selectivity indexes ranging from 344 to 515. Mechanistically, the anti-PRRSV activity of the two compounds is closely associated with their potent suppression on NF-κB activation and enhanced oxidative stress induced by PRRSV infection. Further mechanistic investigations revealed that PDS, but not Andro, is able to directly interact with PRRSV particles. Taken together, our findings suggest that Andro and PDS are promising PRRSV inhibitors in vitro and deserves further in vivo studies in swine.

Genome-wide transcriptomic analysis of highly virulent African swine fever virus infection reveals complex and unique virus host interaction

African swine fever virus (ASFV), one of the most devastating emerging swine pathogens in China, causes nearly 100 % mortality in naive herds. Here, whole-transcriptome RNA-seq analysis was conducted in porcine alveolar macrophages (PAMs) infected with Pig/Heilongjiang/2018 (Pig/HLJ/18) ASFV at different time points. Our data suggested that ASFV genes expression demonstrated a time-depended pattern and ASFV early genes were involved in antagonizing host innate immunity. Moreover, viral small RNA (vsRNA) was generated as well. Meanwhile, transcriptome analysis of host genes suggested a strong inhibition host immunity-related genes by ASFV infection in PAMs, while enhanced chemokine-mediated signaling pathways and neutrophil chemotaxis were observed in ASFV infected PAMs. Furthermore, ASFV infection also down-regulated host microRNAs (miRNAs) that putatively targeted viral genes, while also triggering dysregulation of host metabolism that promoted virus replication at transcription level. Most importantly, infection of PAMs with ASFV induced a different transcriptome pattern from that of highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV), which is known to trigger a host cytokine storm. In conclusion, our transcriptome data implied that ASFV infection in PAMs appeared to be associated with strong inhibition of host immune responses, dysregulation of host chemokine axis and metabolic pathways.

Porcine reproductive and respiratory syndrome virus infection upregulates negative immune regulators and T-cell exhaustion markers

Porcine alveolar macrophage (PAM) is one of the primary cellular targets for PRRSV, but less than 2% of PAMs are infected with the virus during the acute stage of infection. To comparatively analyze the host transcriptional response between PRRSV-infected PAMs and bystanders PAMs that remained uninfected but were exposed to the inflammatory milieu of an infected lung, pigs were infected with a PRRSV strain expressing green fluorescent protein (PRRSV-GFP) and GFP⁺ (PRRSV infected) and GFP^- (bystander) cells were sorted for RNA-sequencing (RNA-seq). Approximately 4.2% of RNA reads from GFP⁺ and 0.06% reads from GFP^- PAMs mapped to the PRRSV genome, indicating that PRRSV-infected PAMs were effectively separated from bystander PAMs. Further analysis revealed that inflammatory cytokines, interferon-stimulated genes, and antiviral genes were highly upregulated in GFP⁺ as compared to GFP^- PAMs. Importantly, negative immune regulators including NF-κB inhibitors (NFKBIA, NFKBID, NFKBIZ, and TNFAIP3), and T-cell exhaustion markers (PD-L1, PD-L2, IL10, IDO1, and TGFB2) were highly upregulated in GFP⁺ cells as compared to GFP^- cells. By using in situ hybridization assay, RNA transcripts of TNF and NF-κB inhibitors were detected in PRRSV-infected PAMs cultured ex vivo and lung sections of PRRSV-infected pigs during the acute stage of infection. Collectively, the results suggest that PRRSV infection upregulates expression of negative immune regulators and T-cell exhaustion markers in PAMs to modulate the host immune response. Our findings provide further insight into PRRSV immunopathogenesis. Importance PRRSV is widespread in many swine producing countries, causing substantial economic loses to the swine industry. PAM is considered the primary target for PRRSV replication in pigs. However, less than 2% of PAM from an acutely infected pigs are infected with the virus. In the present study, we utilized a PRRSV-GFP strain to infect pigs and sorted infected- and bystander- PAMs from the pigs during the acute stage of infection for transcriptome analysis. PRRSV infected PAMs showed a distinctive gene expression profile and contained many uniquely activated pathways compared to bystander PAMs. Interestingly, upregulated expression of and NF-κB signaling inhibitors and T-cell exhaustion molecules were observed in PRRSV-infected PAMs. Our findings provide additional knowledge on the mechanisms that PRRSV employs to modulate the host immune system.

The jigsaw of PRRSV virulence

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of the, probably, most economically important disease for the pig industry worldwide. This disease, characterised by producing reproductive failure in sows and respiratory problems in growing pigs, appeared in the late 1980s in the United States and Canada. Since its appearance, strains capable of producing higher mortality rates as well as greater severity in clinical signs and lesions than classical strains have been identified. However, since the first reports of these "virulent" PRRSV outbreaks, no homogeneity and consensus in their description have been established. Moreover, to the authors' knowledge, there is no published information related to the criteria that a PRRSV strain should fulfil to be considered as a "virulent" strain. In this review, we revise the terminology used and gather the information related to the main characteristics and differences in clinical signs, lesions, viral replication and tropism as well as immunological parameters between virulent and classical PRRSV strains and propose a first approximation to the criteria to define a virulent PRRSV strain.

Up-Regulation of Immune Checkpoints in the Thymus of PRRSV-1-Infected Piglets in a Virulence-Dependent Fashion

Virulent porcine reproductive and respiratory syndrome virus (PRRSV) strains, such as the Lena strain, have demonstrated a higher thymus tropism than low virulent strains. Virulent PRRSV strains lead to severe thymus atrophy, which could be related to marked immune dysregulation. Impairment of T-cell functions through immune checkpoints has been postulated as a strategy executed by PRRSV to subvert the immune response, however, its role in the thymus, a primary lymphoid organ, has not been studied yet. Therefore, the goal of this study was to evaluate the expression of selected immune checkpoints (PD1/PDL1, CTLA4, TIM3, LAG3, CD200R1 and IDO1) in the thymus of piglets infected with two different PRRSV-1 strains. Thymus samples from piglets infected with the low virulent 3249 strain, the virulent Lena strain and mock-infected were collected at 1, 3, 6, 8 and 13 days post-infection (dpi) to analyze PRRSV viral load, relative quantification and immunohistochemical staining of immune checkpoints. PD1/PDL1, CTLA4, TIM3, LAG3 and IDO1 immune checkpoints were significantly up-regulated in the thymus of PRRSV infected piglets, especially in those infected with the virulent Lena strain from 6 dpi onwards. This up-regulation was associated with disease progression, high viral load and cell death. Co-expression of these molecules can affect T-cell development, maturation and selection, negatively regulating the host immune response against PRRSV.

Attenuation of porcine deltacoronavirus disease severity by porcine reproductive and respiratory syndrome virus coinfection in a weaning pig model

Porcine deltacoronavirus (PDCoV) is a potentially emerging zoonotic pathogen that causes severe diarrhea in young pigs, with a risk of fatal dehydration. Its pathogenicity on neonatal piglet has been previously reported, however, it is less known if the coinfection with immunosuppressive pathogens can influence PDCoV disease manifestation. Here, a coinfection model of PDCoV and porcine reproductive and respiratory syndrome virus (PRRSV), a global-spread immunosuppressive virus, was set to study their interaction. Weaning pigs in the coinfection group were intranasally inoculated with PRRSV NADC30-like virus and latterly orally inoculated with PDCoV at three day-post-inoculation (DPI). Unexpectedly, compared with pigs in the PDCoV single-infected group, the coinfected pigs did not show any obvious diarrhea, as PDCoV fecal shedding, average daily weight gain (ADWG), gross and microscopic lesions and PDCoV IHC scores consistently indicated that PRRSV coinfection lessened PDCoV caused diarrhea. Additionally, three proinflammatory cytokines TNF-α, IL-1 and IL-6, which can be secreted by PRRSV infected macrophages, were detected to be highly expressed at the intestine from both PRRSV infected groups. By adding to PDCoV-infected cells, these three cytokines were further confirmed to be able to inhibit the PDCoV replication post its cellular entry. Meanwhile, the inhibition effect of the supernatant from PRRSV-infected PAMs could be obviously blocked by the antagonist of these three cytokines. In conclusion, PRRSV coinfection increased TNF-α, IL-1, and IL-6 in the microenvironment of intestines, which inhibits the PDCoV proliferation, leading to lessened severity of diarrhea. The findings provide some new insight into the pathogenesis and replication regulation of PDCoV.

A broadly neutralizing monoclonal antibody induces broad protection against heterogeneous PRRSV strains in piglets

Neutralizing antibodies (NAbs) have attracted attention as tools for achieving PRRSV control and prevention, but viral antigenic variation undermines the abilities of NAbs elicited by attenuated PRRSV vaccines to confer full protection against heterogeneous PRRSV field isolates. As demonstrated in this study, the monoclonal antibody (mAb) mAb-PN9cx3 exhibited broad-spectrum recognition and neutralizing activities against PRRSV-1 and PRRSV-2 strains in vitro. Furthermore, in vivo experiments revealed that the administration of two 10-mg doses of mAb-PN9cx3 before and after the inoculation of piglets with heterologous PRRSV isolates (HP-PRRSV-JXA1 or PRRSV NADC30-like strain HNhx) resulted in significant reduction of the PRRSV-induced pulmonary pathological changes and virus loads in porcine alveolar macrophages (PAMs) compared with the results obtained with mAb-treated isotype controls. Moreover, minimal hilar lymph node PRRSV antigen levels were observed in mAb-PN9cx3-treated piglets. A transcriptome profile analysis of PAMs extracted from lung tissues of piglets belonging to different groups (except for antibody-isotype controls) indicated that mAb-PN9cx3 treatment reversed the PRRSV infection-induced alterations in expression profiles. A gene ontology (GO) enrichment analysis of these genes traced their functions to pathways that included the immune response, inflammatory response, and response to steroid hormone, and their functions in oogenesis and positive regulation of angiogenesis have been implicated in PRRSV pathogenesis. Overall, NADC30-like HNhx infection affected more gene pathways than HP-PRRSV infection. In conclusion, our research describes a novel immunologic approach involving the use of mAbs that confer cross-protection against serious illness resulting from infection with heterogeneous PRRSV-2 isolates, which is a feat that has not yet been achieved through vaccination. Ultimately, mAb-PN9cx3 will be a powerful addition to our current arsenal for achieving PRRSV prevention and eradication.

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.

Upregulation of HMGB1 secretion in lungs of pigs infected by highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) remains a major driver for substantial economic losses to the swine industry across the world. Pulmonary inflammatory injury is a common manifestation in infected pigs. Previous studies reported that PRRS virus (PRRSV) induces secretion of high mobility group box 1 (HMGB1), a proinflammatory factor, in cultured cells. The objective of this study was to evaluate whether HMGB1 secretion is associated with PRRSV-induced pulmonary inflammatory responses in the early stage of infection in vivo. Three-week-old piglets were inoculated with either HuN4, a highly pathogenic PRRSV (HP-PRRSV) strain, or CH1R, an avirulent PRRSV vaccine strain. Necropsy was performed at 7 days post-infection. The results showed that HuN4 significantly induced the secretion of HMGB1 and inflammatory cytokines (IL-1β, IL-6) into the bronchoalveolar lavage fluid (BALF). HuN4 infection induced severe interstitial pneumonia in the pigs. In contrast, pigs infected by CH1R had mild lung inflammation with minimal HMGB1 secretion. In addition, high viral load of HuN4 was detected in both pulmonary alveolar macrophages (PAMs) and lung tissue, whereas viral RNA of CH1R was confined to PAMs. In consistent with the pneumonia development, HuN4 induced inflammatory cytokines in both PAMs and lung tissue, while their expression in CH1R-infected pigs confined only to PAMs. These results indicate that the HuN4-induced HMGB1 secretion into BALF may enhance the pulmonary inflammatory response and exacerbate the lung injury. This finding provides insights to the inflammatory response and pathogenesis of the HP-PRRSV infection.

Inhibition of porcine reproductive and respiratory syndrome virus by PKC inhibitor dequalinium chloride in vitro

As a severe disease characterized by reproductive failure and respiratory distress, porcine reproductive and respiratory syndrome (PRRS) is one of the most leading threats to the swine industry worldwide. Highly evolving porcine reproductive and respiratory syndrome virus (PRRSV) strains with distinct genetic diversity make the current vaccination strategy much less cost-effective and thus urge alternative protective host directed therapeutic approaches. RACK1-PKC-NF-κB signalling axis was suggested as a potential therapeutic target for PRRS control, therefore we tested the inhibitory effect of PKC inhibitor dequalinium chloride (DECA) on the PRRSV infection in vitro. RT-qPCR, western blot, Co-IP and cytopathic effect (CPE) observations revealed that DECA suppressed PRRSV infection and protected Marc-145 cells and porcine alveolar macrophages (PAMs) from severe cytopathic effects, by repressing the PKCα expression, the interaction between RACK1 and PKCα, and subsequently the NF-κB activation. In conclusion, the data presented in this study shed more light on deeper understanding of the molecular pathogenesis upon PRRSV infection and more importantly suggested DECA as a potential promising drug candidate for PRRS control.

Interferon Inducing Porcine Reproductive and Respiratory Syndrome Virus Vaccine Candidate Protected Piglets from HP-PRRSV Challenge and Evoke a Higher Level of Neutralizing Antibodies Response

Although widespread administration of attenuated porcine reproductive and respiratory syndrome virus (PRRSV) vaccines has been implemented since they first became commercially available two decades ago, PRRSV infection prevalence in swine herds remains high. The limited success of PRRSV vaccines is partly due to the well-established fact that a given vaccine strain confers only partial or no protection against heterologous strains. In our past work, A2MC2-P90, a novel PRRSV vaccine candidate that induced a type I IFNs response in vitro, conferred complete protection against challenge with genetically heterologous PRRSV strains. Here we assessed the ability of the PRRSV vaccine candidate A2MC2-P90 to protect piglets against the HP-PRRSV challenge and compared its efficacy to that of a licensed HP-PRRSV-specific vaccine (TJM-F92) assessed in parallel. A2MC2-P90 provided vaccinated piglets with 100% protection from a lethal challenge with extremely virulent HP-PRRSV-XJA1, while 100% mortality was observed for unvaccinated piglets by day 21 post-challenge. Notably, comparison of partial sequence (GP5) of XJA1 to A2MC2-P90 suggested there was only 88.7% homology. When comparing post-HP-PRRSV challenge responses between piglets administered A2AMC2-P90 versus those immunized with licensed vaccine TJM-F92, A2MC2-P90-vaccinated piglets rapidly developed a stronger protective humoral immune response, as evidenced by much higher titers of neutralizing antibodies, more rapid clearance of viremia and less nasal virus shedding. In conclusion, our data suggest that this novel vaccine candidate A2MC2-P90 has improved protection spectrum against heterologous HP-PRRSV strains.

Screening of PRRSV- and ASFV-encoded proteins involved in the inflammatory response using a porcine iGLuc reporter

Inflammasome plays a major role in innate immune responses by activating caspase-1, resulting in secretion of interleukin-1β (IL-1β) and inflammatory pathologic responses. IL-1β release is widely used as an indirect readout to study inflammasome activation. Here we report an iGLuc reporter (pro-IL-1β-Gluc) of pig origin to monitor cytosolic pro-IL-1β cleavage and mature IL-1β release. Based on the iGLuc reporter, we reconstructed the inflammasome system in vitro and screened PRRSV- and ASFV-encoded proteins involved in regulating inflammasome activation. We found that three non-structural proteins (nsps) of PRRSV, nsp1β, nsp2 and nsp5, activate the NLRP3 inflammasome, and four nsps of PRRSV, nsp1ɑ, nsp7, nsp10 and nsp11, inhibit NLRP3 inflammasome activation, of which nsp10 and nsp11 have a highly significant inhibitory effect. In addition, we also found that four ASFV-encoded proteins, S183L, E199L, O61R and I7L activate the inflammatory response and four ASFV-encoded proteins, I226L, A151R, NP419L and QP383R, inhibit the inflammatory response. Our results provide a highly sensitive and high-throughput tool to screen for proteins that regulate inflammasome activation in vitro.

Why, when and how should exposure be considered at the within-host scale? A modelling contribution to PRRSv infection

Understanding the impact of pathogen exposure on the within-host dynamics and its outcome in terms of infectiousness is a key issue to better understand and control the infection spread. Most experimental and modelling studies tackling this issue looked at the impact of the exposure dose on the infection probability and pathogen load, very few on the within-host immune response. Our aim was to explore the impact on the within-host response not only of the exposure dose, but also of its duration and peak, for contrasted virulence levels. We used an integrative modelling approach of the within-host dynamics at the between-cell level. We focused on the porcine reproductive and respiratory syndrome virus, a major concern for the swine industry. We quantified the impact of exposure and virulence on the viral dynamics and immune response by global sensitivity analyses and descriptive statistics. We found that the area under the viral curve, an indicator of the infection severity, was fully determined by the exposure intensity. The infection duration increased with the strain virulence and, for a given strain, exhibited a positive linear correlation with the exposure intensity logarithm and the exposure duration. Taking into account the exposure intensity is hence necessary. Besides, representing the exposure due to contacts by a single punctual dose would tend to underestimate the infection duration. As the infection severity and duration both contribute to the pig infectiousness, a prolonged exposure of the adequate intensity would be recommended in an immuno-epidemiological context.

Notch signaling contributes to the expression of inflammatory cytokines induced by highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) infection in porcine alveolar macrophages

Notch signaling, an evolutionarily conserved signal pathway has emerged as a key signal pathway to regulate host immune response but the contribution of Notch signaling to immune response in pigs remains unknown. Infection of porcine alveolar macrophages (PAM) with porcine reproductive and respiratory syndrome virus (PRRSV) triggers expression of Jagged1 mRNA, suggesting that Notch signaling might play a role in the immune response to PRRSV infection. To further explore it, we examined the expression profile of Notch molecules in PAM following a highly pathogenic PRRSV (HP-PRRSV) strain infection. We demonstrated that HP-PRRSV infection resulted in the induction of Notch ligands (Jagged1, Dll3, Dll4), the transcription factor RBP-J, and the target gene Hes1, consistent with activation of Notch signaling. Next, using DAPT treatment and the knockdown of RBP-J illustrated that inhibition of activation of Notch signaling attenuated induction of the inflammatory cytokines (TNF-α and IL-1β) instead of viral replication in PAM during HP-PRRSV infection. Furthermore, the knockdown of Jagged1, the most induced ligand not only inhibited activation of Notch signaling, but also reduced the expression of inflammatory cytokines without any influence in viral replication. Moreover, our data revealed that several signaling including NF-κB, MAPK and Notch signaling contributed to the induction of Jagged1 in PAM during HP-PRRSV infection. In summary, these findings reveal that Notch as an important signaling pathway could contribute to the regulation of inflammatory response induced by HP-PRRSV infection.

Activation of pro- and anti-inflammatory responses in lung tissue injury during the acute phase of PRRSV-1 infection with the virulent strain Lena

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Lena virulent strain caused an increase in sera levels of IFN-γ and IL-6.

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Lung viral load and PRRSV-N-protein⁺ cells were inversely correlated with CD163⁺ macrophages in the lung.

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CD14⁺ cells infiltrated interstitium to possibly replenish macrophages subsets.

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Lena-induced microscopic lung injury was linked to an increase of iNOS⁺ cells.

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The increase of CD200R1⁺ and FoxP3⁺ cells was associated with the course of lung injury.

Porcine reproductive and respiratory syndrome virus (PRRSV) plays a key role in porcine respiratory disease complex modulating the host immune response and favouring secondary bacterial infections. Pulmonary alveolar macrophages (PAMs) are the main cells supporting PRRSV replication, with CD163 as the essential receptor for viral infection. Although interstitial pneumonia is by far the representative lung lesion, suppurative bronchopneumonia is described for PRRSV virulent strains. This research explores the role of several immune markers potentially involved in the regulation of the inflammatory response and sensitisation of lung to secondary bacterial infections by PRRSV-1 strains of different virulence. Conventional pigs were intranasally inoculated with the virulent subtype 3 Lena strain or the low virulent subtype 1 3249 strain and euthanised at 1, 3, 6 and 8 dpi. Lena-infected pigs exhibited more severe clinical signs, macroscopic lung score and viraemia associated with an increase of IL-6 and IFN-γ in sera compared to 3249-infected pigs. Extensive areas of lung consolidation corresponding with suppurative bronchopneumonia were observed in Lena-infected pigs. Lung viral load and PRRSV-N-protein⁺ cells were always higher in Lena-infected animals. PRRSV-N-protein⁺ cells were linked to a marked drop of CD163⁺ macrophages. The number of CD14⁺ and iNOS⁺ cells gradually increased along PRRSV-1 infection, being more evident in Lena-infected pigs. The frequency of CD200R1⁺ and FoxP3⁺ cells peaked late in both PRRSV-1 strains, with a strong correlation between CD200R1⁺ cells and lung injury in Lena-infected pigs. These results highlight the role of molecules involved in the earlier and higher extent of lung lesions in piglets infected with the virulent Lena strain, pointing out the activation of routes potentially involved in the restraint of the local inflammatory response.

Porcine reproductive and respiratory syndrome virus infection promotes C1QBP secretion to enhance inflammatory responses

Complement component 1, q subcomponent binding protein (C1QBP) is a receptor for the globular heads of C1q and modulates various biological processes including infection, inflammation, autoimmunity, and cancer. In our previous study to identify differentially expressed secretory proteins in Marc-145 cells infected with porcine reproductive and respiratory syndrome virus (PRRSV), mass spectrum data showed that C1QBP was secreted after PRRSV infection. However, the biological significance of secreted C1QBP remains unclear. In this study, we confirmed that PRRSV infection promoted C1QBP secretion in Marc-145 cells and porcine alveolar macrophages (PAMs), the target cells of PRRSV in vivo. Knockdown of endogenous C1QBP decreased PRRSV-induced inflammatory responses. The purified recombinant porcine C1QBP (poC1QBP) had proinflammatory effects. The exogenous addition of poC1QBP significantly enhanced PRRSV-induced inflammatory responses and abolished the inhibitory effects mediated by poC1QBP-knockdown. Taken together, these results demonstrate that PRRSV infection promotes poC1QBP secretion that enhances inflammatory responses.

Effects of PRRSV Infection on the Porcine Thymus

Porcine reproductive and respiratory syndrome virus (PRRSV) dramatically affects the thymus and its ability to carry out its normal functions. In particular, infection incapacitates PRRSV-susceptible CD14^pos antigen-presenting cells (APCs) in the thymus and throughout the body. PRRSV-induced autophagy in thymic epithelial cells modulates the development of T cells, and PRRSV-induced apoptosis in CD4^posCD8^pos thymocytes modulates cellular immunity against PRRSV and other pathogens. Pigs are less able to resist and/or eliminate secondary infectious agents due the effect of PRRSV on the thymus, and this susceptibility phenomenon is long recognized as a primary characteristic of PRRSV infection.

Evaluation of PRRSv specific, maternally derived and induced immune response in Ingelvac PRRSFLEX EU vaccinated piglets in the presence of maternally transferred immunity

In this study, we analyzed PRRS virus (PRRSv) specific lymphocyte function in piglets vaccinated with Ingelvac PRRSFLEX EU^® at two and three weeks of age in the presence of homologous maternal immunity. Complete analysis of maternal immunity to PRRSv was evaluated postpartum, as well as passive transfer of antibodies and T cells to the piglet through colostrum intake and before and after challenge with a heterologous PRRSv at ten weeks of age. Maternal-derived antibodies were detected in piglets but declined quickly after weaning. However, vaccinated animals restored PRRSv-specific antibody levels by anamnestic response to vaccination. Cell analysis in colostrum and milk revealed presence of PRRSv-specific immune cells at suckling with higher concentrations found in colostrum than in milk. In addition, colostrum and milk contained PRRSv-specific IgA and IgG that may contribute to protection of newborn piglets. Despite the presence of PRRSv-specific Peripheral Blood Mononuclear cells (PBMCs) in colostrum and milk, no PRRSv-specific cells could be detected from blood of the piglets at one or two weeks of life. Nevertheless, cellular immunity was detectable in pre-challenged piglets up to 7 weeks after vaccination while the non-vaccinated control group showed no interferon (IFN) γ response to PRRSv stimulation. After challenge, all piglets developed a PRRSv-specific IFNγ-response, which was more robust at significantly higher levels in vaccinated animals compared to the primary response to PRRSv in non-vaccinated animals. Cytokine analysis in the lung lumen showed a reduction of pro-inflammatory responses to PRRSv challenge in vaccinated animals, especially reduced interferon (IFN) α levels. In conclusion, vaccination of maternally positive piglets at 2 and 3 weeks of age with Ingelvac PRRSFLEX EU induced a humoral and cellular immune response to PRRSv and provided protection against virulent, heterologous PRRSv challenge.

Interaction of PIAS1 with PRRS virus nucleocapsid protein mediates NF-κB activation and triggers proinflammatory mediators during viral infection

Porcine reproductive and respiratory syndrome virus (PRRSV) activates NF-κB during infection. We examined the ability of all 22 PRRSV genes for NF-κB regulation and determined the nucleocapsid (N) protein as the NF-κB activator. Protein inhibitor of activated STAT1 (signal transducer and activator of transcription 1) (PIAS1) was identified as a cellular protein binding to N. PIAS1 is known to bind to p65 (RelA) in the nucleus and blocks its DNA binding, thus functions as a repressor of NF-κB. Binding of N to PIAS1 released p65 for NF-κB activation. The N-terminal half of PIAS1 was mapped as the N-binding domain, and this region overlapped its p65-binding domain. For N, the region between 37 and 72 aa was identified as the binding domain to PIAS1, and this domain alone was able to activate NF-κB. A nuclear localization signal (NLS) knock-out mutant N did not activate NF-κB, and this is mostly likely due to the lack of its interaction with PIAS1 in the nucleus, demonstrating the positive correlation between the binding of N to PIAS1 and the NF-κB activation. Our study reveals a role of N in the nucleus for NF-κB activation and proinflammatory cytokine production during infection.

Matrine inhibits IL-1β secretion in primary porcine alveolar macrophages through the MyD88/NF-κB pathway and NLRP3 inflammasome

Our previous studies demonstrated that matrine directly acts on the replication process of porcine reproductive and respiratory syndrome virus (PRRSV). Matrine inhibits viral replication and is also associated with the NF-κB signalling pathway. These results suggest that matrine has antiviral and anti-inflammatory effects. However, the specific anti-inflammatory mechanism of matrine is still unclear. In this study, we investigated the anti-IL-1β mechanism of matrine, as IL-1β is a major inflammatory cytokine, in porcine alveolar macrophages (PAMs) stimulated with 4 μg PRRSV 5′-untranslated region (UTR) RNA and 1 μg/mL LPS. After 5′UTR RNA and LPS co-stimulation of PAMs for 12 h, the expression of IL-1β, IL-6, IL-8 and TNF-α was significantly increased. The results also showed that co-stimulation induced the expression of MyD88, and activated the NF-κB signalling pathway and NLRP3 inflammasome. Furthermore, matrine treatment downregulated MyD88, NLRP3 and caspase-1 expression, inhibited ASC speck formation, suppressed IκBα phosphorylation, and interfered with the translocation of NF-κB from the cytoplasm to the nucleus. These results suggest that matrine plays an important role in PAMs co-stimulated with PRRSV 5′UTR RNA and LPS via its effect on NF-κB and the NLRP3 inflammasome. These findings lay the foundation for the exploration of the clinical application of matrine in PRRSV disease.

A comparably high virulence strain of porcine reproductive and respiratory syndrome virus isolated in Taiwan

Porcine reproductive and respiratory syndrome virus (PRRSV) has been endemic in Taiwan since 1991. This study aimed to present a highly virulent PRRSV in Taiwan based on farm data collection and both in vitro and in vivo evaluations in virus challenge studies. This virulent PRRSV strain was first noticed on Farm TSYM due to continuously high nursery mortality rate and severe PRRSV-associated pneumonia. In phylogenetic surveillance, the PRRSV TSYM-strain remained in the predominant position for years, even with several other PRRSV strain invasions. In laboratory challenge trials, the TSYM-strain led to prolonged pyrexia, growth retardation, high mortality rates and high viremia titer that similar to the highly pathogenic PRRSV. The TSYM-strain isolate also triggered early interleukin-10 up-regulation and significantly higher infection rates under in vitro experiments. This study provides information of a comparably virulent strain in Taiwan and its appearance in both farm and laboratory levels.

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.

Annexin A2 binds to vimentin and contributes to porcine reproductive and respiratory syndrome virus multiplication

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important globally distributed and highly contagious pathogen that has restricted cell tropism in vivo and in vitro. In the present study, we found that annexin A2 (ANXA2) is upregulated expressed in porcine alveolar macrophages infected with PRRSV. Additionally, PRRSV replication was significantly suppressed after reducing ANXA2 expression in Marc-145 cells using siRNA. Bioinformatics analysis indicated that ANXA2 may be relevant to vimentin, a cellular cytoskeleton component that is thought to be involved in the infectivity and replication of PRRSV. Co-immunoprecipitation assays and confocal analysis confirmed that ANXA2 interacts with vimentin, with further experiments indicating that the B domain (109–174 aa) of ANXA2 contributes to this interaction. Importantly, neither ANXA2 nor vimentin alone could bind to PRRSV and only in the presence of ANXA2 could vimentin interact with the N protein of PRRSV. No binding to the GP2, GP3, GP5, nor M proteins of PRRSV was observed. In conclusion, ANXA2 can interact with vimentin and enhance PRRSV growth. This contributes to the regulation of PRRSV replication in infected cells and may have implications for the future antiviral strategies.

Interferon Independent Non-Canonical STAT Activation and Virus Induced Inflammation

Interferons (IFNs) are a group of secreted proteins that play critical roles in antiviral immunity, antitumor activity, activation of cytotoxic T cells, and modulation of host immune responses. IFNs are cytokines, and bind receptors on cell surfaces to trigger signal transduction. The major signaling pathway activated by IFNs is the JAK/STAT (Janus kinase/signal transducer and activator of transcription) pathway, a complex pathway involved in both viral and host survival strategies. On the one hand, viruses have evolved strategies to escape from antiviral host defenses evoked by IFN-activated JAK/STAT signaling. On the other hand, viruses have also evolved to exploit the JAK/STAT pathway to evoke activation of certain STATs that somehow promote viral pathogenesis. In this review, recent progress in our understanding of the virus-induced IFN-independent STAT signaling and its potential roles in viral induced inflammation and pathogenesis are summarized in detail, and perspectives are provided.

Porcine reproductive and respiratory syndrome virus induces HMGB1 secretion via activating PKC-delta to trigger inflammatory response

Porcine reproductive and respiratory syndrome virus (PRRSV) causes inflammatory injuries in infected pigs. PRRSV induces secretion of high mobility group box 1 (HMGB1) that enhances inflammatory response. However, the mechanism of PRRSV-induced HMGB1 secretion is unknown. Here, we discovered PRRSV induced HMGB1 secretion via activating protein kinase C-delta (PKCδ). HMGB1 secretion was positively correlated with PKCδ activation in PRRSV-infected cells in a dose and time-dependent manner. Suppression of PKCδ with inhibitor and siRNA significantly blocked PRRSV-induced HMGB1 translocation and secretion, which indicates PKCδ activation is essential for the PRRSV-mediated HMGB1 secretion. In addition, PKCδ knockdown in PRRSV-infected cells led to downregulation of inflammatory cytokines, including IL-1beta and IL-6. Moreover, PRRSV E and pORF5a proteins were found to activate PKCδ and consequent HMGB1 secretion. These results demonstrate PRRSV activates PKCδ to induce HMGB1 secretion via E and pORF5a. This finding provides insights on the inflammatory response and pathogenesis of PRRSV infection.

Hypothalamus-pituitary-adrenal axis involves in anti-viral ability through regulation of immune response in piglets infected by highly pathogenic porcine reproductive and respiratory syndrome virus

BACKGROUND

The highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has been responsible for several viral attacks in the Asian porcine industry, since the first outbreak in China in 2006. During the early stages of the HP-PRRSV infection, high levels of proinflammatory cytokines are noted in the host peripheral blood, which are accompanied by severe lesions in the lungs and immune system organs; these are considered as the greatest contributors to the overall disease burden. We hypothesized that the anti-PRRSV response in piglets might be mediated by the hypothalamus-pituitary-adrenal (HPA) axis, which led to a decrease in the psycho-neuroendocrinological manifestation of HP-PRRSV etiology via immune response regulation.

RESULTS

We investigated the regulation of the HPA axis in HP-PRRSV-infected piglets that were treated with 1 mg/kg body weight (b. w.)/day mifepristone (RU486) or 2 mg/kg b.w./day dexamethasone (DEX). Both RU486 and DEX enhanced the disease status of the piglets infected by the HP-PRRSV HuN4 strain, resulting in high mortality and more severe pathological changes in the lungs.

CONCLUSIONS

HP-PRRSV infection activates the HPA axis, and artificial regulation of the immune-endocrine system enhances disease severity in HP-PRRSV-infected piglets. Thus, DEX and RU486 should be avoided in the clinical treatment of HP-PRRS.

Improved Vaccine against PRRSV: Current Progress and Future Perspective

Porcine reproductive and respiratory syndrome virus (PRRSV), one of the most economically significant pathogens worldwide, has caused numerous outbreaks during the past 30 years. PRRSV infection causes reproductive failure in sows and respiratory disease in growing and finishing pigs, leading to huge economic losses for the swine industry. This impact has become even more significant with the recent emergence of highly pathogenic PRRSV strains from China, further exacerbating global food security. Since new PRRSV variants are constantly emerging from outbreaks, current strategies for controlling PRRSV have been largely inadequate, even though our understanding of PRRSV virology, evolution and host immune response has been rapidly expanding. Meanwhile, practical experience has revealed numerous safety and efficacy concerns for currently licensed vaccines, such as shedding of modified live virus (MLV), reversion to virulence, recombination between field strains and MLV and failure to elicit protective immunity against heterogeneous virus. Therefore, an effective vaccine against PRRSV infection is urgently needed. Here, we systematically review recent advances in PRRSV vaccine development. Antigenic variations resulting from PRRSV evolution, identification of neutralizing epitopes for heterogeneous isolates, broad neutralizing antibodies against PRRSV, chimeric virus generated by reverse genetics, and novel PRRSV strains with interferon-inducing phenotype will be discussed in detail. Moreover, techniques that could potentially transform current MLV vaccines into a superior vaccine will receive special emphasis, as will new insights for future PRRSV vaccine development. Ultimately, improved PRRSV vaccines may overcome the disadvantages of current vaccines and minimize the PRRS impact to the swine industry.

Pathogenesis and control of the Chinese highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has remained a major threat to the worldwide swine industry ever since its first discovery in the early 1990s. Under the selective pressures in the field, this positive-stranded RNA virus undergoes rapid genetic evolution that eventually leads to emergence in 2006 of the devastating Chinese highly pathogenic PRRSV (HP-PRRSV). The atypical nature of HP-PRRSV has caused colossal economic losses to the swine producers in China and the surrounding countries. In this review, we summarize the recent advances in our understanding of the pathogenesis, evolution and ongoing field practices on the control of this troubling virus in China.

Dynamic changes in bronchoalveolar macrophages and cytokines during infection of pigs with a highly or low pathogenic genotype 1 PRRSV strain

Porcine reproductive and respiratory syndrome virus (PRRSV) replicates primarily in pulmonary alveolar macrophages (PAMs) and the resulting lung damage is influenced by strain virulence. To better understand the pathogenesis of PRRSV infection, we performed a longitudinal study of the PAM population and lung cytokines in specific pathogen-free pigs infected either with the highly pathogenic Lena strain or with the low pathogenic Finistere strain in comparison to uninfected pigs. Bronchoalveolar lavage fluid (BALF) and blood were collected to follow viral, cellular and cytokine changes in lung with respect to clinical signs and systemic events. Compared to Finistere-infected pigs, Lena-infected pigs exhibited more severe clinical signs and 10- to 100-fold higher viral loads in BALF and blood. Similarly, they showed an earlier drop in BALF cell viability and phagocytic activity along with a decrease in the macrophage count. From 8 to 15 days post-infection (dpi), monocytes increased both in BALF and blood from Lena-infected pigs. BALF and blood showed contrasting cytokine patterns, with low increase of IFN-α and TNF-α levels and high increase for IL-1α and IL-8 in BALF after Lena-infection. In contrast, in the blood, the increase was marked for IFN-α and TNF-α but limited for IL-1β and IL-8. Down-regulation of PAM functions combined with inflammatory cytokine and monocyte recruitment may promote lung pathogenesis and virus replication in PRRSV infections with the highly pathogenic Lena strain. In contrast, the low pathogenic Finistere strain showed prolonged viral replication in lung, possibly related to the weak IFN-γ response.

Interleukin-1 receptor antagonist: an early immunomodulatory cytokine induced by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) infection poorly induces pro-inflammatory cytokines (IL-1, IL-6 and TNF-α) and type I IFN production during the early phase of infection. Our microarray analysis indicated strong upregulation of the IL1RA gene in type 2 PRRSV -infected monocyte-derived dendritic cells. Interleukin-1 receptor antagonist (IL-1Ra) is an early inhibitory cytokine that suppresses pro-inflammatory cytokines and T-lymphocyte responses. To investigate the induction of IL-1Ra by PRRSV, monocyte-derived dendritic cells were cultured with type 2 PRRSV or other swine viruses. PRRSV increased both IL1RA gene expression and IL-1Ra protein production in the culture. The enhanced production of IL-1Ra was further confirmed in PRRSV-cultured PBMC and PRRSV-exposed pigs by flow cytometry. Myeloid cell population appeared to be the major IL-1Ra producer both in vitro and in vivo. In contrast to the type 2 PRRSV, the highly pathogenic (HP)- PRRSV did not upregulate IL1RA gene expression in vitro. To determine the kinetics of PRRSV-induced IL1RA gene expression in relation to other pro-inflammatory cytokine genes, PRRSV-negative pigs were vaccinated with a commercially available type 2 modified-live PRRS vaccine or intranasally inoculated with HP-PRRSV. In modified-live PRRS vaccine pigs, upregulation of IL1RA, but not IL1B and IFNA, gene expression was observed from 2 days post- vaccination. Consistent with the in vitro findings, upregulation of IL1RA gene expression was not observed in the HP-PRRSV-infected pigs throughout the experiment. This study identified IL-1Ra as an early immunomodulatory mediator that could be involved in the immunopathogenesis of PRRSV infections.

Review on the transmission porcine reproductive and respiratory syndrome virus between pigs and farms and impact on vaccination

Porcine reproductive and respiratory syndrome (PRRS) is considered to be one of the most costly diseases affecting intensive pig production worldwide. Control of PRRS is a complex issue and involves a combination of measures including monitoring, diagnosis, biosecurity, herd management, and immunization. In spite of the numerous studies dealing with PRRS virus epidemiology, transmission of the infection is still not fully understood. The present article reviews the current knowledge on PRRSV transmission between and within farm, and the impact of vaccination on virus transmission.

Immune responses to modified live virus vaccines developed from classical or highly pathogenic PRRSV following challenge with a highly pathogenic PRRSV strain

Modified live virus vaccines (MLVs) are used on swine farms to control porcine reproductive and respiratory syndrome virus (PRRSV). MLVs from classical PRRSV (C-PRRSV) provide some protection against emergent highly pathogenic PRRSV (HP-PRRSV). This study characterized the protective efficacy and immune response to MLVs from C-PRRSV (CH-1R) or HP-PRRSV (HuN4-F112) in a challenge using HP-PRRSV (HuN4). The outcomes were clinical signs of disease, pathological changes in the thymus and lungs, viremia, and humoral and cellular immune responses. CH-1R provided some protection against challenge with HuN4, while HuN4-F112 was protective in the HuN4 challenge. Compared to unvaccinated piglets, the vaccinated piglets had milder symptoms and fewer pathological changes in the lung and thymus. Piglets vaccinated with HuN4-F112 had higher antibody titers and lower viral loads than piglets vaccinated with CH-1R post challenge. The differences in outcome between the MLVs suggested that underlying differences in the immune responses might warrant further study.

Sensing of Porcine Reproductive and Respiratory Syndrome Virus-Infected Macrophages by Plasmacytoid Dendritic Cells

Porcine reproductive and respiratory syndrome virus (PRRSV) represents a macrophage (MØ)-tropic virus which is unable to induce interferon (IFN) type I in its target cells. Nevertheless, infected pigs show a short but prominent systemic IFN alpha (IFN-α) response. A possible explanation for this discrepancy is the ability of plasmacytoid dendritic cells (pDC) to produce IFN-α in response to free PRRSV virions, independent of infection. Here, we show that the highly pathogenic PRRSV genotype 1 strain Lena is unique in not inducing IFN-α production in pDC, contrasting with systemic IFN-α responses found in infected pigs. We also demonstrate efficient pDC stimulation by PRRSV Lena-infected MØ, resulting in a higher IFN-α production than direct stimulation of pDC by PRRSV virions. This response was strain-independent, required integrin-mediated intercellular contact, intact actin filaments in the MØ and was partially inhibited by an inhibitor of neutral sphingomyelinase. Although infected MØ-derived exosomes stimulated pDC, an efficient delivery of the stimulatory component was dependent on a tight contact between pDC and the infected cells. In conclusion, with this mechanism the immune system can efficiently sense PRRSV, resulting in production of considerable quantities of IFN-α. This is adding complexity to the immunopathogenesis of PRRSV infections, as IFN-α should alert the immune system and initiate the induction of adaptive immune responses, a process known to be inefficient during infection of pigs.

Quantitative estimation of the replication kinetics of genotype 2 PRRSV strains with different levels of virulence in vitro

Porcine reproductive and respiratory syndrome virus (PRRSV) has become an important pathogen for the swine industry, and has resulted in substantial economic losses. In 2006, highly pathogenic PRRSV (HP-PRRSV) belonging to genotype 2 was first identified in China. Here, the replication kinetics of genotype 2 PRRSV strains were estimated in vitro in MARC-145 cells and porcine alveolar macrophages (PAMs) using a TaqMan-based real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) assay. The lower limit of detection was 10 copies/μL, and the assay was linear between 10(1) and 10(8) copies/μL. The intra-assay coefficients of variation were 0.81-1.36%, and the inter-assay coefficients of variation were 1.77-2.56%. Compared to the low pathogenicity CH-1a-F45 strain, the viral loads of the highly pathogenic HuN4-F45 strain were 10(0.5)-10(1.05) and 10(0.84)-10(1.35) times greater in MARC-145 cells and PAMs, respectively from 12 to 96h after infection (P<0.01). This study is the first to demonstrate that the HuN4-F45 strain replicated at higher levels than CH-1a-F45 in MARC-145 cells and PAMs, suggesting that HuN4-F45 has more robust virus amplification efficiency than CH-1a-F45 in vitro.

Comparison of the immune competence of Turopolje, German Landrace × Turopolje, and German Landrace × Pietrain pigs after PRRSV vaccination

The competences of the immune systems of the ancient pig breed Turopolje (T×T), German Landrace × Turopolje (L×T) and 'modern' pig breed German Landrace × Pietrain (L×P) were compared in this study. All pigs were immunized with a modified live vaccine against 'Porcine Reproductive and Respiratory Syndrome' (PRRS) virus (Ingelvac PRRS MLV(®)) to simulate an infection. Antibody production against PRRS MLV was evaluated in serum. Elimination of the viral infectious fragments during the experimental period was monitored in serum, leukocytes and tonsils by RT-qPCR. Furthermore relevant immune marker genes were quantified either on gene expression level using RT-qPCR [toll like receptor (TLR) 7, TLR8, TRAF6, CD163, SIGLEC1, CD4, CD8, CD14, CD19, tumor necrosis factor alpha (TNFα), interleukin (IL) 1, IL2, IL6, IL12], and on protein level using ELISA [interleukin (IL)-1, IL-2, IL-6, and IL-12]. The three breeds showed individual inactivation efficiencies as a reaction to the PRRS MLV vaccination. T×T eliminated the virus in serum within 16 days, followed by L×T (28 days) and L×P (36 days). The antibody titers against PRRS MLV of L×T and L×P were significantly higher compared to T×T (p<0.05). The gene expression data and protein analysis of interleukins revealed that T×T reacted with a type 1 immune response. In contrast, the two other breeds (L×T and L×P) showed a type 2 immune response, which resulted in the higher synthesis of B-cells and an increased concentration of specific anti-PRRS MLV antibodies.

Highly pathogenic porcine reproductive and respiratory syndrome virus infection and induction of apoptosis in bone marrow cells of infected piglets

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has been shown to have a wide range of tissue tropism, and can directly and indirectly induce cellular apoptosis. However, the impact of HP-PRRSV infection on the bone marrow (BM) of piglets remains unclear. In this study, we investigated the BM as a novel site of infection by the HP-PRRSV strain in piglets. HP-PRRSV infected SWC3+SWC8- cells in the BM and induced BM cells to undergo apoptosis. The number of apoptotic cells highlights the striking effects of HP-PRRSV on the central immune organs (BM and thymus) that may enhance the susceptibility of pigs to secondary infections and lead to high mortality. This study is, to the best of our knowledge, the first to report the impact of HP-PRRSV on the BM and implicate the depletion of BM cells during HP-PRRSV infection in the development of immunosuppression in this disease.