Porcine reproductive and respiratory syndrome: clinical disease, pathology and immunosuppression

Construction and characterization of a gE/gI/TK-gene-deleted recombinant pseudorabies virus variant expressing the GP5 of the highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) and NADC30-like PRRSV

Porcine reproductive and respiratory syndrome (PRRS) and pseudorabies (PR) are still the major problems of the worldwide pork industry. Previous studies showed that PR virus (PRV) and PRRS virus (PRRSV) commercial vaccines available in China could not provide complete protection against PRV variants and currently prevalent PRRSV strains. In the present study, a recombinant pseudorabies virus rPRV-GP5/HP-GP5/NA expressing the GP5 of the highly pathogenic PRRSV (HP-PRRSV) and NADC30-like PRRSV was constructed by transfecting the transfer plasmid pG-GP5/HP-GP5/NA-EGFP into ST cells inoculated with gE/gI/TK-gene-deleted rPRV NY-gE-/gI-/TK- using homologous recombination and CRISPR/Cas9 gene editing technique. The recombinant virus rPRV-GP5/HP was also constructed. The expression of the GP5 protein was confirmed by Western blot and indirect immunofluorescence assay. These two viruses were similar to the parental virus rPRV-gE-/gI-/TK- in terms of growth curve, morphogenesis and virus plaque sizes, and proliferated in different cell types. The animal test results showed that ELISA antibodies against PRRSV could be detected in piglets immunized with these two recombinant viruses, and the antibody levels were slightly lower than those of commercial vaccines, but these two recombinant viruses elicited high levels of PRV ELISA antibody and neutralizing antibody, as is the case with commercial vaccine. These two recombinant viruses could provide some protection against virulent PRRSV and PRV, and could effectively inhibit virus proliferation in tissues. These findings provide insights that these two viruses need to be optimally engineered as promising bivalent vaccine candidates against PRV and PRRSV for the control and eradication of the variant PRV and currently prevalent PRRSV. IMPORTANT: Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine pseudorabies virus (PRV) can infect pigs of all ages with high mortality. Due to the appearance of the PRRSV variant (HP-PRRSV and NADC30-Like-PRRSV) and the outbreak of PRV variant in China, the current commercial vaccines available cannot provide complete protection against PRV variants and prevalent PRRSV strains, which causes a major economic loss in pig industry worldwide. Therefore, safe and effective new vaccines are urgently developed to simultaneously control and even eradicate the two viruses. This study intends to use the modified attenuated PRV strain as the carrier and the main antigen gene ORF5 of PRRSV as the exogenous gene to construct the recombinant virus strain, and further validate the protective effect of recombinant strains in vitro and in vivo against the challenge of PRRSV and PRV, which is expected to become a candidate vaccine strain.

Recombination and pathogenicity analysis of NADC30-like and QYYZ-like PRRSV strains in South China

Since 2010, the Lineage 1 (NADC30-like) and Lineage 3 (QYYZ-like) strains of PRRSV-2 have become widespread in China, undergoing recombination and resulting in varying virulent and immune-evading mutants that have severely impacted the pig farming industry. In this study, we isolated one NADC30-like strain (GXHX20211106) and one QYYZ-like strain (GXGG202007) from pig serum samples collected in southern China. Comparative genomic analysis revealed that GXHX20211106 shares 90 % identity with NADC30, while GXGG202007 shows 91.4 % similarity to QYYZ. Both strains exhibit characteristic amino acids deletions or insertions in the Nsp2 region. Phylogenetic analyses further classified GXHX20211106 within Lineage 1.8 (NADC30-like) and GXGG202007 in Lineage 3 (QYYZ-like). Recombination analysis demonstrated that GXHX20211106 resulted from recombination between NADC30-like and HP-PRRSV-like strains, while GXGG202007 originated from recombination events involving QYYZ-like, VR-2332-like, and HP-PRRSV-like strains. Pathogenicity studies in piglets indicated that both isolates caused moderate clinical signs, with GXHX20211106 showing higher virulence compared to GXGG202007. No deaths were recorded in the infected piglets. These findings highlight the critical role of recombination in shaping PRRSV virulence and underscore the need for ongoing surveillance and control measures to mitigate the impact of recombinant PRRSV strains in southern China.

Assessment of changes in antibiotic use in grow-finish pigs after the introduction of PRRSV in a naïve farrow-to-finish system

Responsible antibiotic usage (ABU) is crucial for both animal and human health and requires constant improvement of antimicrobial stewardship (AMS). The presence of porcine reproductive and respiratory syndrome virus (PRRSV), a viral pathogen with immunosuppressive effects on swine, can intensify bacterial co-infections, alter antibiotic pharmacokinetics, and potentially lead to increased ABU. This study aimed to measure ABU changes in the grow-finish population associated with PRRSV infection and describe the antibiotic classes employed to manage clinical signs from a farrow-to-finish genetic multiplier system. Three PRRSV statuses (naïve, positive epidemic, and positive endemic) were established to classify the lots based on PRRSV circulation, with a total of 135,063 animals evaluated. The number of pig treatments per animal days at risk (PTDR) was calculated by administration route to quantify ABU across PRRSV status using negative binomial regression and non-parametric tests (P-value < 0.05). Moreover, to improve ABU comparability in the international scenario, the milligrams per population correction unit (mg/PCU) was calculated according to the European Medicines Agency guidelines. In the nursery phase, there was a statistically significant difference between PRRSV statuses for the overall PTDR (injectable and water routes of administration), with an ABU increase of 3.79 and 2.51 times the naïve PTDR for positive epidemic and endemic status, respectively. For the finishing phase, there was a statistically significant difference between PRRSV statuses in the injectable PTDR, with an ABU increase of 2.74 and 2.28 times the naïve PTDR level for positive epidemic and endemic statuses, respectively. In the nursery phase, the mean mg/PCU was 22.27 mg/PCU for naïve, 86.71 for positive epidemic, and 33.37 for positive endemic statuses; in the finishing phase, 81.31, 76.55, and 67.09 mg/PCU, respectively. The most frequently injected antibiotic in the nursery phase was ampicillin, with 49 % of total injections, followed by lincomycin (31 %) and enrofloxacin (20 %), and in the finishing phase, 72 % of injections were lincomycin, followed by enrofloxacin (28 %). The results highlight that the PRRSV outbreak in the source was associated with a grow-finish ABU increase, revealing the importance of preventing PRRSV infection to potentially decrease ABU and improve AMS within swine production systems.

Intermolecular disulfide bond of PRRSV GP5 and M facilitates VLPs secretion and cell binding

Porcine reproductive and respiratory syndrome virus (PRRSV), the causative agent of porcine reproductive and respiratory syndrome (PRRS), continues to significantly impact on the global swine industry. GP5 and M are the primary structural proteins of PRRSV, playing crucial roles in the processes of virus attachment, entry, assembly and budding. The co-expression of GP5 and M can result in the formation of virus-like particles (VLPs). However, the underlying mechanisms remain incompletely understood. This study investigated the role of GP5-M interaction in VLPs secretion and cell binding. VLPs were generated by co-expressing GP5 and M via recombinant baculoviruses in Sf9 cells and confirmed by transmission electron microscopy. The secretion of VLPs was modulated by the expression levels of GP5 and M. Using the BirA technique, the GP5-M interaction was confirmed in Sf9 cells. Disruption of the N-terminally intermolecular disulfide bond between GP5 and M weakened, but did not completely abolish, the interaction between the proteins, leading to reduced VLPs secretion. Notably, the absence of this intermolecular disulfide bond resulted in the loss of VLPs' ability to bind to MARC-145 cells. In summary, our findings reveal the critical function of the intermolecular disulfide bond in GP5-M interaction, which significantly contributes to VLPs secretion and cell binding, and suggest potential interaction sites between GP5 and M.

Streptococcus suis Induces Macrophage M1 Polarization and Pyroptosis

Streptococcus suis is an important bacterial pathogen that affects the global pig industry. The immunosuppressive nature of S. suis infection is recognized, and our previous research has confirmed thymus atrophy with a large number of necrotic cells. In this current work, we aimed to uncover the role of pyroptosis in cellular necrosis in thymic cells of S. suis-infected mice. Confocal microscopy revealed that S. suis activated the M1 phenotype and primed pyroptosis in the macrophages of atrophied thymus. Live cell imaging further confirmed that S. suis could induce porcine alveolar macrophage (PAM) pyroptosis in vitro, displaying cell swelling and forming large bubbles on the plasma membrane. Meanwhile, the levels of p-p38, p-extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) were increased, which indicated the mitogen-activated protein kinase (MAPK) and AKT pathways were also involved in the inflammation of S. suis-infected PAMs. Furthermore, RT-PCR revealed significant mRNA expression of pro-inflammatory mediators, including interleukin (IL)-1β, IL-6, IL-18, tumor necrosis factor (TNF)-α and chemokine CXCL8. The data indicated that the inflammation induced by S. suis was in parallel with pro-inflammatory activities of M1 macrophages, pyroptosis and MAPK and AKT pathways. Pyroptosis contributes to necrotic cells and thymocyte reduction in the atrophied thymus of mice.

Porcine reproductive and respiratory syndrome virus triggers Golgi apparatus fragmentation-mediated autophagy to facilitate viral self-replication

Macroautophagy/autophagy is a cellular degradation and recycling process that maintains the homeostasis of organisms. A growing number of studies have reported that autophagy participates in infection by a variety of viruses. Porcine reproductive and respiratory syndrome virus (PRRSV) causes severe financial losses to the global swine industry. Although much research has shown that PRRSV triggers autophagy for its own benefits, the exact molecular mechanisms involved in PRRSV-triggered autophagy remain to be fully elucidated. In the current study, we demonstrated that PRRSV infection significantly induced Golgi apparatus (GA) fragmentation, which promoted autophagy to facilitate viral self-replication. Mechanistically, PRRSV nonstructural protein 2 was identified to interact with and degrade the Golgi reassembly and stacking protein 65 dependent on its papain-like cysteine protease 2 activity, resulting in GA fragmentation. Upon GA fragmentation, GA-resident Ras-like protein in brain 2 was disassociated from Golgi matrix protein 130 and subsequently bound to unc-51 like autophagy activating kinase 1 (ULK1), which enhanced phosphorylation of ULK1 and promoted autophagy. Taken together, all these results expand the knowledge of PRRSV-triggered autophagy as well as PRRSV pathogenesis to support novel potential avenues for prevention and control of the virus. More importantly, these results provide the detailed mechanism of GA fragmentation-mediated autophagy, deepening the understanding of autophagic processes.IMPORTANCEPorcine reproductive and respiratory syndrome virus (PRRSV) infection results in a serious swine disease affecting pig farming worldwide. Despite that numerous studies have shown that PRRSV triggers autophagy for its self-replication, how PRRSV induces autophagy is incompletely understood. Here, we identify that PRRSV Nsp2 degrades GRASP65 to induce GA fragmentation, which dissociates RAB2 from GM130 and activates RAB2-ULK1-mediated autophagy to enhance viral replication. This work expands our understanding of PRRSV-induced autophagy and PRRSV replication, which is beneficial for anti-viral drug development.

Genetic background influences pig responses to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly infectious and economically significant virus that causes respiratory and reproductive diseases in pigs. It results in reduced productivity and increased mortality in pigs, causing substantial economic losses in the industry. Understanding the factors affecting pig responses to PRRSV is crucial to develop effective control strategies. Genetic background has emerged as a significant determinant of susceptibility and resistance to PRRSV in pigs. This review provides an overview of the basic infection process of PRRSV in pigs, associated symptoms, underlying immune mechanisms, and roles of noncoding RNA and alternative splicing in PRRSV infection. Moreover, it emphasized breed-specific variations in these aspects that may have implications for individual treatment options.

Recent Progress in Studies of Porcine Reproductive and Respiratory Syndrome Virus 1 in China

Due to the high incidence of PRRSV mutation and recombination, PRRSV infection is difficult to prevent and control in China and worldwide. Two species of PRRSV, Betaarterivirus suid 1 (PRRSV-1) and Betaarterivirus suid 2 (PRRSV-2), exist in China, and PRRSV-1 has always received less attention in China. However, the number of PRRSV-1 strains detected in China has increased recently. To date, PRRSV-1 has spread to more than 23 regions in China. Based on the phylogenetic analysis of ORF5 and the whole genome of PRRSV-1, Chinese PRRSV-1 can be divided into at least seven independent subgroups. Among them, BJEU06-1-like has become the mainstream subgroup in some regions of China. This subgroup of strains has a 5-aa (4 + 1) characteristic discontinuous deletion pattern at aa 357~aa 360 and aa 411 in Nsp2. Previous studies have indicated that the pathogenicity of PRRSV-1 in China is mild, but recent studies found that the pathogenicity of PRRSV-1 was enhanced in China. Therefore, the emergence of PRRSV-1 deserves attention, and the prevention and control of PRRSV-1 infection in China should be strengthened. PRRSV infection is usually prevented and controlled by a combination of virus monitoring, biosafety restrictions, herd management measures and vaccination. However, the use of PRRSV-1 vaccines is currently banned in China. Thus, we should strengthen the monitoring of PRRSV-1 and the biosafety management of pig herds in China. In this review, we summarize the prevalence of PRRSV-1 in China and clarify the genomic characteristics, pathogenicity, vaccine status, and prevention and control management system of PRRSV-1 in China. Consequently, the purpose of this review is to provide a basis for further development of prevention and control measures for PRRSV-1.

Evaluating anti-viral effect of Tylvalosin tartrate on porcine reproductive and respiratory syndrome virus and analyzing the related gene regulation by transcriptomics

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen, characterized by its genetic and antigenic variation. The PRRSV vaccine is widely used, however, the unsatisfied heterologic protection and the risk of reverse virulence raise the requirement to find some new anti-PRRSV strategies for disease control. Tylvalosin tartrate is used to inhibit PRRSV in the field non-specifically, however, the mechanism is still less known.

METHODS

The antiviral effects of Tylvalosin tartrates from three producers were evaluated in a cell inoculation model. Their safety and efficacy concentrations, and effecting stage during PRRSV infection were analyzed. And, the Tylvalosin tartrates regulated genes and pathways which are potentially related to the anti-viral effect were further explored by using transcriptomics analysis. Last, the transcription level of six anti-virus-related DEGs was selected to confirm by qPCR, and the expression level of HMOX1, a reported anti-PRRSV gene, was proved by western blot.

RESULTS

The safety concentrations of Tylvalosin tartrates from three different producers were 40 µg/mL (Tyl A, Tyl B, and Tyl C) in MARC-145 cells and 20 µg/mL (Tyl A) or 40 µg/mL (Tyl B and Tyl C) in primary pulmonary alveolar macrophages (PAMs) respectively. Tylvalosin tartrate can inhibit PRRSV proliferation in a dose-dependent manner, causing more than 90% proliferation reduction at 40 µg/mL. But it shows no virucidal effect, and only achieves the antiviral effect via long-term action on the cells during the PRRSV proliferation. Furthermore, GO terms and KEGG pathway analysis was carried out based on the RNA sequencing and transcriptomic data. It was found that the Tylvalosin tartrates can regulate the signal transduction, proteolysis, and oxidation-reduction process, as well as some pathways such as protein digestion and absorption, PI3K-Akt signaling, FoxO signaling, and Ferroptosis pathways, which might relate to PRRSV proliferation or host innate immune response, but further studies still need to confirm it. Among them, six antivirus-related genes HMOX1, ATF3, FTH1, FTL, NR4A1, and CDKN1A were identified to be regulated by Tylvalosin tartrate, and the increased expression level of HMOX1 was further confirmed by western blot.

CONCLUSIONS

Tylvalosin tartrate can inhibit PRRSV proliferation in vitro in a dose-dependent manner. The identified DEGs and pathways in transcriptomic data will provide valuable clues for further exploring the host cell restriction factors or anti-PRRSV target.

Codon Pair Deoptimization (CPD)-Attenuated PRRSV-1 Vaccination Exhibit Immunity to Virulent PRRSV Challenge in Pigs

Commercially used porcine respiratory and reproductive syndrome (PRRS) modified live virus (MLV) vaccines provide limited protection with heterologous viruses, can revert back to a virulent form and they tend to recombine with circulating wild-type strains. Codon pair deoptimization (CPD) is an advanced method to attenuate a virus that overcomes the disadvantages of MLV vaccines and is effective in various virus vaccine models. The CPD vaccine against PRRSV-2 was successfully tested in our previous study. The co-existence of PRRSV-1 and -2 in the same herd demands protective immunity against both viruses. In this study, live attenuated PRRSV-1 was constructed by recoding 22 base pairs in the ORF7 gene of the E38 strain. The efficacy and safety of the CPD live attenuated vaccine E38-ORF7 CPD to protect against virulent PRRSV-1 were evaluated. Viral load, and respiratory and lung lesion scores were significantly reduced in animals vaccinated with E38-ORF7 CPD. Vaccinated animals were seropositive by 14 days post-vaccination with an increased level of interferon-γ secreting cells. In conclusion, the codon-pair-deoptimized vaccine was easily attenuated and displayed protective immunity against virulent heterologous PRRSV-1.

Enhancing half-life and cytotoxicity of porcine respiratory and reproductive syndrome virus soluble receptors by taming their Fc domains

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen. Although tremendous effort has been made for the vaccine development, only modified live vaccines are widely used with arguably limited efficacy. Our previous study showed that the Fc-fused first four Ig-like domains of Sn (Sn4D-Fc) and the SRCR domains 5-9 of CD163 (SRCR59-Fc) can act as PRRSV soluble receptors (VSRs). In this study, we improved the VSR-based anti-PRRSV strategy by taming their Fc domains. Sequence alignment showed that the CH3 domain of pig IgG1 contained five putative amino acids involved in the interaction with the neonatal Fc receptor (FcRn). The M455L/N461S variant of SRCR59-Fc/Sn4D-Fc was created for the higher affinity of FcRn binding. Both rBac-SRCR59-lsFc/Sn4D-lsFc and rBac-SRCR59-Fc/Sn4D-Fc expressing the mutated or wild-type VSRs were generated for conceptual validation. Both immunofluorescence and Western blotting analysis showed that the two rBac vectors could express the encoded VSRs in cells with similar expression levels and anti-PRRSV effects. In the rBac-injected mice, the expression of SRCR59-lsFc/Sn4D-lsFc was significantly prolonged than that of SRCR59-Fc/Sn4D-Fc. Both plasma stability and serum half-life of the purified SRCR59-lsFc/Sn4D-lsFc were significantly improved than that of SRCR59-Fc/Sn4D-Fc. SRCR59-lsFc/Sn4D-lsFc-treated peripheral blood mononuclear cells showed significantly stronger cytotoxicity on PRRSV-infected primary alveolar macrophages than SRCR59-Fc/Sn4D-Fc-treated cells. For the first time, we demonstrated that both half-life and effector function of pig IgG Fc-fused proteins could be significantly improved by taming their CH3 domains. The rBac-SRCR59-lsFc/Sn4D-lsFc could be further developed as a novel anti-PRRSV reagent.

Congenital tremor and splay leg in piglets – insights into the virome, local cytokine response, and histology

Background

Atypical porcine pestivirus (APPV) is a neurotropic virus associated with congenital tremor type A-II. A few experimental studies also indicate an association between APPV and splay leg. The overarching aim of the present study was to provide insights into the virome, local cytokine response, and histology of the CNS in piglets with signs of congenital tremor or splay leg.

Results

Characterization of the cytokine profile and virome of the brain in piglets with signs of congenital tremor revealed an APPV-associated upregulation of Stimulator of interferon genes (STING). The upregulation of STING was associated with an increased expression of the gene encoding IFN-α but no differential expression was recorded for the genes encoding CXCL8, IFN-β, IFN-γ, IL-1β, IL-6, or IL-10. No viral agents or cytokine upregulation could be detected in the spinal cord of piglets with signs of splay leg or in the brain of piglets without an APPV-infection. The histopathological examination showed no lesions in the CNS that could be attributed to the APPV-infection, as no difference between sick and healthy piglets could be seen.

Conclusion

The results from this study provide evidence of an APPV-induced antiviral cytokine response but found no lesions related to the infection nor any support for a common causative agent.

Reappraising host cellular factors involved in attachment and entry to develop antiviral strategies against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV), is a highly contagious disease that brings tremendous economic losses to the global swine industry. As an intracellular obligate pathogen, PRRSV infects specific host cells to complete its replication cycle. PRRSV attachment to and entry into host cells are the first steps to initiate the replication cycle and involve multiple host cellular factors. In this review, we recapitulated recent advances on host cellular factors involved in PRRSV attachment and entry, and reappraised their functions in these two stages, which will deepen the understanding of PRRSV infection and provide insights to develop promising antiviral strategies against the virus.

Efficacy of a Modified Live Porcine Reproductive and Respiratory Syndrome Virus 1 (PRRSV-1) Vaccine against Experimental Infection with PRRSV AUT15-33 in Weaned Piglets

In this study, the efficacy of the commercial modified live PRRSV-1 vaccine “Ingelvac PRRSFLEX® EU” was assessed in weaned piglets experimentally infected with PRRSV strain AUT15-33. Seventy-four weaned piglets were allocated to five groups. Vaccinated (groups 1, 2, and 5) and non-vaccinated piglets (groups 3 and 4), infected with either a low dose (103 TCID50/dose; groups 2 and 4) or a high dose (105 TCID50/dose; groups 1 and 3) of the virus, were compared regarding clinical signs, average daily weight gain (ADG), lung lesions, viral load in serum, oral swabs, and tissue samples. In comparison to vaccinated animals, coughing increased notably in the second week after challenge in non-vaccinated piglets. During the same time period, vaccinated, high-dose-infected piglets showed significantly higher ADG (p < 0.05) than non-vaccinated, high-dose-infected animals. All infected piglets reached approximately the same viremia levels, but vaccinated animals showed both a significantly reduced viral load in oral fluid (p < 0.05) and tissue samples and significantly reduced lung lesions (p < 0.05). In conclusion, vaccination was able to increase ADG, reduce the amount of viral shedding via oral fluids, and reduce the severity of lung lesions and the viral load in tissue samples under experimental conditions.

Tumor Susceptibility Gene 101 (TSG101) Contributes to Virion Formation of Porcine Reproductive and Respiratory Syndrome Virus via Interaction with the Nucleocapsid (N) Protein along with the Early Secretory Pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused huge economic losses to global swine industry. As an intracellular obligate pathogen, PRRSV exploits host cellular machinery to establish infection. The endocytic sorting complex required for transport (ESCRT) system has been shown to participate in different life cycle stages of multiple viruses. In the current study, a systematic small interference RNA (siRNA) screening assay identified that certain ESCRT components contributed to PRRSV infection. Among them, tumor susceptibility gene 101 (TSG101) was demonstrated to be important for PRRSV infection by knockdown and overexpression assays. TSG101 was further revealed to be involved in virion formation rather than viral attachment, internalization, RNA replication and nucleocapsid (N) protein translation within the first round of PRRSV life cycle. In detail, TSG101 was determined to specially interact with PRRSV N protein and take effect on its subcellular localization along with the early secretory pathway. Taken together, these results provide evidence that TSG101 is a pro-viral cellular factor for PRRSV assembly, which will be a promising target to interfere with the viral infection. IMPORTANCE PRRSV infection results in a serious swine disease affecting pig farming in the world. However, efficient prevention and control of PRRSV is hindered by its complicated infection process. Up to now, our understanding of PRRSV assembly during infection is especially limited. Here, we identified that TSG101, an ESCRT-I subunit, facilitated virion formation of PRRSV via interaction with the viral N protein along with the early secretory pathway. Our work actually expands the knowledge of PRRSV infection and provides a novel therapeutic target for prevention and control of the virus.

Systemic CD4 cytotoxic T cells improve protection against PRRSV-1 transplacental infection

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the major swine pathogens causing reproductive failure in sows. Although modified-live virus (MLV) vaccines are available, only partial protection against heterologous strains is produced, thus vaccinated sows can be infected and cause transplacental infection. The immune effector mechanisms involved are largely unknown.

Methods

The present study investigated the role of cytotoxic lymphocytes, including cytotoxic T cells (CTL), NKT, and NK cells, from blood in preventing PRRSV-1 transplacental infection in vaccinated primiparous sows (two doses vaccinated). Sows from a PRRSV-1 unstable farm were bled just before the last month of gestation (critical period for transplacental infection), then followed to determine whether sows delivered PRRSV-1-infected (n=8) or healthy (n=10) piglets. After that, functions of CTL, NKT, and NK cells in the two groups of sows were compared.

Results

No difference was found through cell surface staining. But upon in vitro re-stimulation with the circulating field virus, sows that delivered healthy piglets displayed a higher frequency of virus-specific CD107a⁺ IFN-γ-producing T cells, which accumulated in the CD4⁺ compartment including CD4 single-positive (CD4 SP) and CD4/CD8α double-positive (CD4/CD8α DP) subsets. The same group of sows also harbored a higher proportion of CD107a⁺ TNF-α-producing T cells that predominantly accumulated in CD4/CD8α double-negative (CD4/CD8α DN) subset. Consistently, CD4 SP and CD4/CD8α DN T cells from sows delivering healthy piglets had a higher virus-specific proliferative response. Additionally, in sows that delivered PRRSV-1-infected piglets, a positive correlation of virus-specific IFN-γ response with average Ct values of umbilical cords of newborn piglets per litter was observed.

Conclusion

Our data strongly suggest that CTL responses correlate with protection against PRRSV-1 transplacental infection, being executed by CD4 T cells (IFN-γ related) and/or CD4/CD8α DN T cells (TNF-α related).

Vimentin rearrangement by phosphorylation is beneficial for porcine reproductive and respiratory syndrome virus replication in vitro

Vimentin, a member of intermediate filaments, has been documented to be involved in viral infections. Despite several studies focusing on its involvement in porcine reproductive and respiratory syndrome virus (PRRSV) infection, the detailed mechanisms by which vimentin takes effect remain to be fully elucidated. In the present study, we identified a previously unrecognized role of vimentin rearrangement in PRRSV replication. We monitored that PRRSV infection induced vimentin reorganization during post-entry stage, which was beneficial for viral replication. In detail, the serine residue of vimentin was phosphorylated at position 38 (Ser38) by calcium calmodulin-dependent protein kinase II gamma (CaMKIIγ), and vimentin filaments reorganized into cage-like structures enwrapping PRRSV replication complex (RC) at the perinuclear location. Taken together, these results expand the knowledge of PRRSV replication, and provide novel targets for prevention and control of PRRSV.

Structural comparison of CD163 SRCR5 from different species sheds some light on its involvement in porcine reproductive and respiratory syndrome virus-2 infection in vitro

Porcine reproductive and respiratory syndrome (PRRS) is a serious disease burdening global swine industry. Infection by its etiological agent, PRRS virus (PRRSV), shows a highly restricted tropism of host cells and has been demonstrated to be mediated by an essential scavenger receptor (SR) CD163. CD163 fifth SR cysteine-rich domain (SRCR5) is further proven to play a crucial role during viral infection. Despite intense research, the involvement of CD163 SRCR5 in PRRSV infection remains to be elucidated. In the current study, we prepared recombinant monkey CD163 (moCD163) SRCR5 and human CD163-like homolog (hCD163L1) SRCR8, and determined their crystal structures. After comparison with the previously reported crystal structure of porcine CD163 (pCD163) SRCR5, these structures showed almost identical structural folds but significantly different surface electrostatic potentials. Based on these differences, we carried out mutational research to identify that the charged residue at position 534 in association with the one at position 561 were important for PRRSV-2 infection in vitro. Altogether the current work sheds some light on CD163-mediated PRRSV-2 infection and deepens our understanding of the viral pathogenesis, which will provide clues for prevention and control of PRRS.

Insights Into Extracellular Vesicle/Exosome and miRNA Mediated Bi-Directional Communication During Porcine Pregnancy

Spontaneous fetal loss is one of the most important challenges that commercial pig industry is still facing in North America. Research over the decade provided significant insights into some of the associated mechanisms including uterine capacity, placental efficiency, deficits in vasculature, and immune-inflammatory alterations at the maternal-fetal interface. Pigs have unique epitheliochorial placentation where maternal and fetal layers lay in opposition without any invasion. This has provided researchers opportunities to accurately tease out some of the mechanisms associated with maternal-fetal interface adaptations to the constantly evolving needs of a developing conceptus. Another unique feature of porcine pregnancy is the conceptus derived recruitment of immune cells during the window of conceptus attachment. These immune cells in turn participate in pregnancy associated vascular changes and contribute toward tolerance to the semi-allogeneic fetus. However, the precise mechanism of how maternal-fetal cells communicate during the critical times in gestation is not fully understood. Recently, it has been established that bi-directional communication between fetal trophoblasts and maternal cells/tissues is mediated by extracellular vesicles (EVs) including exosomes. These EVs are detected in a variety of tissues and body fluids and their role has been described in modulating several physiological and pathological processes including vascularization, immune-modulation, and homeostasis. Recent literature also suggests that these EVs (exosomes) carry cargo (nucleic acids, protein, and lipids) as unique signatures associated with some of the pregnancy associated pathologies. In this review, we provide overview of important mechanisms in porcine pregnancy success and failure and summarize current knowledge about the unique cargo containing biomolecules in EVs. We also discuss how EVs (including exosomes) transfer their contents into other cells and regulate important biological pathways critical for pregnancy success.

Fusion expression of the two soluble viral receptors of porcine reproductive and respiratory syndrome virus with a single adeno-associated virus vector

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen affecting global swine industry. Our recent study has shown that the first four Ig-like domains of sialoadhesin (Sn4D) and the scavenger receptor cysteine-rich domains 5-9 (SRCR59) of CD163 can act as the soluble viral receptors (SVRs) of PRRSV. Co-injection with the two SVR-expressing recombinant adenovirus (rAd) vectors can protect pigs from the lethal challenge with three PRRSV strains. However, the in vivo expression of the two SVRs persists for only two weeks and thus their long-term anti-PRRSV effects remain to be improved. In this study, we fused the two SVRs with a flexible linker or self-cleaving peptide and expressed them with a single recombinant adeno-associated virus (rAAV) vector. The two rAAVs, namely rAAV-Sn4D-SRCR59-Fc and rAAV-SRCR59-Fc/Sn4D-Fc, were generated by using baculovirus-insect cell system. Western blotting analysis showed that the two SVR fusions were efficiently expressed in and secreted from the rAAV-transduced cells. Viral infection blocking assay showed that PRRSV titers in porcine alveolar macrophage (PAM) cells were reduced by 1.6-2.7 log10 after co-cultivation with rAAV-Sn4D-SRCR59-Fc-transduced cells or by 1.9-3.2 log10 after co-cultivation with rAAV-SRCR59-Fc/Sn4D-Fc-transduced cells. After single-dose injection of mice with the rAAV vectors, the expression of two SVR fusions persisted for at least 35 days, which was significantly longer than SRCR59-Fc expression in rAd-SRCR59-Fc-injected mice. Among the two SVR fusions expressed, both expression level and anti-PRRSV activity of SRCR59-Fc/Sn4D-Fc were higher than that of Sn4D-SRCR59-Fc. Therefore, rAAV-SRCR59-Fc/Sn4D-Fc generated can be developed as a novel anti-PRRSV reagent.

An Outbreak of a Respiratory Disorder at a Russian Swine Farm Associated with the Co-Circulation of PRRSV1 and PRRSV2

We conducted a cross-sectional study to identify the major respiratory pathogen responsible for an outbreak of respiratory disease at a swine farm in West Siberia in 2019. We discovered that the peak of morbidity and mortality coincided with a high level of porcine reproductive and respiratory syndrome virus (PRRSV) 1 and 2-related viremia. Based on longer PRRSV2 viremia, the dominant role of PRRSV2 over PRRSV1 in the outbreak was assumed. Phylogenetic analysis revealed that the PRRSV1 strain belonged to sub-genotype 2—one of the predominant groups of genotype 1 PRRSVs in Russia. A partial open reading frame 7 sequence of the PRRSV2 isolate demonstrated a high identity with modified live vaccine-related strains from Denmark (93%) and wild-type VR2332 (92%). We identified the first instance of PRRSV1/PRRSV2 mixed infection in Russia. This finding indicates that further field investigations are needed to access PRRSV2 epidemiology in eastern Europe.

Elastase-mediated membrane fusion of highly pathogenic porcine reproductive and respiratory syndrome virus at host cell surface

Infection by enveloped viruses includes endocytosis and/or membrane fusion at the plasma membrane, where host cell proteases play an essential role. Among them, elastase-mediated infection has been documented for several enveloped viruses. Porcine reproductive and respiratory syndrome virus (PRRSV), an economically critical factor in global swine industry, is previously reported to infect host cells via low pH-dependent clathrin-mediated endocytosis (CME) and undergo membrane fusion in recycling endosomes. In the current study, we identified that elastase was significantly elevated in the lung tissues of highly pathogenic PRRSV (HP-PRRSV)-infected pigs compared to the mock-infected ones. We subsequently demonstrated that elastase contributed to HP-PRRSV infection in both MARC-145 cells and porcine alveolar macrophages (PAMs). Mechanistically, HP-PRRSV entered host cells at the cell surface via elastase-mediated membrane fusion, independent of low pH and CME, and its glycoprotein 5 (GP5) was cleaved by the protease during this process. All these findings deepen our understanding of HP-PRRSV infection, and are beneficial for prevention and control of the disease.

Histopathological Lesions Accompanied with First-Time Isolation of a PRRSV-2 Strain in Greece

Genotype 2 strains of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV-2) have been reported sporadically in Europe. Even if, PRRSV-2 reported to be genetically homogenous in Europe due to the introduction of an MLV vaccine strain, independent introductions of PRRSV-2 field strains have been reported. The aim of the present study was to report the complete genome sequence and evaluate the histopathological lesions of a PRRSV-2 strain, isolated for the first time in Greece. During a routine blood sampling in a commercial pig farm, the results revealed positive samples in weaners of 40-60 days for the PRRSV-2, using real-time polymerase chain reaction. The clinical picture was characterized from respiratory symptoms in weaners, as well as coughing and poor performance at finishing stage and less than 3% mortality rate from weaning stage to finishing stage. The use of ORF5 for PRRSV phylogenetic analysis of the isolated PRRSV strain, named "x1544-1 strain", was successfully determined, belonging to the genotype PRRSV-2. Comparison of the obtained sequence revealed nucleotide sequence identity >98% with PRRSV-2 strain VR2332 and other related strains from Denmark and China. The histopathological evaluation revealed diffuse interstitial pneumonia, multifocal interstitial nephritis, while in the lymphoid organs, follicular and paracortical hyperplasia, coexisting with necrosis and depletion of germ cells were detected. The results of current study undersign the importance for veterinary practitioners to have up-to-date access to phylogenetic data linked to phenotypic information to follow-up the control and prevention strategies against PRRSV.

Porcine Reproductive and Respiratory Syndrome Virus Utilizes Viral Apoptotic Mimicry as an Alternative Pathway To Infect Host Cells

PRRS has caused huge economic losses to pig farming worldwide. Its causative agent, PRRSV, infects host cells through low pH-dependent clathrin-mediated endocytosis and CD163 is indispensable during the process. Whether there exist alternative infection pathways for PRRSV arouses our interest. Here, we found that PRRSV exposed PS on its envelope and disguised as apoptotic debris. The PS receptor TIM-1/4 recognized PRRSV and induced the downstream signaling pathway to mediate viral infection via CD163-dependent macropinocytosis. The current work deepens our understanding of PRRSV infection and provides clues for the development of drugs and vaccines against the virus.

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV), has led to enormous economic losses in global swine industry. Infection by PRRSV is previously shown to be via low pH-dependent clathrin-mediated endocytosis, and CD163 functions as an essential receptor during viral infection. Despite much research focusing on it, PRRSV infection remains to be fully elucidated. In this study, we demonstrated that PRRSV externalized phosphatidylserine (PS) on the envelope as viral apoptotic mimicry and infected host cells through T-cell immunoglobulin and mucin domain (TIM)-induced and CD163-involved macropinocytosis as an alternative pathway. In detail, we identified that PS receptor TIM-1/4 recognized and interacted with PRRSV as viral apoptotic mimicry and subsequently induced macropinocytosis by the downstream Rho GTPases Rac1, cell division control protein 42 (Cdc42), and p21-activated kinase 1 (Pak1). Altogether, these results expand our knowledge of PRRSV infection, which will support implications for the prevention and control of PRRS.

IMPORTANCE PRRS has caused huge economic losses to pig farming worldwide. Its causative agent, PRRSV, infects host cells through low pH-dependent clathrin-mediated endocytosis and CD163 is indispensable during the process. Whether there exist alternative infection pathways for PRRSV arouses our interest. Here, we found that PRRSV exposed PS on its envelope and disguised as apoptotic debris. The PS receptor TIM-1/4 recognized PRRSV and induced the downstream signaling pathway to mediate viral infection via CD163-dependent macropinocytosis. The current work deepens our understanding of PRRSV infection and provides clues for the development of drugs and vaccines against the virus.

Full-genome analysis and pathogenicity of a genetically distinct Russian PRRSV-1 Tyu16 strain

Porcine reproductive and respiratory syndrome virus-1 (PRRSV-1) strains from Eastern Europe have a high diversity. All three known subtypes (1, 2, 3) of PRRSV-1 have been detected in Russia. There are two different groups of viruses belonging to the subtype 1: pan-European subtype 1 strains, and insufficiently studied Russian strains. The main objective of this study was to characterize the full genomic structure of the atypical Tyu16 strain of the Russian group subtype 1 PRRSV-1 and to assess its pathogenicity. Complete sequencing of the Tyu16 strain revealed that it did not belong to any existing subtype. Comparison of the whole genome sequence of the Tyu16 strain with that of PRRSV-1 prototype strains revealed 78.1 % (subtype 1 Lelystad), 78.1 % (subtype 2 WestSib13) and 77.7 % (subtype 3 Lena) nucleotide identity level, respectively. The coding sequence of different parts of the Tyu16 strain genome demonstrated a varying percentage identity to the different reference PRRSV-1 strains, which may indicate recombination events in its evolutionary history. We assume that among PRRSV-1 isolates, the Tyu16 is the closest relative to the common ancestor of PRRSV-1 and PRRSV-2. Low pathogenicity of the Tyu16 was demonstrated by experimental infection of 70-day-old piglets. Infected animals showed fever not exceeding 7 days, dyspnea in two out of five pigs and reduced weight gain. The virus shedding was undetectable and viremia was at low level.

Ursolic acid derivatives are potent inhibitors against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most devastating viral pathogens of swine and has a substantial economic impact on the global pork industry. Currently, vaccination strategies provide very limited protection against PRRSV transmission. Therefore, there is an urgent need to develop new antiviral strategies to prevent PRRSV pandemics. In this study, we showed that 3-O-β-chacotriosyl ursolic acid (1) and its ester analogs possessed anti-PRRSV activity in vitro, of which bioisosteric surrogates 7-15 were further generated with the aim of enhancing the selective index. Our results showed that amidation of the 17-COOH group of UA could significantly reduce cytotoxicity and enhance anti-PRRSV activity in MARC-145 cells. Among them, compound 9 displayed the strongest anti-PRRSV activity with the least cytotoxicity. Potent inhibition of representative compounds 9 and 12 on PRRSV infection was observed not only in MARC-145 cells, but also in primary porcine alveolar macrophages, PRRSV-target cells in vivo. Furthermore, compounds 8, 9, 12 and 14 exhibited broad-spectrum inhibitory activities in vitro against high pathogenic type 2 PRRSV NADC30-like and GD-XH strains as well as classical CH-1a and VR2332 strains. Mechanistically, compounds 9 and 12 inhibited PRRSV replication by directly inactivating virions and therefore affecting all tested stages of the virus life cycle, including viral entry, replication and progeny virus release, but did not affect cellular susceptibility to PRRSV. Our findings suggest that compound 9 could be a hit PRRSV inhibitor and deserves further in vivo studies in swine.

Evaluation of local and systemic immune responses in pigs experimentally challenged with porcine reproductive and respiratory syndrome virus

The host-associated defence system responsible for the clearance of porcine reproductive and respiratory syndrome virus (PRRSV) from infected pigs is currently poorly understood. To better understand the dynamics of host–pathogen interactions, seventy-five of 100 pigs infected with PRRSV-JA142 and 25 control pigs were euthanized at 3, 10, 21, 28 and 35 days post-challenge (dpc). Blood, lung, bronchoalveolar lavage (BAL) and bronchial lymph node (BLN) samples were collected to evaluate the cellular immune responses. The humoral responses were evaluated by measuring the levels of anti-PRRSV IgG and serum virus-neutralizing (SVN) antibodies. Consequently, the highest viral loads in the sera and lungs of the infected pigs were detected between 3 and 10 dpc, and these resulted in moderate to mild interstitial pneumonia, which resolved accompanied by the clearance of most of the virus by 28 dpc. At peak viremia, the frequencies of alveolar macrophages in infected pigs were significantly decreased, whereas the monocyte-derived DC/macrophage and conventional DC frequencies were increased, and these effects coincided with the early induction of local T-cell responses and the presence of proinflammatory cytokines/chemokines in the lungs, BAL, and BLN as early as 10 dpc. Conversely, the systemic T-cell responses measured in the peripheral blood mononuclear cells were delayed and significantly induced only after the peak viremic stage between 3 and 10 dpc. Taken together, our results suggest that activation of immune responses in the lung could be the key elements for restraining PRRSV through the early induction of T-cell responses at the sites of virus replication.

Glycoprotein 5 Is Cleaved by Cathepsin E during Porcine Reproductive and Respiratory Syndrome Virus Membrane Fusion

Porcine reproductive and respiratory syndrome (PRRS) is a serious viral disease affecting the global swine industry. Its causative agent, PRRS virus (PRRSV), is an enveloped virus, and therefore membrane fusion between its envelope and host cell target membrane is critical for viral infection. Though much research has focused on PRRSV infection, the detailed mechanisms involved in its membrane fusion remain to be elucidated. In the present study, we performed confocal microscopy in combination with a constitutively active (CA) or dominant negative (DN) mutant, specific inhibitors, and small interfering RNAs (siRNAs), as well as multiple other approaches, to explore PRRSV membrane fusion. We first observed that PRRSV membrane fusion occurred in Rab11-recycling endosomes during early infection using labeled virions and subcellular markers. We further demonstrated that low pH and cathepsin E in Rab11-recycling endosomes are critical for PRRSV membrane fusion. Moreover, PRRSV glycoprotein 5 (GP5) is identified as being cleaved by cathepsin E during this process. Taken together, our findings provide in-depth information regarding PRRSV pathogenesis, which support a novel basis for the development of antiviral drugs and vaccines.IMPORTANCE PRRS, caused by PRRSV, is an economically critical factor in pig farming worldwide. As PRRSV is a lipid membrane-wrapped virus, merging of the PRRSV envelope with the host cell membrane is indispensable for viral infection. However, there is a lack of knowledge on its membrane fusion. Here, we first explored when and where PRRSV membrane fusion occurs. Furthermore, we determined which host cell factors were involved in the process. Importantly, PRRSV GP5 is shown to be cleaved by cathepsin E during membrane fusion. Our work not only provides information on PRRSV membrane fusion for the first time but also deepens our understanding of the molecular mechanisms of PRRSV infection, which provides a foundation for future applications in the prevention and control of PRRS.

Porcine reproductive and respiratory syndrome virus up-regulates sialoadhesin via IFN-STAT signaling to facilitate its infection

Porcine reproductive and respiratory syndrome (PRRS) has caused huge economic losses to global swine industry. Porcine sialoadhesin (poSn) was previously reported to be a putative receptor for the causative agent, PRRS virus (PRRSV). In the current study, we first observed that PRRSV infection up-regulated expression of poSn in a dose- and time-dependent manner. Subsequently, we found that PRRSV-triggered transcription of type I interferons (IFNs) was involved in poSn up-regulation through the IFN-signal transducer and activator of transcription (STAT) signaling cascade. Interestingly, poSn up-regulation was shown to promote PRRSV infection during post-entry process. Taken together, this work deepens our understanding of PRRSV pathogenesis and provides a novel idea on its establishment of persistent infection, which will be interesting to unravel the detailed mechanisms in the future.

A review of congenital tremor type A-II in piglets

Congenital tremor (CT) is a neurological disease that affects new-born piglets. It was described in 1922 and six different forms, designated type AI-V and type B, are described based on the causative agents, as well as specific histological findings in the central nervous system (CNS). The various forms present with identical clinical signs consisting of mild to severe tremor of the head and body, sometimes complicated with ataxia. By definition, all A-forms have hypomyelination of the CNS, whereas there are no histopathological lesions with the B-form. The cause of the A-II form was long unknown, however, at present several different viruses have been proposed as the causative agent: porcine circovirus-II (PCV-II), astrovirus, PCV-like virus P1, and atypical porcine pestivirus (APPV). Currently, APPV is the only virus that has been proven to fulfill Mokili's Metagenomic Koch's Postulates. Following infection of the pregnant sow, the virus passes the placental barrier and infects the fetus. Interestingly, no clinical signs of disease have been associated with APPV in adult pigs. Furthermore, other viruses cannot be ruled out as additional potential causes of CT. Given the increased interest and research in CT type A-II, the aim of this review is to summarize current knowledge.

Perturbation of Thymocyte Development Underlies the PRRS Pandemic: A Testable Hypothesis

Porcine reproductive and respiratory syndrome virus (PRRSV) causes immune dysregulation during the Critical Window of Immunological Development. We hypothesize that thymocyte development is altered by infected thymic antigen presenting cells (TAPCs) in the fetal/neonatal thymus that interact with double-positive thymocytes causing an acute deficiency of T cells that produces "holes" in the T cell repertoire allowing for poor recognition of PRRSV and other neonatal pathogens. The deficiency may be the result of random elimination of PRRSV-specific T cells or the generation of T cells that accept PRRSV epitopes as self-antigens. Loss of helper T cells for virus neutralizing (VN) epitopes can result in the failure of selection for B cells in lymph node germinal centers capable of producing high affinity VN antibodies. Generation of cytotoxic and regulatory T cells may also be impaired. Similar to infections with LDV, LCMV, MCMV, HIV-1 and trypanosomes, the host responds to the deficiency of pathogen-specific T cells and perhaps regulatory T cells, by "last ditch" polyclonal B cell activation. In colostrum-deprived PRRSV-infected isolator piglets, this results in hypergammaglobulinemia, which we believe to be a "red herring" that detracts attention from the thymic atrophy story, but leads to our second independent hypothesis. Since hypergammaglobulinemia has not been reported in PRRSV-infected conventionally-reared piglets, we hypothesize that this is due to the down-regulatory effect of passive maternal IgG and cytokines in porcine colostrum, especially TGFβ which stimulates development of regulatory T cells (Tregs).

Evaluation of the Inhibitory Effects of (E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-(naphthalen-1-yl)prop-2-en-1-one (DiNap), a Natural Product Analog, on the Replication of Type 2 PRRSV In Vitro and In Vivo

DiNap [(E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-(naphthalen-1-yl)prop-2-en-1-one], an analog of a natural product (the chalcone flavokawain), was synthesized and characterized in this study. Porcine reproductive and respiratory syndrome virus (PRRSV) is the most challenging threat to the swine industry worldwide. Currently, commercially available vaccines are ineffective for controlling porcine reproductive and respiratory syndrome (PRRS) in pigs. Therefore, a pharmacological intervention may represent an alternative control measure for PRRSV infection. Hence, the present study evaluated the effects of DiNap on the replication of VR2332 (a prototype strain of type 2 PRRSV). Initially, in vitro antiviral assays against VR2332 were performed in MARC-145 cells and porcine alveolar macrophages (PAMs). Following this, a pilot study was conducted in a pig model to demonstrate the effects of DiNap following VR2332 infection. DiNap inhibited VR2332 replication in both cell lines in a dose-dependent manner, and viral growth was completely suppressed at concentrations ≥0.06 mM, without significant cytotoxicity. Consistent with these findings, in the pig study, DiNap also reduced viral loads in the serum and lungs and enhanced the weight gain of pigs following VR2332 infection, as indicated by comparison of the DiNap-treated groups to the untreated control (NC) group. In addition, DiNap-treated pigs had fewer gross and microscopic lesions in their lungs than NC pigs. Notably, virus transmission was also delayed by approximately 1 week in uninfected contact pigs within the same group after treatment with DiNap. Taken together, these results suggest that DiNap has potential anti-PRRSV activity and could be useful as a prophylactic or post-exposure treatment drug to control PRRSV infection in pigs.

Porcine reproductive and respiratory syndrome virus infection of bone marrow: Lesions and pathogenesis

Red bone marrow is physiologically unique in that it is both the major hematopoietic organ and a primary lymphoid organ. Porcine reproductive and respiratory syndrome virus (PRRSV) affects normal bone marrow functions. The cumulative effect of PRRSV infection is acute bone marrow failure, i.e., hypoplasia characterized by the absence of normal myeloid and erythroid precursors and increased red bone marrow M:E ratios. The measurable clinical consequence of PRRSV infection on normal red bone marrow functions is a reduction in the number of cells emigrating to the peripheral blood resulting in leucopenia, anemia, and thrombocytopenia. These observations may be explained by the fact that bone marrow-derived mononuclear cells, i.e., imDCs, mDCs, monocytes, macrophages, and myeloid precursor cells are susceptible to PRRSV. Apoptosis in bone marrow-derived cells occurs both as a direct consequence of infection and indirectly via a bystander effect. Immunologically, PRRSV-susceptible mononuclear cells are the first line of defense against microbial infection and responsible for antigen recognition, processing, and presentation to T and B cells; a critical step in the initiation and development of an effective adaptive immune. Thus, impairment of normal immune function renders the host less able to resist and/or eliminate secondary infectious agents and partially explains the synergy between PRRSV and bacterial and viral co-infections.

A PRRSV GP5-Mosaic vaccine: Protection of pigs from challenge and ex vivo detection of IFNγ responses against several genotype 2 strains

Porcine reproductive and respiratory syndrome virus (PRRSV), is a highly mutable RNA virus that affects swine worldwide and its control is very challenging due to its formidable heterogeneity in the field. In the present study, DNA vaccines constructed with PRRSV GP5-Mosaic sequences were complexed to cationic liposomes and administered to experimental pigs by intradermal and intramuscular injection, followed by three boosters 14, 28 and 42 days later. The GP5-Mosaic vaccine thus formulated was immunogenic and induced protection from challenge in vaccinated pigs comparable to that induced by a wild type (VR2332) GP5 DNA vaccine (GP5-WT). Periodic sampling of blood and testing of vaccine-induced responses followed. Interferon-γ (IFN-γ) mRNA expression by virus-stimulated peripheral blood mononuclear cells (PBMCs) of GP5-Mosaic-vaccinated pigs was significantly higher compared to pigs vaccinated with either GP5-WT or empty vector at 21, 35 and 48 days after vaccination. Cross-reactive cellular responses were also demonstrated in GP5-Mosaic vaccinated pigs after stimulation of PBMCs with divergent strains of PRRSV. Thus, significantly higher levels of IFN-γ mRNA were detected when PBMCs from GP5-Mosaic-vaccinated pigs were stimulated by four Genotype 2 strains (VR2332, NADC9, NADC30 and SDSU73), which have at least 10% difference in GP5 amino acid sequences, while such responses were recorded only upon VR2332 stimulation in GP5-WT-vaccinated pigs. In addition, the levels of virus-specific neutralizing antibodies were higher in GP5-Mosaic or GP5-WT vaccinated pigs than those in vector-control pigs. The experimental pigs vaccinated with either the GP5-Mosaic vaccine or the GP5-WT vaccine were partially protected from challenge with VR2332, as measured by significantly lower viral loads in sera and tissues and lower lung lesion scores than the vector control group. These data demonstrate that the GP5-Mosaic vaccine can induce cross-reactive cellular responses to diverse strains, neutralizing antibodies, and protection in pigs.

Novel and differentially abundant microRNAs in sperm cells, seminal plasma, and serum of boars due to porcine reproduction and respiratory syndrome virus infection

The objectives of this study were to identify and determine relative abundance of miRNAs in boar sperm, seminal plasma (SP), and serum pre- and post-viral infection. Functional enrichment analyses on predicted targets of miRNAs of interest were performed. Boars (n = 6) were inoculated with porcine reproductive and respiratory syndrome virus (PRRSv) strain 1-8-4 (Day 0). Semen and serum were collected on Day -2 and 6. Sperm and SP were separated and aliquots were flash frozen and stored at -80 °C. Serum was frozen and stored at -80 °C. Total RNA was isolated from sperm and SP samples and subjected to RNA sequencing. Microarray analysis was performed using the Day -2 and 6 RNA samples from serum, sperm and SP. Potential miRNA targets were predicted using miRanda 3.3a and targets were then analyzed for enrichment of Gene Ontology) and InterPro terms and were considered to be enriched if P <  0.01 using the Bonferroni correction. Microarray analyses resulted in 83, 13, and 10 miRNAs with differences in abundances in sperm, serum, and SP, respectively, when comparing Day -2 and 6. Results from enrichment analyses indicated that the predicted targets of 35, nine, and five miRNAs with differences in abundances for sperm, SP, and serum, respectively, that have functions and/or conserved protein domains that are enriched when compared to the pig genome. Enriched terms for P2X purinoceptors were identified for sperm, SP and serum. Enriched terms for cell adhesion were identified for sperm and serum transcripts. Enriched terms for cell signaling were identified for sperm and SP transcripts.

Genetic and pathogenic characterization of a Russian subtype 2 PRRSV-1 isolate

Porcine reproductive and respiratory syndrome virus (PRRSV) causes reproductive failure and respiratory problems. Data about the virulence and pathogenicity of subtype 2 PRRSV-1 strains are limited. The main purposes of this investigation were to characterize the full genome sequence of the subtype 2 PRRSV-1 WestSib13 strain and to compare the pathogenicity with that of the subtype 1 PRRSV-1 Lelystad strain. Comparison of the whole genome sequence of the WestSib13 strain with that of PRRSV-1 prototype strains revealed a 76.2% (subtype 1 Lelystad virus) and 79.0% (subtype 3 Lena virus) identity, respectively The virulence and pathogenicity of the European subtype 2 PRRSV strain WestSib13 and the European subtype 1 PRRSV strain Lelystad were compared in 3-week-old piglets upon inoculation of 10^5.4 TCID₅₀ of virus. Non-infected animals (control group) as well as animals infected with the Lelystad strain were clinically healthy until 14days post challenge. In contrast, animals infected with the WestSib13 strain demonstrated dyspnea starting at 3days post-inoculation (dpi). All piglets in this group died between 5 and 8 dpi. During that period, fever was not observed in WestSib13-infected animals. Viremia was detected in animals from both infected groups starting from 2 dpi. Viral loads in serum and lungs upon euthanasia were significantly higher (3 log₁₀) in the WestSib13-infected than in the LV-infected animals. Taken together, this study provides the full genome sequence and the unusual virological and clinical outcome (high level viremia without fever) of the novel WestSib13 strain.

A highly pathogenic porcine reproductive and respiratory syndrome virus candidate vaccine based on Japanese encephalitis virus replicon system

In the swine industry, porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease which causes heavy economic losses worldwide. Effective prevention and disease control is an important issue. In this study, we described the construction of a Japanese encephalitis virus (JEV) DNA-based replicon with a cytomegalovirus (CMV) promoter based on the genome of Japanese encephalitis live vaccine virus SA14-14-2, which is capable of offering a potentially novel way to develop and produce vaccines against a major pathogen of global health. This JEV DNA-based replicon contains a large deletion in the structural genes (C-prM-E). A PRRSV GP5/M was inserted into the deletion position of JEV DNA-based replicons to develop a chimeric replicon vaccine candidate for PRRSV. The results showed that BALB/c mice models with the replicon vaccines pJEV-REP-G-2A-M-IRES and pJEV-REP-G-2A-M stimulated antibody responses and induced a cellular immune response. Analysis of ELSA data showed that vaccination with the replicon vaccine expressing GP5/M induced a better antibodies response than traditional DNA vaccines. Therefore, the results suggested that this ectopic expression system based on JEV DNA-based replicons may represent a useful molecular platform for various biological applications, and the JEV DNA-based replicons expressing GP5/M can be further developed into a novel, safe vaccine candidate for PRRS.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): porcine reproductive and respiratory syndrome (PRRS)

Porcine reproductive and respiratory syndrome (PRRS) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of PRRS to be listed, Article 9 for the categorisation of PRRS according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to PRRS. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, PRRS can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The animal species to be listed for PRRS according to Article 8(3) criteria are domestic pigs and wild boar.

Complete Genome Sequence of a Recombinant Porcine Reproductive and Respiratory Syndrome Virus Strain from Two Genotype 1 Modified Live Virus Vaccine Strains

This paper provides information on the complete genome sequence of a porcine reproductive and respiratory syndrome virus (PRRSV) strain isolated on a French pig farm which was identified as a recombinant strain from two commercial modified live virus vaccine strains of genotype 1 (VP-046BIS and DV strains).

Structural insights into type I and type II of nsp4 porcine reproductive and respiratory syndrome virus (nsp4 PRRSV) by molecular dynamics simulations

Porcine reproductive and respiratory virus (PRRSV) causes major economic concerns for the swine industry worldwide. We have performed molecular dynamics simulations (MD) and principle component analysis (PCA) to investigate the role of the catalytic triad and conformational dynamics of type I and type II of nsp4 PRRSV. The results showed that the RMSF of residues 136-142 near the active site of all models was highly flexible. Moreover, we identified the effect of single structural mutations of the catalytic triad. The percentage of residue with a 0.1nm RMSF value and PCA results revealed that the mutations affected domain I and II suggesting the wild types were more stable than the mutants. At the catalytic triad, the distances between H39 and S118 were very flexible while the distances between H39 and D64 were very stable. H39, D64 and S118 showed high occupancy percentage of the hydrogen bond interaction with many residues that are conserved in PRRSVAS, PRRSVES, LDVC, LDVP and EAV. Moreover, S118 of wild-type protein formed H-bonds with T134 and G135 but these interactions were lost in PRRSVAV (S118A) and PRRSVES (S117A) indicating that the substitution of important H-bond interaction in PRRSVAS (S118A) and PRRSVES (S117A) affected the flexibility around the catalytic triad, conformation and proteolytic activity. Overall, our study may provide the structural basic of the catalytic triad and be useful for testing the protein activity in future experiments.

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.

The Crystal Structure of the Fifth Scavenger Receptor Cysteine-Rich Domain of Porcine CD163 Reveals an Important Residue Involved in Porcine Reproductive and Respiratory Syndrome Virus Infection

Porcine reproductive and respiratory syndrome (PRRS) has become an economically critical factor in swine industry since its worldwide spread in the 1990s. Infection by its causative agent, PRRS virus (PRRSV), was proven to be mediated by an indispensable receptor, porcine CD163 (pCD163), and the fifth scavenger receptor cysteine-rich domain (SRCR5) is essential for virus infection. However, the structural details and specific residues of pCD163 SRCR5 involved in infection have not been defined yet. In this study, we prepared recombinant pCD163 SRCR5 in Drosophila melanogaster Schneider 2 (S2) cells and determined its crystal structure at a high resolution of 2.0 Å. This structure includes a markedly long loop region and shows a special electrostatic potential, and these are significantly different from those of other members of the scavenger receptor cysteine-rich superfamily (SRCR-SF). Subsequently, we carried out structure-based mutational studies to identify that the arginine residue at position 561 (Arg561) in the long loop region is important for PRRSV infection. Further, we showed Arg561 probably takes effect on the binding of pCD163 to PRRSV during virus invasion. Altogether the current work provides the first view of the CD163 SRCR domain, expands our knowledge of the invasion mechanism of PRRSV, and supports a molecular basis for prevention and control of the virus.

IMPORTANCE

PRRS has caused huge economic losses to pig farming. The syndrome is caused by PRRSV, and PRRSV infection has been shown to be mediated by host cell surface receptors. One of them, pCD163, is especially indispensable, and its SRCR5 domain has been further demonstrated to play a significant role in virus infection. However, its structural details and the residues involved in infection are unknown. In this study, we determined the crystal structure of pCD163 SRCR5 and then carried out site-directed mutational studies based on the crystal structure to elucidate which residue is important. Our work not only provides structural information on the CD163 SRCR domain for the first time but also indicates the molecular mechanism of PRRSV infection and lays a foundation for future applications in prevention and control of PRRS.

Effects of Mycoplasma hyopneumoniae on porcine nasal cavity dendritic cells

Mycoplasma hyopneumoniae (Mhp) is the primary etiological agent responsible for swine enzootic pneumonia (EP), a disease that cause tremendous economic losses all over the swine industry. Dendritic cells (DCs), the most effective antigen-presenting cells, are widely distributed beneath respiratory epithelium. DCs uptake and present antigens to T cells, to initiate protective immune responses or generate immune-mediated pathology in different infections. In this study, we investigated the changes in the different DCs subpopulations, T cells and SIgA positive cells counts in porcine nasal cavity after long time Mhp infection. We further evaluated the role of porcine DCs in Mhp exposure. Our results showed that the number of SLA-II-DR⁺SWC3a⁺DCs, SLA-II-DR⁺CD11b⁺ DCs, T cells, SIgA positive cells in nasal cavity were decreased after Mhp 28 days infection in vivo experiment. The antigen presenting ability of DCs were inhibited by Mhp exposure. DCs couldn't activate T-cell proliferation by down-regulating the antigen presenting molecule CD1a expression and promoting high level of IL-10 production. Further more, the expression levels of IL-12 and IFN-γ in DCs were decreased, suggesting that DCs favour for Th2 immune response development after Mhp exposure in vitro. Taken together, Mhp infection impairs the immune function which allows the persistence of Mhp and cause predispose pigs to secondary infections. The decline of DCs presentation ability is the reason why dysfunction and persistence in Mhp infection. These findings are benefit for exploring the pathogenic mechanisms of Mhp in pigs.

Pathological and immunological characteristics of piglets infected experimentally with a HP-PRRSV TJ strain

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) remains a major threat to swine industry all over the world. The aim of this study was to investigate the mechanism of pathogenesis and immune responses caused by a highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV).

RESULTS

All piglets experimentally infected with a HP-PRRSV TJ strain virus developed typical clinical signs of PRRS. The percentages of CD3⁺, CD4⁺, and CD8⁺ lymphocytes significantly decreased in the infected group as compared to the uninfected control animals (p < 0.01). Total WBC dropped in the infected animals during the experiment. The level of ELISA antibody against PRRSV increased in 7-10 days after infection and then started to decline. Pathological observations demonstrated various degree lesions, bleeding and necrosis in the lungs of the infected piglets.

CONCLUSIONS

These results clearly indicated that HP-PRRSV TJ strain infection would activate host humoral immune response at the early period post infection and cause severe pathological damages on lungs and inhibit cellular immune response after infection.

English Pig Farmers' Knowledge and Behaviour towards African Swine Fever Suspicion and Reporting

African swine fever (ASF) is a notifiable, virulent swine disease, and is a major threat to animal health and trade for many European Union (EU) countries. Early detection of the introduction of ASF virus is of paramount importance to be able to limit the potential extent of outbreaks. However, the timely and accurate reporting of ASF primary cases strongly depends on how familiar pig farmers are with the clinical signs, and their motivation to report the disease. Here, an online questionnaire survey was conducted between December 2014 and April 2015 to investigate English pig farmers' knowledge and behaviour towards ASF in terms of clinical suspicion and reporting. Multivariable logistic regression analysis was used to identify factors influencing the two variables of interest: 1) farmers who "would immediately suspect ASF" if they observed clinical signs of fever, lethargy, reduced eating and high mortality on their farm and 2) farmers who "would immediately report ASF" if they suspected ASF on their farm. The questionnaire was completed by 109 pig farmers. Results indicate that pig farmers having poor knowledge about ASF clinical signs and limited concern about ASF compared with other pig diseases are less likely to consider the possibility of an outbreak of ASF on their farm. In addition, pig farmers lacking awareness of outbreaks in other countries, having a perception of the negative impact on them resulting from false positive reporting and the perceived complexity of reporting procedures are less likely to report an ASF suspicion. These findings indicate important areas for educational campaigns targeted at English pig farmers to focus on in an attempt to increase the likelihood of a rapid response in the event of an ASF outbreak.

Establishing Porcine Monocyte-Derived Macrophage and Dendritic Cell Systems for Studying the Interaction with PRRSV-1

Monocyte-derived macrophages (MoMØ) and monocyte-derived dendritic cells (MoDC) are two model systems well established in human and rodent systems that can be used to study the interaction of pathogens with host cells. Porcine reproductive and respiratory syndrome virus (PRRSV) is known to infect myeloid cells, such as macrophages (MØ) and dendritic cells (DC). Therefore, this study aimed to establish systems for the differentiation and characterization of MoMØ and MoDC for subsequent infection with PRRSV-1. M-CSF differentiated MoMØ were stimulated with activators for classical (M1) or alternative (M2) activation. GM-CSF and IL-4 generated MoDC were activated with the well established maturation cocktail containing PAMPs and cytokines. In addition, MoMØ and MoDC were treated with dexamethasone and IL-10, which are known immuno-suppressive reagents. Cells were characterized by morphology, phenotype, and function and porcine MØ subsets highlighted some divergence from described human counterparts, while MoDC, appeared more similar to mouse and human DCs. The infection with PRRSV-1 strain Lena demonstrated different replication kinetics between MoMØ and MoDC and within subsets of each cell type. While MoMØ susceptibility was significantly increased by dexamethasone and IL-10 with an accompanying increase in CD163/CD169 expression, MoDC supported only a minimal replication of PRRSV These findings underline the high variability in the susceptibility of porcine myeloid cells toward PRRSV-1 infection.

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.

The Attenuation Phenotype of a Ribavirin-Resistant Porcine Reproductive and Respiratory Syndrome Virus Is Maintained during Sequential Passages in Pigs

In a previous study, ribavirin-resistant porcine reproductive and respiratory syndrome virus (PRRSV) mutants (RVRp13 and RVRp22) were selected, and their resistance against random mutation was shown in cultured cells. In the present study, these ribavirin-resistant mutants were evaluated in terms of their genetic and phenotypic stability during three pig-to-pig passages in comparison with modified live virus (MLV) (Ingelvac PRRS MLV). Pigs challenged with RVRp22 had significantly lower (P< 0.05) viral loads in sera and tissues than pigs challenged with MLV or RVRp13 at the first passage, and the attenuated replication of RVRp22 was maintained until the third passage. Viral loads in sera and tissues dramatically increased in pigs challenged with MLV or RVRp13 during the second passage. Consistently, all five sequences associated with the attenuation of virulent PRRSV in RVRp13 and MLV quickly reverted to wild-type sequences during the passages, but two attenuation sequences were maintained in RVRp22 even after the third passage. In addition, RVRp22 showed a significantly lower (P< 0.001) mutation frequency in nsp2, which is one of the most variable regions in the PRRSV genome, than MLV. Nine unique mutations were found in open reading frames (ORFs) 1a, 2, and 6 in the RVRp22 genome based on full-length sequence comparisons with RVRp13, VR2332 (the parental virus of RVRp13 and RVRp22), and MLV. Based on these results, it was concluded that RVRp22 showed attenuated replication in pigs; further, because of the high genetic stability of RVRp22, its attenuated phenotype was stable even after three sequential passages in pigs.

IMPORTANCE

PRRSV is a rapidly evolving RNA virus. MLV vaccines are widely used to control PRRS; however, there have been serious concerns regarding the use of MLV as a vaccine virus due to the rapid reversion to virulence during replication in pigs. As previously reported, ribavirin is an effective antiviral drug against many RNA viruses. Ribavirin-resistant mutants reemerged by escaping lethal mutagenesis when the treatment concentration was sublethal, and those mutants were genetically more stable than parental viruses. In a previous study, two ribavirin-resistant PRRSV mutants (RVRp13 and RVRp22) were selected, and their higher genetic stability was shown in vitro Consequently, in the present study, both of the ribavirin-resistant mutants were evaluated in terms of their genetic and phenotypic stability in vivo RVRp22 was found to exhibit higher genetic and phenotypic stability than MLV, and nine unique mutations were identified in the RVRp22 genome based on a full-length sequence comparison with the RVRp13, VR2332, and MLV genomes.

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.