Continuous porcine cell lines developed from alveolar macrophages: partial characterization and virus susceptibility

African swine fever virus A137R protein inhibits NF-κB activation via suppression of MyD88 signaling in PK15 and 3D4/21 cells in vitro

African swine fever (ASF) is an infectious disease with high mortality caused by African swine fever virus (ASFV), which poses a great threat to the global swine industry. ASFV has evolved multiple strategies to evade host antiviral innate immunity by perturbing inflammatory responses and interferon production. However, the molecular mechanisms underlying manipulation of inflammatory responses by ASFV proteins are not fully understood. Here, we report that A137R protein of ASFV is a key suppressor of host inflammatory responses. Ectopic expression of ASFV A137R in HEK293T cells significantly inhibited the activation of IL-8 and NF-κB promoters triggered by Sendai virus (SeV), influenza A virus (IAV), or vesicular stomatitis virus (VSV). Accordingly, forced A137R expression caused a significant decrease in the production of several inflammatory cytokines such as IL-8, IL-6 and TNF-α in the cells infected with SeV or IAV. Similar results were obtained from experiments using A137R overexpressing PK15 and 3D4/21 cells infected with SeV or VSV. Furthermore, we observed that A137R impaired the activation of MAPK and NF-κB signaling pathways, as enhanced expression of A137R significantly decreased the phosphorylation of JNK, p38 and p65 respectively upon viral infection (SeV or IAV) and IL-1β treatment. Mechanistically, we found that A137R interacted with MyD88, and dampened MyD88-mediated activation of MAPK and NF-κB signaling. Together, these findings uncover a critical role of A137R in restraining host inflammatory responses, and improve our understanding of complicated mechanisms whereby ASFV evades innate immunity.

Recent progress on gene-deleted live-attenuated African swine fever virus vaccines

African Swine Fever (ASF) is a highly lethal viral disease in swine, with mortality rates approaching 100%. The disease has spread to many swine-producing countries, leading to significant economic losses and adversely impacting global food security. Extensive efforts have been directed toward developing effective ASF vaccines. Among the vaccinology approaches tested to date, live-attenuated virus (LAV) vaccines produced by rational deleting virulence genes from virulent African Swine Fever Virus (ASFV) strains have demonstrated promising safety and efficacy in experimental and field conditions. Many gene-deleted LAV vaccine candidates have been generated in recent years. The virulence genes targeted for deletion from the genome of virulent ASFV strains can be categorized into four groups: Genes implicated in viral genome replication and transcription, genes from the multigene family located at both 5' and 3' termini, genes participating in mediating hemadsorption and putative cellular attachment factors, and novel genes with no known functions. Some promising LAV vaccine candidates are generated by deleting a single viral virulence gene, whereas others are generated by simultaneously deleting multiple genes. This article summarizes the recent progress in developing and characterizing gene-deleted LAV vaccine candidates.

A sensitive luciferase reporter assay for the detection of infectious African swine fever virus

African swine fever virus (ASFV) is a complex DNA virus causing severe hemorrhagic disease in domestic pigs and wild boar. The disease has spread worldwide, with important socio-economic consequences. Early virus detection and control measures are crucial as there are no effective vaccines nor antivirals on the market. While the diagnosis of ASFV is fast and based primarily on qPCR, the detection of infectious ASFV is a labor-intensive process requiring susceptible macrophages and subsequent antibody-based staining or hemadsorption. The latter cannot detect ASFV isolates devoid of functional CD2v (EP402R) expression. Here, we report the development of a plasmid-based reporter assay (RA) for the sensitive detection and titration of infectious ASFV. To this end, we constructed a plasmid for secreted NanoLuc luciferase (secNluc) expression driven by the ASFV DNA polymerase gene G1211R promoter. Infection of plasmid-transfected immortalized porcine kidney macrophages (IPKM) followed by measurement of secNluc from cell culture supernatants allowed reliable automated quantification of infectious ASFV. The RA-based titers matched the titers determined by conventional p72-staining or hemadsorption protocols. The novel assay is specific for ASFV as it does not detect classical swine fever virus nor porcine reproductive and respiratory syndrome virus. It is applicable to ASFV of different genotypes, virulence, and sources, including ASFV from sera and whole blood from infected pigs as well as non-hemadsorbing ASFV.

Generation and characterization of a monoclonal antibody against an African swine fever virus protein encoded by the A137R gene

The ongoing African swine fever (ASF) pandemic continues to have a major impact on global pork production and trade. Since ASF cannot be distinguished from other swine hemorrhagic fevers clinically, ASF-specific laboratory diagnosis is critical. Thus ASF virus (ASFV)-specific monoclonal antibodies (mAbs) are critical for the development of laboratory diagnostics. In this study, we report one ASFV-specific mAb, F88ASF-55, that was generated and characterized. This mAb recognizes the ASFV A137R-encoded protein (pA137R). Epitope mapping results revealed a highly conserved linear epitope recognized by this mAb, corresponding to amino acids 111-125 of pA137R. We explored the potential use of this mAb in diagnostic applications. Using F88ASF-55 as the detection antibody, six ASFV strains were detected in an enzyme-linked immunosorbent assay (ELISA) with low background. In immunohistochemistry (IHC) assays, this mAb specifically recognized ASFV antigens in the submandibular lymph nodes of animals experimentally infected with different ASFV strains. Although not all ASFV genotypes were tested in this study, based on the conserved ASFV epitope targeted by F88ASF-55, it has the potential to detect multiple ASFV genotypes. In conclusion, this newly generated ASFV pA137R-specific mAb has potential value in ASF diagnostic tool development. It can be used in ELISA, IHC, and possibly-immunochromatographic strip assays for ASFV detection. It also suggests that pA137R may be a good target for diagnostic assays to detect ASFV infection.

A Cell-Adapted Live-Attenuated Vaccine Candidate Protects Pigs against the Homologous Strain VNUA-ASFV-05L1, a Representative Strain of the Contemporary Pandemic African Swine Fever Virus

African swine fever (ASF) is a lethal and highly contagious transboundary animal disease with the potential for rapid international spread. Currently, there is no ASF vaccine commercially available. All infected animals must be isolated and culled immediately upon the confirmation of the presence of the virus. Studies leading to the rational development of protective ASF vaccines are urgently needed. Here, we generated a safe and efficacious live-attenuated vaccine (LAV) VNUA-ASFV-LAVL2 by serially passaging a field isolate (VNUA-ASFV-05L1, genotype II) in porcine alveolar macrophages (PAMs, 65 passages) and an immortalized porcine alveolar macrophage cell line (3D4/21, 55 passages). VNUA-ASFV-LAVL2 can efficiently replicate in both PAMs and 3D4/21 cells. It provides 100% protection, even with the low dose of 102 HAD50, to the vaccinated pigs against the challenge of contemporary pandemic ASFV field isolate. Pigs vaccinated with this LAV in a dose range of 102 to 105 HAD50 remained clinically healthy during both the 28-day observation period of immunization and the 28-day observation period of challenge. VNUA-ASFV-LAVL2 was eliminated from blood by 28 days post-inoculation (DPI), and from feces or oral fluids by 17 DPI. Although the vaccine strain in serum remained a safe and attenuated phenotype after five passages in swine, a reversion-to-virulence study using blood or tissue homogenates at peak viremia will be conducted in the future. ASFV-specific IgG antibodies and significant cellular immunity were detected in vaccinated pigs before the ASFV challenge. These results indicate that the VNUA-ASFV-LAVL2 strain is a safe and efficacious LAV against the genotype II ASFV strain responsible for current ASF outbreaks in Asia.

Porcine Macrophage Markers and Populations: An Update

Besides its importance as a livestock species, pig is increasingly being used as an animal model for biomedical research. Macrophages play critical roles in immunity to pathogens, tissue development, homeostasis and tissue repair. These cells are also primary targets for replication of viruses such as African swine fever virus, classical swine fever virus, and porcine respiratory and reproductive syndrome virus, which can cause huge economic losses to the pig industry. In this article, we review the current status of knowledge on porcine macrophages, starting by reviewing the markers available for their phenotypical characterization and following with the characteristics of the main macrophage populations described in different organs, as well as the effect of polarization conditions on their phenotype and function. We will also review available cell lines suitable for studies on the biology of porcine macrophages and their interaction with pathogens.

Interaction between host cell proteins and open reading frames of porcine circovirus type 2

Postweaning multisystemic wasting syndrome (PMWS) is caused by a systemic inflammation after porcine circovirus type 2 (PCV2) infection. It was one of the most economically important pathogens affecting pig production worldwide before PCV2 vaccine was first introduced in 2006. After the development of a vaccine against PCV2a type, pig farms gradually restored enormous economic losses from PMWS. However, vaccine against PCV2a type could not be fully effective against several different PCV2 genotypes (PCV2b - PCV2h). In addition, PCV2a vaccine itself could generate antigenic drift of PCV2 capsid. Therefore, PCV2 infection still threats pig industry worldwide. PCV2 infection was initially found in local tissues including reproductive, respiratory, and digestive tracks. However, PCV2 infection often leads to a systemic inflammation which can cause severe immunosuppression by depleting peripheral lymphocytes in secondary lymphoid tissues. Subsequently, a secondary infection with other microorganisms can cause PMWS. Eleven putative open reading frames (ORFs) have been predicted to encode PCV2 genome. Among them, gene products of six ORFs from ORF1 to ORF6 have been identified and characterized to estimate its functional role during PCV2 infection. Acquiring knowledge about the specific interaction between each PCV2 ORF protein and host protein might be a key to develop preventive or therapeutic tools to control PCV2 infection. In this article, we reviewed current understanding of how each ORF of PCV2 manipulates host cell signaling related to immune suppression caused by PCV2.

Identification of New Compounds against PRRSV Infection by Directly Targeting CD163

The porcine reproductive and respiratory syndrome viruses (PRRSV) led to a global panzootic and huge economical losses to the pork industry. PRRSV targets the scavenger receptor CD163 for productive infection. However, currently no effective treatment is available to control the spread of this disease. Using bimolecular fluorescence complementation (BiFC) assays, we screened a set of small molecules potentially targeting the scavenger receptor cysteine-rich domain 5 (SRCR5) of CD163. We found that the assay examining protein-protein interactions (PPI) between PRRSV glycoprotein 4 (GP4) and the CD163-SRCR5 domain mainly identifies compounds that potently inhibit PRRSV infection, while examining the PPI between PRRSV-GP2a and the SRCR5 domain maximized the identification of positive compounds, including additional ones with various antiviral capabilities. These positive compounds significantly inhibited both types 1 and 2 PRRSV infection of porcine alveolar macrophages. We confirmed that the highly active compounds physically bind to the CD163-SRCR5 protein, with dissociation constant (KD) values ranging from 28 to 39 μM. Structure-activity-relationship (SAR) analysis revealed that although both the 3-(morpholinosulfonyl)anilino and benzenesulfonamide moieties in these compounds are critical for the potency to inhibit PRRSV infection, the morpholinosulfonyl group can be replaced by chlorine substituents without significant loss of antiviral potency. Our study established a system for throughput screening of natural or synthetic compounds highly effective on blocking of PRRSV infection and shed light on further SAR modification of these compounds. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses to the swine industry worldwide. Current vaccines cannot provide cross protection against different strains, and there are no effective treatments available to hamper the spread of this disease. In this study, we identified a group of new small molecules that can inhibit the PRRSV interaction with its specific receptor CD163 and dramatically block the infection of both types 1 and type 2 PRRSVs to host cells. We also demonstrated the physical association of these compounds with the SRCR5 domain of CD163. In addition, molecular docking and structure-activity relationship analyses provided new insights for the CD163/PRRSV glycoprotein interaction and further improvement of these compounds against PRRSV infection.

Interaction between Porcine Alveolar Macrophage-Tang Cells and Streptococcus suis Strains of Different Virulence: Phagocytosis and Apoptosis

Streptococcus suis is an important swine bacterial pathogen that activates macrophages to secrete inflammatory cytokines. Primary porcine alveolar macrophages (PAMs) are inconvenient to obtain, but it is unknown whether immortalized PAM-Tang cells can replace them as a better cell model for the study of the interaction between S. suis and macrophages. In this study, the phagocytic integrity, polarization, and pro-inflammatory cytokine secretion of PAM-Tang cells were confirmed by live-cell imaging, electron microscopy, confocal microscopy, and ELISA. Interestingly, the S. suis serotype 9 avirulent strain W7119 induced higher levels of adhesion and pro-inflammatory cytokines in PAM-Tang cells than the S. suis serotype 2 virulent strain 700794. Prolonged incubation with S. suis caused more cytotoxic cell damage, and the virulent strain induced higher levels of cytotoxicity to PAM-Tang cells. The virulent strain also induced higher levels of apoptosis in PAM-Tang cells, as shown by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) assay. In addition, it is the first report of virulent and avirulent S. suis inducing PAM-Tang polarization towards pro-inflammatory M1 macrophages and p53- and caspase-dependent apoptosis in PAMs. Taken together, this study contributes to a better understand of interactions between macrophages and S. suis isolates of different virulence, and confirms that PAM-Tang cells provide a long-term, renewable resource for investigating macrophage infections with bacteria.

Modeling senecavirus a replication in immortalized porcine alveolar macrophages triggers a robust interferon-mediated immune response that conversely constrains viral replication

Senecavirus A (SVA) is a newly emerging causative agent of vesicular diseases in swine characterized with wide genetic diversity and rapid evolution. The lack of immunologically active cell culture model impedes the study of SVA-specific innate immunity. Here, an immortalized porcine alveolar macrophages 3D4/21 strongly and productively supported replication of two SVA strains. To elaborate global and dynamic host immune response, we demonstrated that 3D4/21 intrinsically expressed canonical ISGs which were important for pre-empting viral infection. Moreover, 3D4/21 were constitutively abundant in RIG-I-like receptors (RLRs) RIG-I and MDA5 necessary for sensing RNA virus infection, thereby enabling 3D4/21 cells to establish persistent and efficient antiviral status, in particular the most dramatic and sustained expression of type I/II interferons and inflammatory and innate immune genes critical for constraining SVA replication. Our study reveals a pivotal regulatory connection between virus and host that points to the SVA pathogenesis and potential vaccine development.

African Swine Fever Virus MGF110-7L Induces Host Cell Translation Suppression and Stress Granule Formation by Activating the PERK/PKR-eIF2α Pathway

African swine fever (ASF) is a highly contagious and often lethal disease of pigs caused by ASF virus (ASFV) and recognized as the biggest killer in global swine industry. Despite exhibiting incredible self-sufficiency, ASFV remains unconditionally dependent on the host translation machinery for its mRNA translation. However, less is yet known regarding how ASFV-encoded proteins regulate host translation machinery in infected cells. Here, we examined how ASFV interacts with the eukaryotic initiation factor 2α (eIF2α) signaling axis, which directs host translation control and adaptation to cellular stress. We found that ASFV MGF110-7L, a previously uncharacterized member of the multigene family 110, remarkably enhanced the phosphorylation level of eIF2α. In porcine alveolar macrophage 3D4/21 and porcine kidney-15 cells, MGF110-7L triggered eIF2α signaling and the integrated stress response, resulting in the suppression of host translation and the formation of stress granules (SGs). Mechanistically, MGF110-7L-induced phosphorylation of eIF2α was mediated via protein kinase R (PKR) and PKR-like endoplasmic reticulum (ER) kinase (PERK), and this process was essential for host translation repression and SG formation. Notably, our subsequent analyses confirmed that MGF110-7L was overwhelmingly retained in the ER and caused a specific reorganization of the secretory pathway. Further proteomic analyses and biochemical experiments revealed that MGF110-7L could trigger ER stress and activate the unfolded protein response, thus contributing to eIF2α phosphorylation and translation reprogramming. Overall, our study both identifies a novel mechanism by which ASFV MGF110-7L subverts the host protein synthesis machinery and provides further insights into the translation regulation that occurs during ASFV infection. IMPORTANCE African swine fever (ASF) has become a socioeconomic burden and a threat to food security and biodiversity, but no commercial vaccines or antivirals are available currently. Understanding the viral strategies to subvert the host translation machinery during ASF virus (ASFV) infection could potentially lead to new vaccines and antiviral therapies. In this study, we dissected how ASFV MGF110-7L interacts with the eIF2α signaling axis controlling translational reprogramming, and we addressed the role of MGF110-7L in induction of cellular stress responses, eIF2α phosphorylation, translation suppression, and stress granule formation. These results define several molecular interfaces by which ASFV MGF110-7L subverts host cell translation, which may guide research on antiviral strategies and dissection of ASFV pathogenesis.

African Swine Fever Virus Exhibits Distinct Replication Defects in Different Cell Types

African swine fever virus (ASFV) causes one of the most devastating diseases affecting pigs and wild suids, a worldwide epizootic situation exacerbated in recent years due to the lack of vaccine or effective treatment. ASFV has a restricted cell tropism, and is prone to replicate in porcine monocytes and alveolar macrophages with high efficiency. Here, the replication capabilities of ASFV were examined in swine pulmonary alveolar macrophages (PAMs) and compared with 3D4/21, PK-15, MA-104 and Marc-145 cell lines using PCR, qPCR and Western blot with monoclonal antibodies against the viral p30 and p72 proteins. The results showed that ASFV has a variety of infection characteristics in PAMs and showed four cell lines with distinct defects during virus early transcription-translation, genome replication and late protein synthesis. Furthermore, an antiviral role of the stress granule pathway was revealed against ASFV, and ASFV infection inhibited stress granule formation in PAMs but not 3D4/21. These results will help to deepen our knowledge on ASFV infection and to develop ASFV susceptible cell lines.

Establishment and characterization of the immortalized porcine lung-derived mononuclear phagocyte cell line

Mononuclear phagocytes (MNP), including monocytes, dendritic cells (DC), and macrophages, play critical roles in innate immunity. MNP are abundant in the lungs and contribute to host defense against airborne agents and pulmonary immune homeostasis. In this study, we isolated porcine lung-derived MNP (PLuM) from primary cultures of parenchymal lung cells and then immortalized them by transferring the SV40 large T antigen gene and porcine telomerase reverse transcriptase gene using lentiviral vectors. The established cell line, immortalized PLuM (IPLuM), expressed DC/macrophage markers; i.e., CD163, CD172a, and major histocompatibility complex class II, whereas they did not express a porcine monocyte-specific marker, CD52. The expression patterns of these cell surface markers indicate that IPLuM originate from the DC/macrophage lineage rather than the monocyte lineage. The bacterial cell wall components muramyl dipeptide and lipopolysaccharide induced the production of the interleukin-1 family of pro-inflammatory cytokines in IPLuM. Phagocytotic activity was also detected by time-lapse fluorescence imaging of live cells when IPLuM were cultured in the presence of pHrodo dye-conjugated E. coli BioParticles. It is worth noting that IPLuM are susceptible to African swine fever virus infection and support the virus' efficient replication in vitro. Taken together, the IPLuM cell line may be a useful model for investigating host-agent interactions in the respiratory microenvironments of the porcine lung.

Modulation of Alveolar Macrophages by Postimmunobiotics: Impact on TLR3-Mediated Antiviral Respiratory Immunity

Beneficial microbes with immunomodulatory capacities (immunobiotics) and their non-viable forms (postimmunobiotics) could be effectively utilized in formulations towards the prevention of respiratory viral infections. In this study, novel immunobiotic strains with the ability to increase antiviral immunity in porcine alveolar macrophages were selected from a library of Lactobacillus gasseri. Postimmunobiotics derived from the most remarkable strains were also evaluated in their capacity to modulate the immune response triggered by Toll-like receptor 3 (TLR3) in alveolar macrophages and to differentially regulate TLR3-mediated antiviral respiratory immunity in infant mice. We provide evidence that porcine alveolar macrophages (3D4/31 cells) are a useful in vitro tool for the screening of new antiviral immunobiotics and postimmunobiotics by assessing their ability to modulate the expression IFN-β, IFN-λ1, RNAseL, Mx2, and IL-6, which can be used as prospective biomarkers. We also demonstrate that the postimmunobiotics derived from the Lactobacillus gasseri TMT36, TMT39 and TMT40 (HK36, HK39 or HK40) strains modulate the innate antiviral immune response of alveolar macrophages and reduce lung inflammatory damage triggered by TLR3 activation in vivo. Although our findings should be deepened and expanded, the results of the present work provide a scientific rationale for the use of nasally administered HK36, HK39 or HK40 to beneficially modulate TLR3-triggerd respiratory innate immune response.

CD163-Expressing Porcine Macrophages Support NADC30-like and NADC34-like PRRSV Infections

Porcine reproductive and respiratory syndrome virus (PRRSV) has a strict cell tropism. In addition to the primary alveolar macrophages, PRRSV is strictly cytotropic to African green monkey kidney cells, such as MARC-145 cells; however, MARC-145 cells are not infected by most NADC30-like and NADC34-like PRRSV strains. The essential scavenger receptor CD163 has been proved to mediate productive infection of PRRSV in various non-permissive cell lines. In this study, we systematically tested the porcine CD163 stably expressing 3D4/21 cells for infections with various PRRSV strains. The results showed that the porcine CD163-expressing macrophages support the infections of PRRSV2 of lineages 1, 5, and 8, as evidenced by Western blotting, immunofluorescence assay, quantitative PCR, and virus titration assay. Considering the current prevalence of NADC30-like and NADC34-like PRRSV2 of lineage 1 in China, the CD163-expressing macrophages are very useful for PRRSV research and disease management.

Large Fragment InDels Reshape Genome Structure of Porcine Alveolar Macrophage 3D4/21 Cells

The porcine monomyeloid cell line, or 3D4/21 cells, is an effective tool to study the immune characteristics and virus infection mechanism of pigs. Due to the introduction of the neomycin resistance gene and the SV40 large T antigen gene, its genome has undergone essential changes, which are still unknown. Studying the variation in genome structure, especially the large fragments of insertions and deletions (InDels), is one of the proper ways to reveal these issues. In this study, an All-seq method was established by combining Mate-pair and Shotgun sequencing methods, and the detection and verification of large fragments of InDels were performed on 3D4/21 cells. The results showed that there were 844 InDels with a length of more than 1 kb, of which 12 regions were deletions of more than 100 kb in the 3D4/21 cell genome. In addition, compared with porcine primary alveolar macrophages, 82 genes including the CD163 had lost transcription in 3D4/21 cells, and 72 genes gained transcription as well. Further referring to the Hi-C structure, it was found that the fusion of the topologically associated domains (TADs) caused by the deletion may lead to abnormal gene function. The results of this study provide a basis for elaborating the genome structure and functional variation in 3D4/21 cells, provide a method for rapid and convenient detection of large-scale InDels, and provide useful clues for the study of the porcine immune function genome and the molecular mechanism of virus infection.

Isolation and immortalization of macrophages derived from fetal porcine small intestine and their susceptibility to porcine viral pathogen infections

Macrophages are a heterogeneous population of cells that are present in all vertebrate tissues. They play a key role in the innate immune system, and thus, in vitro cultures of macrophages provide a valuable model for exploring their tissue-specific functions and interactions with pathogens. Porcine macrophage cultures are often used for the identification and characterization of porcine viral pathogens. Recently, we have developed a simple and efficient method for isolating primary macrophages from the kidneys and livers of swine. Here, we applied this protocol to fetal porcine intestinal tissues and demonstrated that porcine intestinal macrophages (PIM) can be isolated from mixed primary cultures of porcine small intestine-derived cells. Since the proliferative capacity of primary PIM is limited, we attempted to immortalize them by transferring the SV40 large T antigen and porcine telomerase reverse transcriptase genes using lentiviral vectors. Consequently, immortalized PIM (IPIM) were successfully generated and confirmed to retain various features of primary PIM. We further revealed that IPIM are susceptible to infection by the African swine fever virus and the porcine reproductive and respiratory syndrome virus and support their replication. These findings suggest that the IPIM cell line is a useful tool for developing in vitro models that mimic the intestinal mucosal microenvironments of swine, and for studying the interactions between porcine pathogens and host immune cells.

Investigating Multi-Target Antiviral Compounds by Screening of Phytochemicals From Neem (Azadirachta indica) Against PRRSV: A Vetinformatics Approach

Porcine reproductive and respiratory syndrome virus (PRRSV) is a global health problem for pigs. PRRSV is highly destructive and responsible for significant losses to the swine industry. Vaccines are available but incapable of providing adequate and long-term protection. As a result, effective and safe strategies are urgently needed to combat the virus. The scavenger receptor cysteine-rich domain 5 (SRCR5) in porcine CD163, non-structural protein 4 (Nsp4), and Nsp10 are known to play significant roles in PRRSV infection and disease development. Therefore, we targeted these proteins to identify multi-target antiviral compounds. To identify potent inhibitors, molecular docking of neem phytochemicals was conducted; three compounds [7-deacetyl-7-oxogedunin (CID:1886), Kulactone (CID:15560423), and Nimocin (CASID:104522-76-1)] were selected based on the lowest binding energy and multi-target inhibitory nature. The efficacy and safety of the selected compounds were revealed through the pharmacokinetics analysis and toxicity assessment. Moreover, 100 ns molecular dynamics (MD) simulation was performed to evaluate the stability and dynamic behavior of target proteins and their docked complexes with selected compounds. Besides, molecular mechanics Poisson–Boltzmann surface area method was used to estimate the binding free energy of each protein-ligand complex obtained from the MD simulations and validate the affinities of selected compounds to target proteins. Based on our analysis, we concluded that the identified multi-target compounds can be utilized as lead compounds for the development of natural drugs against PRRSV. If further validated in clinical studies, these compounds can be used individually or in combination against the virus.

Vimentin promotes porcine circovirus type 2 (PCV2) replication in pig alveolar macrophage

Porcine circovirus type 2 (PCV2) is a swine pathogen that causes postweaning multisystemic wasting syndrome, associated with a number of other disease symptoms in pigs. It has caused high economic losses for pig industries in China and worldwide. Vimentin is a cytoskeletal protein involved in the lifecycle of numerous viruses. In this study, the role of Vimentin in PCV2 replication in pig alveolar macrophage (3D4/21) cells was studied. A 3D4/21 cell line overexpressing Vimentin was established using a lentivirus expression system, in which PCV2 replication was significantly enhanced. Meanwhile, in the Vimentin silenced 3D4/21 cells, PCV2 replication was significantly reduced. Furthermore, we found that PCV2 infection in 3D4/21 cells promoted Vimentin phosphorylation and rearranged Vimentin distribution in cells. By inhibition of CaMKII pathway, Vimentin phosphorylation was significantly suppressed and PCV2 replication was significantly inhibited. The results in this study indicated that in 3D4/21 cells, PCV2 promoted CaMKIIγ-medicated Vimentin phosphorylation and altered its cellular distributions to accomplish its own replication.

Cell Lines for the Development of African Swine Fever Virus Vaccine Candidates: An Update

African swine fever virus (ASFV) is the etiological agent of a highly lethal disease in both domestic and wild pigs. The virus has rapidly spread worldwide and has no available licensed vaccine. An obstacle to the construction of a safe and efficient vaccine is the lack of a suitable cell line for ASFV isolation and propagation. Macrophages are the main targets for ASFV, and they have been widely used to study virus–host interactions; nevertheless, obtaining these cells is time-consuming and expensive, and they are not ethically suitable for the production of large-scale vaccines. To overcome these issues, different virulent field isolates have been adapted on monkey or human continuous cells lines; however, several culture passages often lead to significant genetic modifications and the loss of immunogenicity of the adapted strain. Thus, several groups have attempted to establish a porcine cell line able to sustain ASFV growth. Preliminary data suggested that some porcine continuous cell lines might be an alternative to primary macrophages for ASFV research and for large-scale vaccine production, although further studies are still needed. In this review, we summarize the research to investigate the most suitable cell line for ASFV isolation and propagation.

Intranasal delivery of inactivated PRRSV loaded cationic nanoparticles coupled with enterotoxin subunit B induces PRRSV-specific immune responses in pigs

This study was conducted to evaluate the induction of systemic and mucosal immune responses and protective efficacy following the intranasal administration of inactivated porcine reproductive and respiratory syndrome virus (PRRSV) loaded in polylactic acid (PLA) nanoparticles coupled with heat-labile enterotoxin subunit B (LTB) and dimethyldioctadecylammonium bromide (DDA). Here, 42- to 3-week-old PRRSV-free pigs were randomly allocated into 7 groups of 6 pigs each. Two groups represented the negative (nonvaccinated pigs/nonchallenged pigs, NoVacNoChal) and challenge (nonvaccinated/challenged, NoVacChal) controls. The pigs in the other 5 groups, namely, PLA nanoparticles/challenged (blank NPs), LTB-DDA coupled with PLA nanoparticles/challenged (adjuvant-blank NPs), PLA nanoparticles-encapsulating inactivated PRRSV/challenged (KNPs), LTB-DDA coupled with PLA nanoparticles loaded with inactivated PRRSV/challenged pigs (adjuvant-KNPs) and inactivated PRRSV/challenged pigs (inactivated PRRSV), were intranasally vaccinated with previously described vaccines at 0, 7 and 14 days post-vaccination (DPV). Serum and nasal swab samples were collected weekly and assayed by ELISA to detect the presence of IgG and IgA, respectively. Viral neutralizing titer (VNT) in sera, IFN-γ-producing cells and IL-10 secretion in stimulated peripheral blood mononuclear cells (PBMCs) were also measured. The pigs were intranasally challenged with PRRSV-2 at 28 DPV and necropsied at 35 DPV, and then macro- and microscopic lung lesions were evaluated. The results demonstrated that following vaccination, adjuvant-KNP-vaccinated pigs had significantly higher levels of IFN-γ-producing cells, VNT and IgG in sera, and IgA in nasal swab samples and significantly lower IL-10 levels than the other vaccinated groups. Following challenge, the adjuvant-KNP-vaccinated pigs had significantly lower PRRSV RNA and macro- and microscopic lung lesions than the other vaccinated groups. In conclusion, the results of the study demonstrated that adjuvant-KNPs are effective in eliciting immune responses against PRRSV and protecting against PRRSV infections over KNPs and inactivated PRRSV and can be used as an adjuvant for intranasal PRRSV vaccines.

A Multi-Laboratory Comparison of Methods for Detection and Quantification of African Swine Fever Virus

African swine fever is a viral disease of the family Suidae. Methods to detect and quantify African swine fever virus (ASFV) include qPCR and virus infectivity assays. Individual laboratories often use in-house procedures for these assays, which can hamper the comparison of results. The objective of this study was to estimate the probability of ASFV detection using these assays, and to determine the inter-test correlations between results. This was achieved by testing a panel of 80 samples at three reference laboratories. Samples were analysed using nucleic acid extraction and qPCR, as well as virus infectivity assays. For qPCR, a very high probability (ranging from 0.96 to 1.0) of detecting ASFV DNA was observed for all tested systems. For virus infectivity assays in cells, the probability of detecting infectious ASFV varied from 0.68 to 0.90 and was highest using pulmonary alveolar macrophages, followed by MARC145 cells, peripheral blood monocytes, and finally wild boar lung cells. Intraclass correlation coefficient estimates of 0.97 (0.96–0.98) between qPCR methods, 0.80 (0.74–0.85) to 0.94 (0.92–0.96) between virus infectivity assays, and 0.77 (0.68–0.83) to 0.95 (0.93–0.96) between qPCR methods and virus infectivity assays were obtained. These findings show that qPCR gives the highest probability for the detection of ASFV.

Influenza A Virus Infection Activates NLRP3 Inflammasome through Trans-Golgi Network Dispersion

The NLRP3 inflammasome consists of NLRP3, ASC, and pro-caspase-1 and is an important arm of the innate immune response against influenza A virus (IAV) infection. Upon infection, the inflammasome is activated, resulting in the production of IL-1β and IL-18, which recruits other immune cells to the site of infection. It has been suggested that in the presence of stress molecules such as nigericin, the trans-Golgi network (TGN) disperses into small puncta-like structures where NLRP3 is recruited and activated. Here, we investigated whether IAV infection could lead to TGN dispersion, whether dispersed TGN (dTGN) is responsible for NLRP3 inflammasome activation, and which viral protein is involved in this process. We showed that the IAV causes dTGN formation, which serves as one of the mechanisms of NLRP3 inflammasome activation in response to IAV infection. Furthermore, we generated a series of mutant IAVs that carry mutations in the M2 protein. We demonstrated the M2 proton channel activity, specifically His37 and Trp41 are pivotal for the dispersion of TGN, NLRP3 conformational change, and IL-1β induction. The results revealed a novel mechanism behind the activation and regulation of the NLRP3 inflammasome in IAV infection.

African Swine Fever Virus pE199L Induces Mitochondrial-Dependent Apoptosis

African swine fever (ASF) is a severe hemorrhagic disease in swine characterized by massive lymphocyte depletion and cell death, with apoptosis and necrosis in infected lymphoid tissues. However, the molecular mechanism regarding ASFV-induced cell death remains largely unknown. In this study, 94 ASFV-encoded proteins were screened to determine the viral proteins involved in cell death in vitro, and pE199L showed the most significant effect. Ectopic expression of pE199L in porcine cells (CRL-2843) and human cells (HEK293T and HeLa cells) induced cell death remarkably, showing obvious shrinking, blistering, apoptotic bodies, and nuclear DNA fragments. Meanwhile, cell death was markedly alleviated when the expression of pE199L was knocked down during ASFV infection. Additionally, the expression of pE199L caused a loss of mitochondrial membrane potential, release of cytochrome C, and caspase-9 and -3/7 activation, indicating that the mitochondrial apoptotic pathway was involved in pE199L-induced apoptosis. Further investigations showed that pE199L interacted with several anti-apoptotic BCL-2 subfamily members (such as BCL-XL, MCL-1, BCL-W, and BCL-2A1) and competed with BAK for BCL-XL, which promoted BAK and BAX activation. Taken together, ASFV pE199L induces the mitochondrial-dependent apoptosis, which may provide clues for a comprehensive understanding of ASFV pathogenesis.

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

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

Expression of reprogramming factors in mesenchymal stem cells isolated from equine umbilical cord Wharton’s jelly and amniotic fluid

Stem cells represent the most promising population for regenerative cell therapy and have gained much attention during the recent past. Mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into trilineages. Like haematopoietic cells, mesenchymal cells have been shown to proliferate and form fibroblast-like colonies in vitro. Despite major progress in our general knowledge related to the application of adult stem cells, finding alternative sources for bone marrow MSCs has remained a challenge. A wide diversity of isolation procedures for mesenchymal stromal cells from various tissues of the placenta, umbilical cord and Wharton's jelly have been described for humans and other species. In this study, we isolated established umbilical cord Wharton’s jelly as a primary source for isolation of mesenchymal stem cells since it is a rich source of stem cells and no ethical concerns are involved. Equine umbilical cord Wharton’s jelly segments were collected during foaling time and digested enzymatically and cultured in-vitro in culture medium. In addition to the study of their morphology and colony forming units, the expression of reprogramming factors by the isolated MSCs were also studied. The isolated MSCs were observed to be plastic adherent, clonogenic and their morphology were polygonal, star shaped and fibroblast like. They revealed a strong expression of pluripotent stemness markers OCT-4, SOX-2, Nanog and KLF-4. From the current study, it can be concluded that Wharton's jelly is a rich source of stem cells with stemness properties expressing the reprogramming factors and mesenchymal like morphology and could be used as an alternate for the bone marrow derived mesenchymal stem cells for cell based regenerative therapies.

pMGF505-7R determines pathogenicity of African swine fever virus infection by inhibiting IL-1β and type I IFN production

Inflammatory factors and type I interferons (IFNs) are key components of host antiviral innate immune responses, which can be released from the pathogen-infected macrophages. African swine fever virus (ASFV) has developed various strategies to evade host antiviral innate immune responses, including alteration of inflammatory responses and IFNs production. However, the molecular mechanism underlying inhibition of inflammatory responses and IFNs production by ASFV-encoded proteins has not been fully understood. Here we report that ASFV infection only induced low levels of IL-1β and type I IFNs in porcine alveolar macrophages (PAMs), even in the presence of strong inducers such as LPS and poly(dA:dT). Through further exploration, we found that several members of the multigene family 360 (MGF360) and MGF505 strongly inhibited IL-1β maturation and IFN-β promoter activation. Among them, pMGF505-7R had the strongest inhibitory effect. To verify the function of pMGF505-7R in vivo, a recombinant ASFV with deletion of the MGF505-7R gene (ASFV-Δ7R) was constructed and assessed. As we expected, ASFV-Δ7R infection induced higher levels of IL-1β and IFN-β compared with its parental ASFV HLJ/18 strain. ASFV infection-induced IL-1β production was then found to be dependent on TLRs/NF-κB signaling pathway and NLRP3 inflammasome. Furthermore, we demonstrated that pMGF505-7R interacted with IKKα in the IKK complex to inhibit NF-κB activation and bound to NLRP3 to inhibit inflammasome formation, leading to decreased IL-1β production. Moreover, we found that pMGF505-7R interacted with and inhibited the nuclear translocation of IRF3 to block type I IFN production. Importantly, the virulence of ASFV-Δ7R is reduced in piglets compared with its parental ASFV HLJ/18 strain, which may due to induction of higher IL-1β and type I IFN production in vivo. Our findings provide a new clue to understand the functions of ASFV-encoded pMGF505-7R and its role in viral infection-induced pathogenesis, which might help design antiviral agents or live attenuated vaccines to control ASF.

African swine fever virus (ASFV) causes a highly lethal swine disease that is currently present in many countries, severely affecting the pig industry. Despite extensive research, effective vaccines and antiviral strategies are still lacking and relevant gaps in knowledge of the fundamental biology of the viral infection cycle exist. In this study, we found that ASFV infection only induced low levels of IL-1β and type I IFNs in porcine alveolar macrophages (PAMs) and identified that pMGF505-7R, a member of the multigene family 505 (MGF505), strongly inhibited IL-1β and IFN-β production. ASFV lacking the MGF505-7R gene (ASFV-Δ7R) had reduced virulence in piglets and induced increased IL-1β and IFN-β production in PAMs and pigs compared with its parental ASFV HLJ/18 strain. Our results significantly increase our knowledge to understand functions of ASFV-encoded pMGF505-7R and its roles in pathogenesis, which may shed light on future research on live attenuated vaccines and antiviral strategies.

Recent Advances in PRRS Virus Receptors and the Targeting of Receptor-Ligand for Control

Cellular receptors play a critical role in viral infection. At least seven cellular molecules have been identified as putative viral entry mediators for porcine reproductive and respiratory syndrome virus (PRRSV). Accumulating data indicate that among these candidates, CD163, a cysteine-rich scavenger receptor on macrophages, is the major receptor for PRRSV. This review discusses the recent advances and understanding of the entry of PRRSV into cells, viral pathogenesis in CD163 gene-edited swine, and CD163 as a potential target of receptor–ligand for the control of PRRS.

Glaesserella parasuis induces inflammatory response in 3D4/21 cells through activation of NLRP3 inflammasome signaling pathway via ROS

Glaesserella parasuis (G. parasuis) is an important pathogenic bacterium that can cause Glässer's disease, and it has resulted in tremendous economic losses to the global swine industry. The intensive pulmonary inflammatory response caused by G. parasuis infection is the main cause of lung injury and death in pigs. However, the exact mechanism by which it causes severe pulmonary inflammation is not fully understood yet. In this study, severe pneumonia was observed in piglets infected with G. parasuis; and an infection cell model was established using porcine alveolar macrophages cell line 3D4/21, which was determined to be susceptible to G. parasuis infection in vitro. G. parasuis infection of 3D4/21 cells induced upregulation of proinflammatory cytokines TNF-α, IL-1β, IL-18 and production of intracellular reactive oxygen species (ROS). The expression of IL-1β related to activation of the NLRP3 inflammasome signaling pathway, which had not been shown before in G. parasuis infection. Furthermore, it was first found that release of intracellular ROS, which was mediated by NADPH oxidase in 3D4/21 cells, was found crucial for the activation of the NLRP3 signaling pathway and promoted the expression of proinflammatory cytokines, such as TNF-α and IL-1. In general, this study explored the specific mechanism of severe pulmonary inflammation caused by G. parasuis infection, and provides a foundation for further elucidating the pathogenic mechanism of G. parasuis.

The Isolation and Replication of African Swine Fever Virus in Primary Renal-Derived Swine Macrophages

African swine fever virus (ASFV) causes hemorrhagic disease in domestic pigs by replicating mainly in monocyte/macrophage lineages. Various primary cells including pulmonary alveolar macrophages have been used for the propagation of ASFV on this account. However, ethical constraints and consistency problems exist as it is necessary to harvest same phenotype of primary cells in order to continue a study. We suggested renal-derived swine macrophages as a novel primary cell candidate to address these issues. These primary cells proved to be permissive to both cell adapted ASFV and a wild-type ASFV. Compared to the commercial cell line MA-104, the renal-derived macrophages were more suitable to isolate the field virus. The consistent molecular characteristics of the renal-derived macrophages were demonstrated by immunocytochemistry with antibodies against macrophage cell surface markers including CD163, CD172a, and Iba-1. Viral protein p30 and p72 expression in ASFV infected macrophages was confirmed by immunocytochemistry by use of specific monoclonal antibodies. We observed increase of cell-free viral DNA and infectious virus titer in infected cell supernatant in successive days-post-infection. These results demonstrated that primary renal-derived swine macrophages are useful for ASFV isolation and propagation in terms of cell phenotypes, susceptibility to the virus, and virus production.

An immortalized porcine macrophage cell line competent for the isolation of African swine fever virus

African swine fever virus (ASFV) is the etiological agent of African swine fever (ASF), a fatal hemorrhagic disease of domestic pigs and wild boar. The virus primarily infects macrophage and monocyte host cells, these do not grow in vitro. Many attempts have been made to establish sustainable ASFV-sensitive cell lines, but which supported only low viral replication levels of limited, mostly artificially attenuated strains of ASFV. Here, we examined the competence of a novel cell line of immortalized porcine kidney macrophages (IPKM) for ASFV infection. We demonstrated that IPKM cells can facilitate high levels (> 10^7.0 TCID₅₀/mL) of viral replication of ASFV, and hemadsorption reactions and cytopathic effects were observed as with porcine alveolar macrophages when inoculated with virulent field isolates: Armenia07, Kenya05/Tk-1, and Espana75. These results suggested that IPKM may be a valuable tool for the isolation, replication, and genetic manipulation of ASFV in both basic and applied ASF research.

C1QBP inhibits proliferation of porcine circovirus type 2 by restricting nuclear import of the capsid protein

Complement component 1 Q subcomponent-binding protein (C1QBP) has been shown to interact with the porcine circovirus type 2 (PCV2) Cap protein. Here, using yeast two-hybrid (Y2H) and co-immunoprecipitation assays, as well as laser confocal microscopy, the interaction between C1QBP and Cap was confirmed. Furthermore, overexpression of C1QBP in cells altered the intracellular location of Cap, which was observed using confocal microscopy and verified by detection of Cap in nuclear protein extracts in a Western blot assay. By inhibiting nuclear transport of Cap, overexpression of C1QBP downregulated PCV2 proliferation in PK-15 cells, as determined by quantitative polymerase chain reaction (qPCR). As C1QBP plays a similar role in a fusion of green fluorescent protein (GFP) with the Cap nuclear localisation signal (NLS) sequence, (CapNLS-GFP), we propose that the target site for C1QBP in Cap is possibly located in the NLS region. Considering all the results together, this study demonstrated that C1QBP interacts with the Cap NLS region, resulting in changes in the intracellular localisation of the Cap protein. We confirmed that overexpression of C1QBP inhibits the proliferation of PCV2, and this is possibly related to the function of C1QBP in controlling nuclear transport of Cap.

Susceptibility of immortalized porcine kidney macrophages to porcine reproductive and respiratory syndrome virus-2 infection

Porcine reproductive and respiratory syndrome virus (PRRSV) displays restricted tropism to porcine alveolar macrophages in nature. Meanwhile, non-porcine cell lines derived from African green monkey kidney cell lines are permissive to PRRSV, resulting in their widespread use in PRRSV research. Furthermore, genetically modified cell lines expressing receptors targeted by PRRSV have been established. We previously established porcine immortalized kidney-derived macrophages (IPKMs) that maintained typical macrophage function. In the present study, we demonstrated the advantages of IPKMs for PRRSV research. IPKMs expressed receptors for PRRSV such as CD163 and CD169. The efficiency of virus isolation from field biological samples was higher for IPKMs than for MARC-145 cells. Five different clusters of North American type PRRSV were propagated in IPKMs. Four field strains continuously produced progeny viruses during 10 continuous passages. The efficiency of virus isolation from field biological samples and continuous progeny virus production in the sequential passages using IPKMs indicated that these cells are good vessels for PRRSV research.

Transcriptome analysis of pig macrophages expressing porcine reproductive and respiratory syndrome virus non-structural protein 1

Porcine reproductive and respiratory syndrome virus (PRRSV) is a causative pathogen of PRRS, one of the most economically disastrous swine diseases. Non-structural protein 1 (NSP1) of PRRSV consists of NSP1α and NSP1β which exhibit papain like cysteine protease activity. Recent evidence demonstrates that PRRSV NSP1 may be participated in modulating host immunity, but very few host proteins were discovered as targets for NSP1. In this study, we used RNA-seq to investigate the functional role of PRRSV NSP1 in porcine alveolar macrophages, 3D4/31 cells. Compared to empty vector (mock) transfectant, NSP1, NSP1α, and NSP1β expressing 3D4/31 cells displayed a total of 60 genes, 63 genes, and 80 genes as differentially expressed genes (DEGs), respectively. Most of DEGs are involved in early inflammatory responses including interleukin (IL)-17 signaling pathway, chemokine signaling pathway, tumor necrosis factor (TNF)-α signaling pathway, and cell adhesion molecules. Interestingly, PRRSV NSP1 expression in 3D4/31 cells decreased mRNA transcripts of Fosb and Gdf15 known to be involved in host cell signaling or host cell protection during inflammation. Therefore, PRRSV NSP1 might block the signaling involved in host immune surveillance. Further study is required to define the mechanism on how PRRSV NSP1 protein represses mRNA transcripts of specific host genes.

A Wide-Ranging Antiviral Response in Wild Boar Cells Is Triggered by Non-coding Synthetic RNAs From the Foot-and-Mouth Disease Virus Genome

Foot-and-mouth disease virus (FMDV) is the causative agent of a highly contagious viral disease that affects multiple cloven-hooved hosts including important livestock (pigs, cattle, sheep and goats) as well as several wild animal species. Crossover of FMDV between domestic and wildlife populations may prolong virus circulation during outbreaks. The wild boar (Sus scrofa) is considered a reservoir of various pathogens that can infect other wildlife, domestic animals, and humans. As wild boar and domestic pigs are susceptible to the same pathogens and can infect each other, infected wild boar populations may represent a threat to the pig industry and to international trade. The ncRNAs are synthetic non-coding RNA transcripts, mimicking structural domains in the FMDV genome, known to exert a broad-spectrum antiviral and immunomodulatory effect in swine, bovine and mice cells. Here, we show the type I interferon-dependent, robust and broad range antiviral activity induced by the ncRNAs in a cell line derived from wild boar lung cells (WSL). Transfection of WSL cells with the ncRNAs exerted a protective effect against infection with FMDV, vesicular stomatitis virus (VSV), swine vesicular disease virus (SVDV) and African swine fever virus (ASFV). Our results prove the biological activity of the ncRNAs in cells of an FMDV wild animal host species against a variety of viruses affecting pigs, including relevant viral pathogens of epizootic risk.

Small molecules block the interaction between porcine reproductive and respiratory syndrome virus and CD163 receptor and the infection of pig cells

Background

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating diseases affecting the pork industry globally. PRRS is caused by PRRS virus (PRRSV). Currently there are no effective treatments against this swine disease.

Methods

Through artificial intelligence molecular screening, we obtained a set of small molecule compounds predicted to target the scavenger receptor cysteine-rich domain 5 (SRCR5) of CD163, which is a cell surface receptor specific for PRRSV infection. These compounds were screened using a cell-based bimolecular fluorescence complementation (BiFC) assay, and the function of positive hit was further evaluated and validated by PRRSV-infection assay using porcine alveolar macrophages (PAMs).

Results

Using the BiFC assay, we identified one compound with previously unverified function, 4-Fluoro-2-methyl-N-[3-(3-morpholin-4-ylsulfonylanilino)quinoxalin-2-yl]benzenesulfonamide (designated here as B7), that significantly inhibits the interaction between the PRRSV glycoprotein (GP2a or GP4) and the CD163-SRCR5 domain. We further demonstrated that compound B7 inhibits PRRSV infection of PAMs, the primary target of PRRSV in a dose-dependent manner. B7 significantly inhibited the infection caused by both type I and type II PRRSV strains. Further comparison and functional evaluation of chemical compounds structurally related to B7 revealed that the 3-(morpholinosulfonyl)aniline moiety of B7 or the 3-(piperidinylsulfonyl)aniline moiety in a B7 analogue is important for the inhibitory function against PRRSV infection.

Conclusions

Our study identified a novel strategy to potentially prevent PRRSV infection in pigs by blocking the PRRSV-CD163 interaction with small molecules.

Establishment and characterization of fantail goldfish fin (FtGF) cell line from goldfish, Carassius auratus for in vitro propagation of Cyprinid herpes virus-2 (CyHV-2)

Background

Herpesviral hematopoietic necrosis disease, caused by cyprinid herpesvirus-2 (CyHV-2), is responsible for massive mortalities in the aquaculture of goldfish, Carassius auratus. Permissive cell lines for the isolation and propagation of CyHV-2 have been established from various goldfish tissues by sacrificing the fish. Here, we report the development of a cell line, FtGF (Fantail Goldfish Fin), from caudal fin of goldfish using non-lethal sampling. We also describe a simple protocol for successful establishment and characterization of a permissive cell line through explant method and continuous propagation of CyHV-2 with high viral titer using this cell line.

Methods

Caudal fin tissue samples were collected from goldfish without killing the fish. Cell culture of goldfish caudal fin cells was carried out using Leibovitz’s L-15 (L-15) medium containing 20% FBS and 1X concentration of antibiotic antimycotic solution, incubated at 28 °C. Cells were characterized and origin of the cells was confirmed by sequencing fragments of the 16S rRNA and COI genes. CyHV-2 was grown in the FtGF cells and passaged continuously 20 times. The infectivity of the CyHV-2 isolated using FtGF cells was confirmed by experimental infection of naïve goldfish.

Results

The cell line has been passaged up to 56 times in L-15 with 10% FBS. Karyotyping of FtGF cells at 30^th, 40^th and 56^th passage indicated that modal chromosome number was 2n = 104. Species authentication of FtGF was performed by sequencing of the 16S rRNA and COI genes. The cell line was used for continuous propagation of CyHV-2 over 20 passages with high viral titer of 10^7.8±0.26 TCID₅₀/mL. Following inoculation of CyHV-2 positive tissue homogenate, FtGF cells showed cytopathic effect by 2^nd day post-inoculation (dpi) and complete destruction of cells was observed by the 10^th dpi. An experimental infection of naïve goldfish using supernatant from infected FtGF cells caused 100% mortality and CyHV-2 infection in the challenged fish was confirmed by the amplification of DNA polymerase gene, histopathology and transmission electron microscopy. These findings provide confirmation that the FtGF cell line is highly permissive to the propagation of CyHV-2.

A porcine alveolar macrophage cell line stably expressing CD163 demonstrates virus replication and cytokine secretion characteristics similar to primary alveolar macrophages following PRRSV infection

The in vitro investigation of cytokine secretion induced by porcine reproductive and respiratory syndrome virus (PRRSV) requires porcine alveolar macrophages (PAMs) and their interaction with immunocytes. However, immortalized monoclonal PAMs (mPAMs) are non-permissive for PRRSV infection. The porcine CD163 receptor isolated from primary PAMs (pPAMs) confers susceptibility to PRRSV infection; thus, this approach could be used to establish a novel cell line to facilitate the exploration of PRRSV infection kinetics. Here, we amplified the coding region of the CD163 gene from pPAMs and integrated it into an mPAM line using a lentivirus expression system. After verification, the monoclonal PAM cell line stably expressing CD163 (mPAM-CD163-GFP) was infected with either the highly pathogenic PRRSV strain JXA1 or the classical PRRSV strain SD1, which produced high infectious titers of progeny virus reaching > 10⁹ copies/mL or a 50 % tissue culture infective dose of 10^5.5 over at least 100 cell generations. We also investigated cytokine and Toll-like receptor expression in infected mPAM-CD163-GFP cells and pPAMs. The mPAM-CD163-GFP cell line showed similar patterns of viral replication and cytokine secretion compared with pPAMs, so it may be extremely useful for replacing primary cells for in vitro investigations of the mechanisms of cytokine secretion and interactions between PRRSV-infected PAMs and immunocytes.

Alphaherpesvirus gB Homologs Are Targeted to Extracellular Vesicles, but They Differentially Affect MHC Class II Molecules

Herpesvirus envelope glycoprotein B (gB) is one of the best-documented extracellular vesicle (EVs)-incorporated viral proteins. Regarding the sequence and structure conservation between gB homologs, we asked whether bovine herpesvirus-1 (BoHV-1) and pseudorabies virus (PRV)-encoded gB share the property of herpes simplex-1 (HSV-1) gB to be trafficked to EVs and affect major histocompatibility complex (MHC) class II. Our data highlight some conserved and differential features of the three gBs. We demonstrate that mature, fully processed BoHV-1 and PRV gBs localize to EVs isolated from constructed stable cell lines and EVs-enriched fractions from virus-infected cells. gB also shares the ability to co-localize with CD63 and MHC II in late endosomes. However, we report here a differential effect of the HSV-1, BoHV-1, and PRV glycoprotein on the surface MHC II levels, and MHC II loading to EVs in stable cell lines, which may result from their adverse ability to bind HLA-DR, with PRV gB being the most divergent. BoHV-1 and HSV-1 gB could retard HLA-DR exports to the plasma membrane. Our results confirm that the differential effect of gB on MHC II may require various mechanisms, either dependent on its complex formation or on inducing general alterations to the vesicular transport. EVs from virus-infected cells also contained other viral glycoproteins, like gD or gE, and they were enriched in MHC II. As shown for BoHV-1 gB- or BoHV-1-infected cell-derived vesicles, those EVs could bind anti-virus antibodies in ELISA, which supports the immunoregulatory potential of alphaherpesvirus gB.

Coinfection with porcine circovirus type 2 and Streptococcus suis serotype 2 enhances pathogenicity by dysregulation of the immune responses in piglets

Porcine circovirus type 2 (PCV-2) and Streptococcus suis (S. suis) are common pathogens in pigs. Both pathogens are associated with the porcine respiratory disease complex. Clinically, coinfection of PCV-2 and S. suis are often detected in pigs with respiratory symptoms, while interactions between the two pathogens during coinfection and the coinfection pathogenesis are poorly understood. In this study, a piglet model coinfected with PCV-2 and Streptococcus suis serotype 2 (SS2) was established; coinfection of piglets increased the contents of SS2 in blood, and piglets showed more severe pneumonia, myocarditis and arthritis. Peripheral blood mononuclear cells (PBMCs) were collected and coinfected piglets showed high expression levels of inflammatory cytokines and TLR2, TLR4, while levels of CD4, CD8 and MHC II were reduced. In addition, in order to further explore the mechanisms of coinfection induced cytokine overexpression, an in vitro model of coinfection with PCV-2 and SS2 was established using cells of the porcine monocytic line 3D4/21. Similar to the in vivo results,coinfected cells exhibited increased expression of the cytokines IL-6, IL-8, TNF-α and the receptors TLR2, TLR4, while they showed a lower expression of MHC II than cells infected with SS2 alone. Furthermore, in coinfected 3D4/21 cells, both MAPK and NF-κB signaling pathways were activated, and the increased expression of IL-8 was related to TLR4. In general, coinfection with PCV-2 and SS2 exacerbated the inflammatory response and probably impaired macrophage antigen presentation, resulting in immune dysregulation and increasing the severity of host infection.

Establishment and cryopreservation of a cell line derived from caudal fin of endangered catfish Clarias dussumieri Valenciennes, 1840

We describe a new cell line, Clarias dussumieri fin (ClDuF), from the caudal fin of C. dussumieri using the explant technique followed by cryopreservation. The cryopreserved CiDuF cells were validated for quality and other characteristics. They showed typical epithelial morphology in vitro and epithelial cells outgrew their fibroblast cells after the fifth passage. ClDuF cells had a characteristic sigmoid curve with population doubling in 24 h. Immunotyping of the ClDuF cells against cytokeratin suggested the epithelial lineage. Chromosome analysis showed normal diploid (2n = 50) numbers and the cells did not contain any contamination, including Mycoplasma and other microbes. Partial sequencing of fragments of mitochondrial 16s rRNA and COI genes of ClDuF confirmed that the cell line was initiated from C. dussumieri. Cells at the 10th and 25th passages had more than 80% and 70% viability in the culture, respectively, after 6 months of storage at LN₂ . These ClDuF cells were morphologically identical to the cells before freezing and the genetic resource of C. dussumieri was preserved. The species-specific cells can serve as a valuable source for virus isolation, conservation and cloning of somatic cells.

Porcine Circovirus Type 2 Induces Single Immunoglobulin Interleukin-1 Related Receptor (SIGIRR) Downregulation to Promote Interleukin-1β Upregulation in Porcine Alveolar Macrophage

Multisystemic inflammation in pigs affected by porcine circovirus type 2 (PCV2) indicates the disordered expression of inflammatory cytokines. However, the PCV2-induced expression profile of inflammation cytokines and its regulating mechanism remain poorly understood. In this study, inflammatory cytokines and receptors in porcine alveolar macrophages (PAMs) after PCV2 infection were profiled in vitro by an RT² Profiler^TM PCR array assay. The regulatory mechanism of interleukin-1β (IL-1β) expression was investigated. Results showed that 49 of 84 inflammation cytokines and receptors were differentially expressed (p < 0.05, absolute fold change ≥2) in PAMs at different stages post-PCV2 infection. Moreover, the overexpression of single-immunoglobulin interleukin-1 related receptor (SIGIRR) or the blocking of NF-κB activation by its inhibitor markedly decreased IL-1β secretion. This finding suggested that PCV2-induced overexpression of IL-1β was associated with the downregulation of SIGIRR and the activation of NF-κB. Furthermore, the excessive activity of NF-κB in SIGIRR-knockout PAMs cell line, indicating that SIGIRR negatively regulated IL-1β production by inhibiting the activation of NF-κB. Overall, PCV2-induced downregulation of SIGIRR induction of NF-κB activation is a critical process in enhancing IL-1β production in PAMs. This study may provide insights into the underlying inflammatory response that occurs in pigs following PCV2 infection.

A simple and efficient method for the generation of a porcine alveolar macrophage cell line for high-efficiency Porcine reproductive and respiratory syndrome virus 2 infection

CD163 is a cellular receptor for Porcine reproductive and respiratory syndrome virus (PRRSV). Transgenic expression of CD163 can predispose a variety of PRRSV non-permissive cells to PRRSV infection. These resulting cells can then be used for PRRSV production and the study of PRRSV biology. The PiggyBac (PB) transposon is a non-viral, plasmid-based mobile genetic element that can be used for gene delivery into mammalian cells. In this study, a simple and efficient method for the transfection of the porcine CD163 transgene into an immortalized porcine alveolar macrophage cell line (3D4/21), a non-permissive cell line to PRRSV infection, by PB transposition was demonstrated. The resultant stably transformed 3D4/21/CD163 cells expressed CD163 constitutively and were shown to be fully permissive for PRRSV-2 strains and yielded an excess of 10⁶ TCID₅₀/mL of progeny virus. The PRRSV replicated more efficiently in the 3D4/21/CD163 cells than in Marc-145 cells, and the titers of the progeny PRRSV produced in the 3D4/21/CD163 cells were higher than those produced in Marc-145 cells. This simplified PB transposon-generated PRRSV-2 permissive 3D4/21/CD163 cell line could facilitate PRRSV production and accelerate the study of virus-host interactions in vitro.

Porcine Reproductive and Respiratory Syndrome Virus Nonstructural Protein 1 Beta Interacts with Nucleoporin 62 To Promote Viral Replication and Immune Evasion

Porcine reproductive and respiratory syndrome virus (PRRSV) blocks host mRNA nuclear export to the cytoplasm, and nonstructural protein 1 beta (nsp1β) of PRRSV has been identified as the protein that disintegrates the nuclear pore complex. In the present study, the molecular basis for the inhibition of host mRNA nuclear export was investigated. Nucleoporin 62 (Nup62) was found to bind to nsp1β, and the region representing the C-terminal residues 328 to 522 of Nup62 was determined to be the binding domain for nsp1β. The nsp1β L126A mutant in the SAP domain did not bind to Nup62, and in L126A-expressing cells, host mRNA nuclear export occurred normally. The vL126A mutant PRRSV generated by reverse genetics replicated at a lower rate, and the titer was lower than for wild-type virus. In nsp1β-overexpressing cells or small interfering RNA (siRNA)-mediated Nup62 knockdown cells, viral protein synthesis increased. Notably, the production of type I interferons (IFN-α/β), IFN-stimulated genes (PKR, OAS, Mx1, and ISG15 genes), IFN-induced proteins with tetratricopeptide repeats (IFITs) 1 and 2, and IFN regulatory factor 3 decreased in these cells. As a consequence, the growth of vL126A mutant PRRSV was rescued to the level of wild-type PRRSV. These findings are attributed to nuclear pore complex (NPC) disintegration by nsp1β, resulting in increased viral protein production and decreased host protein production, including antiviral proteins in the cytoplasm. Our study reveals a new strategy of PRRSV for immune evasion and enhanced replication during infection.IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) causes PRRS and is known to effectively suppress host innate immunity. The PRRSV nsp1β protein blocks host mRNA nuclear export, which has been shown to be one of the viral mechanisms for inhibition of antiviral protein production. nsp1β binds to the cellular protein nucleoporin 62 (Nup62), and as a consequence, the nuclear pore complex (NPC) is disintegrated and the nucleocytoplasmic trafficking of host mRNAs and host proteins is blocked. We show the dual benefits of Nup62 and nsp1β binding for PRRSV replication: the inhibition of host antiviral protein expression and the exclusive use of host translation machinery by the virus. Our study unveils a novel strategy of PRRSV for immune evasion and enhanced replication during infection.

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.

Development of vaccines against African swine fever virus

An outbreak in the Caucasus in 2007 initiated the spread of ASFV through Russia and Eastern Europe, subsequently affecting Ukraine, Belarus, Poland, the Baltic States, the Czech Republic, Moldova, Romania and Bulgaria. The declaration of outbreaks in China and Central Europe in August 2018, definitely confirms the serious threat that the extension of ASF represents for the global swine industry and the environment. Despite the efforts of several groups to generate a vaccine against ASFV, currently only control and eradication measures are available based mainly on the early detection and implementation of strict sanitary procedures, including the mass slaughter of animals, both domestic and wild boar. However, the rapid spread of the disease shows that these actions are clearly insufficient to control the current pandemic situation, and the development of a vaccine is urgently required.

The first complete genomic sequences of African swine fever virus isolated in Poland

African swine fever (ASF) is a contagious, notifiable viral disease, which is considered a significant threat not only for European, but also for worldwide pork production, since recently the virus emerged within numerous Chinese pig herds. The disease was introduced in Poland in 2014 and up to the end of 2018,  213 outbreaks in pigs and 3347 cases in wild boars have been reported. The presented study describes the whole genome sequencing of seven Polish isolates, collected between 2016 and 2017, using next generation sequencing (NGS) technology. The complete, genomic sequences of these isolates were compared against five other closely related ASFV genomes, annotated in the NCBI database. The obtained sequences were from 189.393 to 189.405 bp long and encoded 187-190 open reading frames (ORFs). The isolates were grouped within genotype II and showed 99.941 to 99.956% nucleotide identity to the Georgia 2007/1 reference strain.

Development of a Cell-Based High-Throughput Screening Assay to Identify Porcine Host Defense Peptide-Inducing Compounds

Novel alternatives to antibiotics are needed for the swine industry, given increasing restrictions on subtherapeutic use of antibiotics. Augmenting the synthesis of endogenous host defense peptides (HDPs) has emerged as a promising antibiotic-alternative approach to disease control and prevention. To facilitate the identification of HDP inducers for swine use, we developed a stable luciferase reporter cell line, IPEC-J2/PBD3-luc, through permanent integration of a luciferase reporter gene driven by a 1.1 kb porcine β-defensin 3 (PBD3) gene promoter in porcine IPEC-J2 intestinal epithelial cells. Such a stable reporter cell line was employed in a high-throughput screening of 148 epigenetic compounds and 584 natural products, resulting in the identification of 41 unique hits with a minimum strictly standardized mean difference (SSMD) value of 3.0. Among them, 13 compounds were further confirmed to give at least a 5-fold increase in the luciferase activity in the stable reporter cell line, with 12 being histone deacetylase (HDAC) inhibitors. Eight compounds were subsequently observed to be comparable to sodium butyrate in inducing PBD3 mRNA expression in parental IPEC-J2 cells in the low micromolar range. Six HDAC inhibitors including suberoylanilide hydroxamine (SAHA), HC toxin, apicidin, panobinostat, SB939, and LAQ824 were additionally found to be highly effective HDP inducers in a porcine 3D4/31 macrophage cell line. Besides PBD3, other HDP genes such as PBD2 and cathelicidins (PG1–5) were concentration-dependently induced by those compounds in both IPEC-J2 and 3D4/31 cells. Furthermore, the antibacterial activities of 3D4/31 cells were augmented following 24 h exposure to HDAC inhibitors. In conclusion, a cell-based high-throughput screening assay was developed for the discovery of porcine HDP inducers, and newly identified HDP-inducing compounds may have potential to be developed as alternatives to antibiotics for applications in swine and possibly other animal species.

Breed Differences in PCV2 Uptake and Disintegration in Porcine Monocytes

Porcine circovirus type 2 (PCV2) is associated with various diseases which are designated as PCV2-associated diseases (PCVADs). Their severity varies among breeds. In the diseased pigs, virus is present in monocytes, without replication or full degradation. PCV2 entry and viral outcome in primary porcine monocytes and the role of monocytes in PCV2 genetic susceptibility have not been studied. Here, virus uptake and trafficking were analyzed and compared among purebreds Piétrain, Landrace and Large White and hybrid Piétrain × Topigs20. Viral capsids were rapidly internalized into monocytes, followed by a slow disintegration to a residual level. PCV2 uptake was decreased by chlorpromazine, cytochalasin D and dynasore. The internalized capsids followed the endosomal trafficking pathway, ending up in lysosomes. PCV2 genome was nicked by lysosomal DNase II in vitro, but persisted in monocytes in vivo. Monocytes from purebred Piétrain and the hybrid showed a higher level of PCV2 uptake and disintegration, compared to those from Landrace and Large White. In conclusion, PCV2 entry occurs via clathrin-mediated endocytosis. After entry, viral capsids are partially disintegrated, while viral genomes largely escape from the pathway to avoid degradation. The degree of PCV2 uptake and disintegration differ among pig breeds.

Isolation and culture of putative mesenchymal stem cells from equine umbilical cord Wharton’s jelly

Despite major progress and knowledge related to the application of adult stem cells, finding alternative sources for bone marrow MSCs has remained a challenge in both humans and animals. In the current study, two protocols namely sequential enzymatic tissue digestion and tissue explant techniques were tried for successful establishment of MSC culture. Umbilical tissues were isolated each time of foaling from five sequential foalings of Marwari mares. Total cell yield, their growth potential and cryopreservation potential were studied. Adherent cell colonies could be established using both isolation methods. Both the cell populations yielded from different protocols performed similarly in terms of population doubling and CFU number value. Additionally, the cells proliferated vigourously and displayed a similar morphology of mesenchymal stem cells. The MSCs were plastic adherent, colonogenic and their morphology was polygonal and fibroblast like. During the proliferation, the cells exhibited density dependent inhibition; analysis of microbial contamination from bacteria, mycoplasma and fungi were negative; the population doubling time of the MSCs isolated was 34.8 h and 40.2 h in enzymatic treatment and tissue explant methods respectively, and diploid chromosome number of the cells was 64, and the diploid frequency was higher than 80%. In conclusion, this study reveals that both the techniques proved to be non-invasive, efficient, simple and quick for isolation and establishment of MSC culture of extra embryonic tissues from equines.