Foot-and-mouth disease virus replicates only transiently in well-differentiated porcine nasal epithelial cells

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

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

Picornaviruses: A View from 3A

Picornaviruses are comprised of a positive-sense RNA genome surrounded by a protein shell (or capsid). They are ubiquitous in vertebrates and cause a wide range of important human and animal diseases. The genome encodes a single large polyprotein that is processed to structural (capsid) and non-structural proteins. The non-structural proteins have key functions within the viral replication complex. Some, such as 3D^pol (the RNA dependent RNA polymerase) have conserved functions and participate directly in replicating the viral genome, whereas others, such as 3A, have accessory roles. The 3A proteins are highly divergent across the Picornaviridae and have specific roles both within and outside of the replication complex, which differ between the different genera. These roles include subverting host proteins to generate replication organelles and inhibition of cellular functions (such as protein secretion) to influence virus replication efficiency and the host response to infection. In addition, 3A proteins are associated with the determination of host range. However, recent observations have challenged some of the roles assigned to 3A and suggest that other viral proteins may carry them out. In this review, we revisit the roles of 3A in the picornavirus life cycle. The 3AB precursor and mature 3A have distinct functions during viral replication and, therefore, we have also included discussion of some of the roles assigned to 3AB.

Primary Swine Respiratory Epithelial Cell Lines for the Efficient Isolation and Propagation of Influenza A Viruses

Influenza virus isolation from clinical samples is critical for the identification and characterization of circulating and emerging viruses. Yet efficient isolation can be difficult. In these studies, we isolated primary swine nasal and tracheal respiratory epithelial cells and immortalized swine nasal epithelial cells (siNEC) and tracheal epithelial cells (siTEC) that retained the abilities to form tight junctions and cilia and to differentiate at the air-liquid interface like primary cells. Critically, both human and swine influenza viruses replicated in the immortalized cells, which generally yielded higher-titer viral isolates from human and swine nasal swabs, supported the replication of isolates that failed to grow in Madin-Darby canine kidney (MDCK) cells, and resulted in fewer dominating mutations during viral passaging than MDCK cells.IMPORTANCE Robust in vitro culture systems for influenza virus are critically needed. MDCK cells, the most widely used cell line for influenza isolation and propagation, do not adequately model the respiratory tract. Therefore, many clinical isolates, both animal and human, are unable to be isolated and characterized, limiting our understanding of currently circulating influenza viruses. We have developed immortalized swine respiratory epithelial cells that retain the ability to differentiate and can support influenza replication and isolation. These cell lines can be used as additional tools to enhance influenza research and vaccine development.

The immune response to a recombinant Lactococcus lactis oral vaccine against foot-and-mouth disease virus in mice

Objective

Development of an effective mucosal vaccine to induce specific immune responses against Foot-and-mouth disease virus (FMDV).

Results

For this purpose, the FMDV VP1 gene (SPVP1) was optimized and synthesized based on the codon bias of Lactococcus lactis (L. lactis), and then incorporated in the plasmid pNZ8148. L. lactis NZ9000 containing the pNZ8148-SPVP1 recombinant plasmid was used as an oral delivery vehicle to induce anti-FMDV mucosal and systemic immune responses in mice. After confirmation that the SPVP1 protein was expressed successfully in the recombinant L. latic, the mice were orally challenged with NZ9000-pNZ8148, NZ9000-pNZ8148-SPVP1, phosphate-buffered saline as a mock infection group, or with inactivated vaccine as a positive group. Mice immunized with NZ9000-pNZ8148-SPVP1 produced high levels of mucosal secretory IgA (sIgA), antigen-specific serum IgG, IgA, and neutralizing antibodies, and developed stronger cell-mediated immune reactions and significant T spleen lymphocyte proliferation. Furthermore, the recombinant group generated much higher levels of IFN-γ, IL-2, IL-4, IL-5, and IL-10 than the other groups.

Conclusions

Potent immune responses were successfully elicited in mice with FMDV VP1 delivered through L. lactis.

Poly (rC) binding protein 2 interacts with VP0 and increases the replication of the foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) causes a highly contagious and debilitating disease in cloven-hoofed animals, which leads to devastating economic consequences. Previous studies have reported that some FMDV proteins can interact with host proteins to affect FMDV replication. However, the influence of the interactions between FMDV VP0 protein and its partners on FMDV replication remains unknown. In this study, we found that the overexpression of poly (rC) binding protein 2 (PCBP2) promoted FMDV replication, whereas the knockdown of PCBP2 suppressed FMDV replication. Furthermore, PCBP2 can interact with FMDV VP0 protein to promote the degradation of VISA via the apoptotic pathway. Further studies demonstrated that FMDV VP0 protein enhanced the formation of the PCBP2-VISA complex. Ultimately, we found that the degradation of VISA was weaker in PCBP2-knockdown and FMDV VP0-overexpressing cells, or FMDV VP0-knockdown cells than in the control cells. Summarily, our data revealed that the interaction between PCBP2 and VP0 could promote FMDV replication via the apoptotic pathway.

Swine Influenza Virus (H1N2) Characterization and Transmission in Ferrets, Chile

Phylogenetic analysis of the influenza hemagglutinin gene (HA) has suggested that commercial pigs in Chile harbor unique human seasonal H1-like influenza viruses, but further information, including characterization of these viruses, was unavailable. We isolated influenza virus (H1N2) from a swine in a backyard production farm in Central Chile and demonstrated that the HA gene was identical to that in a previous report. Its HA and neuraminidase genes were most similar to human H1 and N2 viruses from the early 1990s and internal segments were similar to influenza A(H1N1)pdm09 virus. The virus replicated efficiently in vitro and in vivo and transmitted in ferrets by respiratory droplet. Antigenically, it was distinct from other swine viruses. Hemagglutination inhibition analysis suggested that antibody titers to the swine Chilean H1N2 virus were decreased in persons born after 1990. Further studies are needed to characterize the potential risk to humans, as well as the ecology of influenza in swine in South America.

Three-dimensional cell culture models for investigating human viruses

Three-dimensional (3D) culture models are physiologically relevant, as they provide reproducible results, experimental flexibility and can be adapted for high-throughput experiments. Moreover, these models bridge the gap between traditional two-dimensional (2D) monolayer cultures and animal models. 3D culture systems have significantly advanced basic cell science and tissue engineering, especially in the fields of cell biology and physiology, stem cell research, regenerative medicine, cancer research, drug discovery, and gene and protein expression studies. In addition, 3D models can provide unique insight into bacteriology, virology, parasitology and host-pathogen interactions. This review summarizes and analyzes recent progress in human virological research with 3D cell culture models. We discuss viral growth, replication, proliferation, infection, virus-host interactions and antiviral drugs in 3D culture models.

An Epithelial Integrin Regulates the Amplitude of Protective Lung Interferon Responses against Multiple Respiratory Pathogens

The healthy lung maintains a steady state of immune readiness to rapidly respond to injury from invaders. Integrins are important for setting the parameters of this resting state, particularly the epithelial-restricted αVβ6 integrin, which is upregulated during injury. Once expressed, αVβ6 moderates acute lung injury (ALI) through as yet undefined molecular mechanisms. We show that the upregulation of β6 during influenza infection is involved in disease pathogenesis. β6-deficient mice (β6 KO) have increased survival during influenza infection likely due to the limited viral spread into the alveolar spaces leading to reduced ALI. Although the β6 KO have morphologically normal lungs, they harbor constitutively activated lung CD11b+ alveolar macrophages (AM) and elevated type I IFN signaling activity, which we traced to the loss of β6-activated transforming growth factor-β (TGF-β). Administration of exogenous TGF-β to β6 KO mice leads to reduced numbers of CD11b+ AMs, decreased type I IFN signaling activity and loss of the protective phenotype during influenza infection. Protection extended to other respiratory pathogens such as Sendai virus and bacterial pneumonia. Our studies demonstrate that the loss of one epithelial protein, αVβ6 integrin, can alter the lung microenvironment during both homeostasis and respiratory infection leading to reduced lung injury and improved survival.

3D rotating wall vessel and 2D cell culture of four veterinary virus pathogens: A comparison of virus yields, portions of infectious particles and virus growth curves

Only very few comparative studies have been performed that evaluate general trends of virus growth under 3D in comparison with 2D cell culture conditions. The aim of this study was to investigate differences when four animal viruses are cultured in 2D and 3D. Suid herpesvirus 1 (SuHV-1), Vesicular stomatitis virus (VSIV), Bovine adenovirus (BAdV) and Bovine parainfluenza 3 virus (BPIV-3) were cultivated in 3D rotating wall vessels (RWVs) and conventional 2D cultures. The production of virus particles, the portion of infectious particles, and the infectious growth curves were compared. For all viruses, the production of virus particles (related to cell density), including the non-infectious ones, was lower in 3D than in 2D culture. The production of only infectious particles was significantly lower in BAdV and BPIV-3 in 3D cultures in relation to cell density. The two cultivation approaches resulted in significantly different virus particle-to-TCID50 ratios in three of the four viruses: lower in SuHV-1 and BPIV-3 and higher in BAdV in 3D culture. The infectious virus growth rates were not significantly different in all viruses. Although 3D RWV culture resulted in lower production of virus particles compared to 2D systems, the portion of infectious particles was higher for some viruses.

Persistent Foot-and-Mouth Disease Virus Infection in the Nasopharynx of Cattle; Tissue-Specific Distribution and Local Cytokine Expression

Tissues obtained post-mortem from cattle persistently infected with foot-and-mouth disease virus (FMDV) were analyzed to characterize the tissue-specific localization of FMDV and partial transcriptome profiles for selected immunoregulatory cytokines. Analysis of 28 distinct anatomic sites from 21 steers infected with FMDV serotype A, O or SAT2, had the highest prevalence of overall viral detection in the dorsal nasopharynx (80.95%) and dorsal soft palate (71.43%). FMDV was less frequently detected in laryngeal mucosal tissues, oropharyngeal mucosal sites, and lymph nodes draining the pharynx. Immunomicroscopy indicated that within persistently infected mucosal tissues, FMDV antigens were rarely detectable within few epithelial cells in regions of mucosa-associated lymphoid tissue (MALT). Transcriptome analysis of persistently infected pharyngeal tissues by qRT-PCR for 14 cytokine genes indicated a general trend of decreased mRNA levels compared to uninfected control animals. Although, statistically significant differences were not observed, greatest suppression of relative expression (RE) was identified for IP-10 (RE = 0.198), IFN-β (RE = 0.269), IL-12 (RE = 0.275), and IL-2 (RE = 0.312). Increased relative expression was detected for IL-6 (RE = 2.065). Overall, this data demonstrates that during the FMDV carrier state in cattle, viral persistence is associated with epithelial cells of the nasopharynx in the upper respiratory tract and decreased levels of mRNA for several immunoregulatory cytokines in the infected tissues.

The gene expression profile of porcine alveolar macrophages infected with a highly pathogenic porcine reproductive and respiratory syndrome virus indicates overstimulation of the innate immune system by the virus

Since the highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) variant emerged in 2006, it has caused death in more than 20 million pigs in China and other Southeast Asian countries, making it the most destructive swine pathogen currently in existence. To characterize the cellular responses to HP-PRRSV infection, the gene expression profile of porcine alveolar macrophage (PAM) cells, the primary target cells of PRRSV, was analyzed in HP-PRRSV-infected and uninfected PAMs by suppression subtractive hybridization. After confirmation by Southern blot, genes that were differentially expressed in the HP-PRRSV-infected and uninfected PAMs were sequenced and annotated. Genes that were upregulated mainly in HP-PRRSV-infected PAM cells were related to immunity and cell signaling. Among the differentially expressed genes, Mx1 and HSP70 protein expression was confirmed by western blotting, and IL-8 expression was confirmed by ELISA. In PAM cells isolated from HP-PRRSV-infected piglets, the differential expression of 21 genes, including IL-16, TGF-beta type 1 receptor, epidermal growth factor, MHC-I SLA, Toll-like receptor, hepatoma-derived growth factor, FTH1, and MHC-II SLA-DRB1, was confirmed by real-time PCR. To our knowledge, this is the first study to demonstrate differential gene expression between HP-PRRSV-infected and uninfected PAMs in vivo. The results indicate that HP-PRRSV infection excessively stimulates genes involved in the innate immune response, including proinflammatory cytokines and chemokines.

Mina: a Th2 response regulator meets TGFβ

The JmjC protein Mina is an important immune response regulator. Classical forward genetics first discovered its immune role in 2009 in connection with the development of T helper 2 (Th2) cells. This prompted investigation into Mina's role in the two best-studied contexts where Th2 responses are essential: atopic asthma and helminth expulsion. In work focused on a mouse model of atopic asthma, Mina deficiency was found to ameliorate airway hyper-resistance and pulmonary inflammation. And, in a case-control study genetic variation at the human MINA locus was found to be associated with the development of childhood atopic asthma. Although the underlying cellular and molecular mechanism of Mina's involvement in pulmonary inflammation remains unknown, our recent work on parasitic helminth expulsion suggests the possibility that, rather than T cells, epithelial cells responding to TGFβ may play the dominant role. Here we review the growing body of literature on the emerging Mina pathway in T cells and epithelial cells and attempt to set these into a broader context.

Characterization of innate responses to influenza virus infection in a novel lung type I epithelial cell model

Type I alveolar epithelial cells are a replicative niche for influenza in vivo, yet their response to infection is not fully understood. To better characterize their cellular responses, we have created an immortalized murine lung epithelial type I cell line (LET1). These cells support spreading influenza virus infection in the absence of exogenous protease and thus permit simultaneous analysis of viral replication dynamics and host cell responses. LET1 cells can be productively infected with human, swine and mouse-adapted strains of influenza virus and exhibit expression of an antiviral transcriptional programme and robust cytokine secretion. We characterized influenza virus replication dynamics and host responses of lung type I epithelial cells and identified the capacity of epithelial cell-derived type I IFN to regulate specific modules of antiviral effectors to establish an effective antiviral state. Together, our results indicate that the type I epithelial cell can play a major role in restricting influenza virus infection without contribution from the haematopoietic compartment.

Differential host response, rather than early viral replication efficiency, correlates with pathogenicity caused by influenza viruses

Influenza viruses exhibit large, strain-dependent differences in pathogenicity in mammalian hosts. Although the characteristics of severe disease, including uncontrolled viral replication, infection of the lower airway, and highly inflammatory cytokine responses have been extensively documented, the specific virulence mechanisms that distinguish highly pathogenic strains remain elusive. In this study, we focused on the early events in influenza infection, measuring the growth rate of three strains of varying pathogenicity in the mouse airway epithelium and simultaneously examining the global host transcriptional response over the first 24 hours. Although all strains replicated equally rapidly over the first viral life-cycle, their growth rates in both lung and tracheal tissue strongly diverged at later times, resulting in nearly 10-fold differences in viral load by 24 hours following infection. We identified separate networks of genes in both the lung and tracheal tissues whose rapid up-regulation at early time points by specific strains correlated with a reduced viral replication rate of those strains. The set of early-induced genes in the lung that led to viral growth restriction is enriched for both NF-κB binding site motifs and members of the TREM1 and IL-17 signaling pathways, suggesting that rapid, NF-κB –mediated activation of these pathways may contribute to control of viral replication. Because influenza infection extending into the lung generally results in severe disease, early activation of these pathways may be one factor distinguishing high- and low-pathogenicity strains.

Microarray analysis of differentially expressed transcripts in porcine intestinal epithelial cells (IPEC-J2) infected with porcine sapelovirus as a model to study innate immune responses to enteric viruses

The local intestinal mucosa, the largest mucosal immune system in animals, plays an important role in resistance against intestinal pathogen infection. However, the molecular antiviral mechanisms of the intestinal mucosa remain poorly understood. In this study, we screened and identified differentially expressed transcripts in (PSV) porcine intestinal epithelial cells (IPEC-J2) infected with porcine sapelovirus using microarray analysis. A total of 2298 differentially expressed genes were screened at four time points during PSV infection. These genes were involved in numerous physical systems and molecular pathways, and particularly, some innate immune-associated pathways were significant. The results showed that large amounts of type I interferon were induced, and the related interferon effect pathway was activated when IPEC-J2 cells were infected with PSV. Three pathways of innate immune receptors, including Toll-like, NOD-like, and RIG-I-like receptors, were also activated. The antigen was then processed and presented through the MHCI and MHCII pathways. Interestingly, we found that the secretion network of IgA was activated in the early stage of PSV infection. Two exogenous and endogenous apoptosis pathways were also activated during PSV infection. The results revealed changes in gene transcription, particularly those of innate immune pathway genes that were associated with PSV infection in IPEC-J2 cells.

Differentiated swine airway epithelial cell cultures for the investigation of influenza A virus infection and replication

Please cite this paper as: Bateman et al. (2013) Differentiated swine airway epithelial cell cultures for the investigation of influenza A virus infection and replication. Influenza and Other Respiratory Viruses 7(2) 139–150.

Background  Differentiated human airway epithelial cell cultures have been utilized to investigate cystic fibrosis, wound healing, and characteristics of viral infections. These cultures, grown at an air–liquid interface (ALI) in media with defined hormones and growth factors, recapitulate many aspects of the in vivo respiratory tract and allow for experimental studies at the cellular level.

Objectives  To optimize growth conditions for differentiated swine airway epithelial cultures and to use these cultures to examine influenza virus infection and replication.

Methods  Primary swine respiratory epithelial cells were grown at an air–liquid interface with varying amounts of retinoic acid and epidermal growth factor. Cells grown with optimized concentrations of these factors for 4 weeks differentiated into multilayer epithelial cell cultures resembling the lining of the swine respiratory tract. Influenza virus infection and replication were examined in these cultures.

Results/Conclusions  Retinoic acid promoted ciliogenesis, whereas epidermal growth factor controlled the thickness of the pseudoepithelium. The optimal concentrations for differentiated swine cell cultures were 1·5 ng/ml epidermal growth factor and 100 nm retinoic acid. Influenza A viruses infected and productively replicated in these cultures in the absence of exogenous trypsin, suggesting that the cultures express a protease capable of activating influenza virus hemagglutinin. Differences in virus infection and replication characteristics found previously in pigs in vivo were recapitulated in the swine cultures. This system could be a useful tool for a range of applications, including investigating influenza virus species specificity, defining cell tropism of influenza viruses in the swine respiratory epithelium, and studying other swine respiratory diseases.

Identification of the role of RIG-I, MDA-5 and TLR3 in sensing RNA viruses in porcine epithelial cells using lentivirus-driven RNA interference

Pathogen recognition receptors are essential for antiviral host immune responses. These specialized receptors detect conserved viral compounds and induce type I interferons (IFN) and pro-inflammatory cytokines. Here we evaluated the contribution of RIG-I, MDA-5 and TLR3 to the recognition of classical swine fever (CSFV), foot-and-mouth disease virus (FMDV), vesicular stomatitis virus (VSV) and influenza A virus (IAV) to IFN-β responses in the porcine epithelial cell line PK-15. To this end, we identified porcine gene specific small interfering RNA sequences and employed a lentivirus (LV)-based system to deliver the corresponding short hairpin RNA. With this, gene knockdown cell lines were created and tested with regard to the knockdown levels over time and following IFN-β stimulation. During several passages of the transduced cells, the expression of both the reporter gene eGFP and the reduced RNA levels of the targeted gene were stable, although the latter was relatively variable. IFN-β induced IFN-responsive genes such as RIG-I, but the levels of the silenced cell line remained reduced compared to the control cells. Based on virus-induced IFN-β mRNA responses, our results indicate that in PK-15 cells FMDV-detection is solely mediated by MDA-5, whereas VSV and IAV are mainly detected by RIG-I with a minor contribution of MDA-5, and CSFV is sensed by MDA-5, RIG-I and TLR3.