Structural alteration of tight and adherens junctions in villous and crypt epithelium of the small and large intestine of conventional nursing piglets infected with porcine epidemic diarrhea virus

Surface display of the COE antigen of porcine epidemic diarrhoea virus on Bacillus subtilis spores

Porcine epidemic diarrhoea virus (PEDV) infects pigs of all ages by invading small intestine, causing acute diarrhoea, vomiting, and dehydration with high morbidity and mortality among newborn piglets. However, current PEDV vaccines are not effective to protect the pigs from field epidemic strains because of poor mucosal immune response and strain variation. Therefore, it is indispensable to develop a novel oral vaccine based on epidemic strains. Bacillus subtilis spores are attractive delivery vehicles for oral vaccination on account of the safety, high stability, and low cost. In this study, a chimeric gene CotC-Linker-COE (CLE), comprising of the B. subtilis spore coat gene cotC fused to the core neutralizing epitope CO-26 K equivalent (COE) of the epidemic strain PEDV-AJ1102 spike protein gene, was constructed. Then recombinant B. subtilis displaying the CLE on the spore surface was developed by homologous recombination. Mice were immunized by oral route with B. subtilis 168-CLE, B. subtilis 168, or phosphate-buffered saline (PBS) as control. Results showed that the IgG antibodies and cytokine (IL-4, IFN-γ) levels in the B. subtilis 168-CLE group were significantly higher than the control groups. This study demonstrates that B. subtilis 168-CLE can generate specific systemic immune and mucosal immune responses and is a potential vaccine candidate against PEDV infection.

An isotonic protein solution favorably modulated the porcine intestinal immune response and cellular adhesion markers and reduced PEDV shedding in vivo

Porcine epidemic diarrhea virus (PEDV) causes immensely large economic losses worldwide in the swine industry. PEDV attacks the intestine, disrupts intestinal epithelium morphology and barrier integrity, and results in profound diarrhea and high mortality. A commercially available isotonic protein solution (IPS) (Tonisity Px) has anecdotally been reported to be effective in supportive treatment of piglets with active PEDV infections. This study evaluated the effects of supplementing (or not) the drinking water of 14 day old PEDV-infected piglets with the IPS on the content of E-cadherin, fibronectin, interferon-alpha (IFN-α), and matrix metalloproteinase 9 (MMP-9) in duodenal tissue. The content of PEDV DNA in feces was also measured. Though both groups had similar PEDV shedding at day 1, IPS piglets had significantly lower PEDV shedding at day 5, 14 and 21. The IPS group also had a shorter duration of PEDV virus shedding. Levels of E-cadherin and fibronectin, both of which are structural proteins in the intestine, remained unchanged from baseline in the IPS group, whereas the same molecules decreased significantly in the control group. IFN-α, an antiviral cytokine, and MMP-9, an enzyme that aids in tissue remodeling, were increased at days 5 and 14 post infection, and then decreased at day 21 post-infection in the IPS group compared to control. Overall, the IPS used in this study enhanced epithelial intercellular adhesion (E-cadherin) and extracellular matrix structure (fibronectin), resulted in significantand favorable changes in MMP-9 activity, and favorably modulated IFN-α production. This is the first report of this panel of biomarkers, especially MMP-9 and IFN-α, in the face of in vivo PEDV infection. This is also the first report to investigate a commercially available swine product that does not need to be administered in solid feed, and that is already registered for use throughout Asia, Europe, South America, and North America. Overall, the results of this study serve to clarify the behavior of 4 key biomarkers in the presence of in vivo PEDV infection. The results also indicate that IPS (Tonisity Px) supplementation is a viable intervention to modulate the porcine intestinal immune response with favorable effects on the intestine.

Oral administration of PEDV-dissolved Alg-CS gel induces high and sustained mucosal immunity in mice

Porcine epidemic diarrhea (PED) is a serious disease in piglets that leads to high mortality. An effective measure that provides higher IgA levels in the intestine and milk is required to decrease losses. Porcine epidemic diarrhea virus (PEDV) was dissolved in calcium alginate (Alg) and combined with chitosan (CS) via electrostatic interactions between cationic chitosan and anionic alginate to create a porous gel (Alg-CS+PEDV). The gel was used to immunize mice orally or in combination with subcutaneous injections of inactivated PEDV vaccine. At 12 and 24 days after immunization, levels of IgA and IgG in Alg-CS+PEDV were higher than with normal PEDV oral administration. At 24 days after immunization, the concentration of IFN-γ in Alg-CS+PEDV was higher than with normal PEDV oral administration. Furthermore, oral administration combining subcutaneous immunization induced higher levels of IgG and IgA than oral administration alone. Our study provides a new method for the preparation and administration of oral vaccines to achieve enhanced mucosal immunity against PEDV.

Intestinal tuft cell immune privilege enables norovirus persistence

The persistent murine norovirus strain MNVCR6 is a model for human norovirus and enteric viral persistence. MNVCR6 causes chronic infection by directly infecting intestinal tuft cells, rare chemosensory epithelial cells. Although MNVCR6 induces functional MNV-specific CD8+ T cells, these lymphocytes fail to clear infection. To examine how tuft cells promote immune escape, we interrogated tuft cell interactions with CD8+ T cells by adoptively transferring JEDI (just EGFP death inducing) CD8+ T cells into Gfi1b-GFP tuft cell reporter mice. Unexpectedly, some intestinal tuft cells partially resisted JEDI CD8+ T cell-mediated killing-unlike Lgr5+ intestinal stem cells and extraintestinal tuft cells-despite seemingly normal antigen presentation. When targeting intestinal tuft cells, JEDI CD8+ T cells predominantly adopted a T resident memory phenotype with decreased effector and cytotoxic capacity, enabling tuft cell survival. JEDI CD8+ T cells neither cleared nor prevented MNVCR6 infection in the colon, the site of viral persistence, despite targeting a virus-independent antigen. Ultimately, we show that intestinal tuft cells are relatively resistant to CD8+ T cells independent of norovirus infection, representing an immune-privileged niche that can be leveraged by enteric microbes.

Effects of monolaurin on intestinal barrier, blood biochemical profile, immunity and antioxidant function in porcine epidemic diarrhoea virus-infected piglets

The effects of monolaurin (ML) on the health of piglets infected with porcine epidemic diarrhoea virus (PEDV) have not been fully understood. This study aimed to investigate its role in blood biochemical profile, intestinal barrier function, antioxidant function and the expression of antiviral genes in piglets infected with PEDV. Thirty-two piglets were randomly divided into four groups: control group, ML group, PEDV group and ML + PEDV group. Piglets were orally administrated with ML at a dose of 100 mg/kg·BW for 7 d before PEDV infection. Results showed that PEDV infection significantly decreased D-xylose content and increased intestinal fatty acid-binding protein content, indicating that PEDV infection destroyed intestinal barrier and absorption function. While it could be repaired by ML administration. Moreover, ML administration significantly decreased plasma blood urea nitrogen and total protein content upon PEDV infection. These results suggested ML may increase protein utilisation efficiency. ML administration significantly decreased the number of large unstained cells and Hb and increased the number of leucocytes and eosinophils in the blood of PEDV-infected piglets, indicating ML could improve the immune defense function of the body. In the presence of PEDV infection, ML administration significantly increased superoxide dismutase and catalase activities in blood and colon, respectively, indicating ML could improve antioxidant capacity. Besides, ML administration reversed the expression of ISG15, IFIT3 and IL-29 throughout the small intestine and Mx1 in jejunum and ileum, indicating the body was in recovery from PEDV infection. This study suggests that ML could be used as a kind of feed additive to promote swine health upon PEDV infection.

Adult Animal Stem Cell-Derived Organoids in Biomedical Research and the One Health Paradigm

Preclinical biomedical research is limited by the predictiveness of in vivo and in vitro models. While in vivo models offer the most complex system for experimentation, they are also limited by ethical, financial, and experimental constraints. In vitro models are simplified models that do not offer the same complexity as living animals but do offer financial affordability and more experimental freedom; therefore, they are commonly used. Traditional 2D cell lines cannot fully simulate the complexity of the epithelium of healthy organs and limit scientific progress. The One Health Initiative was established to consolidate human, animal, and environmental health while also tackling complex and multifactorial medical problems. Reverse translational research allows for the sharing of knowledge between clinical research in veterinary and human medicine. Recently, organoid technology has been developed to mimic the original organ's epithelial microstructure and function more reliably. While human and murine organoids are available, numerous other organoids have been derived from traditional veterinary animals and exotic species in the last decade. With these additional organoid models, species previously excluded from in vitro research are becoming accessible, therefore unlocking potential translational and reverse translational applications of animals with unique adaptations that overcome common problems in veterinary and human medicine.

LncRNA446 Regulates Tight Junctions by Inhibiting the Ubiquitinated Degradation of Alix after Porcine Epidemic Diarrhea Virus Infection

Porcine epidemic diarrhea (PED) is a highly contagious disease, caused by porcine epidemic diarrhea virus (PEDV), which causes huge economic losses. Tight junction-associated proteins play an important role during virus infection; therefore, maintaining their integrity may be a new strategy for the prevention and treatment of PEDV. Long noncoding RNAs (lncRNAs) participate in numerous cellular functional activities, yet whether and how they regulate the intestinal barrier against viral infection remains to be elucidated. Here, we established a standard system for evaluating intestinal barrier integrity and then determined the differentially expressed lncRNAs between PEDV-infected and healthy piglets by lncRNA-seq. A total of 111 differentially expressed lncRNAs were screened, and lncRNA446 was identified due to significantly higher expression after PEDV infection. Using IPEC-J2 cells and intestinal organoids as in vitro models, we demonstrated that knockdown of lncRNA446 resulted in increased replication of PEDV, with further damage to intestinal permeability and tight junctions. Mechanistically, RNA pulldown and an RNA immunoprecipitation (RIP) assay showed that lncRNA446 directly binds to ALG-2-interacting protein X (Alix), and lncRNA446 inhibits ubiquitinated degradation of Alix mediated by TRIM25. Furthermore, Alix could bind to ZO1 and occludin and restore the expression level of the PEDV M gene and TJ proteins after lncRNA446 knockdown. Additionally, Alix knockdown and overexpression affects PEDV infection in IPEC-J2 cells. Collectively, our findings indicate that lncRNA446, by inhibiting the ubiquitinated degradation of Alix after PEDV infection, is involved in tight junction regulation. This study provides new insights into the mechanisms of intestinal barrier resistance and damage repair triggered by coronavirus. IMPORTANCE Porcine epidemic diarrhea is an acute, highly contagious enteric viral disease severely affecting the pig industry, for which current vaccines are inefficient due to the high variability of PEDV. Because PEDV infection can lead to severe injury of the intestinal epithelial barrier, which is the first line of defense, a better understanding of the related mechanisms may facilitate the development of new strategies for the prevention and treatment of PED. Here, we demonstrate that the lncRNA446 directly binds one core component of the actomyosin-tight junction complex named Alix and inhibits its ubiquitinated degradation. Functionally, the lncRNA446/Alix axis can regulate the integrity of tight junctions and potentially repair intestinal barrier injury after PEDV infection.

The novel Nsp9-interacting host factor H2BE promotes PEDV replication by inhibiting endoplasmic reticulum stress-mediated apoptosis

Porcine epidemic diarrhoea (PED) caused by porcine epidemic diarrhoea virus (PEDV) has led to significant economic losses in the swine industry worldwide. Histone Cluster 2, H2BE (HIST2H2BE), the main protein component in chromatin, has been proposed to play a key role in apoptosis. However, the relationship between H2BE and PEDV remains unclear. In this study, H2BE was shown to bind and interact with PEDV nonstructural protein 9 (Nsp9) via immunoprecipitation-mass spectrometry (IP-MS). Next, we verified the interaction of Nsp9 with H2BE by immunoprecipitation and immunofluorescence. H2BE colocalized with Nsp9 in the cytoplasm and nuclei. PEDV Nsp9 upregulated the expression of H2BE by inhibiting the expression of IRX1. We demonstrated that overexpression of H2BE significantly promoted PEDV replication, whereas knockdown of H2BE by small interfering RNA (siRNA) inhibited PEDV replication. Overexpression of H2BE led to significantly inhibited GRP78 expression, phosphorylated PERK (p-PERK), phosphorylated eIF2 (p-eIF2), phosphorylated IRE1 (p-IRE1), and phosphorylated JNK (p-JNK); negatively regulated CHOP and Bax expression and caspase-9 and caspase-3 cleavage; and promoted Bcl-2 production. Knocking down H2BE exerted the opposite effects. Furthermore, we found that after deletion of amino acids 1-28, H2BE did not promote PEDV replication. In conclusion, these studies revealed the mechanism by which H2BE is associated with ER stress-mediated apoptosis to regulate PEDV replication. Nsp9 upregulates H2BE. H2BE plays a role in inhibiting apoptosis and thus facilitating viral replication, which depends on the N-terminal region of H2BE (amino acids 1-28). These findings provide a reference for host-PEDV interactions and offer the possibility for developing strategies for PEDV decontamination and prevention.

Identification of Cell Types and Transcriptome Landscapes of Porcine Epidemic Diarrhea Virus-Infected Porcine Small Intestine Using Single-Cell RNA Sequencing

Swine coronavirus-porcine epidemic diarrhea virus (PEDV) with specific susceptibility to pigs has existed for decades, and recurrent epidemics caused by mutant strains have swept the world again since 2010. In this study, single-cell RNA sequencing was used to perform for the first time, to our knowledge, a systematic analysis of pig jejunum infected with PEDV. Pig intestinal cell types were identified by representative markers and identified a new tuft cell marker, DNAH11. Excepting enterocyte cells, the goblet and tuft cells confirmed susceptibility to PEDV. Enrichment analyses showed that PEDV infection resulted in upregulation of cell apoptosis, junctions, and the MAPK signaling pathway and downregulation of oxidative phosphorylation in intestinal epithelial cell types. The T cell differentiation and IgA production were decreased in T and B cells, respectively. Cytokine gene analyses revealed that PEDV infection downregulated CXCL8, CXCL16, and IL34 in tuft cells and upregulated IL22 in Th17 cells. Further studies found that infection of goblet cells with PEDV decreased the expression of MUC2, as well as other mucin components. Moreover, the antimicrobial peptide REG3G was obviously upregulated through the IL33-STAT3 signaling pathway in enterocyte cells in the PEDV-infected group, and REG3G inhibited the PEDV replication. Finally, enterocyte cells expressed almost all coronavirus entry factors, and PEDV infection caused significant upregulation of the coronavirus receptor ACE2 in enterocyte cells. In summary, this study systematically investigated the responses of different cell types in the jejunum of piglets after PEDV infection, which deepened the understanding of viral pathogenesis.

Cell Cultures at the Air-Liquid Interface and Their Application in Cancer Research

Air-liquid interface (ALI) cell cultures are considered a valid tool for the replacement of animals in biomedical research. By mimicking crucial features of the human in vivo epithelial barriers (e.g., lung, intestine, and skin), ALI cell cultures enable proper structural architectures and differentiated functions of normal and diseased tissue barriers. Thereby, ALI models realistically resemble tissue conditions and provide in vivo-like responses. Since their implementation, they are routinely used in several applications, from toxicity testing to cancer research, receiving an appreciable level of acceptance (in some cases a regulatory acceptance) as attractive testing alternatives to animals. In this chapter, an overview of the ALI cell cultures will be presented together with their application in cancer cell culture, highlighting the potential advantages and disadvantages of the model.

Multifaceted Effects and Mechanisms of N-Acetylcysteine on Intestinal Injury in a Porcine Epidemic Diarrhea Virus-Infected Porcine Model

SCOPE

This study investigates the potential effects of N-acetylcysteine (NAC) on intestinal injury in a porcine epidemic diarrhea virus (PEDV)-infected porcine model.

METHODS AND RESULTS

Thirty-two piglets are randomly assigned to one of four groups: the control, PEDV, NAC, and NAC+PEDV. Piglets in the NAC+PEDV group are orally administrated with NAC (100 mg (kg·BW)^-1  day^-1 ) for 4 consecutive days after 2 days of PEDV infection. The results show that NAC administration decreases the diarrhea rate and improves intestinal morphology. The concentration of diamine oxidase and intestinal fatty-acid binding protein, as well as IL-1β, IL-8, and TNF-α in the plasma, is decreased by NAC. Intriguingly, NAC administration significantly increases the viral load in the jejunum and ileum and down-regulates the expression of interferon-related genes. Microarray and proteomic analyses show that the differentially expressed genes/proteins between NAC+PEDV and PEDV groups are highly enriched in substance transport. Furthermore, aquaporin 8/10 expression is significantly increased by NAC upon PEDV infection.

CONCLUSION

NAC administration alleviates PEDV-induced intestinal injury by inhibiting inflammatory responses and improving substance transport, but promotes viral replication by inhibiting interferon signaling. These results suggest NAC exhibits multifaceted effects upon PEDV infection, and thus caution is required when using NAC as a dietary supplement to prevent viral infection.

1,25-Dihydroxyvitamin D3 Negatively Regulates the Inflammatory Response to Porcine Epidemic Diarrhea Virus Infection by Inhibiting NF-κB and JAK/STAT Signaling Pathway in IPEC-J2 Porcine Epithelial Cells

Porcine epidemic diarrhea virus (PEDV) infection causes watery diarrhea and vomiting in piglets. The pathogenesis of PEDV infection is related to intestinal inflammation. It is known that 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) has potent anti-inflammatory activity, but it is unknown whether 1,25(OH)₂D₃ can inhibit the PEDV-induced inflammatory response and the underlying mechanism. We used transcriptome analysis, gene and protein expression, RNA interference and overexpression, and other techniques to study the anti-inflammatory effects of 1,25(OH)₂D₃ on PEDV infection in IPEC-J2 cells. The results showed that interleukin 19 (IL-19) and C-C motif chemokine ligand 20 (CCL20) gene expression were enhanced with the increase in PEDV infection time in IPEC-J2 cells. Interestingly, 1,25(OH)₂D₃ supplementation obviously inhibited IL-19 and CCL20 expression induced by PEDV. Meanwhile, we also found that 1,25(OH)₂D₃ reduced p-NF-κB, p-STAT1, and p-STAT3 protein levels induced by PEDV at 24 h post-infection. IκBα and SOCS3, NF-κB, and STAT inhibitor respectively, were increased by 1,25(OH)₂D₃ supplementation upon PEDV infection. In addition, 1,25(OH)₂D₃ supplementation inhibited ISG15 and MxA expression induced by PEDV. Although 1,25(OH)₂D₃ suppressed the JAK/STAT signal pathway and antiviral gene expression, it had no significant effects on PEDV replication and IFN-α-induced antiviral effects. In addition, when the vitamin D receptor (VDR) was silenced by siRNA, the anti-inflammatory effect of 1,25(OH)₂D₃ was inhibited. Meanwhile, the overexpression of VDR significantly downregulated IL-19 and CCL20 expression induced by PEDV infection. Together, our results provide powerful evidence that 1,25(OH)₂D₃ could alleviate PEDV-induced inflammation by regulating the NF-κB and JAK/STAT signaling pathways through VDR. These results suggest that vitamin D could contribute to inhibiting intestinal inflammation and alleviating intestinal damage in PEDV-infected piglets, which offers new approaches for the development of nutritional strategies to prevent PEDV infection in piglets.

A Functional Variant in the Aquaporin-3 Promoter Modulates Its Expression and Correlates With Resistance to Porcine Epidemic Virus Infection in Porcine Intestinal Epithelial Cells

Porcine epidemic diarrhea virus (PEDV) causes a highly contagious intestinal disease in neonatal pigs. Aquaporin-3 (AQP3) plays important roles in maintenance of intestinal barrier function and regulation of immune responses. However, the roles of AQP3 in mediating PEDV infection to host cells and the regulatory mechanisms of AQP3 expression remain poorly understood. Here, we identified one 16 bp (GGGCGGGGTTGCGGGC) insertion mutation in the AQP3 gene promoter in Large White pigs, with the frequencies of 49.3% of heterozygotes and 31.3% of mutant homozygotes. Functional analysis by luciferase activity assay indicated that the insertion mutation results in significant enhancement in AQP3 transcriptional activity (P < 0.01). Mechanistic analysis showed that the inserted sequence adds binding sites for transcription factor CEBPA, which promotes the expression of AQP3. Downregulation of AQP3 by shRNA silencing in porcine intestinal epithelial cells revealed obvious increases in genome copies and viral titers of PEDV. Expression of proinflammatory cytokines (IL-6, IL-8, and IL-18) and interferons (IFN-α and IFN-β) were significantly reduced (P < 0.01) in AQP3 knockdown cells upon PEDV infection. Furthermore, decreased level of ZO-1 protein was also detected in AQP3 knockdown cells in response to PEDV infection. Our findings suggested a previously unknown mechanism linking the effects of promoter genetic variants on the expression of AQP3, revealed the roles of AQP3 in response to PEDV pathogenesis, and indicated the potential associations of the 16 bp insertion mutation with resistance to PEDV infection in porcine intestinal epithelial cells.

Gut Dysbiosis Is Associated With the Severity of Cryptogenic Stroke and Enhanced Systemic Inflammatory Response

Studies implicate that gut dysbiosis is related with many neurological diseases. However, the potential role of gut dysbiosis in cryptogenic stroke (CS) has not been elucidated yet. In this study, a high prevalence of gastrointestinal (GI) dysfunction and gut inflammation with increased intestinal permeability have been found in CS patients compared with normal controls (NCs). The systemic inflammation in CS patients was also identified by measuring the levels of plasma C-reactive protein (CRP), lipopolysaccharide (LPS), LPS-binding protein (LBP), and white blood cells (WBC) count. Using 16S rRNA sequencing, we found increased alpha diversity, accompanied by a higher abundance of Enterobacteriaceae, Streptococcaceae, and Lactobacillaceae at the family level and Escherichia–Shigella, Streptococcus, Lactobacillus, and Klebsilla at the genus level in the intestinal microbiota of CS patients compared to NCs. Our results showed that the abundance of Klebsilla was positively correlated with the systemic inflammation, the National Institutes of Health Stroke Scale (NIHSS) scores, and the infarct volumes. In conclusion, gut dysbiosis in CS patients was associated with the severity of CS and the systemic inflammation. Maintaining the intestinal homeostasis may be a potential strategy for the treatment of CS.

Exosomal miRNA-328-3p targets ZO-3 and inhibits porcine epidemic diarrhea virus proliferation

As essential transfer carriers for cell-to-cell communication and genetic material, exosomes carry microRNAs that participate in the regulation of various biological processes. MicroRNAs are a type of single-stranded noncoding RNA that bind to specific target gene mRNAs to degrade or inhibit their translation, thereby regulating target gene expression. Although it is known that a variety of microRNAs are involved in the viral infection process, there are few reports on specific microRNAs involved in porcine epidemic diarrhea virus (PEDV) infection. In this study, we isolated and identified exosomes in PEDV-infected Vero E6 cells. Using transcriptomics technology, we found that miRNA-328-3p was significantly downregulated in exosomes following PEDV infection. Moreover, exosomal miRNA-328-3p inhibited infection by PEDV by targeting and inhibiting tight junction protein 3 (TJP-3/ZO-3) in recipient cells. Our findings provide evidence that, after infecting cells, PEDV downregulates expression of miRNA-328-3p, and the resulting reduced inhibition of the target protein ZO-3 helps to enhance PEDV infection. These results provide new insight for understanding the regulatory mechanism of PEDV infection.

Membrane proteomic analysis identifies the polarity protein PARD3 as a novel antiviral protein against PEDV infection

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic enteric coronavirus causing lethal watery diarrhea in suckling piglets. PEDV could remodel host membrane structures for their replication, assembly and escape from host cells. However, little is known about the host membrane proteins of PEDV infection. In this study, we analyzed differentially abundant proteins (DAPs) between PEDV infection group and control group and identified the polarity protein PARD3 as one of the most significantly DAPs. PARD3 is implicated in the formation of tight junctions at epithelial cell-cell contacts. Then, we found that PEDV infection promoted the degradation of PARD3 via the ubiquitin proteasome pathway. Moreover, knockdown of PARD3 promoted the proliferation of PEDV. Further study showed that the downregulation of PARD3 altered the normal morphology of the tight junction proteins and promoted apical and basolateral virus proliferation. Tight junctions enable epithelial cells to form physical barriers, which act as an innate immune mechanism that can impede viral infection and PEDV affected the barrier functions by causing degradation of PARD3. Taken together, this work is the first time to investigate the membrane protein profile of PEDV-infected cells using quantitative proteomics and suggests that PARD3 could be a potential novel antiviral protein against PEDV infection.

Significance

Membrane proteins are involved in various physiological and biochemical functions critical for cellular function. It is also dynamic in nature, where many proteins are changed during in response to environmental stress. However, membrane proteins are difficult to study because of their hydrophobicity. Membrane proteomic methods using mass spectrometry analysis have been developed and applied for the characterization of the plasma membrane and subcellular organelles of various virus infected cells. Porcine epidemic diarrhea virus (PEDV) is an enteric pathogen of importance to the swine industry, causing high mortality in neonatal piglets. Because PEDV infected Vero cells can lead to significant changes in cell membrane morphology and form syncytial lesions. Here, we isolated the membrane proteins of PEDV infected and control cells and applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantitatively identify the differentially abundant proteins (DAPs) in PEDV-infected Vero cells and confirmed the DAPs by performing RT-qPCR and Western blot analysis. Among these differential proteins, we focused on a down-regulated protein PARD3 which is important for cell tight junction and cell polarity. Loss of PARD3 can destroy the tight junction of cells and promote the proliferation of PEDV in the apical and basolateral sides. These findings will provide valuable information to better understand the mechanisms underlying the host defense responses to PEDV infection.

Porcine Epidemic Diarrhea Virus Envelope Protein Blocks SLA-DR Expression in Barrow-Derived Dendritic Cells by Inhibiting Promoters Activation

Porcine epidemic diarrhea (PED) is an acute, highly contagious intestinal swine disease caused by porcine epidemic diarrhea virus (PEDV). In addition to known PEDV infection targets (villous small intestinal epithelial cells), recent reports suggest that dendritic cells (DCs) may also be targeted by PEDV in vivo. Thus, in this study we used bone marrow-derived dendritic cells (BM-DCs) as an in vitro model of antigen-presenting cells (APCs). Our results revealed that PEDV replicated in BM-DCs and that PEDV infection of cells inhibited expression of swine leukocyte antigen II DR (SLA-DR), a key MHC-II molecule involved in antigen presentation and initiation of CD4⁺ T cell activation. Notably, SLA-DR inhibition in BM-DCs did not require PEDV replication, suggesting that PEDV structural proteins participated in SLA-DR transcriptional inhibition. Moreover, reporter assay-based screening indicated that PEDV envelope protein blocked activation of SLA-DRα and β promoters, as did PEDV-ORF3 protein when present during PEDV replication. Meanwhile, treatment of PEDV-infected BM-DCs with MG132, a ubiquitin-proteasome degradation pathway inhibitor, did not restore SLA-DR protein levels. Additionally, PEDV infection of BM-DCs did not alter SLA-DR ubiquitination status, suggesting that PEDV infection did not affect SLA-DR degradation. Furthermore, additions of PEDV structural proteins to HEK-293T-SLA-DR stably transfected cells had no effect on SLA-DR protein levels, indicating that PEDV-mediated inhibition of SLA-DR expression acted mainly at the transcriptional level, not at the protein level. These results provide novel insights into PEDV pathogenic mechanisms and viral-host interactions.

Innate Immune Evasion of Porcine Epidemic Diarrhea Virus through Degradation of F-box and WD repeat domain-containing 7 protein via Ubiquitin-proteasome Pathway

Porcine epidemic diarrhea virus (PEDV) causes a porcine disease associated with swine epidemic diarrhea. Different antagonistic strategies have been identified, and the mechanism by which PEDV infection impairs the production of interferon (IFN) and delays the activation of the IFN response to escape host innate immunity has been determined, but the pathogenic mechanisms of PEDV infection remain enigmatic. Our preliminary results revealed that endogenous F-box and WD repeat domain-containing 7 (FBXW7), the substrate recognition component of the SCF-type E3 ubiquitin ligase, is downregulated in PEDV-infected Vero E6 cells, according to the results from an isobaric tags for relative and absolute quantification (iTRAQ) analysis. Overexpression of FBXW7 in target cells makes them more resistant to PEDV infection, whereas ablation of FBXW7 expression by small interfering RNA (siRNA) significantly promotes PEDV infection. In addition, FBXW7 was verified as an innate antiviral factor capable of enhancing the expression of RIG-I and TBK1, and it was found to induce interferon-stimulated genes (ISGs), which led to an elevated antiviral state of the host cells. Moreover, we revealed that PEDV nonstructural protein 2 (nsp2) interacts with FBXW7 and targets FBXW7 for degradation through the K48-linked ubiquitin-proteasome pathway. Consistent with the results proven in vitro, FBXW7 reduction was also confirmed in different intestinal tissues from PEDV-infected specific-pathogen-free (SPF) pigs. Taken together, the data indicated that PEDV has evolved with a distinct antagonistic strategy to circumvent the host antiviral response by targeting the ubiquitin-proteasome-mediated degradation of FBXW7. Our findings provide novel insights into PEDV infection and pathogenesis. IMPORTANCE To counteract the host antiviral defenses, most viruses, including coronaviruses, have evolved with diverse strategies to dampen host IFN-mediated antiviral response, wither by interfering with or evading specific host regulators at multiple steps of this response. In this study, a novel antagonistic strategy was revealed showing that PEDV infection could circumvent the host innate response by targeted degradation of endogenous FBXW7 in target cells, a process that was verified to be a positive modulator for the host innate immune system. Degradation of FBXW7 hampers host innate antiviral activation and facilitates PEDV replication. Our findings reveal a new mechanism exploited by PEDV to suppress the host antiviral response.

Effect of Promoter Methylation on the Expression of Porcine MUC2 Gene and Resistance to PEDV Infection

Integrity of the intestinal mucosal barrier is closely related to the occurrence of diarrhea. As an important component protein of the intestinal mucosal barrier, Mucin 2 (MUC2) plays a critical role in preventing the invasion of pathogens, toxins, and foreign bodies. In the present study, we preliminary verified the function of the porcine MUC2 gene in resisting porcine epidemic diarrhea virus (PEDV) infection and investigated the effect of DNA methylation in the promoter region on MUC2 gene expression. The results showed that after PEDV infection, the intestinal mucosal barrier was damaged. Moreover, MUC2 expression was significantly higher in PEDV-infected piglets than in healthy piglets (P < 0.01). The mRNA expression of MUC2 was significantly higher in PEDV-infected IPEC-J2 cells than in non-infected IPEC-J2 cells (P < 0.05). Methylation of the mC-5 site in the MUC2 promoter inhibited the binding of Yin Yang 1 (YY1) to the promoter, down regulated the expression of MUC2 and increased the susceptibility of piglets to PEDV. In conclusion, this study suggests that MUC2 plays an essential regulatory role in PEDV infection. High MUC2 expression improves the resistance of pigs to PEDV infection. The binding of YY1 to the MUC2 promoter is hindered by the methylation of the mC-5 site, which downregulates MUC2 expression and ultimately affects the resistance of pigs to PEDV infection.

Analysis of Intestinal Mucosa Integrity and GLP-2 Gene Functions upon Porcine Epidemic Diarrhea Virus Infection in Pigs

Porcine epidemic diarrhea virus (PEDV) infects intestinal epithelial cells, destroys the intestinal mucosal barrier and then causes diarrhea in piglets. Glucagon-like peptide-2 (GLP-2) is a specific intestinal growth hormone that promotes the repair of damaged intestinal mucosa and improves the intestinal barrier. In this study, we investigated the functions of porcine GLP-2 gene in regulating PEDV infection. The intestinal tissues with damaged intestinal structures caused by PEDV infection were first confirmed and collected. Expression analysis indicated that the GLP-2 gene was expressed in the duodenum, jejunum and ileum tissues, and the mRNA level was significantly down-regulated in jejunum and ileum of piglets with damaged intestinal mucosa. Infection of PEDV to porcine small intestinal epithelial cells in vitro showed that GLP-2 gene was significantly decreased, which was consistent with the expression pattern in intestinal tissues. In addition, we silenced the GLP-2 gene by shRNA interfering and found that the copy numbers of PEDV were remarkably increased in the GLP-2 gene silencing cells. Our findings suggest that the GLP-2 gene was potentially involved in regulating PEDV infection and in maintaining the integrity of the intestinal mucosal barrier structure, which could contribute to our understanding of the mechanisms of PEDV pathogenesis and provide a theoretical basis for the identification and application of resistant genes in pig selective breeding for porcine epidemic diarrhea.

Regional Intestinal Drug Absorption: Biopharmaceutics and Drug Formulation

The gastrointestinal tract (GIT) can be broadly divided into several regions: the stomach, the small intestine (which is subdivided to duodenum, jejunum, and ileum), and the colon. The conditions and environment in each of these segments, and even within the segment, are dependent on many factors, e.g., the surrounding pH, fluid composition, transporters expression, metabolic enzymes activity, tight junction resistance, different morphology along the GIT, variable intestinal mucosal cell differentiation, changes in drug concentration (in cases of carrier-mediated transport), thickness and types of mucus, and resident microflora. Each of these variables, alone or in combination with others, can fundamentally alter the solubility/dissolution, the intestinal permeability, and the overall absorption of various drugs. This is the underlying mechanistic basis of regional-dependent intestinal drug absorption, which has led to many attempts to deliver drugs to specific regions throughout the GIT, aiming to optimize drug absorption, bioavailability, pharmacokinetics, and/or pharmacodynamics. In this Editorial we provide an overview of the Special Issue "Regional Intestinal Drug Absorption: Biopharmaceutics and Drug Formulation". The objective of this Special Issue is to highlight the current progress and to provide an overview of the latest developments in the field of regional-dependent intestinal drug absorption and delivery, as well as pointing out the unmet needs of the field.

Single-Blinded Study Highlighting the Differences between the Small Intestines of Neonatal and Weaned Piglets

Simple Summary

The gut mucosa of pigs, which contains intestinal epithelium and subepithelial immune cells, forms a barrier against microorganisms. Nonetheless, infectious diseases of the digestive tract remain the most frequent and recurrent conditions in the swine industry. Changes in intestinal morphology and structure primarily occur at birth and during weaning. However, the difference in the intestinal structures between neonatal and weaned piglets remains unclear. In this study, for the first time, we evaluated the differences in the small intestine between neonatal (0-day-old) and weaned piglets (21-day-old) and analyzed the morphology and immunological components of the small intestines of 0- and 21-day-old piglets, thereby providing preliminary data for future mechanistic studies.

Abstract

The gut is one of the body’s major immune structures, and the gut mucosa, which contains intestinal epithelium and subepithelial immune cells, is the primary site for eliciting local immune responses to foreign antigens. Intestinal immune system development in pigs is a transitional period during birth and weaning. This study compares the morphological and immunological differences in the small intestine of neonatal and weaned piglets to potentially prevent intestinal infectious diseases in neonatal piglets. Histological analyses of weaned piglet intestines showed increased crypt depth, higher IEL count, and larger ileal Peyer’s patches compared with those of neonates. Additionally, the ileal villi of weaned piglets were longer than those of neonatal piglets, and claudin-3 protein expression was significantly higher in weaned than in neonatal piglets. The numbers of CD3⁺ T, goblet, and secretory cells were also higher in the small intestines of weaned piglets than in those of neonates. No significant differences were observed in the secretory IgA-positive cell number in the jejunum of weaned and neonatal piglets. The mRNA expression of most pattern recognition receptors genes in the duodenum and jejunum was higher in the weaned than neonatal piglets; however, the opposite was true in the ileum. The mRNA levels of IL-1β and TNF-α in the jejunal and ileal mucosa were higher in weaned piglets than in neonatal piglets. There were significantly fewer CD3⁺, CD4⁺, and CD8⁺ T cells from peripheral blood-mononuclear cells in neonatal piglets. Our study provides insights regarding the different immune mechanisms within the small intestines of 0- and 21-day-old piglets. Studies on the additional developmental stages and how differences in the small intestines affect the response of pigs to pathogens remain warranted.

Porcine enteric coronaviruses: an updated overview of the pathogenesis, prevalence, and diagnosis

The recent prevalence of coronavirus (CoV) poses a serious threat to animal and human health. Currently, porcine enteric coronaviruses (PECs), including the transmissible gastroenteritis virus (TGEV), the novel emerging swine acute diarrhoea syndrome coronavirus (SADS-CoV), porcine delta coronavirus (PDCoV), and re-emerging porcine epidemic diarrhoea virus (PEDV), which infect pigs of different ages, have caused more frequent occurrences of diarrhoea, vomiting, and dehydration with high morbidity and mortality in piglets. PECs have the potential for cross-species transmission and are causing huge economic losses in the pig industry in China and the world, which therefore needs to be urgently addressed. Accordingly, this article summarises the pathogenicity, prevalence, and diagnostic methods of PECs and provides an important reference for their improved diagnosis, prevention, and control.

Epithelial-mesenchymal transition of absorptive enterocytes and depletion of Peyer's patch M cells after PEDV infection

This study focused on intestinal restitution including phenotype switching of absorptive enterocytes and the abundance of different enterocyte subtypes in weaned pigs after porcine epidemic diarrhea virus (PEDV) infection. At 10 days post-PEDV-inoculation, the ratio of villus height to crypt depth in both jejunum and ileum had restored, and the PEDV antigen was not detectable. However, enterocytes at the villus tips revealed epithelial-mesenchymal transition (EMT) in the jejunum in which E-cadherin expression decreased while expression of N-cadherin, vimentin, and Snail increased. Additionally, there was reduced expression of actin in microvilli and Zonula occludens-1 (ZO-1) in tight junctions. Moreover, the protein concentration of transforming growth factor β1 (TGFβ1), which mediates EMT and cytoskeleton alteration, was increased. We also found a decreased number of Peyer's patch M cells in the ileum. These results reveal incomplete restitution of enterocytes in the jejunum and potentially impaired immune surveillance in the ileum after PEDV infection.

Acute porcine epidemic diarrhea virus infection reshapes the intestinal microbiota

The intestinal microbiota is crucial to intestinal homeostasis. Porcine epidemic diarrhea virus (PEDV) is high pathogenic to intestines, causing diarrhea, even death in piglets. To investigate the detailed relationship between PEDV infection and intestinal microbiota, the composition and distribution of intestinal microbiota from pigs were first analyzed using 16S rRNA sequencing technology. The results demonstrated that the composition and distribution of microbes in different intestinal segments were quite similar between 1-week-old and 2-week-old piglets but different from 4-week-old (weaned) piglets. Then piglets at different ages were inoculated with PEDV. The results showed that the 1-week-old piglets exhibited the most severe pathogenicity comparing to the other age groups. Further investigations indicated that Lactobacillus, Escherichia coli, and Lactococcus in the intestinal microbiota of piglets were significantly changed by PEDV infection. These results strengthen our understanding of viruses influencing intestinal microbes and remind us of the potential association between PEDV and intestinal microbes.

Transferrin receptor 1 levels at the cell surface influence the susceptibility of newborn piglets to PEDV infection

Porcine epidemic diarrhea virus (PEDV) mainly infects the intestinal epithelial cells of newborn piglets causing acute, severe atrophic enteritis. The underlying mechanisms of PEDV infection and the reasons why newborn piglets are more susceptible than older pigs remain incompletely understood. Iron deficiency is common in newborn piglets. Here we found that high levels of transferrin receptor 1 (TfR1) distributed in the apical tissue of the intestinal villi of newborns, and intracellular iron levels influence the susceptibility of newborn piglets to PEDV. We show that iron deficiency induced by deferoxamine (DFO, an iron chelating agent) promotes PEDV infection while iron accumulation induced by ferric ammonium citrate (FAC, an iron supplement) impairs PEDV infection in vitro and in vivo. Besides, PEDV infection was inhibited by occluding TfR1 with antibodies or decreasing TfR1 expression. Additionally, PEDV infection was increased in PEDV-resistant Caco-2 and HEK 293T cells over-expressed porcine TfR1. Mechanistically, the PEDV S1 protein interacts with the extracellular region of TfR1 during PEDV entry, promotes TfR1 re-localization and clustering, then activates TfR1 tyrosine phosphorylation mediated by Src kinase, and heightens the internalization of TfR1, thereby promoting PEDV entry. Taken together, these data suggest that the higher expression of TfR1 in the apical tissue of the intestinal villi caused by iron deficiency, accounts for newborn piglets being acutely susceptible to PEDV.

Newborn piglets are particularly susceptible to infection by PEDV, with 80–100% dying within days of infection. The reasons for newborns’ acute susceptibility to PEDV infection have not been elucidated clearly. The primarily target of PEDV is the porcine intestinal epithelial cells. Here, we show that the high expression of TfR1 in the apical tissue of intestinal villi in newborn piglets with iron deficiency is a reason for their susceptibility to PEDV. Further, we demonstrate that iron supplementation reduces PEDV infection. This study reveals that iron plays an important role in the susceptibility of newborn piglets to PEDV and provides insights into therapies for the prevention and treatment of PEDV infections.

Alterations in Intestinal Innate Mucosal Immunity of Weaned Pigs During Porcine Epidemic Diarrhea Virus Infection

In the small intestine, localized innate mucosal immunity is critical for intestinal homeostasis. Porcine epidemic diarrhea virus (PEDV) infection induces villus injury and impairs digestive function. Moreover, the infection might comprise localized innate mucosal immunity. This study investigated specific enterocyte subtypes and innate immune components of weaned pigs during PEDV infection. Four-week-old pigs were orally inoculated with PEDV IN19338 strain (n = 40) or sham-inoculated (n = 24). At day post inoculation (DPI) 2, 4, and 6, lysozyme expression in Paneth cells, cellular density of villous and Peyer's patch microfold (M) cells, and the expression of polymeric immunoglobulin receptor (pIgR) were assessed in the jejunum and ileum by immunohistochemistry, and interleukin (IL)-1β and tumor necrosis factor (TNF)-α were measured in the jejunum by ELISA. PEDV infection led to a decrease in the ratios of villus height to crypt depth (VH-CD) in jejunum at DPI 2, 4, and 6 and in ileum at DPI 4. The number of villous M cells was reduced in jejunum at DPI 4 and 6 and in ileum at DPI 6, while the number of Peyer's patch M cells in ileum increased at DPI 2 and then decreased at DPI 6. PEDV-infected pigs also had reduced lysozyme expression in ileal Paneth cells at DPI 2 and increased ileal pIgR expression at DPI 4. There were no significant changes in IL-1β and TNF-α expression in PEDV-infected pigs compared to controls. In conclusion, PEDV infection affected innate mucosal immunity of weaned pigs through alterations in Paneth cells, villous and Peyer's patch M cells, and pIgR expression.

Porcine epidemic diarrhea virus (PEDV): An update on etiology, transmission, pathogenesis, and prevention and control

Porcine epidemic diarrhea virus (PEDV), a member of the genus Alphacoronavirus in the family Coronaviridae, causes acute diarrhea and/or vomiting, dehydration and high mortality in neonatal piglets. Two different genogroups of PEDV, S INDEL [PEDV variant containing multiple deletions and insertions in the S1 subunit of the spike (S) protein, G1b] and non-S INDEL (G2b) strains were detected during the diarrheal disease outbreak in US swine in 2013-2014. Similar viruses are also circulating globally. Continuous improvement and update of biosecurity and vaccine strains and protocols are still needed to control and prevent PEDV infections worldwide. Although the non-S INDEL PEDV was highly virulent and the S INDEL PEDV caused milder disease, the latter has the capacity to cause illness in a high number of piglets on farms with low biosecurity and herd immunity. The main PEDV transmission route is fecal-oral, but airborne transmission via the fecal-nasal route may play a role in pig-to-pig and farm-to-farm spread. PEDV infection of neonatal pigs causes fecal virus shedding (alongside frequent detection of PEDV RNA in the nasal cavity), acute viremia, severe atrophic enteritis (mainly jejunum and ileum), and increased pro-inflammatory and innate immune responses. PEDV-specific IgA effector and memory B cells in orally primed sows play a critical role in sow lactogenic immunity and passive protection of piglets. This review focuses on the etiology, transmission, pathogenesis, and prevention and control of PEDV infection.

The Network of Colonic Host Defense Peptides as an Innate Immune Defense Against Enteropathogenic Bacteria

Host defense peptides, abundantly secreted by colonic epithelial cells and leukocytes, are proposed to be critical components of an innate immune response in the colon against enteropathogenic bacteria, including Shigella spp., Salmonella spp., Clostridium difficile, and attaching and effacing Escherichia coli and Citrobacter rodentium. These short cationic peptides are bactericidal against both Gram-positive and -negative enteric pathogens, but may also exert killing effects on intestinal luminal microbiota. Simultaneously, these peptides modulate numerous cellular responses crucial for gut defenses, including leukocyte chemotaxis and migration, wound healing, cytokine production, cell proliferation, and pathogen sensing. This review discusses recent advances in our understanding of expression, mechanisms of action and microbicidal and immunomodulatory functions of major colonic host defense peptides, namely cathelicidins, β-defensins, and members of the Regenerating islet-derived protein III (RegIII) and Resistin-like molecule (RELM) families. In a theoretical framework where these peptides work synergistically, aspects of pathogenesis of infectious colitis reviewed herein uncover roles of host defense peptides aimed to promote epithelial defenses and prevent pathogen colonization, mediated through a combination of direct antimicrobial function and fine-tuning of host immune response and inflammation. This interactive host defense peptide network may decode how the intestinal immune system functions to quickly clear infections, restore homeostasis and avoid damaging inflammation associated with pathogen persistence during infectious colitis. This information is of interest in development of host defense peptides (either alone or in combination with reduced doses of antibiotics) as antimicrobial and immunomodulatory therapeutics for controlling infectious colitis.

Microarray analysis reveals the inhibition of intestinal expression of nutrient transporters in piglets infected with porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) infection can induce intestinal dysfunction, resulting in severe diarrhea and even death, but the mode of action underlying these viral effects remains unclear. This study determined the effects of PEDV infection on intestinal absorption and the expression of genes for nutrient transporters via biochemical tests and microarray analysis. Sixteen 7-day-old healthy piglets fed a milk replacer were randomly allocated to one of two groups. After 5-day adaption, piglets (n = 8/group) were orally administrated with either sterile saline or PEDV (the strain from Yunnan province) at 10^4.5 TCID₅₀ (50% tissue culture infectious dose) per pig. All pigs were orally infused D-xylose (0.1 g/kg BW) on day 5 post PEDV or saline administration. One hour later, jugular vein blood samples as well as intestinal samples were collected for further analysis. In comparison with the control group, PEDV infection increased diarrhea incidence, blood diamine oxidase activity, and iFABP level, while reducing growth and plasma D-xylose concentration in piglets. Moreover, PEDV infection altered plasma and jejunal amino acid profiles, and decreased the expression of aquaporins and amino acid transporters (L-type amino acid transporter 1, sodium-independent amino acid transporter, B(°^,+)-type amino acid transport protein, sodium-dependent neutral amino acid transporter 1, sodium-dependent glutamate/aspartate transporter 3, and peptide transporter (1), lipid transport and metabolism-related genes (lipoprotein lipase, apolipoprotein A1, apolipoprotein A4, apolipoprotein C2, solute carrier family 27 member 2, solute carrier family 27 member 4, fatty acid synthase, and long-chain acyl-CoA synthetase (3), and glucose transport genes (glucose transporter-2 and insulin receptor) in the jejunum. However, PEDV administration increased mRNA levels for phosphoenolpyruvate carboxykinase 1, argininosuccinate synthase 1, sodium/glucose co-transporter-1, and cystic fibrosis transmembrane conductance regulator in the jejunum. Collectively, these comprehensive results indicate that PEDV infection induces intestinal injury and inhibits the expression of genes encoding for nutrient transporters.

Tight Junction Proteins in the Weaned Piglet Intestine: Roles and Regulation

The intestinal epithelial barrier plays a crucial role in the health and growth of weaned piglets. Proper epithelial function mainly depends on tight junctions (TJs), which act as both ion channels and a barrier against noxious molecules. TJs are multiprotein complexes consisting of transmembrane and membrane-associated proteins. Because the intestine in piglets is immature and incomplete, its structure and function are easily impaired by various stresses, infections, and food-related factors. Certain nutrients have been demonstrated to participate in intestinal TJ regulation. Probiotics, amino acids, fibers, oligosaccharide, and certain micronutrients can enhance barrier integrity and counteract infections through elevated TJ protein expression and distribution. In this review, the distribution and classification of intestinal TJs is described, the factors influencing TJs after weaning are summarized, and the regulation of weaning piglet intestinal TJs by nutrients is discussed.

Manipulation of Intestinal Antiviral Innate Immunity and Immune Evasion Strategies of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) infection causes watery diarrhea, dehydration, and high mortality in neonatal pigs, due to its clinical pathogenesis of the intestinal mucosal barrier dysfunction. The host's innate immune system is the first line of defence upon virus invasion of the small intestinal epithelial cells. In turn, the virus has evolved to modulate the host's innate immunity during infection, resulting in pathogen virulence, survival, and the establishment of successful infection. In this review, we gather current knowledge concerning the interplay between PEDV and components of host innate immunity, focusing on the role of cytokines and interferons in intestinal antiviral innate immunity, and the mechanisms underlying the immune evasion strategies of PEDV invasion. Finally, we provide some perspectives on the potential prevention and treatment for PEDV infection.

Mucosal immune responses induced by oral administration recombinant Bacillus subtilis expressing the COE antigen of PEDV in newborn piglets

Porcine epidemic diarrhea (PED) is a highly contagious disease in newborn piglets and causes substantial economic losses in the world. PED virus (PEDV) spreads by fecal–oral contact and can be prevented by oral immunization. Therefore, it is necessary to develop an effective oral vaccine against PEDV infection. Currently, Bacillus subtilis as recombinant vaccine carrier has been used for antigen delivery and proved well in immune effect and safety. The present study evaluated the immunogenicity of recombinant Bacillus subtilis (B. subtilis-RC) in piglets via oral administration. After oral immunization in piglets, B. subtilis-RC significantly increased the local mucosal immune responses. Oral administration with B. subtilis-RC significantly improved the level of specific mucosal immunoglobulin A (IgA) antibodies against PEDV infection, through enlarging the area of Peyer’s patches (PPs) and increasing the number of ileum IgA⁺ secreting (SIgA) cells. In the meantime, B. subtilis-RC remarkably increased the number of intraepithelial lymphocytes (IELs). We also observed that oral administration of B. subtilis-RC significantly increased CD3⁺T lymphocytes’ numbers and up-regulated the ratio of CD4⁺/CD8⁺ T cells. Furthermore, high titers of specific serum immunoglobulin G (IgG) revealed satisfactory systemic immune response against PEDV infection. In summary, our study demonstrated that oral administration of B. subtilis-RC could trigger a high level of local and systemic immune responses and would be a promising candidate vaccine against PEDV infection in piglets.

Human cathelicidin improves colonic epithelial defenses against Salmonella typhimurium by modulating bacterial invasion, TLR4 and pro-inflammatory cytokines

The intestinal mucosa contributes to frontline gut defenses by forming a barrier (physical and biochemical) and preventing the entry of pathogenic microbes. One innate role of the human colonic epithelium is to secrete cathelicidin, a peptide with broad antimicrobial and immunomodulatory functions. In this study, the effect of cathelicidin in the maintenance of epithelial integrity, Toll-like receptor recognition, bacterial invasion and initiation of inflammatory response against Salmonella typhimurium is investigated in cultured human colonic epithelium. We found exogenous human cathelicidin restores the epithelial integrity in S. typhimurium-infected colonic epithelial (T84) cells by mostly post-translational effects associated with reorganization of zonula occludens (ZO)-1 tight junction proteins. Endogenous cathelicidin prevents S. typhimurium internalization as shown in colonic epithelial cells genetically deficient in the only human cathelicidin, LL-37 (shLL-37). Moreover, supplementation of shLL-37 cells with synthetic LL-37 reduces the grade of S. typhimurium internalization in a dose-dependent manner. Mechanistically, shLL-37 cells have lower gene expression of TLR4 and pro-inflammatory cytokine IL-1β in response to S. typhimurium. Thus, human cathelicidin aids in the early colonic epithelial defenses against enteric S. typhimurium by preventing bacterial invasion and maintaining epithelial barrier integrity, likely to occur due to the production of sensing TLR4 and pro-inflammatory cytokines.

Porcine Intestinal Enteroids: a New Model for Studying Enteric Coronavirus Porcine Epidemic Diarrhea Virus Infection and the Host Innate Response

PEDV is a highly contagious enteric coronavirus that causes significant economic losses, and the lack of a good in vitro model system is a major roadblock to an in-depth understanding of PEDV pathogenesis. Here, we generated a porcine intestinal enteroid model for PEDV infection. Utilizing porcine intestinal enteroids, we demonstrated that PEDV infects multiple lineages of the intestinal epithelium and preferably infects ileal enteroids over colonoids and that enteroids prefer to respond to IFN lambda 1 over IFN-α. These events recapitulate the events that occur in vivo. This study constitutes the first use of a primary intestinal enteroid model to investigate the susceptibility of porcine enteroids to PEDV and to determine the antiviral response following infection. Our study provides important insights into the events associated with PEDV infection of the porcine intestine and provides a valuable in vitro model for studying not only PEDV but also other swine enteric viruses.

Porcine epidemic diarrhea virus (PEDV), a member of the group of alphacoronaviruses, is the pathogen of a highly contagious gastrointestinal swine disease. The elucidation of the events associated with the intestinal epithelial response to PEDV infection has been limited by the absence of good in vitro porcine intestinal models that recapitulate the multicellular complexity of the gastrointestinal tract. Here, we generated swine enteroids from the intestinal crypt stem cells of the duodenum, jejunum, or ileum and found that the generated enteroids are able to satisfactorily recapitulate the complicated intestinal epithelium in vivo and are susceptible to infection by PEDV. PEDV infected multiple types of cells, including enterocytes, stem cells, and goblet cells, and exhibited segmental infection discrepancies compared with ileal enteroids and colonoids, and this finding was verified in vivo. Moreover, the clinical isolate PEDV-JMS propagated better in ileal enteroids than the cell-adapted isolate PEDV-CV777, and PEDV infection suppressed interferon (IFN) production early during the infection course. IFN lambda elicited a potent antiviral response and inhibited PEDV in enteroids more efficiently than IFN alpha (IFN-α). Therefore, swine enteroids provide a novel in vitro model for exploring the pathogenesis of PEDV and for the in vitro study of the interplay between a host and a variety of swine enteric viruses.

IMPORTANCE PEDV is a highly contagious enteric coronavirus that causes significant economic losses, and the lack of a good in vitro model system is a major roadblock to an in-depth understanding of PEDV pathogenesis. Here, we generated a porcine intestinal enteroid model for PEDV infection. Utilizing porcine intestinal enteroids, we demonstrated that PEDV infects multiple lineages of the intestinal epithelium and preferably infects ileal enteroids over colonoids and that enteroids prefer to respond to IFN lambda 1 over IFN-α. These events recapitulate the events that occur in vivo. This study constitutes the first use of a primary intestinal enteroid model to investigate the susceptibility of porcine enteroids to PEDV and to determine the antiviral response following infection. Our study provides important insights into the events associated with PEDV infection of the porcine intestine and provides a valuable in vitro model for studying not only PEDV but also other swine enteric viruses.

Quantitative Proteomics Reveals Changes in Vero Cells in Response to Porcine Epidemic Diarrhea Virus

Outbreaks of porcine epidemic diarrhea virus (PEDV) have caused significant lethality rates in neonatal piglets, which pose a serious threat to the swine industry worldwide. Available commercial vaccines fail to protect against the emergence of high virulence of PEDV variants. Therefore, the endemic state of the PEDV infection in suckling piglets highlights the urgent need for uncovering the molecular determinants of the disease pathogenesis. In this study, stable isotope labeling by amino acids in cell culture (SILAC), combined with high-performance liquid chromatography/tandem mass spectrometry was performed to determine proteomic differences between PEDV-infected and mock-infected Vero cells at 18 h postinfection. The SILAC-based approach identified 4508 host-cell proteins, of which 120 were significantly up-regulated and 103 were significantly down-regulated at ≥95% confidence. Alterations in the expression of selected proteins were verified by Western blot. Several signaling metabolic pathways including mevalonate pathway I and the superpathway of cholesterol biosynthesis were triggered by the infection of the highly virulent strain and are linked to host innate immunity. 25-HC, an inhibitor of the mevalonate pathway, exhibited potent antiviral activity against PEDV infection. Meanwhile, the cell-cycle-related functions were significantly regulated, which may likely be responsible for the viral replication and pathogenicity of PEDV.

Oral administration of inactivated porcine epidemic diarrhea virus activate DCs in porcine Peyer's patches

BACKGROUND

Peyer's patches (PPs) can be considered as the immune site of the intestine. Within PPs, Dendritic cells (DCs) can uptake antigens from the gut lumen by extending dendrites into epithelium, and process it and then present to lymphocytes, which effectively antigen produces an immune response. Porcine epidemic diarrhea virus (PEDV) is the causative agent of porcine epidemic diarrhea (PED), an acute and highly contagious enteric viral disease. The interaction between inactivated porcine epidemic diarrhea virus and porcine monocyte-derived dendritic cells (Mo-DCs) has been reported. However, little is known about the interaction between inactivated PEDV and DCs in porcine PPs.

RESULTS

In this study, for the first time we investigated the role of DCs in porcine PPs after oral administration inactivated PEDV. Firstly, a method to isolate DCs from porcine PPs was established, in which the purity of SWC3a+/MHC-II+ DCs was more than 90%. Our findings clearly indicate that DCs in porcine PPs after oral administration of inactivated PEDV not only stimulated the proliferation of allogeneic lymphocytes, but also secreted cytokines (IL-1, IL-4). Furthermore, the number of DCs and IgA+ cells in porcine intestinal mucosal significantly increased and the levels of anti-PEDV specific IgG antibody in the serum and SIgA antibody in the feces increased after oral administration inactivated PEDV.

CONCLUSIONS

Our findings indicate that oral administration of inactivated PEDV activate DCs in porcine Peyer's patches and inactivated PEDV may be a useful and safe vaccine to trigger adaptive immunity.

Epitope selection and their placement for increased virus neutralization in a novel vaccination strategy for porcine epidemic diarrhea virus utilizing the Hepatitis B virus core antigen

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Hepatitis B core antigen (HBcAg) protein with PEDV epitopes can assemble into virus like particles.

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Epitope placement within HBcAg can affect the immunogenicity of a vaccine.

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The YSNIGVCK antigen from PEDV has a strong correlation with virus neutralization.

Porcine epidemic diarrhea virus (PEDV) is a member of the Alphacoronaviridae genus within the Coronaviridae family. It is the causative agent of porcine epidemic diarrhea, a disease that can have mortality rates as high as 100% in suckling piglets. PEDV causes severe economic loss, and has been in existence for decades. A panzootic starting in 2010 renewed interest in the development of a universal vaccine toward PEDV. This report details several design changes made to a Hepatitis B virus core antigen (HBcAg)-based recombinant vaccine strategy, and their effect in vivo. Initially, several multi-antigen vaccine candidates were able to elicit antibodies specific to three out of four B-cell epitopes inserted into the chimeric proteins. However, a lack of virus neutralization led to a redesign of the vaccines. The focus of the newly redesigned vaccines was to elicit a strong immune response to the YSNIGVCK amino acid motif from PEDV. Genetically modified new vaccine candidates were able to elicit a strong antibody (Ab) response to the YSNIGVCK epitope, which correlated with an increased ability to neutralize the CO strain of PEDV. Additionally, the location of the inserted PEDV epitopes within the vector protein was shown to affect the immune recognition toward the native HBcAg during vaccination.

Swine enteric coronavirus disease: A review of 4 years with porcine epidemic diarrhoea virus and porcine deltacoronavirus in the United States and Canada

Swine enteric coronaviruses, including porcine epidemic diarrhoea virus (PEDV) and porcine deltacoronavirus (PDCoV), have emerged and spread throughout the North American swine industry over the last four years. These diseases cause significant losses within the pork industry and within the first year after PEDV introduction, approximately 10% of the US herd died due to the disease. Similar to other enteric coronaviruses, such as transmissible gastroenteritis virus (TGEV), these emerging swine enteric coronavirus diseases (SECD) are age-dependent, with high morbidity and mortality in neonatal pigs. Since the introduction of SECD, research has focused on investigating viral pathogenesis through experimental inoculation, increasing maternal antibody for neonatal protection, understanding transmission risks through feed and transportation, and outlining the importance of biosecurity in preventing SECD introduction and spread. A survey of swine professionals conducted for this review revealed that the majority of respondents (75%) believe SECD can be eradicated and that most herds have been successful at long-term elimination of SECD after exposure (80%). However, unique properties of SECD, such as ineffective immunity through parenteral vaccination and a low oral infectious dose, play a major role in management of SECD. This review serves to describe the current knowledge of SECD and the characteristics of these viruses which provide both opportunities and challenges for long-term disease control and potential eradication from the US swine population.

Effects of porcine epidemic diarrhea virus infection on nursery pig intestinal function and barrier integrity

The pig intestinal epithelium can be compromised by pathogens leading to reduced integrity and function. Porcine epidemic diarrhea virus (PEDV), recently detected in North America, exemplifies intestinal epithelial insult. Although several studies have investigated the molecular aspects and host immune response to PEDV, there are little data on the impact of PEDV on pig intestinal physiology. The objective of this study was to investigate the longitudinal impact of PEDV on nursery pig intestinal function and integrity. Fifty recently-weaned, 5-week-old barrows and gilts (BW=9.92±0.49kg) were sorted based on body weight (BW) and sex into two treatments: 1) Control or 2) PEDV inoculated. At 2, 5, 7, and 14days post inoculation (dpi), 4 pigs per treatment were euthanized and jejunum sections collected. PEDV antigen was detected in inoculated pigs by immunohistochemistry in 50% (2/4) at dpi 2, 100% (4/4) at dpi 5, and none at later time points. PEDV-infected pigs had reduced (P<0.05) villus height and decreased transepithelial resistance compared with controls. Total acidic mucins, particularly sialomucin, were reduced in PEDV pigs at dpi 2 and then increased compared with controls at dpi 7 and 14. In addition, PEDV pigs had increased stem cell proliferation (P<0.05) and a numerical increase in DNA fragmentation compared with controls through dpi 7 which coincided with an observed return of digestive function to that of controls. Collectively, these data reveal that PEDV infection results in time-dependent changes not only in intestinal morphology but also barrier integrity and function.

Nursery pig growth performance and tissue accretion modulation due to porcine epidemic diarrhea virus or porcine deltacoronavirus challenge

Porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) are both members of the family Coronaviridae which induce clinical signs of diarrhea, dehydration, and in some circumstances, mortality. Most research has been focused on isolation, genome sequencing, pathogenicity, and virulence of these viruses, but there is little information on long-term growth performance and tissue accretion of pigs inoculated with PEDV or PDCoV. Therefore, our objective was to determine the effect of PEDV or PDCoV infection on growth performance and tissue accretion over 42 d following inoculation. A total of 75 Choice Genetics Large White Pureline barrows and gilts (BW = 10.81 ± 0.81 kg) at approximately 2 wk post-wean and naïve for PEDV and PDCoV were selected. Pigs were allotted based on BW and sex, stratified across 3 treatments with 8 pens per treatment. Treatments were: 1) Control (n = 8); 2) PEDV inoculated (n = 8); and 3) PDCoV inoculated (n = 8). On day post inoculation (dpi) 2, 5, 7, and 14 pigs were euthanized for tissue collection and analyses from these tissues are discussed elsewhere. Pen feed intake and BW were recorded on dpi 2, 5, 7, and weekly thereafter until dpi 42. On 1 designated pig per pen, initial and final body composition was determined using dual-energy X-ray absorptiometry (DXA) and tissue accretion rates were calculated over 6 wk test period. Peak PEDV infection was noted at 3 dpi compared with 4 dpi for PDCoV pigs as determined by fecal swab quantitative real-time PCR (RT-PCR). Control pigs remained negative for PEDV and PDCoV throughout the experiment. Overall, Control and PDCoV pigs did not differ in ADG, ADFI or G:F (P > 0.05). Compared to Control and PDCoV pigs, the overall 42 d ADFI was reduced in the challenged PEDV pigs (P < 0.05) by 19 and 27%, respectively. PEDV did not significantly reduce the overall ADG or G:F compared with Control and PDCoV pigs; however, the biggest reduction in ADG and ADFI for PEDV pigs was within 14 dpi compared to the Control pigs (P < 0.05). Whole body tissue accretion was altered due to PED, with fat, lean, protein, and bone mineral accretion reductions by 24, 20, 21, and 42%, respectively (P < 0.05) compared with Control pigs. Overall, nursery pig performance was greatly impacted by PEDV challenge. Surprisingly, the PDCoV challenge did not negatively influence nursery pig performance. This study provides further insight into the longitudinal impact swine enteric coronaviruses have on growing pigs.

Tight Junction Protein Occludin Is a Porcine Epidemic Diarrhea Virus Entry Factor

Porcine epidemic diarrhea virus (PEDV), the causative agent of porcine epidemic diarrhea, has caused huge economic losses in pig-producing countries. Although PEDV was long believed to replicate in the intestinal epithelium by using aminopeptidase N as a receptor, the mechanisms of PEDV infection are not fully characterized. In this study, we found that PEDV infection of epithelial cells results in disruption of the tight junctional distribution of occludin to its intracellular location. Overexpression of occludin in target cells makes them more susceptible to PEDV infection, whereas ablation of occludin expression by use of small interfering RNA (siRNA) in target cells significantly reduces their susceptibility to virus infection. However, the results observed with occludin siRNA indicate that occludin is not required for virus attachment. We conclude that occludin plays an essential role in PEDV infection at the postbinding stages. Furthermore, we observed that macropinocytosis inhibitors blocked occludin internalization and virus entry, indicating that virus entry and occludin internalization are closely coupled. However, the macropinocytosis inhibitors could not impede virus replication once the virus had entered host cells. This suggests that occludin internalization by macropinocytosis or a macropinocytosis-like process is involved in the virus entry events. Immunofluorescence confocal microscopy showed that PEDV was trapped at cellular junctional regions upon macropinocytosis inhibitor treatment, indicating that occludin may serve as a scaffold in the vicinity of virus entry. Collectively, these data show that occludin plays an essential role in PEDV infection during late entry events. Our observation may provide novel insights into PEDV infection and related pathogenesis.IMPORTANCE Tight junctions are highly specialized membrane domains whose main function is to attach adjacent cells to each other, thereby forming intercellular seals. Here we investigate, for the first time, the role of the tight junction protein occludin in PEDV infection. We observed that PEDV infection induced the internalization of occludin. By using genetic modification methods, we demonstrate that occludin plays an essential role in PEDV infection. Moreover, PEDV entry and occludin internalization seem to be closely coupled. Our findings reveal a new mechanism of PEDV infection.

Reactivity of Porcine Epidemic Diarrhea Virus Structural Proteins to Antibodies against Porcine Enteric Coronaviruses: Diagnostic Implications

The development of porcine epidemic diarrhea virus (PEDV) antibody-based assays is important for detecting infected animals, confirming previous virus exposure, and monitoring sow herd immunity. However, the potential cross-reactivity among porcine coronaviruses is a major concern for the development of pathogen-specific assays. In this study, we used serum samples (n = 792) from pigs of precisely known infection status and a multiplex fluorescent microbead-based immunoassay and/or enzyme-linked immunoassay platform to characterize the antibody response to PEDV whole-virus (WV) particles and recombinant polypeptides derived from the four PEDV structural proteins, i.e., spike (S), nucleocapsid (N), membrane (M), and envelope (E). Antibody assay cutoff values were selected to provide 100% diagnostic specificity for each target. The earliest IgG antibody response, mainly directed against S1 polypeptides, was observed at days 7 to 10 postinfection. With the exception of nonreactive protein E, we observed similar antibody ontogenies and patterns of seroconversion for S1, N, M, and WV antigens. Recombinant S1 provided the best diagnostic sensitivity, regardless of the PEDV strain, with no cross-reactivity detected against transmissible gastroenteritis virus (TGEV), porcine respiratory coronavirus (PRCV), or porcine deltacoronavirus (PDCoV) pig antisera. The WV particles showed some cross-reactivity to TGEV Miller and TGEV Purdue antisera, while N protein presented some cross-reactivity to TGEV Miller. The M protein was highly cross-reactive to TGEV and PRCV antisera. Differences in the antibody responses to specific PEDV structural proteins have important implications in the development and performance of antibody assays for the diagnosis of PEDV enteric disease.

The effect of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus challenge on growing pigs II: Intestinal integrity and function

The objective of this study was to determine if intestinal function and integrity is altered due to porcine reproductive and respiratory syndrome (PRRS) virus and porcine epidemic diarrhea (PED) virus infection in growing pigs. Forty-two gilts (16.8 ± 0.6 kg BW), naïve for PRRS and PED, were selected and randomly assigned to 1 of 4 treatments: 1) a control (CON; = 6), 2) PRRS virus challenge only (PRRS; = 12), 3) PED virus challenge only (; = 12), or 4) coinfection of PRRS + PED viruses (PRP; = 12). Treatments 2 and 4 were inoculated with a live field strain of PRRS virus on d 0 after inoculation. Treatments 3 and 4 were inoculated with PED virus on 14 d after inoculation (dpi) and all pigs were euthanized 7 d later (21 dpi). Infection with PRRS virus was determined by viremia and seroconversion. Fecal quantitative PCR was used to confirm PED virus infection. Control pigs remained PRRS and PED virus negative throughout the study. Compared with the CON, intestinal morphology was unaffected by PRRS. As expected, PED and PRP treatments resulted in duodenum, jejunum, and ileum villus atrophy compared with the CON treatment ( < 0.01). Ex vivo transepithelial electrical resistance (TER) did not differ between CON and PRRS pigs (P < 0.05) but was reduced by 40% in PED alone ( < 0.01). Interestingly, TER was increased ( < 0.01) in the PRP pigs. Active transport of glucose was increased in PRRS pigs over CON pigs ( < 0.01), whereas PED had pigs increased ( < 0.01) active glutamine transport over the CON pigs. Jejunum GLUT2 mRNA abundance and sucrase, maltase, and Na+/K+ adenosine triphosphatase activities tended to be increased in PRRS pigs compared with CON pigs ( < 0.06). The jejunum AA transporter, SLC6A14, and mucin 2 mRNA abundance tended to be increased in PED-only pigs ( < 0.10). These data suggest that PRRS infection supports a higher affinity for glucose uptake, whereas PED favors glutamine uptake. Interestingly, digestive machinery during PED challenge remained intact. Altogether, PED but not PRRS challenges alter intestinal morphology and integrity in growing pigs.

Immune evasion of porcine enteric coronaviruses and viral modulation of antiviral innate signaling

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Enteric coronaviruses have evolved to modulate the host innate immunity.

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Viral IFN antagonists have been identified and they are mostly redundant.

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For protection of intestinal epithelia from enteric viruses, type III IFN plays a major role.

Porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) are emerged and reemerging viruses in pigs, and together with transmissible gastroenteritis virus (TGEV), pose significant economic concerns to the swine industry. These viruses infect epithelial cells of the small intestine and cause watery diarrhea, dehydration, and a high mortality in neonatal piglets. Type I interferons (IFN-α/β) are major antiviral cytokines forming host innate immunity, and in turn, these enteric coronaviruses have evolved to modulate the host innate immune signaling during infection. Accumulating evidence however suggests that IFN induction and signaling in the intestinal epithelial cells differ from other epithelial cells, largely due to distinct features of the gut epithelial mucosal surface and commensal microflora, and it appears that type III interferon (IFN-λ) plays a key role to maintain the antiviral state in the gut. This review describes the recent understanding on the immune evasion strategies of porcine enteric coronaviruses and the role of different types of IFNs for intestinal antiviral innate immunity.

Porcine deltacoronavirus infection: Etiology, cell culture for virus isolation and propagation, molecular epidemiology and pathogenesis

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Porcine deltacoronavirus (PDCoV) is a novel swine enteropathogenic coronavirus.

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The etiology and molecular epidemiology of PDCoV are described.

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The cell culture for PDCoV isolation and propagation are demonstrated.

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The disease mechanisms and pathogenesis of PDCoV are reviewed.

Porcine deltacoronavirus (PDCoV) (family Coronaviridae, genus Deltacoronavirus) is a novel swine enteropathogenic coronavirus that causes acute diarrhea/vomiting, dehydration and mortality in seronegative neonatal piglets. PDCoV diarrhea was first reported in the US in early 2014, concurrently with co-circulation of porcine epidemic diarrhea virus (PEDV) (family Coronaviridae, genus Alphacoronavirus). The origin of PDCoV in pigs and also its sudden emergence or route of introduction into the US still remains unclear. In the US, since 2013–2014, the newly emerged PDCoV and PEDV have spread nationwide, causing a high number of pig deaths and significant economic impacts. The current US PDCoV strains are enteropathogenic and infect villous epithelial cells of the entire small and large intestines although the jejunum and ileum are the primary sites of infection. Similar to PEDV infections, PDCoV infections also cause acute, severe atrophic enteritis accompanied by transient viremia (viral RNA) that leads to severe diarrhea and/or vomiting, followed by dehydration as the potential cause of death in nursing piglets. At present, differential diagnosis of PDCoV, PEDV, and transmissible gastroenteritis virus (TGEV) is essential to control viral diarrheas in US swine. Cell culture-adapted US PDCoV (TC-PDCoV) strains have been isolated and propagated by us and in several other laboratories. TC-PDCoV strains will be useful to develop serologic assays and to evaluate if serial cell-culture passage attenuates TC-PDCoV as a potential vaccine candidate strain. A comprehensive understanding of the pathogenesis and epidemiology of epidemic PDCoV strains is currently needed to prevent and control the disease in affected regions and to develop an effective vaccine. This review focuses on the etiology, cell culture isolation and propagation, molecular epidemiology, disease mechanisms and pathogenesis of PDCoV infection.

Pathogenesis comparison between the United States porcine epidemic diarrhoea virus prototype and S-INDEL-variant strains in conventional neonatal piglets

At least two genetically different porcine epidemic diarrhoea virus (PEDV) strains have been identified in the USA: US PEDV prototype and S-INDEL-variant strains. The objective of this study was to compare the pathogenicity differences of the US PEDV prototype and S-INDEL-variant strains in conventional neonatal piglets under experimental infections. Fifty PEDV-negative 5-day-old pigs were divided into five groups of ten pigs each and were inoculated orogastrically with three US PEDV prototype isolates (IN19338/2013, NC35140/2013 and NC49469/2013), an S-INDEL-variant isolate (IL20697/2014), and virus-negative culture medium, respectively, with virus titres of 104 TCID50 ml- 1, 10 ml per pig. All three PEDV prototype isolates tested in this study, regardless of their phylogenetic clades, had similar pathogenicity and caused severe enteric disease in 5-day-old pigs as evidenced by clinical signs, faecal virus shedding, and gross and histopathological lesions. Compared with pigs inoculated with the three US PEDV prototype isolates, pigs inoculated with the S-INDEL-variant isolate had significantly diminished clinical signs, virus shedding in faeces, gross lesions in small intestines, caeca and colons, histopathological lesions in small intestines, and immunohistochemistry staining in ileum. However, the US PEDV prototype and the S-INDEL-variant strains induced similar viraemia levels in inoculated pigs. Whole genome sequences of the PEDV prototype and S-INDEL-variant strains were determined, but the molecular basis of virulence differences between these PEDV strains remains to be elucidated using a reverse genetics approach.