Development and use of a polarized equine upper respiratory tract mucosal explant system to study the early phase of pathogenesis of a European strain of equine arteritis virus

The alphaherpesvirus gE/gI glycoprotein complex and proteases jointly orchestrate invasion across the host's upper respiratory epithelial barrier

Alphaherpesviruses, including herpes simplex virus type 1 (HSV-1), pseudorabies virus (PRV), and bovine herpesvirus type 1 (BoHV-1), are significant pathogens affecting humans and animals. These viruses penetrate the upper respiratory tract mucosa, yet the mechanisms facilitating this invasion are not fully understood. This study investigates the role of the gE/gI glycoprotein complex and proteases in mucosal invasion by these viruses. Using species-specific respiratory mucosal explants, we observed that the removal of extracellular calcium disrupts epithelial junction integrity, enhancing viral infection across all viruses and suggesting a common mechanism of targeting a basolaterally located receptor. PRV exhibited significantly faster replication and deeper invasion compared to HSV-1 and BoHV-1. The gE glycoprotein was consistently polarized at the basement membrane across all viruses, indicating a critical role in the process of viral entry and subsequent spread through the epithelium. In this context, "infection" refers to the virus's attachment to its cell-surface receptor, entry into the cell, and completion of the viral life cycle, culminating in the production of progeny virions. Notably, in gE/gI null mutants of PRV and HSV-1, while the infection was not abortive and the viral life cycle was completed, the infection was delayed, and the invasion into the deeper layers of the epithelium and underlying mucosa was significantly reduced. In BoHV-1 mutants, this effect was even more pronounced, with infection restricted to the apical cells, failing to progress to the basal cells. In addition, PRV and HSV-1 invasion involved serine protease activity, unlike BoHV-1, which correlates with its slower invasion pace. Notably, the protease facilitating PRV invasion was identified as a urokinase plasminogen activator (uPA), while the specific protease for HSV-1 remains unidentified. These findings highlight the critical roles of the gE/gI complex and proteases in alphaherpesvirus pathogenesis, offering potential targets for therapeutic intervention.

IMPORTANCE

Herpes simplex virus type 1 (HSV-1) infections are a worldwide issue. More than three billion people are infected with HSV-1 globally. Although most infections with HSV-1 occur subclinically, severe symptoms and complications are numerous and can be life-threatening. Complications include encephalitis and blindness. Recently, HSV-1 infections have been associated with the development of Alzheimer's Disease. To date, no effective vaccines against HSV-1 are on the market. Pseudorabies virus (PRV) and bovine herpesvirus type 1 (BoHV-1) are two alphaherpesviruses of major veterinary importance. Although efforts have been made to eradicate these viruses from livestock animals, clinical problems still occur, resulting in great economic losses for farmers. It is evident that new insights into the pathogenesis of alphaherpesviruses are needed, to develop effective treatments and novel preventive therapies.

Development of an Oral Epithelial Ex Vivo Organ Culture Model for Biocompatibility and Permeability Assessment of Biomaterials

In the present study, a customized device (Epi-ExPer) was designed and fabricated to facilitate an epithelial organ culture, allowing for controlled exposure to exogenous chemical stimuli and accommodating the evaluation of permeation of the tissue after treatment. The Epi-ExPer system was fabricated using a stereolithography (SLA)-based additive manufacturing (AM) method. Human and porcine oral epithelial mucosa tissues were inserted into the device and exposed to resinous monomers commonly released by dental restorative materials. The effect of these xenobiotics on the morphology, viability, permeability, and expression of relevant markers of the oral epithelium was evaluated. Tissue culture could be performed with the desired orientation of air-liquid interface (ALI) conditions, and exposure to xenobiotics was undertaken in a spatially guarded and reproducible manner. Among the selected monomers, HEMA and TEGDMA reduced tissue viability at high concentrations, while tissue permeability was increased by the latter. Xenobiotics affected the histological image by introducing the vacuolar degeneration of epithelial cells and increasing the expression of panCytokeratin (pCK). Epi-ExPer device offers a simple, precise, and reproducible study system to evaluate interactions of oral mucosa with external stimuli, providing a biocompatibility and permeability assessment tool aiming to an enhanced in vitro/ex vivo-to-in vivo extrapolation (IVIVE) that complies with European Union (EU) and Food and Durg Administration (FDI) policies.

The mucosal immunity in crustaceans: Inferences from other species

Crustaceans such as shrimps and crabs, hold significant ecological significance and substantial economic value within marine ecosystems. However, their susceptibility to disease outbreaks and pathogenic infections has posed major challenges to production in recent decades. As invertebrate, crustaceans primarily rely on their innate immune system for defense, lacking the adaptive immune system found in vertebrates. Mucosal immunity, acting as the frontline defense against a myriad of pathogenic microorganisms, is a crucial aspect of their immune repertoire. This review synthesizes insights from comparative immunology, highlighting parallels between mucosal immunity in vertebrates and innate immune mechanisms in invertebrates. Despite lacking classical adaptive immunity, invertebrates, including crustaceans, exhibit immune memory and rely on inherent "innate immunity factors" to combat invading pathogens. Drawing on parallels from mammalian and piscine systems, this paper meticulously explores the complex role of mucosal immunity in regulating immune responses in crustaceans. Through the extrapolation from well-studied models like mammals and fish, this review infers the potential mechanisms of mucosal immunity in crustaceans and provides insights for research on mucosal immunity in crustaceans.

Aspergillus Fumigatus Spore Proteases Alter the Respiratory Mucosa Architecture and Facilitate Equine Herpesvirus 1 Infection

Numerous Aspergillus fumigatus (Af) airborne spores are inhaled daily by humans and animals due to their ubiquitous presence. The interaction between the spores and the respiratory epithelium, as well as its impact on the epithelial barrier function, remains largely unknown. The epithelial barrier protects the respiratory epithelium against viral infections. However, it can be compromised by environmental contaminants such as pollen, thereby increasing susceptibility to respiratory viral infections, including alphaherpesvirus equine herpesvirus type 1 (EHV-1). To determine whether Af spores disrupt the epithelial integrity and enhance susceptibility to viral infections, equine respiratory mucosal ex vivo explants were pretreated with Af spore diffusate, followed by EHV-1 inoculation. Spore proteases were characterized by zymography and identified using mass spectrometry-based proteomics. Proteases of the serine protease, metalloprotease, and aspartic protease groups were identified. Morphological analysis of hematoxylin-eosin (HE)-stained sections of the explants revealed that Af spores induced the desquamation of epithelial cells and a significant increase in intercellular space at high and low concentrations, respectively. The increase in intercellular space in the epithelium caused by Af spore proteases correlated with an increase in EHV-1 infection. Together, our findings demonstrate that Af spore proteases disrupt epithelial integrity, potentially leading to increased viral infection of the respiratory epithelium.

Lung and lymph node explants to study the interaction between host cells and canine distemper virus

Canine distemper virus (CDV, family Paramyxoviridae) is a widely known fatal disease in unvaccinated dogs and wild carnivores. The virus enters via the respiratory tract and rapidly spreads to the lymphoid organs. To investigate viral entry into these tissues, a dog tissue explant model was developed for lung and lymph nodes. Canine lung explants were cultured with CDV for three days. During this time CDV antigens were visible on alveolar cells, which were CD163-positive and SLAM-positive (signaling lymphocytic activation molecule), demonstrating that they were macrophages. The lymph node explants were maintained for five days. During this time the viral replication increased progressively by each day post infection and syncytia were observed by day three, post exposure. The microscopic distribution of CDV-positive cells in the lymph nodes, including the syncytia, and co-expression of CD163 and SLAM, demonstrated that they were macrophages. These findings suggest that alveolar macrophages are the first cells in the lung to become infected during CDV infection, and lymph node explants showed similar replication rates and virus-cell interactions as seen in experimental live animals. This demonstrates the utility of canine respiratory and lymphoid explant model to evaluate cell entry and viral replication of CDV and other morbilliviruses in dogs or other susceptible carnivores.

Innate antiviral responses in porcine nasal mucosal explants inoculated with influenza A virus are comparable with responses in respiratory tissues after viral infection

Nasal mucosal explant (NEs) cultured at an air–liquid interface mimics in vivo conditions more accurately than monolayer cultures of respiratory cell lines or primary cells cultured in flat-bottom microtiter wells. NEs might be relevant for studies of host-pathogen interactions and antiviral immune responses after infection with respiratory viruses, including influenza and corona viruses.

Pigs are natural hosts for swine influenza A virus (IAV) but are also susceptible to IAV from humans, emphasizing the relevance of porcine NEs in the study of IAV infection. Therefore, we performed fundamental characterization and study of innate antiviral responses in porcine NEs using microfluidic high-throughput quantitative real-time PCR (qPCR) to generate expression profiles of host genes involved in inflammation, apoptosis, and antiviral immune responses in mock inoculated and IAV infected porcine NEs.

Handling and culturing of the explants ex vivo had a significant impact on gene expression compared to freshly harvested tissue. Upregulation (2–43 fold) of genes involved in inflammation, including IL1A and IL6, and apoptosis, including FAS and CASP3, and downregulation of genes involved in viral recognition (MDA5 (IFIH1)), interferon response (IFNA), and response to virus (OAS1, IFIT1, MX1) was observed. However, by comparing time-matched mock and virus infected NEs, transcription of viral pattern recognition receptors (RIG-I (DDX58), MDA5 (IFIH1), TLR3) and type I and III interferons (IFNB1, IL28B (IFNL3)) were upregulated 2–16 fold in IAV-infected NEs. Furthermore, several interferon-stimulated genes including MX1, MX2, OAS, OASL, CXCL10, and ISG15 was observed to increase 2–26 fold in response to IAV inoculation. NE expression levels of key genes involved in antiviral responses including IL28B (IFNL3), CXCL10, and OASL was highly comparable to expression levels found in respiratory tissues including nasal mucosa and lung after infection of pigs with the same influenza virus isolate.

Bacterial Toxins from Staphylococcus aureus and Bordetella bronchiseptica Predispose the Horse's Respiratory Tract to Equine Herpesvirus Type 1 Infection

Respiratory disease in horses is caused by a multifactorial complex of infectious agents and environmental factors. An important pathogen in horses is equine herpesvirus type 1 (EHV-1). During co-evolution with this ancient alphaherpesvirus, the horse’s respiratory tract has developed multiple antiviral barriers. However, these barriers can become compromised by environmental threats. Pollens and mycotoxins enhance mucosal susceptibility to EHV-1 by interrupting cell junctions, allowing the virus to reach its basolateral receptor. Whether bacterial toxins also play a role in this impairment has not been studied yet. Here, we evaluated the role of α-hemolysin (Hla) and adenylate cyclase (ACT), toxins derived from the facultative pathogenic bacterium Staphylococcus aureus (S. aureus) and the primary pathogen Bordetella bronchiseptica (B. bronchiseptica), respectively. Equine respiratory mucosal explants were cultured at an air–liquid interface and pretreated with these toxins, prior to EHV-1 inoculation. Morphological analysis of hematoxylin–eosin (HE)-stained sections of the explants revealed a decreased epithelial thickness upon treatment with both toxins. Additionally, the Hla toxin induced detachment of epithelial cells and a partial loss of cilia. These morphological changes were correlated with increased EHV-1 replication in the epithelium, as assessed by immunofluorescent stainings and confocal microscopy. In view of these results, we argue that the ACT and Hla toxins increase the susceptibility of the epithelium to EHV-1 by disrupting the epithelial barrier function. In conclusion, this study is the first to report that bacterial exotoxins increase the horse’s sensitivity to EHV-1 infection. Therefore, we propose that horses suffering from infection by S. aureus or B. bronchiseptica may be more susceptible to EHV-1 infection.

Replication of Equine arteritis virus is efficiently suppressed by purine and pyrimidine biosynthesis inhibitors

RNA viruses are responsible for a large variety of animal infections. Equine Arteritis Virus (EAV) is a positive single-stranded RNA virus member of the family Arteriviridae from the order Nidovirales like the Coronaviridae. EAV causes respiratory and reproductive diseases in equids. Although two vaccines are available, the vaccination coverage of the equine population is largely insufficient to prevent new EAV outbreaks around the world. In this study, we present a high-throughput in vitro assay suitable for testing candidate antiviral molecules on equine dermal cells infected by EAV. Using this assay, we identified three molecules that impair EAV infection in equine cells: the broad-spectrum antiviral and nucleoside analog ribavirin, and two compounds previously described as inhibitors of dihydroorotate dehydrogenase (DHODH), the fourth enzyme of the pyrimidine biosynthesis pathway. These molecules effectively suppressed cytopathic effects associated to EAV infection, and strongly inhibited viral replication and production of infectious particles. Since ribavirin is already approved in human and small animal, and that several DHODH inhibitors are in advanced clinical trials, our results open new perspectives for the management of EAV outbreaks.

Deoxynivalenol, but not fumonisin B1, aflatoxin B1 or diesel exhaust particles disrupt integrity of the horse's respiratory epithelium and predispose it for equine herpesvirus type 1 infection

The horse's respiratory tract daily encounters a plethora of respirable hazards including air pollutants, mycotoxins and airborne pathogens. To date, the precise effect of air pollution and mycotoxins on respiratory epithelial integrity and subsequent pathogen invasion in the horse has not been studied. Here, diesel exhaust particles (DEP) and three major mycotoxins (deoxynivalenol [DON], aflatoxin B1 [AFB1] and fumonisin B1 [FB1]) were applied to the apical surfaces of both ex vivo respiratory mucosal explants and in vitro primary equine respiratory epithelial cells (EREC) cultivated at the air-liquid interface, prior to inoculation with equine herpesvirus type 1 (EHV1). DON, but not AFB1, FB1 and DEP affected epithelial integrity in both ex vivo and in vitro systems, as demonstrated by histological changes in respiratory epithelial morphology and a drop in transepithelial electrical resistance across the EREC monolayer. Further, DON-pretreated explants showed on average 6.5 ± 4.5-fold more EHV1 plaques and produced on average 1 log₁₀ more extracellular virus particles compared to control diluent- and FB1-pretreated respiratory mucosal explants. Similarly, EHV1 infection was greatly enhanced in EREC upon pretreatment with DON. Based on our findings, we propose that inhalation of DON predisposes horses for EHV1 infection by affecting respiratory epithelial integrity.

Pollens destroy respiratory epithelial cell anchors and drive alphaherpesvirus infection

Pollens are well-known triggers of respiratory allergies and asthma. The pollen burden in today's ambient air is constantly increasing due to rising climate change and air pollution. How pollens interact with the respiratory mucosa remains largely unknown due to a lack of representative model systems. We here demonstrate how pollen proteases of Kentucky bluegrass, white birch and hazel selectively destroy integrity and anchorage of columnar respiratory epithelial cells, but not of basal cells, in both ex vivo respiratory mucosal explants and in vitro primary equine respiratory epithelial cells (EREC). In turn, this pollen protease-induced damage to respiratory epithelial cell anchorage resulted in increased infection by the host-specific and ancestral alphaherpesvirus equine herpesvirus type 1 (EHV1). Pollen proteases of all three plant species were characterized by zymography and those of white birch were fully identified for the first time as serine proteases of the subtilase family and meiotic prophase aminopeptidase 1 using mass spectrometry-based proteomics. Together, our findings demonstrate that pollen proteases selectively and irreversibly damage integrity and anchorage of columnar respiratory epithelial cells. In turn, alphaherpesviruses benefit from this partial loss-of-barrier function, resulting in increased infection of the respiratory epithelium.

Abortigenic but Not Neurotropic Equine Herpes Virus 1 Modulates the Interferon Antiviral Defense

Equine herpesvirus 1 (EHV1) is considered as a major pathogen of Equidae, causing symptoms from mild respiratory disease to late-term abortion and neurological disorders. Different EHV1 strains circulating in the field have been characterized to be of abortigenic or neurovirulent phenotype. Both variants replicate in a plaque-wise manner in the epithelium of the upper respiratory tract (URT), where the abortigenic strains induce more prominent viral plaques, compared to the neurovirulent strains. Considering the differences in replication at the URT, we hypothesized that abortigenic strains may show an increased ability to modulate the type I IFN secretion/signaling pathway, compared to strains that display the neurovirulent phenotype. Here, we analyze IFN levels induced by abortigenic and neurovirulent EHV1 using primary respiratory epithelial cells (EREC) and respiratory mucosa ex vivo explants. Similar levels of IFNα (~70 U/ml) were detected in explants inoculated with both types of EHV1 strains from 48 to 72 hpi. Second, EREC and mucosa explants were treated with recombinant equine IFNα (rEqIFNα) or Ruxolitinib (Rux), an IFN signaling inhibitor, prior to and during inoculation with abortigenic or neurovirulent EHV1. Replication of both EHV1 variants was suppressed by rEqIFNα. Further, addition of Rux increased replication in a concentration-dependent manner, indicating an IFN-susceptibility for both variants. However, in two out of three horses, at a physiological concentration of 100 U/ml of rEqIFNα, an increase in abortigenic EHV1 replication was observed compared to 10 U/ml of rEqIFNα, which was not observed for the neurovirulent strains. Moreover, in the presence of Rux, the plaque size of the abortigenic variants remained unaltered, whereas the typically smaller viral plaques induced by the neurovirulent variants became larger. Overall, our results demonstrate the importance of IFNα in the control of EHV1 replication in the URT for both abortigenic and neurovirulent variants. In addition, our findings support the speculation that abortigenic variants of EHV1 may have developed anti-IFN mechanisms that appear to be absent or less pronounced in neurovirulent EHV1 strains.

Access to a main alphaherpesvirus receptor, located basolaterally in the respiratory epithelium, is masked by intercellular junctions

The respiratory epithelium of humans and animals is frequently exposed to alphaherpesviruses, originating from either external exposure or reactivation from latency. To date, the polarity of alphaherpesvirus infection in the respiratory epithelium and the role of respiratory epithelial integrity herein has not been studied. Equine herpesvirus type 1 (EHV1), a well-known member of the alphaherpesvirus family, was used to infect equine respiratory mucosal explants and primary equine respiratory epithelial cells (EREC), grown at the air-liquid interface. EHV1 binding to and infection of mucosal explants was greatly enhanced upon destruction of the respiratory epithelium integrity with EGTA or N-acetylcysteine. EHV1 preferentially bound to and entered EREC at basolateral cell surfaces. Restriction of infection via apical inoculation was overcome by disruption of intercellular junctions. Finally, basolateral but not apical EHV1 infection of EREC was dependent on cellular N-linked glycans. Overall, our findings demonstrate that integrity of the respiratory epithelium is crucial in the host’s innate defence against primary alphaherpesvirus infections. In addition, by targeting a basolaterally located receptor in the respiratory epithelium, alphaherpesviruses have generated a strategy to efficiently escape from host defence mechanisms during reactivation from latency.

Equine Arteritis Virus Has Specific Tropism for Stromal Cells and CD8+ T and CD21+ B Lymphocytes but Not for Glandular Epithelium at the Primary Site of Persistent Infection in the Stallion Reproductive Tract

Equine arteritis virus (EAV) has a global impact on the equine industry as the causative agent of equine viral arteritis (EVA), a respiratory, systemic, and reproductive disease of equids. A distinctive feature of EAV infection is that it establishes long-term persistent infection in 10 to 70% of infected stallions (carriers). In these stallions, EAV is detectable only in the reproductive tract, and viral persistence occurs despite the presence of high serum neutralizing antibody titers. Carrier stallions constitute the natural reservoir of the virus as they continuously shed EAV in their semen. Although the accessory sex glands have been implicated as the primary sites of EAV persistence, the viral host cell tropism and whether viral replication in carrier stallions occurs in the presence or absence of host inflammatory responses remain unknown. In this study, dual immunohistochemical and immunofluorescence techniques were employed to unequivocally demonstrate that the ampulla is the main EAV tissue reservoir rather than immunologically privileged tissues (i.e., testes). Furthermore, we demonstrate that EAV has specific tropism for stromal cells (fibrocytes and possibly tissue macrophages) and CD8⁺ T and CD21⁺ B lymphocytes but not glandular epithelium. Persistent EAV infection is associated with moderate, multifocal lymphoplasmacytic ampullitis comprising clusters of B (CD21⁺) lymphocytes and significant infiltration of T (CD3⁺, CD4⁺, CD8⁺, and CD25⁺) lymphocytes, tissue macrophages, and dendritic cells (Iba-1⁺ and CD83⁺), with a small number of tissue macrophages expressing CD163 and CD204 scavenger receptors. This study suggests that EAV employs complex immune evasion mechanisms that warrant further investigation.IMPORTANCE The major challenge for the worldwide control of EAV is that this virus has the distinctive ability to establish persistent infection in the stallion's reproductive tract as a mechanism to ensure its maintenance in equid populations. Therefore, the precise identification of tissue and cellular tropism of EAV is critical for understanding the molecular basis of viral persistence and for development of improved prophylactic or treatment strategies. This study significantly enhances our understanding of the EAV carrier state in stallions by unequivocally identifying the ampullae as the primary sites of viral persistence, combined with the fact that persistence involves continuous viral replication in fibrocytes (possibly including tissue macrophages) and T and B lymphocytes in the presence of detectable inflammatory responses, suggesting the involvement of complex viral mechanisms of immune evasion. Therefore, EAV persistence provides a powerful new natural animal model to study RNA virus persistence in the male reproductive tract.

CCL2 and CCL5 driven attraction of CD172a+ monocytic cells during an equine herpesvirus type 1 (EHV-1) infection in equine nasal mucosa and the impact of two migration inhibitors, rosiglitazone (RSG) and quinacrine (QC)

Equine herpesvirus type 1 (EHV-1) causes respiratory disease, abortion and neurological disorders in horses. Besides epithelial cells, CD172a⁺ monocytic cells become infected with EHV-1 in the respiratory mucosa and transport the virus from the apical side of the epithelium to the lamina propria en route to the lymph and blood circulation. Whether CD172a⁺ monocytic cells are specifically recruited to the infection sites in order to pick up virus is unknown. In our study, equine nasal mucosa explants were inoculated with EHV-1 neurological strains 03P37 and 95P105 or the non-neurological strains 97P70 and 94P247 and the migration of monocytic cells was examined by immunofluorescence. Further, the role of monokines CCL2 and CCL5 was determined and the effect of migration inhibitors rosiglitazone (RSG) or quinacrine was analyzed. It was shown that with neurological strains but not with the non-neurological strains, CD172a⁺ cells specifically migrated towards EHV-1 infected regions and that CCL2 and CCL5 were involved. CCL2 started to be expressed in infected epithelial cells at 24 h post-incubation (hpi) and CCL5 at 48 hpi, which corresponded with the CD172a⁺ migration. RSG treatment of EHV-1-inoculated equine nasal mucosa had no effect on the virus replication in the epithelium, but decreased the migration of CD172a⁺ cells in the lamina propria. Overall, these findings bring new insights in the early pathogenesis of EHV-1 infections, illustrate differences between neurological and non-neurological strains and show the way for EHV-1 treatment.

Detection of equine arteritis virus by two chromogenic RNA in situ hybridization assays (conventional and RNAscope(®)) and assessment of their performance in tissues from aborted equine fetuses

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis, a respiratory and reproductive disease of equids. EAV infection can induce abortion in pregnant mares, fulminant bronchointerstitial pneumonia in foals, and persistent infection in stallions. Here, we developed two RNA in situ hybridization (ISH) assays (conventional and RNAscope(®) ISH) for the detection of viral RNA in formalin-fixed paraffin-embedded (FFPE) tissues and evaluated and compared their performance with nucleocapsid-specific immunohistochemistry (IHC) and virus isolation (VI; gold standard) techniques. The distribution and cellular localization of EAV RNA and antigen were similar in tissues from aborted equine fetuses. Evaluation of 80 FFPE tissues collected from 16 aborted fetuses showed that the conventional RNA ISH assay had a significantly lower sensitivity than the RNAscope(®) and IHC assays, whereas there was no difference between the latter two assays. The use of oligonucleotide probes along with a signal amplification system (RNAscope(®)) can enhance detection of EAV RNA in FFPE tissues, with sensitivity comparable to that of IHC. Most importantly, these assays provide important tools with which to investigate the mechanisms of EAV pathogenesis.

Productive replication of nephropathogenic infectious bronchitis virus in peripheral blood monocytic cells, a strategy for viral dissemination and kidney infection in chickens

In the present study, the replication kinetics of nephropathogenic (B1648) and respiratory (Massachusetts-M41) IBV strains were compared in vitro in respiratory mucosa explants and blood monocytes (KUL01⁺ cells), and in vivo in chickens to understand why some IBV strains have a kidney tropism. B1648 was replicating somewhat better than M41 in the epithelium of the respiratory mucosa explants and used more KUL01⁺ cells to penetrate the deeper layers of the respiratory tract. B1648 was productively replicating in KUL01⁺ monocytic cells in contrast with M41. In B1648 inoculated animals, 10^2.7–6.8 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8, 10 and 12 days post inoculation (dpi), 10^2.4–4.5 viral RNA copies/mL in plasma at 2, 4, 6, 8, 10 and 12 dpi and 10^1.8–4.4 viral RNA copies/10⁶ mononuclear cells in blood at 2, 4, 6 and 8 dpi. In M41 inoculated animals, 10^2.6–7.0 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8 and 10 dpi, but viral RNA was not demonstrated in plasma and mononuclear cells (except in one chicken at 6 dpi). Infectious virus was detected only in plasma and mononuclear cells of the B1648 group. At euthanasia (12 dpi), viral RNA and antigen positive cells were detected in lungs, liver, spleen and kidneys of only the B1648 group and in tracheas of both the B1648 and M41 group. In conclusion, only B1648 can easily disseminate to internal organs via a cell-free and -associated viremia with KUL01⁺ cells as important carrier cells.

Isolation and characterization of equine nasal mucosal CD172a + cells

The nasal mucosa surface is continuously confronted with a broad variety of environmental antigens, ranging from harmless agents to potentially harmful pathogens. This area is under rigorous control of professional antigen presenting cells (APCs), such as dendritic cells (DCs) and macrophages. Mucosal APCs play a crucial role in inducing primary immune responses and the establishment of an immunological memory. In the present study, a detailed characterization of CD172a(+) cells, containing the APCs residing in the equine nasal mucosa was performed for the first time. CD172a(+) cells were isolated from collagenase-treated equine nasal mucosa fragments by MACS. Expression of surface markers was determined by flow cytometry and functional analysis was done by measuring the uptake of FITC conjugated ovalbumin (FITC-OVA). Cell surface phenotype of the isolated cells was as follows: 90% CD172a(+), 30% CD1c(+), 46% CD83(+), 42% CD206(+) and 28% MHC II(+). This clearly differs from the phenotype of blood-derived monocytes: 96% CD172a(+), 4% CD1c(+), 11% CD83(+), 9% CD206(+), 72% MHC II(+) and blood monocyte derived DCs: 99% CD172a(+), 13% CD1c(+), 30% CD83(+), 51% CD206(+) and 93% MHC II(+). The CD172a(+) nasal mucosal cells were functionally able to endocytose FITC-OVA but to a lesser degree than monocyte-derived DCs. Together, these results demonstrate that the isolated CD172a(+) nasal mucosal cells resemble immature DCs in the nasal area.

Replication characteristics of porcine reproductive and respiratory syndrome virus (PRRSV) European subtype 1 (Lelystad) and subtype 3 (Lena) strains in nasal mucosa and cells of the monocytic lineage: indications for the use of new receptors of PRRSV (Lena)

Recently, it has been demonstrated that subtype 3 strains of European type porcine reproductive and respiratory syndrome virus (PRRSV) are more virulent/pathogenic than subtype 1 strains. This points to differences in the pathogenesis. In the present study, a new polarized nasal mucosa explant system was used to study the invasion of the low virulent subtype 1 PRRSV strain Lelystad (LV) and the highly virulent subtype 3 PRRSV strain Lena at the portal of entry. Different cell types of the monocytic lineage (alveolar macrophages (PAM), cultured blood monocytes and monocyte-derived dendritic cells (moDC)) were enclosed to examine replication kinetics of both strains in their putative target cells. At 0, 12, 24, 48 and 72 hours post inoculation (hpi), virus production was analyzed and the infected cells were quantified and identified. Lena replicated much more efficiently than LV in the nasal mucosa explants and to a lesser extent in PAM. Differences in replication were not found in monocytes and moDC. Confocal microscopy demonstrated that for LV, almost all viral antigen positive cells were CD163⁺Sialoadhesin (Sn)⁺, which were mainly located in the lamina propria of the respiratory mucosa. In Lena-infected nasal mucosa, CD163⁺Sn⁺, CD163⁺Sn^- and to a lesser extent CD163^-Sn^- monocytic subtypes were involved in infection. CD163⁺Sn^- cells were mostly located within or in the proximity of the epithelium. Our results show that, whereas LV replicates in a restricted subpopulation of CD163⁺Sn⁺ monocytic cells in the upper respiratory tract, Lena hijacks a broader range of subpopulations to spread within the mucosa. Replication in CD163⁺Sn^- cells suggests that an alternative entry receptor may contribute to the wider tropism of Lena.