Equine Herpesvirus Type 1 Enhances Viral Replication in CD172a+ Monocytic Cells upon Adhesion to Endothelial Cells

Upregulation of torso-like protein (perforin) and granzymes B and G in non-adherent, lymphocyte-like haemocytes during a WSSV infection in shrimp

Invertebrates only have an innate immunity in which haemocytes play an important role. In our lab, 5 subpopulations of haemocytes were identified in the past by an iodixanol density gradient: hyalinocytes, granulocytes, semi-granulocytes and two subpopulations of non-phagocytic cells. For the two latter subpopulations, the haemocytes have small cytoplasm rims, do not adhere to the bottom of plastic cell-culture grade wells and present folds in the nucleus. These characteristics are similar to those of mammalian lymphocytes. Therefore, they were designated lymphocyte-like haemocytes. Although little is known about their function, we hypothesize, based on their morphology, that they may have a cytotoxic activity. First, a fast isolation technique was developed to separate the non-adherent haemocytes from the adherent haemocytes. After 60 min incubation on cell culture plates, the non-adherent haemocytes were collected. The purity reached 93% as demonstrated by flow cytometry and light microscopy upon a Hematoxylin and Eosin (H&E) staining. Cytotoxicity by lymphocytes is mediated by molecules such as perforin and granzymes and therefore, we searched for their genes in the shrimp genome. Genes coding for a torso-like protein, granzyme B and granzyme G were identified. Primers were designed and RT-PCR/RT-qPCR assays were developed. The results demonstrated that torso-like protein, granzyme B and granzyme G were mainly expressed in non-adherent haemocytes. The shrimp torso-like protein gene was most related to that of the crab torso-like protein; granzyme B gene was most related to that of mouse granzyme B and granzyme G gene was most related to that of zebrafish granzyme G. In a 72-hour in vivo WSSV infection challenge, the mRNA expression of shrimp torso-like protein, granzyme B and granzyme G in haemocytes was increasing over time, which indicated that torso-like protein, granzyme B and granzyme G of shrimp haemocytes are involved in the immune response during a viral infection. In the future, antibodies will be raised against these proteins for more in-depth functional analyses.

Comparing the immunomodulatory properties of equine BM-MSCs culture expanded in autologous platelet lysate, pooled platelet lysate, equine serum and fetal bovine serum supplemented culture media

Joint injury often leads to cartilage damage and posttraumatic inflammation, which drives continued extracellular matrix degradation culminating in osteoarthritis. Mesenchymal stem cells (MSCs) have been proposed as a biotherapeutic to modulate inflammation within the joint. However, concerns have been raised regarding the immunogenicity of MSCs cultured in traditional fetal bovine serum (FBS) containing media, and the potential of xenogenic antigens to activate the immune system causing rejection and destruction of the MSCs. Xenogen-free alternatives to FBS have been proposed to decrease MSC immunogenicity, including platelet lysate (PL) and equine serum. The objective of this study was to compare the immunomodulatory properties of BM-MSCs culture-expanded in media supplemented with autologous PL (APL), pooled PL (PPL), equine serum (ES) or FBS. We hypothesized that BM-MSCs culture expanded in media with xenogen-free supplements would exhibit superior immunomodulatory properties to those cultured in FBS containing media. Bone marrow-derived MSCs (BM-MSCs) were isolated from six horses and culture expanded in each media type. Blood was collected from each horse to isolate platelet lysate. The immunomodulatory function of the BM-MSCs was assessed via a T cell proliferation assay and through multiplex immunoassay quantification of cytokines, including IL-1β, IL-6, IL-8, IL-10, and TNFα, following preconditioning of BM-MSCs with IL-1β. The concentration of platelet-derived growth factor BB (PDGF-BB), IL-10, and transforming growth factor-β (TGF-β) in each media was measured via immunoassay. BM-MSCs cultured in ES resulted in significant suppression of T cell proliferation (p = 0.02). Cell culture supernatant from preconditioned BM-MSCs cultured in ES had significantly higher levels of IL-6. PDGF-BB was significantly higher in APL media compared to FBS media (p = 0.016), while IL-10 was significantly higher in PPL media than ES and FBS (p = 0.04). TGF-β was highest in APL media, with a significant difference in comparison to ES media (p = 0.03). In conclusion, expansion of equine BM-MSCs in ES may enhance their immunomodulatory abilities, while PL containing media may have some inherent therapeutic potential associated with higher concentrations of growth factors. Further studies are needed to elucidate which xenogen-free supplement optimizes BM-MSC performance.

Equine Herpesvirus-1 Myeloencephalopathy

Although equine herpesvirus myeloencephalopathy (EHM) is a relatively uncommon manifestation of equine herpesvirus-1 (EHV-1) infection, it can cause devastating losses during outbreaks. Antemortem diagnosis of EHM relies mainly on the molecular detection of EHV-1 in nasal secretions and blood. Management of horses affected by EHM is aimed at supportive nursing and nutritional care, at reducing central nervous system inflammation and preventing thromboembolic sequelae. Horses exhibiting sudden and severe neurologic signs consistent with a diagnosis of EHM pose a definite risk to the surrounding horse population. Consequently, early intervention to prevent the spread of infection is required.

Contribution of the immune response to the pathogenesis of equine herpesvirus-1 (EHV-1): Are there immune correlates that predict increased risk or protection from EHV-1 myeloencephalopathy?

Equine herpesvirus-1 (EHV-1) myeloencephalopathy (EHM) is a devastating consequence of EHV-1 infection that has significant economic consequences. However, clinical EHM is relatively rare and occurs in only approximately 10% of infected horses. While there is a positive correlation between the duration and magnitude of viremia and incidence of EHM, it is likely that a combination of host and viral factors determine whether EHM occurs. The identification of these factors is of high interest for the equine community and has been the topic of much research for vaccine development and to predict which horses might be most at risk for developing EHM. The aim of this review is to highlight host immunity contributions to EHM pathogenesis at different sites of EHV-1 infection to shed light on the different aspects and interdependence of the response to EHV-1 in the time course of infection.

Peptide Mediated Adhesion to Beta-Lactam Ring of Equine Mesenchymal Stem Cells: A Pilot Study

Simple Summary

In recent years, stem cell therapy has emerged as a promising potential treatment for chronic wounds in both human and veterinary medicine. Particularly, mesenchymal stem cells (MSCs) may be an attractive therapeutic tool for regenerative medicine and tissue engineering because these cells play a critical role in wound repair and tissue regeneration due to their immunosuppressive properties and multipotency. The use of biomaterials with integrin agonists could promote cell adhesion increasing tissue repair processes. This pilot study focuses on the adhesion ability of equine adult (adipose tissue) and fetal adnexa (Wharton’s jelly) derived MSCs mediated by GM18, an α4β1 integrin agonist, alone and combined with a biodegradable polymeric scaffold. Results show that a 24 h exposition to soluble GM18 affects equine MSCs adhesion ability with a donor-related variability and might suggest that WJ-MSCs more easily adhere to poly L-lactic acid (PLLA) nanofibers combined with GM18. These preliminary results need to be confirmed by further studies on the interactions between the different types of equine MSCs and GM18 incorporated PLLA scaffolds before drawing definitive conclusions on which cells and scaffolds could be successfully used for the treatment of decubitus ulcers.

Abstract

Regenerative medicine applied to skin lesions is a field in constant improvement. The use of biomaterials with integrin agonists could promote cell adhesion increasing tissue repair processes. The aim of this pilot study was to analyze the effect of an α4β1 integrin agonist on cell adhesion of equine adipose tissue (AT) and Wharton’s jelly (WJ) derived MSCs and to investigate their adhesion ability to GM18 incorporated poly L-lactic acid (PLLA) scaffolds. Adhesion assays were performed after culturing AT- and WJ-MSCs with GM18 coating or soluble GM18. Cell adhesion on GM18 containing PLLA scaffolds after 20 min co-incubation was assessed by HCS. Soluble GM18 affects the adhesion of equine AT- and WJ-MSCs, even if its effect is variable between donors. Adhesion to PLLA scaffolds containing GM18 is not significantly influenced by GM18 for AT-MSCs after 20 min or 24 h of culture and for WJ-MSCs after 20 min, but increased cell adhesion by 15% GM18 after 24 h. In conclusion, the α4β1 integrin agonist GM18 affects equine AT- and WJ-MSCs adhesion ability with a donor-related variability. These preliminary results represent a first step in the study of equine MSCs adhesion to PLLA scaffolds containing GM18, suggesting that WJ-MSCs might be more suitable than AT-MSCs. However, the results need to be confirmed by increasing the number of samples before drawing definite conclusions.

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.

The Pathogenesis and Immune Evasive Mechanisms of Equine Herpesvirus Type 1

Equine herpesvirus type 1 (EHV-1) is an alphaherpesvirus related to pseudorabies virus (PRV) and varicella-zoster virus (VZV). This virus is one of the major pathogens affecting horses worldwide. EHV-1 is responsible for respiratory disorders, abortion, neonatal foal death and equine herpes myeloencephalopathy (EHM). Over the last decade, EHV-1 has received growing attention due to the frequent outbreaks of abortions and/or EHM causing serious economical losses to the horse industry worldwide. To date, there are no effective antiviral drugs and current vaccines do not provide full protection against EHV-1-associated diseases. Therefore, there is an urgent need to gain a better understanding of the pathogenesis of EHV-1 in order to develop effective therapies. The main objective of this review is to provide state-of-the-art information on the pathogenesis of EHV-1. We also highlight recent findings on EHV-1 immune evasive strategies at the level of the upper respiratory tract, blood circulation and endothelium of target organs allowing the virus to disseminate undetected in the host. Finally, we discuss novel approaches for drug development based on our current knowledge of the pathogenesis of EHV-1.

Identification of Host Factors Associated with the Development of Equine Herpesvirus Myeloencephalopathy by Transcriptomic Analysis of Peripheral Blood Mononuclear Cells from Horses

Equine herpesvirus-1 is the cause of respiratory disease, abortion, and equine herpesvirus myeloencephalopathy (EHM) in horses worldwide. EHM affects as many as 14% of infected horses and a cell-associated viremia is thought to be central for EHM pathogenesis. While EHM is infrequent in younger horses, up to 70% of aged horses develop EHM. The aging immune system likely contributes to EHM pathogenesis; however, little is known about the host factors associated with clinical EHM. Here, we used the “old mare model” to induce EHM following EHV-1 infection. Peripheral blood mononuclear cells (PBMCs) of horses prior to infection and during viremia were collected and RNA sequencing with differential gene expression was used to compare the transcriptome of horses that did (EHM group) and did not (non-EHM group) develop clinical EHM. Interestingly, horses exhibiting EHM did not show respiratory disease, while non-EHM horses showed significant respiratory disease starting on day 2 post infection. Multiple immune pathways differed in EHM horses in response to EHV-1. These included an upregulation of IL-6 gene expression, a dysregulation of T-cell activation through AP-1 and responses skewed towards a T-helper 2 phenotype. Further, a dysregulation of coagulation and an upregulation of elements in the progesterone response were observed in EHM horses.

Transcriptomic Profiling of Equine and Viral Genes in Peripheral Blood Mononuclear Cells in Horses during Equine Herpesvirus 1 Infection

Equine herpesvirus 1 (EHV-1) affects horses worldwide and causes respiratory disease, abortions, and equine herpesvirus myeloencephalopathy (EHM). Following infection, a cell-associated viremia is established in the peripheral blood mononuclear cells (PBMCs). This viremia is essential for transport of EHV-1 to secondary infection sites where subsequent immunopathology results in diseases such as abortion or EHM. Because of the central role of PBMCs in EHV-1 pathogenesis, our goal was to establish a gene expression analysis of host and equine herpesvirus genes during EHV-1 viremia using RNA sequencing. When comparing transcriptomes of PBMCs during peak viremia to those prior to EHV-1 infection, we found 51 differentially expressed equine genes (48 upregulated and 3 downregulated). After gene ontology analysis, processes such as the interferon defense response, response to chemokines, the complement protein activation cascade, cell adhesion, and coagulation were overrepresented during viremia. Additionally, transcripts for EHV-1, EHV-2, and EHV-5 were identified in pre- and post-EHV-1-infection samples. Looking at micro RNAs (miRNAs), 278 known equine miRNAs and 855 potentially novel equine miRNAs were identified in addition to 57 and 41 potentially novel miRNAs that mapped to the EHV-2 and EHV-5 genomes, respectively. Of those, 1 EHV-5 and 4 equine miRNAs were differentially expressed in PBMCs during viremia. In conclusion, this work expands our current knowledge about the role of PBMCs during EHV-1 viremia and will inform the focus on future experiments to identify host and viral factors that contribute to clinical EHM.

Viral-Immune Cell Interactions at the Maternal-Fetal Interface in Human Pregnancy

The human decidua and placenta form a distinct environment distinguished for its promotion of immunotolerance to infiltrating semiallogeneic trophoblast cells to enable successful pregnancy. The maternal-fetal interface also successfully precludes transmission of most pathogens. This barrier function occurs in conjunction with a diverse influx of decidual immune cells including natural killer cells, macrophages and T cells. However, several viruses, among other microorganisms, manage to escape destruction by the host adaptive and innate immune system, leading to congenital infection and adverse pregnancy outcomes. In this review, we describe mechanisms of pathogenicity of two such viral pathogens, Human cytomegalovirus (HCMV) and Zika virus (ZIKV) at the maternal-fetal interface. Host decidual immune cell responses to these specific pathogens will be considered, along with their interactions with other cell types and the ways in which these immune cells may both facilitate and limit infection at different stages of pregnancy. Neither HCMV nor ZIKV naturally infect commonly used animal models [e.g., mice] which makes it challenging to understand disease pathogenesis. Here, we will highlight new approaches using placenta-on-a-chip and organoids models that are providing functional and physiologically relevant ways to study viral-host interaction at the maternal-fetal interface.

Equid Herpesvirus-1 Exploits the Extracellular Matrix of Mononuclear Cells to Ensure Transport to Target Cells

Mononuclear cells are the first line of defense against microbial infection. Yet, several viruses have evolved different mechanisms to overcome host defenses to ensure their spread. Here, we show unique mechanisms of how equid herpesvirus-1 manipulates peripheral blood mononuclear cells (PBMC) to travel further in the body. (1) "PBMC-hitching": at the initial contact, herpesviruses lurk in the extracellular matrix (ECM) of PBMC without entering the cells. The virus exploits the components of the ECM to bind, transport, and then egress to infect other cells. (2) "Intracellular delivery": transendothelial migration is a physiological mechanism where mononuclear cells can transmigrate through the endothelial cells. The virus was intangible and probably did not interfere with such a mechanism where the infected PBMC can probably deliver the virus inside the endothelium. (3) "Classical-fusion": this process is well mastered by herpesviruses due to a set of envelope glycoproteins that facilitate cell-cell fusion and virus spread.

Equine Herpesvirus Type 1 Modulates Cytokine and Chemokine Profiles of Mononuclear Cells for Efficient Dissemination to Target Organs

Equine herpesvirus type 1 (EHV-1) causes encephalomyelopathy and abortion, for which cell-associated viremia and subsequent virus transfer to and replication in endothelial cells (EC) are responsible and prerequisites. Viral and cellular molecules responsible for efficient cell-to-cell spread of EHV-1 between peripheral blood mononuclear cells (PBMC) and EC remain unclear. We have generated EHV-1 mutants lacking ORF1, ORF2, and ORF17 genes, either individually or in combination. Mutant viruses were analyzed for their replication properties in cultured equine dermal cells, PBMC infection efficiency, virus-induced changes in the PBMC proteome, and cytokine and chemokine expression profiles. ORF1, ORF2, and ORF17 are not essential for virus replication, but ORF17 deletion resulted in a significant reduction in plaque size. Deletion of ORF2 and ORF17 gene significantly reduced cell-to-cell virus transfer from virus-infected PBMC to EC. EHV-1 infection of PBMC resulted in upregulation of several pathways such as Ras signaling, oxidative phosphorylation, platelet activation and leukocyte transendothelial migration. In contrast, chemokine signaling, RNA degradation and apoptotic pathways were downregulated. Deletion of ORF1, ORF2 and ORF17 modulated chemokine signaling and MAPK pathways in infected PBMC, which may explain the impairment of virus spread between PBMC and EC. The proteomic results were further confirmed by chemokine assays, which showed that virus infection dramatically reduced the cytokine/chemokine release in infected PBMC. This study uncovers cellular proteins and pathways influenced by EHV-1 after PBMC infection and provide an important resource for EHV-1 pathogenesis. EHV-1-immunomodulatory genes could be potential targets for the development of live attenuated vaccines or therapeutics against virus infection.

Endothelial cells and angiogenesis in the horse in health and disease-A review

The cardiovascular system is the first functional organ in the embryo, and its blood vessels form a widespread conductive network within the organism. Blood vessels develop de novo, by the differentiation of endothelial progenitor cells (vasculogenesis) or by angiogenesis, which is the formation of new blood vessels from existing ones. This review presents an overview of the current knowledge on physiological and pathological angiogenesis in the horse including studies on equine endothelial cells. Principal study fields in equine angiogenesis research were identified: equine endothelial progenitor cells; equine endothelial cells and angiogenesis (heterogeneity, markers and assessment); endothelial regulatory molecules in equine angiogenesis; angiogenesis research in equine reproduction (ovary, uterus, placenta and conceptus, testis); angiogenesis research in pathological conditions (tumours, ocular pathologies, equine wound healing, musculoskeletal system and laminitis). The review also includes a table that summarizes in vitro studies on equine endothelial cells, either describing the isolation procedure or using previously isolated endothelial cells. A particular challenge of the review was that results published are fragmentary and sometimes even contradictory, raising more questions than they answer. In conclusion, angiogenesis is a major factor in several diseases frequently occurring in horses, but relatively few studies focus on angiogenesis in the horse. The challenge for the future is therefore to continue exploring new therapeutic angiogenesis strategies for horses to fill in the missing pieces of the puzzle.

Characterization of feline herpesvirus-1 deletion mutants in tissue explant cultures

Feline herpesvirus-1 (FHV-1) is the primary cause of viral respiratory and ocular disease in cats. While commercial vaccines can provide clinical protection, they do not protect from infection or prevent latency. Moreover, they are not safe for intranasal administration. Our overall objective is to develop a new mucosal vaccine against FHV-1 disease to address these shortcomings. Feline herpesvirus-1 deletion mutants of glycoprotein C (gC-), gE (gE-), US3-encoded serine/threonine protein kinase (PK-), and both gE and thymidine kinase (gE-TK-) were generated by bacterial artificial chromosome (BAC) mutagenesis. Tracheal tissue explants from eight cats were used to compare the pattern of viral infection and associated tissue damage, as well as virus spread through the basement membrane following inoculation with wild-type virus (WT), and gE-, gE-TK-, PK-, and gC- mutants. Tissues were collected at 24, 48, or 72  hours post-inoculation (hpi) followed by immunohistochemistry (IHC) for FHV-1. Histological changes were graded based on the distribution of virus infected cells and the severity of tissue damage. Inoculations with the WT virus resulted in maximal scores at 72 hpi both at a multiplicity of infection (MOI) of 1 and 0.1. Inoculation with the gE- mutant produced scores similar to scores of explants inoculated with the WT virus at 24 and 48 hpi, but scores were significantly decreased at 72 hpi. Explants inoculated with the gE-TK- mutant showed significantly decreased scores at all time points. Further, the majority of explants inoculated with the PK- mutant resulted in scores of zero at all time points, regardless of MOI. Finally, inoculation with WT resulted in significant stromal invasion below the infected epithelium, while stromal invasion was observed in less than 50 % of the samples following inoculation with gE-, gE-TK-, PK-, or gC- mutants and confined closely to the area surrounding the infected epithelium. In conclusion, the gE-TK- and PK- mutants exhibited significantly reduced virulence, tissue damage and spread to the underlying stroma, suggesting that they may be good vaccine candidates for in vivo testing.

Zika virus enhances monocyte adhesion and transmigration favoring viral dissemination to neural cells

Zika virus (ZIKV) invades and persists in the central nervous system (CNS), causing severe neurological diseases. However the virus journey, from the bloodstream to tissues through a mature endothelium, remains unclear. Here, we show that ZIKV-infected monocytes represent suitable carriers for viral dissemination to the CNS using human primary monocytes, cerebral organoids derived from embryonic stem cells, organotypic mouse cerebellar slices, a xenotypic human-zebrafish model, and human fetus brain samples. We find that ZIKV-exposed monocytes exhibit higher expression of adhesion molecules, and higher abilities to attach onto the vessel wall and transmigrate across endothelia. This phenotype is associated to enhanced monocyte-mediated ZIKV dissemination to neural cells. Together, our data show that ZIKV manipulates the monocyte adhesive properties and enhances monocyte transmigration and viral dissemination to neural cells. Monocyte transmigration may represent an important mechanism required for viral tissue invasion and persistence that could be specifically targeted for therapeutic intervention.

Zika virus (ZIKV) can infect the central nervous system, but it is not clear how it reaches the brain. Here, Ayala-Nunez et al. show in ex vivo and in vivo models that ZIKV can hitch a ride in monocytes in a Trojan Horse manner to cross the endothelium and disseminate the virus.

EHV-1 Pathogenesis: Current in vitro Models and Future Perspectives

Primary infection and pathogenesis of equine herpesvirus type 1 (EHV-1) require an intricate interaction of virus with the mucosal epithelium, mononuclear cells and the vascular endothelium. Studies on EHV-1 have been facilitated by the development of different in vitro models that recapitulate the in vivo tissue complexity. The available in vitro assays can be categorized into (i) models mimicking the epithelium-peripheral blood mononuclear cell (PBMC) interaction, which include ex vivo mucosal (nasal and vaginal) explants and equine respiratory epithelial cells (EREC) cultures; and (ii) PBMC-endothelium mimicking models, including flow chamber and contact assays. These in vitro models have proven their worth in attempts to recapitulate the in vivo architecture and complexity, produce data relevant to natural host infection, and reduce animal use due to in vivo experiments. Although horse models are still needed for certain experiments, e.g., EHV-1 myeloencephalopathy or vaccination studies, available in vitro models can be used to obtain highly valuable data on virus-host tissue interactions. Microfluidic based 3D culture system (e.g., horse-on-a-chip) could be a potential upgraded version of these in vitro models for future research.

Comparison of the Chondrogenic Differentiation Potential of Equine Synovial Membrane-Derived and Bone Marrow-Derived Mesenchymal Stem Cells

Focal cartilage injury occurs commonly and often precipitates OA. Mesenchymal stem cells (MSCs) may be useful for repairing cartilage lesions, thereby preventing joint degeneration. Although MSCs isolated from bone marrow have been shown to have chondrogenic potential, synovial membrane-derived MSCs (SM-MSCs) may have superior chondrogenic abilities due to a common progenitor cell between synovium and cartilage. The objective of this study was to directly compare the immunophenotype, proliferative capabilities, and chondrogenic potential of equine SM-MSCs and bone marrow-derived MSCs (BM-MSCs). In order to do this, MSCs were isolated from synovial membrane and bone marrow collected from 6 adult horses. Flow cytometric analysis was used to assess cell surface marker expression including CD29, CD44, CD90, CD105, CD45, CD-79α, MHCI, and MHCII. Proliferation rates and doubling time were quantified in P1 and P2 cells. Trilineage differentiation assays were performed. MSC pellets were cultured in chondrogenic induction media for 28 days. Pellets were stained with toluidine blue to assess proteoglycan deposition. Expression of the chondrogenic-related genes ACAN, COL2b, and SOX9 was quantified using qRT-PCR. The immunophenotypes of BM-MSCs and SM-MSCs were similar with both cell types being positive for expression of stem cell markers (CD29, CD44, CD90, CD105, and MHCI) and negative for exclusion markers (CD45 and CD79α). Although SM-MSCs did not express the exclusion marker, MHCII, expression of MHCII was moderate in BM-MSCs. Overall, chondrogenic differentiation was not significantly between the cell types with histologic parameters, proteoglycan content and gene expression being similar. BM-MSCs showed enhanced osteogenic differentiation compared to SM-MSCs. Synovial membrane is a feasible source of MSCs in the horse, however, superior chondrogenesis in vitro should not be expected under currently described culture conditions.

Beyond Gut Instinct: Metabolic Short-Chain Fatty Acids Moderate the Pathogenesis of Alphaherpesviruses

Short-chain fatty acids (SCFA), such as sodium butyrate (SB), sodium propionate (SPr), and sodium acetate (SAc), are metabolic end-products of the fermentation of dietary fibers. They are linked with multiple beneficial effects on the general mammalian health, based on the sophisticated interplay with the host immune response. Equine herpesvirus 1 (EHV1) is a major pathogen, which primarily replicates in the respiratory epithelium, and disseminates through the body via a cell-associated viremia in leukocytes, even in the presence of neutralizing antibodies. Infected monocytic CD172a⁺ cells and T-lymphocytes transmit EHV1 to the endothelium of the endometrium or central nervous system (CNS), causing reproductive or neurological disorders. Here, we questioned whether SCFA have a potential role in shaping the pathogenesis of EHV1 during the primary replication in the URT, during the cell-associated viremia, or at the level of the endothelium of the pregnant uterus and/or CNS. First, we demonstrated the expression of SCFA receptors, FFA2 and FFA3, within the epithelium of the equine respiratory tract, at the cell surface of immune cells, and equine endothelium. Subsequently, EHV1 replication was evaluated in the URT, in the presence or absence of SB, SPr, or SAc. In general, we demonstrated that SCFA do not affect the number of viral plaques or virus titer upon primary viral replication. Only SB and SPr were able to reduce the plaque latitudes. Similarly, pretreatment of monocytic CD172a⁺ cells and T-lymphocytes with different concentrations of SCFA did not alter the number of infected cells. When endothelial cells were treated with SB, SPr, or SAc, prior to the co-cultivation with EHV1-inoculated mononuclear cells, we observed a reduced number of adherent immune cells to the target endothelium. This was associated with a downregulation of endothelial adhesion molecules ICAM-1 and VCAM-1 in the presence of SCFA, which ultimately lead to a significant reduction of the EHV1 endothelial plaques. These results indicate that physiological concentrations of SCFA may affect the pathogenesis of EHV1, mainly at the target endothelium, in favor of the fitness of the horse. Our findings may have significant implications to develop innovative therapies, to prevent the devastating clinical outcome of EHV1 infections.

Equine Herpesvirus 1 Bridles T Lymphocytes To Reach Its Target Organs

Equine herpesvirus 1 (EHV1) is an ancestral alphaherpesvirus that is related to herpes simplex virus 1 and causes respiratory, reproductive, and neurological disorders in Equidae. EHV1 is indisputably a master at exploiting leukocytes to reach its target organs, accordingly evading the host immunity. However, the role of T lymphocytes in cell-associated viremia remains poorly understood. Here we show that activated T lymphocytes efficiently become infected and support viral replication despite the presence of protective immunity. We demonstrate a restricted expression of viral proteins on the surfaces of infected T cells, which prevents immune recognition. In addition, we indicate a hampered release of progeny, which results in the accumulation of nucleocapsids in the T cell nucleus. Upon engagement with the target endothelium, late viral proteins orchestrate viral synapse formation and viral transfer to the contact cell. Our findings have significant implications for the understanding of EHV1 pathogenesis, which is essential for developing innovative therapies to prevent the devastating clinical symptoms of infection.

Equine herpesvirus 1 (EHV1) replicates in the respiratory epithelium and disseminates through the body via a cell-associated viremia in leukocytes, despite the presence of neutralizing antibodies. “Hijacked” leukocytes, previously identified as monocytic cells and T lymphocytes, transmit EHV1 to endothelial cells of the endometrium or central nervous system, causing reproductive (abortigenic variants) or neurological (neurological variants) disorders. In the present study, we questioned the potential route of EHV1 infection of T lymphocytes and how EHV1 misuses T lymphocytes as a vehicle to reach the endothelium of the target organs in the absence or presence of immune surveillance. Viral replication was evaluated in activated and quiescent primary T lymphocytes, and the results demonstrated increased infection of activated versus quiescent, CD4⁺ versus CD8⁺, and blood- versus lymph node-derived T cells. Moreover, primarily infected respiratory epithelial cells and circulating monocytic cells efficiently transferred virions to T lymphocytes in the presence of neutralizing antibodies. Albeit T-lymphocytes express all classes of viral proteins early in infection, the expression of viral glycoproteins on their cell surface was restricted. In addition, the release of viral progeny was hampered, resulting in the accumulation of viral nucleocapsids in the T cell nucleus. During contact of infected T lymphocytes with endothelial cells, a late viral protein(s) orchestrates T cell polarization and synapse formation, followed by anterograde dynein-mediated transport and transfer of viral progeny to the engaged cell. This represents a sophisticated but efficient immune evasion strategy to allow transfer of progeny virus from T lymphocytes to adjacent target cells. These results demonstrate that T lymphocytes are susceptible to EHV1 infection and that cell-cell contact transmits infectious virus to and from T lymphocytes.

IMPORTANCE Equine herpesvirus 1 (EHV1) is an ancestral alphaherpesvirus that is related to herpes simplex virus 1 and causes respiratory, reproductive, and neurological disorders in Equidae. EHV1 is indisputably a master at exploiting leukocytes to reach its target organs, accordingly evading the host immunity. However, the role of T lymphocytes in cell-associated viremia remains poorly understood. Here we show that activated T lymphocytes efficiently become infected and support viral replication despite the presence of protective immunity. We demonstrate a restricted expression of viral proteins on the surfaces of infected T cells, which prevents immune recognition. In addition, we indicate a hampered release of progeny, which results in the accumulation of nucleocapsids in the T cell nucleus. Upon engagement with the target endothelium, late viral proteins orchestrate viral synapse formation and viral transfer to the contact cell. Our findings have significant implications for the understanding of EHV1 pathogenesis, which is essential for developing innovative therapies to prevent the devastating clinical symptoms of infection.

Exogenous Expression of Equine MHC Class I Molecules in Mice Increases Susceptibility to Equine Herpesvirus 1 Pulmonary Infection

Equine herpesvirus 1 (EHV-1) uses equine major histocompatibility complex class I (MHC class I) as an entry receptor. Exogenous expression of equine MHC class I genes in murine cell lines confers susceptibility to EHV-1 infection. To examine the in vivo role of equine MHC class I as an entry receptor for EHV-1, we generated transgenic (Tg) mice expressing equine MHC class I under the control of the CAG promoter. Equine MHC class I protein was expressed in the liver, spleen, lung, and brain of Tg mice, which was confirmed by Western blot. However, equine MHC class I antigen was only detected in bronchiolar epithelium and not in other tissues, using the immunofluorescence method employed in this study. Both Tg and wild-type (WT) mice developed pneumonia 3 days after intranasal infection with EHV-1. The bronchiolar epithelial cells of Tg mice showed more severe necrosis, compared with those in WT mice. In addition, the number of virus antigen-positive cells in the lungs was higher in Tg mice than in WT mice. These results suggest that exogenous expression of equine MHC class I renders mice more susceptible to EHV-1 infection.

Deficient humoral responses and disrupted B-cell immunity are associated with fatal SFTSV infection

Severe Fever with Thrombocytopenia Syndrome (SFTS), an emerging infectious disease caused by a novel phlebovirus, is associated with high fatality. Therapeutic interventions are lacking and disease pathogenesis is yet to be fully elucidated. The anti-viral immune response has been reported, but humoral involvement in viral pathogenesis is poorly understood. Here we show defective serological responses to SFTSV is associated with disease fatality and a combination of B-cell and T-cell impairment contribute to disruption of anti-viral immunity. The serological profile in deceased patients is characterized by absence of specific IgG to viral nucleocapsid and glycoprotein due to failure of B-cell class switching. Expansion and impairment of antibody secretion is a signature of fatal SFTSV infection. Apoptosis of monocytes in the early stage of infection diminishes antigen-presentation by dendritic cells, impedes differentiation and function of T follicular helper cells, and contributes to failure of the virus-specific humoral response.

SFTSV is a novel phlebovirus associated with high fatality, but understanding of pathogenesis is lacking. Here the authors show defective cellular immunity, deficient antibody production and defunct humoral immunity is associated with fatal infection in human cases of infection.

Production of antibody against elephant endotheliotropic herpesvirus (EEHV) unveils tissue tropisms and routes of viral transmission in EEHV-infected Asian elephants

Elephant endotheliotropic herpesvirus (EEHV) is one of the most devastating viral infectious diseases in elephants worldwide. To date, it remains unclear how elephants get infected by the virus, where the virus persists, and what mechanisms drive the pathogenesis of the disease. The present study was aimed to develop an antibody against glycoprotein B (gB) of EEHV, investigate the EEHV tissue tropisms, and provide the possible routes of EEHV transmission in Asian elephants. Samples from elephant organs that had died from EEHV1A and EEHV4 infections, peripheral blood mononuclear cells (PBMC) from EEHV4- and non-EEHV-infected calves were used in this study. The results of western immunoblotting indicated that the antibody can be used for detection of gB antigens in both EEHV1A- and EEHV4-infected samples. Immunohistochemical detection indicated that the EEHV gB antigens were distributed mainly in the epithelial cells of the salivary glands, stomach and intestines. Immunofluorescence test of PBMC for EEHV gB in the EEHV4-infected calf indicated that the virus was observed predominantly in the mononuclear phagocytic cells. The findings in the present study unveil tissue tropisms in the EEHV1A- and EEHV4-infected calves and point out that saliva and intestinal content are likely sources for virus transmission in EEHV-infected Asian elephants.

Intramuscular Immunization of Mice with the Live-Attenuated Herpes Simplex Virus 1 Vaccine Strain VC2 Expressing Equine Herpesvirus 1 (EHV-1) Glycoprotein D Generates Anti-EHV-1 Immune Responses in Mice

Vaccination remains the best option to combat equine herpesvirus 1 (EHV-1) infection, and several different strategies of vaccination have been investigated and developed over the past few decades. Herein, we report that the live-attenuated herpes simplex virus 1 (HSV-1) VC2 vaccine strain, which has been shown to be unable to enter into neurons and establish latency in mice, can be utilized as a vector for the heterologous expression of EHV-1 glycoprotein D (gD) and that the intramuscular immunization of mice results in strong antiviral humoral and cellular immune responses. The VC2-EHV-1-gD recombinant virus was constructed by inserting an EHV-1 gD expression cassette under the control of the cytomegalovirus immediate early promoter into the VC2 vector in place of the HSV-1 thymidine kinase (UL23) gene. The vaccines were introduced into mice through intramuscular injection. Vaccination with both the VC2-EHV-1-gD vaccine and the commercially available vaccine Vetera EHV^XP 1/4 (Vetera; Boehringer Ingelheim Vetmedica) resulted in the production of neutralizing antibodies, the levels of which were significantly higher in comparison to those in VC2- and mock-vaccinated animals (P < 0.01 or P < 0.001). Analysis of EHV-1-reactive IgG subtypes demonstrated that vaccination with the VC2-EHV-1-gD vaccine stimulated robust IgG1 and IgG2a antibodies after three vaccinations (P < 0.001). Interestingly, Vetera-vaccinated mice produced significantly higher levels of IgM than mice in the other groups before and after challenge (P < 0.01 or P < 0.05). Vaccination with VC2-EHV-1-gD stimulated strong cellular immune responses, characterized by the upregulation of both interferon- and tumor necrosis factor-positive CD4⁺ T cells and CD8⁺ T cells. Overall, the data suggest that the HSV-1 VC2 vaccine strain may be used as a viral vector for the vaccination of horses as well as, potentially, for the vaccination of other economically important animals.IMPORTANCE A novel virus-vectored VC2-EHV-1-gD vaccine was constructed using the live-attenuated HSV-1 VC2 vaccine strain. This vaccine stimulated strong humoral and cellular immune responses in mice, suggesting that it could protect horses against EHV-1 infection.

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.

Anti-inflammatory drugs decrease infection of brain endothelial cells with EHV-1 in vitro

BACKGROUND

Equine herpesvirus-associated myeloencephalopathy is the result of endothelial cell infection of the spinal cord vasculature with equine herpesvirus-1 (EHV-1) during cell-associated viraemia. Endothelial cell infection requires contact between infected peripheral blood mononuclear and endothelial cells. Inflammation generated during viraemia likely upregulates adhesion molecule expression on both cell types increasing contact and facilitating endothelial cell infection.

OBJECTIVES

Evaluating the role of anti-inflammatory drugs in decreasing endothelial cell infection with EHV-1.

STUDY DESIGN

In vitro assay, crossover design, multiple drug testing.

METHODS

In vitro modified infectious centre assay using immortalised carotid artery endothelial cells or primary brain endothelial cells with plaque counts per well as outcome. Cells were either anti-inflammatory drug treated or left untreated.

RESULTS

Significant reduction of plaque count when cells were treated compared with untreated cells. No dose-dependent effect when drug concentrations were increased to 10× dose. Treatment of both peripheral blood mononuclear cells (PBMC) and endothelial cells (EC) is required for significant plaque count reduction.

MAIN LIMITATIONS

In vitro study.

CONCLUSIONS

Anti-inflammatory drugs decrease infection of endothelial cells likely by reducing contact between EHV-1 infected PBMC and endothelial cells in vitro. The role of adhesion molecules in this process needs further investigation. In vitro results suggest anti-inflammatory drug therapy during EHV-1 infection and viraemia in horses could be clinically relevant.

Replication of neurovirulent equine herpesvirus type 1 (EHV-1) in CD172a+ monocytic cells

Equine herpesvirus type 1 (EHV-1) is responsible for respiratory disorders, abortion and myeloencephalopathy (EHM) in horses. Two pathotypes of EHV-1 strains are circulating in the field: neurovirulent (N) and non-neurovirulent (NN). For both strains, CD172a⁺ monocytic cells are one of the main carrier cells of EHV-1 during primary infection, allowing the virus to invade the horse's body. Recently, we showed that EHV-1 NN strains showed a restricted and delayed replication in CD172a⁺ cells. Here we characterize the in vitro replication kinetics of two EHV-1N strains in CD172a⁺ cells and investigate if the replication of these strains is similarly silenced as shown for EHV-1 NN strains. We found that EHV-1N replication was restricted to 7-8% in CD172a⁺ cells compared to 100% in control RK-13 cells. EHV-1N replication was not delayed in CD172a⁺ cells but virus production was significant lower (10^3.0 TCID₅₀/10⁵ inoculated cells) than in RK-13 cells (10^8.5 TCID₅₀/10⁵ inoculated cells). Approximately 0.04% of CD172a⁺ cells produced and transmitted infectious EHV-1 to neighbour cells compared to 65% of RK-13 cells. Unlike what we observed for the NN strain, pretreatment of CD172a⁺ cells with histone deacetylases inhibitors (HDACi) did not influence the replication of EHV-1N strains in these cells. Overall, these results show that the EHV-1 replication of N strains in CD172a⁺ cells differs from that observed for NN strains, which may contribute to their different pathogeneses in vivo.

Entry of equid herpesvirus 1 into CD172a+ monocytic cells

Equid herpesvirus 1 (EHV-1) causes respiratory disease, abortion and neurological disorders in horses. Cells from the myeloid lineage (CD172a+) are one of the main target cells of EHV-1 during primary infection. Recently, we showed that EHV-1 restricts and delays its replication in CD172a+ cells as part of an immune-evasive strategy to disseminate to target organs. Here, we hypothesize that a low efficiency of EHV-1 binding to and entry in CD172a+ cells is responsible for this restriction. Thus, we characterized EHV-1 binding and entry into CD172a+ cells, and showed that EHV-1 only bound to 15-20 % of CD172a+ cells compared with 70 % of RK-13 control cells. Enzymic removal of heparan sulphate did not reduce EHV-1 infection, suggesting that EHV-1 does not use heparan sulphate to bind and enter CD172a+ cells. In contrast, we found that treatment of cells with neuraminidase (NA) reduced infection by 85-100 % compared with untreated cells, whilst NA treatment of virus had no effect on infection. This shows that sialic acid residues present on CD172a+ cells are essential in the initiation of EHV-1 infection. We found that αVβ3 integrins are involved in the post-binding stage of CD172a+ cell infection. Using pharmacological inhibitors, we showed that EHV-1 does not enter CD172a+ cells via a clathrin- or caveolae-dependent endocytic pathway, nor by macropinocytosis, but requires cholesterol, tyrosine kinase, actin, dynamin and endosomal acidification, pointing towards a phagocytic mechanism. Overall, these results show that the narrow tropism of EHV-1 amongst CD172a+ cells is determined by the presence of specific cellular receptors.