Virulent and avirulent strains of equine arteritis virus induce different quantities of TNF-alpha and other proinflammatory cytokines in alveolar and blood-derived equine macrophages

Equine Arteritis Virus in Monocytic Cells Suppresses Differentiation and Function of Dendritic Cells

Equine viral arteritis is an infectious disease of equids caused by equine arteritis virus (EAV), an RNA virus of the family Arteriviridae. Dendritic cells (DC) are important modulators of the immune response with the ability to present antigen to naïve T cells and can be generated in vitro from monocytes (MoDC). DC are important targets for many viruses and this interaction is crucial for the establishment-or rather not-of an anti-viral immunity. Little is known of the effect EAV has on host immune cells, particularly DC. To study the interaction of eqDC with EAV in vitro, an optimized eqMoDC system was used, which was established in a previous study. MoDC were infected with strains of different genotypes and pathogenicity. Virus replication was determined through titration and qPCR. The effect of the virus on morphology, phenotype and function of cells was assessed using light microscopy, flow cytometry and in vitro assays. This study confirms that EAV replicates in monocytes and MoDC. The replication was most efficient in mature MoDC, but variable between strains. Only the virulent strain caused a significant down-regulation of certain proteins such as CD14 and CD163 on monocytes and of CD83 on mature MoDC. Functional studies conducted after infection showed that EAV inhibited the endocytic and phagocytic capacity of Mo and mature MoDC with minimal effect on immature MoDC. Infected MoDC showed a reduced ability to stimulate T cells. Ultimately, EAV replication resulted in an apoptosis-mediated cell death. Thus, EAV evades the host anti-viral immunity both by inhibition of antigen presentation early after infection and through killing infected DC during replication.

Role of Innate Immunity in Initiation and Progression of Osteoarthritis, with Emphasis on Horses

Osteoarthritis (OA) is a common condition with diverse etiologies, affecting horses, humans, and companion animals. Importantly, OA is not a single disease, but rather a disease process initiated by different events, including acute trauma, irregular or repetitive overload of articular structures, and spontaneous development with aging. Our understanding of the pathogenesis of OA is still evolving, and OA is increasingly considered a multifactorial disease in which the innate immune system plays a key role in regulating and perpetuating low-grade inflammation, resulting in sustained cartilage injury and destruction. Macrophages within the synovium and synovial fluid are considered the key regulators of immune processes in OA and are capable of both stimulating and suppressing joint inflammation, by responding to local and systemic cues. The purpose of this review is to examine the role of the innate immune system in the overall pathogenesis of OA, drawing on insights from studies in humans, animal models of OA, and from clinical and research studies in horses. This review also discusses the various therapeutic immune modulatory options currently available for managing OA and their mechanisms of action.

New mAbs facilitate quantification of secreted equine TNF-α and flow cytometric analysis in monocytes and T cells

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine, that is involved in acute inflammation and is employed as a biomarker of inflammatory diseases in several species for which reliable quantification is available. We aimed to develop suitable tools to quantify TNF-α in equine samples. We generated two new mAbs against equine TNF-α (clones 48 and 292), evaluated their specificity for this cytokine, and confirmed detection of native TNF-α in stimulated equine PBMC. The TNF-α mAbs were paired in a fluorescent bead-based assay for quantification of equine TNF-α. The TNF-α assay had a wide quantification range of 12 pg/mL - 38.4 ng/mL. In addition, TNF-α mAb 48 was used for a detailed analysis of TNF-α production in PBMC by intracellular staining and flow cytometry. TNF-α was expressed by CD14⁺ monocytes after LPS stimulation and by monocytes and lymphocytes after polyclonal stimulation with PMA and ionomycin in vitro. TNF-α expressing lymphocytes consisted mainly of CD4⁺ T cells. CD8⁺ T cells and other lymphocytes also expressed TNF-α. The new mAbs evaluated here for soluble and intracellular TNF-α will enable the detailed analysis of this important pro-inflammatory cytokine during equine immune responses and inflammatory diseases of the horse.

Consumptive coagulopathy of severe yellow fever occurs independently of hepatocellular tropism and massive hepatic injury

Fatal cases of yellow fever are preceded by the development of hemorrhagic complications. While yellow fever virus is known to infect hepatocytes, the relationship between hepatocyte infection and the development of hemorrhage is currently undefined. Here, we identified high concentrations of D-dimer in the blood of yellow fever patients, indicative of a process that involves the activation and consumption of clotting factors. We then developed a mouse model in which only transplanted human hepatocytes could be infected at high levels. By examining clotting parameters in this model, we determined that hepatocyte infection alone is insufficient to cause the activation and consumption of coagulation factors observed in severe cases of yellow fever in humans and nonhuman primates.

Yellow fever (YF) is a mosquito-transmitted viral disease that causes tens of thousands of deaths each year despite the long-standing deployment of an effective vaccine. In its most severe form, YF manifests as a hemorrhagic fever that causes severe damage to visceral organs. Although coagulopathy is a defining feature of severe YF in humans, the mechanism by which it develops remains uncertain. Hepatocytes are a major target of yellow fever virus (YFV) infection, and the coagulopathy in severe YF has long been attributed to massive hepatocyte infection and destruction that results in a defect in clotting factor synthesis. However, when we analyzed blood from Brazilian patients with severe YF, we found high concentrations of plasma D-dimer, a fibrin split product, suggestive of a concurrent consumptive process. To define the relationship between coagulopathy and hepatocellular tropism, we compared infection and disease in Fah^−/−, Rag2^−/−, and Il2rɣ^−/− mice engrafted with human hepatocytes (hFRG mice) and rhesus macaques using a highly pathogenic African YFV strain. YFV infection of macaques and hFRG mice caused substantial hepatocyte infection, liver damage, and coagulopathy as defined by virological, clinical, and pathological criteria. However, only macaques developed a consumptive coagulopathy whereas YFV-infected hFRG mice did not. Thus, infection of cell types other than hepatocytes likely contributes to the consumptive coagulopathy associated with severe YF in primates and humans. These findings expand our understanding of viral hemorrhagic disease and associated coagulopathy and suggest directions for clinical management of severe YF cases.

The equine mononuclear phagocyte system: The relevance of the horse as a model for understanding human innate immunity

The mononuclear phagocyte system (MPS) is a family of cells of related function that includes bone marrow progenitors, blood monocytes and resident tissue macrophages. Macrophages are effector cells in both innate and acquired immunity. They are a major resident cell population in every organ and their numbers increase in response to proinflammatory stimuli. Their function is highly regulated by a wide range of agonists, including lymphokines, cytokines and products of microorganisms. Macrophage biology has been studied most extensively in mice, yet direct comparisons of rodent and human macrophages have revealed many functional differences. In this review, we provide an overview of the equine MPS, describing the variation in the function and phenotype of macrophages depending on their location and the similarities and differences between the rodent, human and equine immune response. We discuss the use of the horse as a large animal model in which to study macrophage biology and pathological processes shared with humans. Finally, following the recent update to the horse genome, facilitating further comparative analysis of regulated gene expression between the species, we highlight the importance of future transcriptomic macrophage studies in the horse, the findings of which may also be applicable to human as well as veterinary research.

Reproductive effects of arteriviruses: equine arteritis virus and porcine reproductive and respiratory syndrome virus infections

Equine arteritis virus (EAV) and porcine reproductive and respiratory syndrome virus (PRRSV) are the most economically important members of the family Arteriviridae. EAV and PRRSV cause reproductive and respiratory disease in equids and swine, respectively and constitute a significant economic burden to equine and swine industries around the world. Furthermore, they both cause abortion in pregnant animals and establish persistent infection in their natural hosts, which fosters viral shedding in semen leading to sexual transmission. The primary focus of this article is to provide an update on the effects of these two viruses on the reproductive tract of their natural hosts and provide a comparative analysis of clinical signs, virus-host interactions, mechanisms of viral pathogenesis and viral persistence.

Antibody-dependent enhancement of serotype II feline enteric coronavirus infection in primary feline monocytes

Feline coronavirus (FCoV) has been classified into two biotypes: avirulent feline coronavirus (feline enteric coronavirus: FECV) and virulent feline coronavirus (feline infectious peritonitis virus: FIPV). In FIPV infection, antibody-dependent enhancement (ADE) has been reported and was shown to be associated with severe clinical disease. On the other hand, the potential role of ADE in FECV infection has not been examined. In this study, using laboratory strains of serotype II FIPV WSU 79-1146 (FIPV 79-1146) and serotype II FECV WSU 79-1683 (FECV 79-1683), we investigated the relationship between ADE and induction of inflammatory cytokines, which are pathogenesis-related factors, for each strain. As with ADE of FIPV 79-1146 infection, a monoclonal antibody against the spike protein of FCoV (mAb 6-4-2) enhanced FECV 79-1683 replication in U937 cells and primary feline monocytes. However, the ADE activity of FECV 79-1683 was lower than that of FIPV 79-1146. Moreover, mRNA levels of inflammatory cytokines (TNF-α, IL-1β, and IL-6) significantly increased with ADE of FIPV 79-1146 infection in primary feline monocytes, but FECV 79-1683 did not demonstrate an increase in these levels. In conclusion, infection of monocytes by FECV was enhanced by antibodies, but the efficiency of infection was lower than that of FIPV.

Modulation of innate immune signaling by nonstructural protein 1 (nsp1) in the family Arteriviridae

Arteriviruses infect immune cells and may cause persistence in infected hosts. Inefficient induction of pro-inflammatory cytokines and type I IFNs are observed during infection of this group of viruses, suggesting that they may have evolved to escape the host immune surveillance for efficient survival. Recent studies have identified viral proteins regulating the innate immune signaling, and among these, nsp1 (nonstructural protein 1) is the most potent IFN antagonist. For porcine reproductive and respiratory syndrome virus (PRRSV), individual subunits (nsp1α and nsp1β) of nsp1 suppress type I IFN production. In particular, PRRSV-nsp1α degrades CREB (cyclic AMP responsive element binding)-binding protein (CBP), a key component of the IFN enhanceosome, whereas PRRSV-nsp1β degrades karyopherin-α1 which is known to mediate the nuclear import of ISGF3 (interferon-stimulated gene factor 3). All individual subunits of nsp1 of PRRSV, equine arteritis virus (EAV), lactate dehydrogenase-elevating virus (LDV), and simian hemorrhagic fever virus (SHFV) appear to contain IFN suppressive activities. As with PRRSV-nsp1α, CBP degradation is evident by LDV-nsp1α and partly by SHFV-nsp1γ. This review summarizes the biogenesis and the role of individual subunits of nsp1 of arteriviruses for innate immune modulation.

Differential responses of disease-resistant and disease-susceptible primate macrophages and myeloid dendritic cells to simian hemorrhagic fever virus infection

Simian hemorrhagic fever virus (SHFV) causes a fatal hemorrhagic fever in macaques but an asymptomatic, persistent infection in baboons. To investigate factors contributing to this differential infection outcome, the targets of SHFV infection, macrophages (MΦs) and myeloid dendritic cells (mDCs), were differentiated from macaque and baboon peripheral blood monocytes and used to compare viral replication and cell responses. SHFV replicated in >90% of macaque MΦs but in only ∼10% of baboon MΦs. Although SHFV infected ∼50% of macaque and baboon mDCs, virus replication was efficient in macaque but not in baboon mDCs. Both types of macaque cultures produced higher virus yields than baboon cultures. A more efficient type I interferon response and the production of proinflammatory cytokines, including interleukin-1β (IL-1β), IL-6, IL-12/23(p40), tumor necrosis factor alpha (TNF-α), and macrophage inflammatory protein 1α (MIP-1α), in response to SHFV infection were observed in macaque but not baboon cultures, suggesting less efficient counteraction of these responses by viral proteins in macaque cells. Baboon cultures produced higher levels of IL-10 than macaque cultures both prior to and after SHFV infection. In baboon but not macaque cell cultures, SHFV infection upregulated IL-10R1, a subunit of the IL-10 receptor (IL-10R), and also SOCS3, a negative regulator of proinflammatory cytokine production. Incubation of macaque cultures with human IL-10 before and/or after SHFV infection decreased production of IL-6, IL-1β, and MIP-1α but not TNF-α, suggesting a role for IL-10 in suppressing SHFV-induced proinflammatory cytokine production in macaques.

Equine arteritis virus

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis (EVA), a respiratory and reproductive disease of equids. There has been significant recent progress in understanding the molecular biology of EAV and the pathogenesis of its infection in horses. In particular, the use of contemporary genomic techniques, along with the development and reverse genetic manipulation of infectious cDNA clones of several strains of EAV, has generated significant novel information regarding the basic molecular biology of the virus. Therefore, the objective of this review is to summarize current understanding of EAV virion architecture, replication, evolution, molecular epidemiology and genetic variation, pathogenesis including the influence of host genetics on disease susceptibility, host immune response, and potential vaccination and treatment strategies.

Arterivirus molecular biology and pathogenesis

Arteriviruses are positive-stranded RNA viruses that infect mammals. They can cause persistent or asymptomatic infections, but also acute disease associated with a respiratory syndrome, abortion or lethal haemorrhagic fever. During the past two decades, porcine reproductive and respiratory syndrome virus (PRRSV) and, to a lesser extent, equine arteritis virus (EAV) have attracted attention as veterinary pathogens with significant economic impact. Particularly noteworthy were the 'porcine high fever disease' outbreaks in South-East Asia and the emergence of new virulent PRRSV strains in the USA. Recently, the family was expanded with several previously unknown arteriviruses isolated from different African monkey species. At the molecular level, arteriviruses share an intriguing but distant evolutionary relationship with coronaviruses and other members of the order Nidovirales. Nevertheless, several of their characteristics are unique, including virion composition and structure, and the conservation of only a subset of the replicase domains encountered in nidoviruses with larger genomes. During the past 15 years, the advent of reverse genetics systems for EAV and PRRSV has changed and accelerated the structure-function analysis of arterivirus RNA and protein sequences. These systems now also facilitate studies into host immune responses and arterivirus immune evasion and pathogenesis. In this review, we have summarized recent advances in the areas of arterivirus genome expression, RNA and protein functions, virion architecture, virus-host interactions, immunity, and pathogenesis. We have also briefly reviewed the impact of these advances on disease management, the engineering of novel candidate live vaccines and the diagnosis of arterivirus infection.

The equine alveolar macrophage: functional and phenotypic comparisons with peritoneal macrophages

Alveolar macrophages (AMs) constitute the first line of defence in the lung of all species, playing a crucial role in the regulation of immune responses to inhaled pathogens. A detailed understanding of the function and phenotype of AMs is a necessary pre-requisite to both elucidating their role in preventing opportunistic bacterial colonisation of the lower respiratory tract and developing appropriate preventative strategies. The purpose of the study was to characterise this important innate immune cell at the tissue level by making functional and phenotypic comparisons with peritoneal macrophages (PMs). We hypothesised that the tissue of origin determines a unique phenotype of AMs, which may constitute an appropriate therapeutic target for certain equine respiratory diseases. Macrophages isolated from the lung and the peritoneal cavity of 9 horses were stimulated with various toll like receptor (TLR) ligands and the production of nitrite, tumour necrosis factor alpha (TNFα), interleukin (IL) 10 and indoleamine 2,3-dioxygenase (IDO) were measured by the Griess reaction and enzyme linked immunosorbent assay (ELISA) and/or quantitative polymerase chain reaction, respectively. Cells were also compared on the basis of phagocytic-capacity and the expression of several cell surface markers. AMs, but not PMs, demonstrated increased TNFα release following stimulation with LPS, polyinosinic polycytidylic acid (Poly IC) and heat-killed Salmonella typhinurium and increased TNFα and IDO mRNA expression when stimulated with LPS. AMs showed high expression of the specific macrophage markers cluster of differentiation (CD) 14, CD163 and TLR4, whereas PMs showed high expression of TLR4 only. AMs, but not PMs, demonstrated efficient phagocytic activity. Our results demonstrate that AMs are more active than PMs when stimulated with various pro-inflammatory ligands, thus supporting the importance of the local microenvironment in the activation status of the macrophage. This information provides a valuable knowledge base on which to improve our understanding of the role of macrophages and their microenvironment in equine innate immunity.

Recent progress in studies of arterivirus- and coronavirus-host interactions

Animal coronaviruses, such as infectious bronchitis virus (IBV), and arteriviruses, such as porcine reproductive and respiratory syndrome virus (PRRSV), are able to manifest highly contagious infections in their specific native hosts, thereby arising in critical economic damage to animal industries. This review discusses recent progress in studies of virus-host interactions during animal and human coronavirus and arterivirus infections, with emphasis on IBV-host cell interactions. These interactions may be directly involved in viral replication or lead to the alteration of certain signaling pathways, such as cell stress response and innate immunity, to facilitate viral replication and pathogenesis.

Complex interactions between the major and minor envelope proteins of equine arteritis virus determine its tropism for equine CD3+ T lymphocytes and CD14+ monocytes

Extensive cell culture passage of the virulent Bucyrus (VB) strain of equine arteritis virus (EAV) to produce the modified live virus (MLV) vaccine strain has altered its tropism for equine CD3(+) T lymphocytes and CD14(+) monocytes. The VB strain primarily infects CD14(+) monocytes and a small subpopulation of CD3(+) T lymphocytes (predominantly CD4(+) T lymphocytes), as determined by dual-color flow cytometry. In contrast, the MLV vaccine strain has a significantly reduced ability to infect CD14(+) monocytes and has lost its capability to infect CD3(+) T lymphocytes. Using a panel of five recombinant chimeric viruses, we demonstrated that interactions among the GP2, GP3, GP4, GP5, and M envelope proteins play a major role in determining the CD14(+) monocyte tropism while the tropism for CD3(+) T lymphocytes is determined by the GP2, GP4, GP5, and M envelope proteins but not the GP3 protein. The data clearly suggest that there are intricate interactions among these envelope proteins that affect the binding of EAV to different cell receptors on CD3(+) T lymphocytes and CD14(+) monocytes. This study shows, for the first time, that CD3(+) T lymphocytes may play an important role in the pathogenesis of equine viral arteritis when horses are infected with the virulent strains of EAV.

Equine viral arteritis: current status and prevention

Recently, there has been increased interest in equine viral arteritis (EVA) among veterinarians and horse owners. Outbreaks of the disease were identified initially in New Mexico, USA in 2006, and in the Normandy region of France in the summer of 2007. Both occurrences were associated with AI of cool-shipped semen. Each was linked to respiratory illness, neonatal death, abortion, development of carrier stallions, and cancellation of equestrian events. In light of the increased interest, this paper will present a brief case history, followed by a review addressing common concerns regarding EVA, current status, and control and prevention strategies, including vaccination, and recommended bio-security measures.

Disease transmission in horses

Bacterial, viral and protozoal infections may cause severe reproductive losses. The present paper reviews the risk factors, clinical signs and preventive measures for the most important venereal or potential sexually transmitted diseases in horses. The stallion and use of semen for artificial insemination represent major risk factors for the transmission of bacterial contaminants of the penis, including Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa and Klebsiella pneumoniae, known to cause endometritis and infertility in the mare. The role of the stallion in disease transmission is also due to the non-clinical manifestation of diseases such as contagious equine metritis and equine viral arteritis. Dourine has been eradicated from many countries, but continues to be a problem in other areas of the globe. Strategies for the prevention of introduction and transmission of diseases in breeding operation are discussed.

Evaluation of cytokine production by equine alveolar macrophages exposed to lipopolysaccharide, Aspergillus fumigatus, and a suspension of hay dust

OBJECTIVE

To evaluate cytokine production by equine alveolar macrophages after exposure to lipopolysaccharide (LPS), Aspergillus fumigatus, and hay dust, and determine the effect of clenbuterol on the cytokine response.

ANIMALS

6 horses.

PROCEDURE

Alveolar macrophages were exposed to PBS solution (negative control), LPS, hyphae and conidia of Aspergillus fumigatus (AF), or a suspension of hay dust (HDS) and incubated for 24 hours at 37 degrees C. Concentrations of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta were measured in the supernatant. The procedure was repeated with cells that were concurrently incubated with 0.5 microM clenbuterol.

RESULTS

Exposure to HDS and AF significantly increased production of TNF-alpha by equine alveolar macrophages. The increase in TNF-alpha produced in response to HDS and AF was 5 and 7 times as great, respectively, as the increase measured in response to LPS. The concentration of IL-1beta in the supernatant was significantly increased after exposure of cells to AF. Clenbuterol was effective at inhibiting TNF-alpha production by cells exposed to LPS, HDS, or AF.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased production of TNF-alpha and IL-1 indicated that the pro-inflammatory cytokines produced by alveolar macrophages in response to allergens may play a role in recurrent airway obstruction (RAO) in horses. Equine alveolar macrophages are not only a primary pulmonary defense mechanism but may also influence the pathogenesis of equine RAO. The beta2-adrenoceptor agonist clenbuterol, a drug that is commonly used for treatment of equine RAO, promotes immediate bronchodilation and may also contribute to downward modulation of the inflammatory response.

Equine viral arteritis

EVA is an important if uncommon disease of horses. Potential economic losses attributable to EVA include direct losses from abortion, pneumonia in neonates, and febrile disease in performance horses. Indirect losses are those associated with national and international trade/animal movement regulations, particularly those pertaining to persistently infected carrier stallions and their semen. However, EAV infection and EVA are readily prevented through serological and virological screening of horses, coupled with sound management practices that include appropriate quarantine and strategic vaccination.

Rho-kinase (ROCK-1 and ROCK-2) upregulation in oleic acid-induced lung injury and its restoration by Y-27632

The possible contribution of Rho/Rho-kinase signalling in oleic acid (100 mg kg-1, i.v., for 4 h)-induced lung injury was investigated in rats. Furthermore, the possible protective effect of the administration of a Rho-kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632, 0.5-5 mg kg-1, i.v., 15 min before the administration of oleic acid), was also examined. Western blot analysis as well as histopathological examination revealed that Rho-kinase (ROCK-1 and ROCK-2) was upregulated in lungs obtained from oleic acid-administrated rats. In addition, the markers of oxidative and nitrosative stress, i.e., malondialdehyde, myeloperoxidase, 3-nitro-L-tyrosine and nitrite/nitrate, in serum and lung tissue were also increased in the injury group. Treatment of rats with 5 mg kg-1 Y-27632 reversed the oleic acid-induced lung damage, which was demonstrated by histopathological assessment and confirmed in Western blot experiments: ROCK-blots were more intense in the oleic acid group than in control and Y-27632 treatment reversed ROCK upregulation. In addition, malondialdehyde, myeloperoxidase, 3-nitro-L-tyrosine and nitrite/nitrate were also normalized after the administration of Y-27632 (0.5 mg kg-1 and 5 mg kg-1). These findings suggest that ROCK-1 and ROCK-2 are involved in oleic acid-induced lung damage in rats, and that inhibition of this enzyme by Y-27632 may have a protective effect against such damage. Consequently, Rho kinase inhibitors may be potential therapeutic agents in the treatment of acute respiratory distress syndrome (ARDS).

The immune response to equine arteritis virus: potential lessons for other arteriviruses

The members of the family Arteriviridae, genus Arterivirus, include equine arteritis virus (EAV), porcine reproductive and respiratory syndrome virus (PRRSV), lactate dehydrogenase-elevating virus (LDV) of mice, and simian hemorrhagic fever virus (SHFV). PRRSV is the newest member of the family (first isolated in North America and Europe in the early 1990s), whereas the other three viruses were recognized earlier (EAV in 1953, LDV in 1960, and SHFV in 1964). Although arterivirus infections are strictly species-specific, the causative agents share many biological and molecular properties, including their virion morphology, replication strategy, unique properties of their structural proteins, and their ability to establish distinctive persistent infections in their natural hosts. The arteriviruses are each antigenically distinct and cause different disease syndromes in their natural hosts. Similarly, the mechanism(s) responsible for the prolonged and/or persistent infections that characterize infections with each arterivirus in their natural hosts are remarkably different. The objective of this review is to compare and contrast the immune response to EAV with that to the other three arteriviruses, and emphasize the potential relevance of apparent similarities and differences in the neutralization characteristics of each virus.