Characterization of an equine macrophage cell line: application to studies of EIAV infection

Different expression patterns of DNA methyltransferases during horse testis development

DNA methyltransferases (DNMTs) are important epigenetic modification during spermatogenesis. To further evaluate the pattern of DNMTs in horse testes during development, we investigated the expression and localization of DNMT1, DNMT3a and DNMT3b at different time points. The qRT-PCR results showed that DNMT1 expression was maintained in testes tissue from 6-month-old (0.5y) to 2-year-old (2y) of age and decreased after 3-year-old (3y) (P < 0.01). The expression levels of DNMT3a and DNMT3b peaked in testes tissue at 3y (P < 0.01). At 4-year-old (4y), the expression of DNMT3a and DNMT3b was decreased and became similar to that at 0.5y. Immunofluorescence of DNMT1, DNMT3a and DNMT3b on testis samples confirmed the differential expression and localization of these three DNA methylation transferases during horse development. Further molecular biological studies are needed to understand the implications of the expression patterns of these DNMTs in horse testes.

Fecal extract from obese horses induces an inflammatory response by murine macrophages in vitro

OBJECTIVE

To compare the inflammatory response of murine macrophages exposed to the enteric microbiome of obese horses versus nonobese horses.

SAMPLE

Fecal samples from 12 obese horses (body condition score ≥ 7/9) and 12 nonobese horses (body condition score 4 to 5/9) with similar dietary management.

PROCEDURES

Fecal supernatant was prepared from frozen fecal samples. RAW 264.7 macrophage cells were exposed to the fecal extract. Inflammatory cytokine (interleukin-1β, tumor necrosis factor-α, and interleukin-6) gene expression was quantified via real-time quantitative reverse transcription PCR assay, and cytokine concentration was quantified via ELISA. Lipopolysaccharide was evaluated in fecal extract via chromo-limulus amoebocyte lysate assay.

RESULTS

Compared with fecal extracts from nonobese horses, fecal extracts from obese horses presented higher concentrations of lipopolysaccharide and induced a heightened expression of the proinflammatory cytokines interleukin-1β, tumor necrosis factor-α, and interleukin-6 from macrophages.

CLINICAL RELEVANCE

The increased levels of inflammatory markers induced in murine macrophages by the microbiome of obese horses in vitro suggested important differences in the enteric microbial composition of these horses, compared with nonobese horses. Overall, this study showed that the microbiome may play a role in mediating an inflammatory response within the gastrointestinal tract of obese horses. Mechanisms of obesity in the horse have not been fully elucidated. Improved understanding of the pathophysiology of disease will guide future research into potential diagnostic and therapeutic interventions for equine obesity.

Immunohistochemical study of morphology and distribution of CD163+ve macrophages in the normal adult equine gastrointestinal tract

Intestinal macrophages are the largest group of mononuclear phagocytes in the body and play a role in intestinal innate immunity, neuroimmune interactions and maintaining intestinal homeostasis. Conversely, they also are implicated in numerous pathologies of the gastrointestinal tract, such as postoperative ileus and inflammatory bowel disease. As a result, macrophages could be potential therapeutic targets. To date, there are limited studies on the morphology and distribution of macrophages in the equine gastrointestinal tract (GIT). The aim of this study was to identify the location and abundance of resident macrophages in the equine GIT using CD163 as an immunohistochemical marker. Tissue samples were obtained post-mortem from 14 sites along the gastrointestinal tracts of 10 horses free from gastrointestinal disease; sample sites extended from the stomach to the small colon. CD163^+ve cells were present in all regions of the equine GIT from stomach to small colon. CD163^+ve cells were also identified in all tissue layers of the intestinal wall, namely, mucosa, submucosa, muscularis externa (ME), myenteric plexus and serosa. Consistent with a proposed function in regulation of intestinal motility, CD163^+ve cells were regularly distributed within the ME, with accumulations closely associated with the myenteric plexus and effector cells such as neurons and the interstitial cells of Cajal (ICC).

In vitro effects of poly(ADP-ribose) polymerase inhibitors on the production of tumor necrosis factor-α by interferon- γ - and lipopolysaccharide-stimulated peripheral blood mononuclear cells of horses

OBJECTIVE

To evaluate effects of poly(ADP-ribose) polymerase-1 (PARP1) inhibitors on the production of tumor necrosis factor-α (TNF-α) by interferon-γ (IFN-γ)- and lipopolysaccharide (LPS)-stimulated peripheral blood mononuclear cells (PBMCs) of horses as an in vitro model of inflammation in horses.

SAMPLE

1,440 samples of PBMCs from 6 healthy research horses.

PROCEDURES

From heparinized whole blood samples, PBMC cultures were obtained. An initial dose-response trial on 48 PBMC samples from 2 horses (24 samples each) was used to determine concentrations of IFN-γ and LPS for use as low- and high-level stimulation concentrations. Seventy-two PBMC samples from 6 horses were assigned equally to 1 of 4 PARP1 inhibition categories: no PARP1 inhibitor (PARP1 inhibition control); 2-((R)-2-methylpyrrolidin-2-yl)-1H-benzimidazole-4-carbozamide dihydrochloride (ABT888);4-(3-(1-(cyclopropanecarbonyl)piperazine-4-carbonyl)-4-fluorobenzyl)phthalazin-1(2H)-one (AZD2281); or N-(6-oxo-5,6-dihydrophenanthridin-2-yl) -N,N-dimethylacetamide hydrochloride (PJ34). Samples of PBMCs from each horse and each PARP1 inhibition category were then assigned to 1 of 3 levels of IFN-γ and LPS stimulation: none (control), low stimulation, or high stimulation. After a 24-hour incubation period, a TNF-α ELISA was used to measure TNF-α concentration in the supernatant. Results were compared across treatments and for each horse. Data were analyzed with repeated-measures ANOVA.

RESULTS

Median TNF-α concentration was significantly lower for PJ34-treated, high-level stimulated PBMCs than for PARP1 inhibition control, high-level stimulated PBMCs; however, no other meaningful differences in TNF-α concentration were detected among the inhibition and stimulation combinations.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that PJ34 PARP1 inhibition may reduce TNF-α production in horses, a potential benefit in reducing inflammation and endotoxin-induced damage in horses.

A comprehensive analysis of e-CAS cell line reveals they are mouse macrophages

The 3Rs principles (Replacement, Reduction and Refinement) are focused on finding alternatives to the use of animals in research. In this regard, cell lines are popular and useful tools for the replacement of primary cells in in vitro studies. However, around 15–30% of cell lines used in research have been misidentified or cross-contaminated generating concerns about the results obtained from experiments that use them. Here we described how old aliquots of an equine macrophage cell line (e-CAS) stored at the Animal Health Trust did not contain equine cells but macrophages of murine origin (m-CAS).

[Mouse embryonic stem cells - a new cellular system for studying the equine infectious anemia virus in vitro and in vivo]

The complexity of the pathogenesis and insufficient knowledge about the slow retroviral infections, which include equine infectious anemia, necessitates finding an adequate laboratory model for the study of the infection process and immunogenesis to create means of prevention and treatment of diseases. Data about strains and cellular tropism of the virus are discussed. It was shown that mouse embryonic stem cells (ESCS) exhibited unique properties and characteristics. In contrast to fibroblasts and other cell types, these cells can be considered as a new cell system for studying EIAV in vitro and in vivo. Under differentiation-inducing conditions they are able to reproduce in vitro embryogenesis cells and form cells of three germ layers. Differentiation of mouse ESCs in the direction of hematopoiesis could contribute new knowledge and understanding of viral tropism EIAV in vitro. ESC can be returned back to the early pre-implantation embryo. Once in the germ cell environment, they participate in the formation of tissues and organs of the developing fetus. Thus, the adaptation of the mouse ESC to the equine EIAV through genetic transformation makes it possible to get closer to the creation of a laboratory model for the study of the in vivo immune response in the lentiviral infection.

The molecular basis for recognition of bacterial ligands at equine TLR2, TLR1 and TLR6

TLR2 recognises bacterial lipopeptides and lipoteichoic acid, and forms heterodimers with TLR1 or TLR6. TLR2 is relatively well characterised in mice and humans, with published crystal structures of human TLR2/1/Pam3CSK4 and murine TLR2/6/Pam2CSK4. Equine TLR4 is activated by a different panel of ligands to human and murine TLR4, but less is known about species differences at TLR2. We therefore cloned equine TLR2, TLR1 and TLR6, which showed over 80% sequence identity with these receptors from other mammals, and performed a structure-function analysis. TLR2/1 and TLR2/6 from both horses and humans dose-dependently responded to lipoteichoic acid from Staphylococcus aureus, with no significant species difference in EC50 at either receptor pair. The EC50 of Pam2CSK4 was the same for equine and human TLR2/6, indicating amino acid differences between the two species’ TLRs do not significantly affect ligand recognition. Species differences were seen between the responses to Pam2CSK4 and Pam3CSK4 at TLR2/1. Human TLR2/1, as expected, responded to Pam3CSK4 with greater potency and efficacy than Pam2CSK4. At equine TLR2/1, however, Pam3CSK4 was less potent than Pam2CSK4, with both ligands having similar efficacies. Molecular modelling indicates that the majority of non-conserved ligand-interacting residues are at the periphery of the TLR2 binding pocket and in the ligand peptide-interacting regions, which may cause subtle effects on ligand positioning. These results suggest that there are potentially important species differences in recognition of lipopeptides by TLR2/1, which may affect how the horse deals with bacterial infections.

Development of an equine-tropic replication-competent lentivirus assay for equine infectious anemia virus-based lentiviral vectors

The release of lentiviral vectors for clinical use requires the testing of vector material, production cells, and, if applicable, ex vivo-transduced cells for the presence of replication-competent lentivirus (RCL). Vectors derived from the nonprimate lentivirus equine infectious anemia virus (EIAV) have been directly administered to patients in several clinical trials, with no toxicity observed to date. Because EIAV does not replicate in human cells, and because putative RCLs derived from vector components within human vector production cells would most likely be human cell-tropic, we previously developed an RCL assay using amphotropic murine leukemia virus (MLV) as a surrogate positive control and human cells as RCL amplification/indicator cells. Here we report an additional RCL assay that tests for the presence of theoretical "equine-tropic" RCLs. This approach provides further assurance of safety by detecting putative RCLs with an equine cell-specific tropism that might not be efficiently amplified by the human cell-based RCL assay. We tested the ability of accessory gene-deficient EIAV mutant viruses to replicate in a highly permissive equine cell line to direct our choice of a suitable EIAV-derived positive control. In addition, we report for the first time the mathematical rationale for use of the Poisson distribution to calculate minimal infectious dose of positive control virus and for use in monitoring assay positive/spike control failures in accumulating data sets. No RCLs have been detected in Good Manufacturing Practice (GMP)-compliant RCL assays to date, further demonstrating that RCL formation is highly unlikely in contemporary minimal lentiviral vector systems.

The pathogenic and vaccine strains of equine infectious anemia virus differentially induce cytokine and chemokine expression and apoptosis in macrophages

The attenuated equine infectious anemia virus (EIAV) vaccine was the first attenuated lentivirus vaccine to be used in a large-scale application and has been used to successfully control the spread of equine infectious anemia (EIA) in China. To better understand the potential role of cytokines in the pathogenesis of EIAV infection and resulting immune response, we used branched DNA technology to compare the mRNA expression levels of 12 cytokines and chemokines, including IL-1α, IL-1β, IL-4, IL-10, TNF-α, IFN-γ, IP-10, IL-8, MIP-1α, MIP-1β, MCP-1, and MCP-2, in equine monocyte-derived macrophages (eMDMs) infected with the EIAV(DLV121) vaccine strain or the parental EIAV(DLV34) pathogenic strain. Infection with EIAV(DLV34) and EIAV(DLV121) both caused changes in the mRNA levels of various cytokines and chemokines in eMDMs. In the early stage of infection with EIAV(DLV34) (0-24h), the expression of the pro-inflammatory cytokines TNF-α and IL-1β were significantly up-regulated, while with EIAV(DLV121), expression of the anti-inflammatory cytokine IL-4 was markedly up-regulated. The effects on the expression of other cytokines and chemokines were similar between these two strains of virus. During the first 4 days after infection, the expression level of IL-4 in cells infected with the pathogenic strain were significantly higher than that in cells infected with the vaccine strain, but the expression of IL-1α and IL-1β induced by the vaccine strain was significantly higher than that observed with the pathogenic strain. In addition, after 4 days of infection with the pathogenic strain, the expression levels of 5 chemokines, but not IP-10, were markedly increased in eMDMs. In contrast, the vaccine strain did not up-regulate these chemokines to this level. Contrary to our expectation, induced apoptosis in eMDMs infected with the vaccine strain was significantly higher than that infected with the pathogenic strain 4 days and 6 days after infection. Together, these results contribute to a greater understanding of the pathogenesis of EIAV and of the mechanisms by which the immune response is induced after EIAV infection.

Restriction of equine infectious anemia virus by equine APOBEC3 cytidine deaminases

The mammalian APOBEC3 (A3) proteins comprise a multigene family of cytidine deaminases that act as potent inhibitors of retroviruses and retrotransposons. The A3 locus on the chromosome 28 of the horse genome contains multiple A3 genes: two copies of A3Z1, five copies of A3Z2, and a single copy of A3Z3, indicating a complex evolution of multiple gene duplications. We have cloned and analyzed for expression the different equine A3 genes and examined as well the subcellular distribution of the corresponding proteins. Additionally, we have tested the functional antiretroviral activity of the equine and of several of the human and nonprimate A3 proteins against the Equine infectious anemia virus (EIAV), the Simian immunodeficiency virus (SIV), and the Adeno-associated virus type 2 (AAV-2). Hematopoietic cells of horses express at least five different A3s: A3Z1b, A3Z2a-Z2b, A3Z2c-Z2d, A3Z2e, and A3Z3, whereas circulating macrophages, the natural target of EIAV, express only part of the A3 repertoire. The five A3Z2 tandem copies arose after three consecutive, recent duplication events in the horse lineage, after the split between Equidae and Carnivora. The duplicated genes show different antiviral activities against different viruses: equine A3Z3 and A3Z2c-Z2d are potent inhibitors of EIAV while equine A3Z1b, A3Z2a-Z2b, A3Z2e showed only weak anti-EIAV activity. Equine A3Z1b and A3Z3 restricted AAV and all equine A3s, except A3Z1b, inhibited SIV. We hypothesize that the horse A3 genes are undergoing a process of subfunctionalization in their respective viral specificities, which might provide the evolutionary advantage for keeping five copies of the original gene.