Differential induction of Toll-like receptor gene expression in equine monocytes activated by Toll-like receptor ligands or TNF-α

Influence of Age and Immunostimulation on the Level of Toll-Like Receptor Gene (TLR3, 4, and 7) Expression in Foals

Simple Summary

Detailed knowledge of the molecular mechanisms of immunoglobulin synthesis appears necessary for a better understanding of foal immunity maturity and its influencing factors. At the same time, it encourages studies regarding the influence of the signaling cascade’s proteins on the primary immunological response, which provides an opportunity to develop extremely precise methods of regulating acquired immunity. The results revealed that the expression of theTLR3 and TLR4 genes, as well as the levels of immunoglobulins and interleukins, can be modulated by stimulation with the pharmacological agent, and that the expression of the TLR3 and TLR4genes in peripheral blood cells is dependent on age.

Abstract

The aim of this study was to investigate the molecular mechanisms leading to the identification of pathogens by congenital immune receptors in foals up to 60 days of age. The study was conducted on 16 foal Polish Pony Horses (Polish Konik) divided into two study groups: control (n = 9) and experimental (n = 7). Foals from the experimental group received an intramuscular duplicate injection of 5 mL of Biotropina (Biowet) at 35 and 40 days of age. The RNA isolated from venous blood was used to evaluate the expression of theTLR3, TLR4, and TLR7 genes using RT-PCR. The results of the experiment demonstrated a statistically significant increase in the level of TLR3 gene expression and a decrease in the level ofTLR4 gene expression with foal aging. The level of TLR7 gene expression did not show age dependence. Immunostimulation with Biotropina had a significant impact on the level of the genes’ expression for Toll-like receptors. It increased the level of TLR4 expression and decreased TLR3 expression. Thus, it was concluded that the expression of theTLR3 and TLR4genes in peripheral blood cells is dependent on age. This experiment demonstrated a strong negative correlation between TLR3 and TLR4 gene expression.

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.

West Nile Virus Challenge Alters the Transcription Profiles of Innate Immune Genes in Rabbit Peripheral Blood Mononuclear Cells

The peripheral innate immune response to West Nile virus (WNV) is crucial for control of virus spread to the central nervous system. Therefore, transcriptomes encoding the innate immune response proteins against WNV were investigated in peripheral blood mononuclear cells (PBMCs) of New Zealand White rabbits, a recently established novel rabbit model for WNV pathogenesis studies. PBMCs were challenged with an Australian WNV strain, WNV_NSW2011, in vitro, and mRNA expression of selected immune response genes were quantified at 2-, 6-, 12-, and 24-h post-infection (pi) using qRT-PCR. Compared to mock-inoculated PBMCs, WNV-stimulated PBMCs expressed high levels of interferon (IFN) alpha (IFNA), gamma (IFNG), IL6, IL12, IL22, CXCL10, and pentraxin 3 (PTX3) mRNA. Likewise, TLR1, 2, 3, 4, 6, and 10 mRNA became up-regulated with the highest expression seen for TLR3, 4, and 6. TLRs-signaling downstream genes (MyD88, STAT1, TRAF3, IRF7, and IRF9) subsequently became up-regulated. The high expression of IFNs, TLR3, TLR4, TRAF3, STAT1, IRF7, and IRF9 are in accordance with antiviral activities, while expression of TNFA, HO1, iNOS, caspase 3, and caspase 9 transcripts suggests the involvement of oxidative stress and apoptosis in WNV-stimulated rabbit PBMCs, respectively. The level of WNV_NSW2011 RNA increased at 24-h pi in PBMCs challenged with virus in vitro compared to input virus. The expression dynamics of selected genes were validated in PBMCs from rabbits experimentally infected with WNV in vivo. Higher expression of IFNA, IFN beta (IFNB), IFNG, TNFA, IL6, IL22, PTX3, TLR3 and TLR4, IRF7, IRF9, STST1, TRAF3, caspase 3, and caspase 9 were seen in PBMCs from WNV-infected rabbits on day 3 post-intradermal virus inoculation compared to PBMCs from uninfected control rabbits. This study highlights the array of cytokines and TLRs involved in the host innate immune response to WNV in the rabbit leukocytes and suggests that these cells may be a useful in vitro model for WNV infection study.

Is it the systemic inflammatory response syndrome or endotoxemia in horses with colic?

Some veterinarians describe particularly sick horses or neonatal foals as being endotoxemic, whereas others refer to the same animals as having the systemic inflammatory response syndrome. This article reviews the basis for the use of each of these terms in equine practice, and highlights the mechanisms underlying the response of the horse's innate immune system to key structural components of the microorganisms that initiate these conditions, including how some of those responses differ from other species. Current approaches used to treat horses with these conditions are summarized, and caution advised on extrapolating findings from other species to the horse.

Toll-like receptor and pro-inflammatory cytokine expression during prolonged hyperinsulinaemia in horses: implications for laminitis

Equine laminitis, a disease of the lamellar structure of the horse's hoof, can be incited by numerous factors that include inflammatory and metabolic aetiologies. However, the role of inflammation in hyperinsulinaemic laminitis has not been adequately defined. Toll-like receptor (TLR) activation results in up-regulation of inflammatory pathways and the release of pro-inflammatory cytokines, including interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α), and may be a pathogenic factor in laminitis. The aim of this study was to determine whether TLR4 expression and subsequent pro-inflammatory cytokine production is increased in lamellae and skeletal muscle during equine hyperinsulinaemia. Standardbred horses were treated with either a prolonged, euglycaemic hyperinsulinaemic clamp (p-EHC) or a prolonged, glucose infusion (p-GI), which induced marked and moderate hyperinsulinaemia, respectively. Age-matched control horses were treated simultaneously with a balanced electrolyte solution. Treated horses developed clinical (p-EHC) or subclinical (p-GI) laminitis, whereas controls did not. Skeletal muscle and lamellar protein extracts were analysed by Western blotting for TLR4, IL-6, TNF-α and suppressor of cytokine signalling 3 (SOCS3) expression. Lamellar protein expression of TLR4 and TNF-α, but not IL-6, was increased by the p-EHC, compared to control horses. A significant positive correlation was found between lamellar TLR4 and SOCS3. Skeletal muscle protein expression of TLR4 signalling parameters did not differ between control and p-EHC-treated horses. Similarly, the p-GI did not result in up-regulation of lamellar protein expression of any parameter. The results suggest that insulin-sensitive tissues may not accurately reflect lamellar pathology during hyperinsulinaemia. While TLR4 is present in the lamellae, its activation appears unlikely to contribute significantly to the developmental pathogenesis of hyperinsulinaemic laminitis. However, inflammation may have a role to play in the later stages (e.g., repair or remodelling) of the disease.

Experimental model of equine alveolar macrophage stimulation with TLR ligands

Pulmonary diseases are common in horses and have a major economic impact on the equine industry. Some of them could be associated with an inadequate immune response in the lung, but methods to evaluate this response in horses are lacking. The aim of this study was to develop and validate an experimental model that could be applied in several physiological and pathological conditions to assess the innate immune response of equine pulmonary cells. Equine alveolar macrophages (AMs) obtained from bronchoalveolar lavages were isolated from other cells by adhesion. TLR2, 3, and 4 expression in AMs was studied and their responses to commercial ligands (respectively FSL-1, Poly(I:C), and LPS) were evaluated after determination of the appropriate dose and time of incubation. TLR responses were assessed by measuring cytokine production using (1) gene expression of TNFα, IFNβ, Il-1β, and IFNα by qPCR (indirect method); and (2) cytokine production for TNFα and IFNβ by ELISA (direct method). TLR 2, 3, and 4 were expressed by AMs. TLR 2 stimulation with 10 ng/mL of FSL-1 during 3h significantly increased IL-1β and TNFα gene expression. TLR 3 stimulation with 1000 ng/mL of Poly(I:C) during 1h increased IFNβ, IFNα, Il-1β and TNFα expression. TLR 4 stimulation with 100 ng/mL of LPS during 3h increased TNFα, IFNβ, and Il-1β expression. Results obtained by ELISA quantification of TNFα and IFNβ produced by AMs following stimulation during 6h were similar: FSL-1 increased TNFα production but not IFNβ, Poly(I:C) and LPS increased production of IFNβ and TNFα. In conclusion, pulmonary innate immunity of horses can be assessed ex vivo by measuring cytokine production following stimulation of AMs with TLR agonists. This experimental model could be applied under several conditions especially to improve the understanding of equine respiratory disease pathogenesis, and to suggest novel therapeutic opportunities.

Pattern recognition receptors in equine endotoxaemia and sepsis

Pattern recognition receptors (PRRs) on host cells detect pathogens to activate innate immunity which, in turn, initiates inflammatory and adaptive immune responses. Successful activation of PRRs is, therefore, critical to controlling infections and driving pathogen‐specific adaptive immunity, but overactivity of PRRs causes systemic inflammation, which is detrimental to the host. Here we review the PRR literature as it relates to horses and speculate on the role PRRs may play in sepsis and endotoxaemia.

The immunopathology of sepsis: pathogen recognition, systemic inflammation, the compensatory anti-inflammatory response, and regulatory T cells

Sepsis, the systemic inflammatory response to infection, represents the major cause of death in critically ill veterinary patients. Whereas important advances in our understanding of the pathophysiology of this syndrome have been made, much remains to be elucidated. There is general agreement on the key interaction between pathogen-associated molecular patterns and cells of the innate immune system, and the amplification of the host response generated by pro-inflammatory cytokines. More recently, the concept of immunoparalysis in sepsis has also been advanced, together with an increasing recognition of the interplay between regulatory T cells and the innate immune response. However, the heterogeneous nature of this syndrome and the difficulty of modeling it in vitro or in vivo has both frustrated the advancement of new therapies and emphasized the continuing importance of patient-based clinical research in this area of human and veterinary medicine.