Molecular cloning and tissue expression of canine Toll-like receptor 2 (TLR2)

Exploiting Leishmania-Primed Dendritic Cells as Potential Immunomodulators of Canine Immune Response

Dendritic cells (DCs) capture pathogens and process antigens, playing a crucial role in activating naïve T cells, bridging the gap between innate and acquired immunity. However, little is known about DC activation when facing Leishmania parasites. Thus, this study investigates in vitro activity of canine peripheral blood-derived DCs (moDCs) exposed to L. infantum and L. amazonensis parasites and their extracellular vesicles (EVs). L. infantum increased toll-like receptor 4 gene expression in synergy with nuclear factor κB activation and the generation of pro-inflammatory cytokines. This parasite also induced the expression of class II molecules of major histocompatibility complex (MHC) and upregulated co-stimulatory molecule CD86, which, together with the release of chemokine CXCL16, can attract and help in T lymphocyte activation. In contrast, L. amazonensis induced moDCs to generate a mix of pro- and anti-inflammatory cytokines, indicating that this parasite can establish a different immune relationship with DCs. EVs promoted moDCs to express class I MHC associated with the upregulation of co-stimulatory molecules and the release of CXCL16, suggesting that EVs can modulate moDCs to attract cytotoxic CD8+ T cells. Thus, these parasites and their EVs can shape DC activation. A detailed understanding of DC activation may open new avenues for the development of advanced leishmaniasis control strategies.

Activation of Canine, Mouse and Human TLR2 and TLR4 by Inactivated Leptospira Vaccine Strains

Canine Leptospira vaccines contain inactivated strains of pathogenic Leptospira, the causative agents of leptospirosis. For an effective response to vaccination, activation of the innate immune system via pattern recognition receptors such as TLRs is crucial. However, it is not known which TLRs are activated by Leptospira in dogs. To investigate the involvement of canine TLR2, TLR4, and TLR5 in the recognition of Leptospira, we stimulated canine moDC and reporter cells expressing canine TLR2 with either whole-inactivated bacteria or purified LPS of Leptospira strains, representing the serogroups generally used in canine leptospirosis vaccines. Using the endotoxin neutralizing reagent polymyxin B and TLR4 antagonist RS-LPS, we demonstrate that Leptospira LPS and canine TLR4 are involved in IL-1β production as well as in the uptake of inactivated Leptospira in canine moDC. Furthermore, polymyxin B only partially inhibited IL-1β production induced by inactivated Leptospira, suggesting that next to TLR4, also other TLRs may be involved. The observed activation of canine TLR2-expressing reporter cells by inactivated Leptospira strains indicates that TLR2 could be one of these TLRs. Next, we analyzed TLR2 and TLR4 activating capabilities by the same Leptospira strains using human and mouse TLR-expressing reporter cells. Inactivated Leptospira and leptospiral LPS activated not only mouse, but also human TLR4 and this activation was shown to be LPS dependent in both cases. Additionally, inactivated Leptospira activated mouse and human TLR2-expressing reporter cell lines. In our study, we could not identify significant species differences in the recognition of Leptospira by TLR2 and TLR4 between dog, human and mouse. Lastly, we show that these inactivated Leptospira strains are recognized by both mouse and human TLR5 reporter cells only after exposure to additional heat-treatment. Unfortunately, we were not able to confirm this in the canine system. Our data show that TLR2 and TLR4 are involved in the recognition of Leptospira strains used in the production of canine Leptospira vaccines. This study contributes to the understanding of Leptospira-induced innate immune responses in dogs, humans, and mice. Future studies are needed to further explore the role of canine TLR2, TLR4 and TLR5 in the induction of vaccine-mediated immunity against Leptospira.

Leishmania infantum exerts immunomodulation in canine Kupffer cells reverted by meglumine antimoniate

Kupffer cells (KC) are the liver macrophage population that resides in the hepatic sinusoids and efficiently phagocyte pathogens by establishing an intimate contact with circulating blood. KC constitute the liver host cells in Leishmania infection, nevertheless little is described about their role, apart from their notable contribution in granulomatous inflammation. The present study aims to investigate how canine KC sense and react to the presence of Leishmania infantum promastigotes and amastigotes by evaluating the gene expression of specific innate immune cell receptors and cytokines, as well as the induction of nitric oxide and urea production. Complementarily, the impact of a leishmanicidal drug - meglumine antimoniate (MgA) - in infected KC was also explored. KC revealed to be susceptible to both parasite forms and no major differences were found in the immune response generated. L. infantum parasites seem to interact with KC innate immune receptors and induce an anergic state, promoting immune tolerance and parasite survival. The addition of MgA to infected KC breaks the parasite imposed silence and increased gene expression of Toll-like receptors (TLR) 2 and TLR4, possibly activating downstream pathways. Understanding how KC sense and react to parasite presence could bring new insights into the control or even elimination of canine leishmaniasis.

Targeting TLR2 for vaccine development

Novel and more effective immunization strategies against many animal diseases may profit from the current knowledge on the modulation of specific immunity through stimulation of innate immune receptors. Toll-like receptor (TLR)2-targeting formulations, such as synthetic lipopeptides and antigens expressed in fusion with lipoproteins, have been shown to have built-in adjuvant properties and to be effective at inducing cellular and humoral immune mechanisms in different animal species. However, contradictory data has arisen concerning the profile of the immune response elicited. The benefits of targeting TLR2 for vaccine development are thus still debatable and more studies are needed to rationally explore its characteristics. Here, we resume the main features of TLR2 and TLR2-induced immune responses, focusing on what has been reported for veterinary animals.

Expression of Toll-like receptors 2 and 9 in cells of dog jejunum and colon naturally infected with Leishmania infantum

BACKGROUND

Infection with parasite protozoa is a long-term health issue in tropical and subtropical regions throughout the world. The Toll-like receptor (TLR) signaling pathway is one of the first-responding defense systems against Leishmania. The aim of this study was to investigate the expression of TLR2 and TLR9 in jejunum and colon and its correlation with CD11c, CD11b, and CD14 receptors used as markers for dendritic cells and macrophages.

METHODS

Twenty four dogs infected with Leishmania infantum were used in this study. Cytometry was carried out in lamina propria cells from jejunum and colon using markers for TLR2, TLR9, CD11b, CD11c and CD14.

RESULTS

Cellular inflammatory exudate was diffuse in the mucosa and submucosa, predominately comprising mononuclear cells: plasma cells, macrophages, and lymphocytes. Despite the parasite load, microscopy showed no erosion was evident in the epithelial mucosa layers. The colon harbored more parasites than the jejunum. Flow cytometry revealed higher frequency of TLR2+ and CD11c+ dendritic cells in the colon than in the jejunum. Conversely, TLR9-expressing cells were more frequent in jejunum. Moreover, frequency of macrophages (CD11b+ and CD14+) expressing simultaneity TLR9 were lower in the colon than in jejunum, while CD11c+ cells predominated in the colon. Despite of the negative ELISA serum results, IL-10 and TNF-α were higher in jejunum than colon of infected animals. However, IL-4 was higher in colon than jejunum of infected animals. A higher expression these cytokines were demonstrated in infected dogs compared to uninfected dogs.

CONCLUSIONS

There was no correlation between clinical signs and pathological changes and immunological and parasitological findings in the gastrointestinal tract in canine visceral leishmaniasis. However, jejunum showed a lower parasite load with increased frequency and expression of CD11b, TLR9, CD14/CD11b/TLR9 receptors and IL-10 and TNF-α cytokines. Conversely, the colon showed a higher parasite load along with increased frequency and expression of TLR2, CD11c receptors, and IL-4 cytokine. Thus, Leishmania infantum is able to interfere in jejunum increased expression of TLR2, TLR9, CD11b, CD14, CD14/CD11b/TLR9 receptors, IL-10, and TNF-α; and in colon increased expression of CD11c, TLR2, TLR9, CD11b, CD14 e, CD14/CD11b/TLR9 receptors, IL-10, and TNF-α.

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.

Toll receptors type-2 and CR3 expression of canine monocytes and its correlation with immunohistochemistry and xenodiagnosis in visceral leishmaniasis

The aim of the present study was to investigate TLR2 expression in peripheral blood monocytes from dogs naturally infected with Leishmania (Leishmania) infantum to determine whether it correlates with CD11b/CD18 (CR3) expression, and to evaluate the potential of dogs as sources of infection using phlebotomine xenodiagnosis. Forty eight dogs were serologically diagnosed with L. infantum infection by indirect immunofluorescence antibody test (IFAT) and enzyme linked immunosorbent assay (ELISA). Parasitological exams from bone-marrow aspirates were positive by PCR analysis. All dogs were clinical defined as symptomatic. Ear skin tissue samples were obtained for immunohistochemistry (IHQ) analysis. The potential of these dogs as a source of infection using phlebotomine xenodiagnosis (XENO) was evaluated. Flow cytometry was carried out on peripheral blood mononuclear cells using superficial receptors including CD14, CD11b, TLR2 and MHCII. IHQ ear skin tissue parasite load and XENO where done where we found a strict correlation (r = 0.5373). Dogs with higher expression of MFI of CD11b inside CD14 monocytes were represented by dogs without parasite ear tissue load that were unable to infect phlebotomines (IHQ⁻/XENO⁻). Dogs with lower expression of MFI of CD11b inside CD14 monocytes were represented by dogs with parasite ear tissue load and able to infect phlebotomines (IHQ⁺/XENO⁺) (p = 0,0032). Comparable results were obtained for MFI of MHCII (p = 0.0054). In addition, considering the population frequency of CD11b⁺TLR2⁺ and CD11b⁺MHCII⁺, higher values were obtained from dogs with IHQ⁻/XENO⁻ than dogs with IHQ⁺/XENO⁺ (p = 0.01; p = 0.0048, respectively). These data, together with the TLR2 and NO assays results (CD11b⁺TLR2⁺ and NO with higher values for dogs with IHQ⁻/XENO⁻ than dogs with IHQ⁺/XENO⁺, led to the conclusion that IHQ⁻/XENO⁻ dogs are more resistant or could modulate the cellular immune response essential for Leishmania tissue clearance.

Antibodies specific for human or murine Toll-like receptors detect canine leukocytes by flow cytometry

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns on microbes, and ligand recognition results in production of pro-inflammatory cytokines, reactive oxygen and nitrogen intermediates, and upregulation of costimmulatory molecules. The purpose of this study was to test antibodies specific for human or murine TLR2, 3, 4, 5 and 9 for their use in dogs. Twenty-two antibodies were assessed for recognition of canine monocytes (Mo), granulocytes (Gr) or lymphocytes (Ly) by flow cytometry, and results were compared with isotype-matched controls and other antibodies against the same TLR. Nine monoclonal antibodies detected canine leukocyte subpopulations. Antibodies TL2.1 and TL2.3 (specific for human TLR2), HTA125 (specific for human TLR4), as well as 85B152.5 and 19D759.2 (specific for human TLR5) recognized Mo and Gr but not Ly without permeabilization, and putatively cross-react with canine TLR2, 4 and 5, respectively. Antibodies 40C1285.6 and TLR3.7 (specific for human TLR3) as well as 26C593.2 and 5G5 (specific for human and murine TLR9) recognized Mo, Gr and Ly after their permeabilization and putatively cross-react with canine TLR3 and 9, respectively, inside the cell. None of these nine antibodies recognized paraformaldehyde-treated (4%) canine leukocytes but all except 40C1285.6, TLR3.7 and 5G5 recognized methanol-fixed cells, suggesting that they might be useful also in immunohistochemistry.

Expression of immune response genes in the stifle joint of dogs with oligoarthritis and degenerative cranial cruciate ligament rupture

Dysregulation of immune responses within joints plays an important role in development of inflammatory arthritis. We determined expression of a panel of immune response and matrix turnover genes in synovial fluid collected from a group of dogs with stifle oligoarthritis and associated degenerative cranial cruciate ligament (CCL) rupture (n=27). We also studied synovial fluid gene expression in dogs affected with other forms of degenerative arthritis (n=9) and in the stifle joint of healthy dogs with intact CCL (n=14). After collection, synovial cells were pelleted and RNA was isolated. Relative expression of cathepsin K, cathepsin S, tartrate-resistant acid phosphatase (TRAP), matrix metalloproteinase-9 (MMP-9), invariant chain (li), toll-like receptor-2 (TLR-2), and TLR-9 was determined using real-time quantitative RT-PCR. Data were normalized to peripheral blood mononuclear cells (PBMC) as an internal control. Relative expression of cathepsin K, MMP-9, TRAP, and li was increased in the stifle synovial fluid of dogs with oligoarthritis, when compared with the stifles of healthy dogs (P<0.05). In contrast, relative expression of all of the genes-of-interest in synovial fluid from joints affected with other forms of arthritis was not significantly different from the stifles of healthy dogs. TRAP expression was also significantly increased in the stifle joints of dogs with oligoarthritis, when compared to joint expression of TRAP in dogs with other forms of degenerative arthritis (P<0.05). In the dogs with stifle oligoarthritis, expression of both matrix turnover and immune response genes was increased in stifle synovial fluid, when compared with the internal PBMC control, whereas in healthy dogs and dogs with other forms of arthritis, only expression of matrix turnover genes was increased in synovial fluid, when compared with the internal PBMC control (P<0.05). Taken together, these findings suggest that antigen-specific immune responses within the stifle joint may be involved in the pathogenesis of persistent synovitis and associated joint degradation in dogs with oligoarthritis and degenerative CCL rupture.

Role of sugars in surface microbe?host interactions and immune reaction modulation

Sugars in the form of monosaccharides, oligosaccharides, polysaccharides and glycoconjugates (glycoproteins, glycolipids) are vital components of infecting microbes and host cells, and are involved in cell signalling associated with modulation of inflammation in all integumental structures. Indeed, sugars are the molecules most commonly involved in cell recognition and communication. In skin, they are essential to epidermal development and homeostasis. They play important roles in microbial adherence, colonization and biofilm formation, and in virulence. Two groups of pathogen recognition receptors, C-type lectins (CTL) and their receptors (CTLR), and the Toll-like receptors enable the host to recognize pathogen-associated molecular patterns (PAMPs), which are mainly glycolipids. The CTLs can recognize a wide variety of bacteria, fungi and parasites and are important in phagocytosis and endocytosis. TLRs are expressed on the surfaces of a variety of cells, including keratinocytes, dendritic cells, monocytes and macrophages; they play a major role in innate immunity. Interaction of TLRs with PAMPs initiates a cascade of events leading to production of reactive oxygen intermediates, cytokines and chemokines, and promotes inflammation. Exogenous sugars can block carbohydrate receptors and competitively displace bacteria from attachment to cells, including keratinocytes. Thus sugars may provide valuable adjunctive anti-inflammatory and/or antimicrobial treatment. A promising approach is the use of a panel of carbohydrate derivatives with anti-adhesive efficacy against bacteria frequently involved in diseases affecting skin and other epithelia. More complete characterization of sugar receptors and their ligands will provide further keys to use of carbohydrates in immunomodulation and infection control in skin.

Toll-like receptor 3 (TLR3): A new marker of canine monocytes-derived dendritic cells (cMo-DC)

Toll-like receptors (TLRs) are a family of functionally important receptors for recognition of pathogen-associated molecular pattern (PAMP) since they trigger the pro-inflammatory response and upregulation of costimulatory molecules, linking the rapid innate response to adaptative immunity. In human leukocytes, TLR3 has been found to be specifically expressed in dendritic cells (DC). This study examined the expression of TLR3 in canine monocytes-derived DC (cMo-DC) and PBMC using three new anti-TLR3 mAbs (619F7, 722E2 and 713E4 clones). The non-adherent cMo-DC generated after culture in canine IL-4 plus canine GM-CSF were labelled with the three anti-TLR3 clones by flow cytometry, with a strong expression shown for 619F7 and 722E2 clones. By contrast, TLR3 expression was low to moderate in canine monocytes and lymphocytes. These results were confirmed by Western blot using 619F7 and 722E2 clones and several polypeptide bands were observed, suggesting a possible cleavage of TLR3 molecule or different glycosylation states. In addition, TLR3 was detectable in immunocytochemistry by using 722E2 clone. In conclusion, this first approach to study canine TLR3 protein expression shows that three anti-TLR3 clones detect canine TLR3 and can be used to better characterize canine DC and the immune system of dogs.

Pattern recognition receptors in companion and farm animals - the key to unlocking the door to animal disease?

The innate immune system is essential for host defence and is responsible for early detection of potentially pathogenic microorganisms. Upon recognition of microbes by innate immune cells, such as macrophages and dendritic cells, diverse signalling pathways are activated that combine to define inflammatory responses that direct sterilisation of the threat and/or orchestrate development of the adaptive immune response. Innate immune signalling must be carefully controlled and regulation comes in part from interactions between activating and inhibiting signalling receptors. In recent years, an increasing number of pattern recognition receptors (PRRs), including C-type lectin receptors and Toll-like receptors (TLRs), has been described that participate in innate recognition of microbes, especially through the so called pathogen-associated molecular patterns (PAMPs). Recent studies demonstrate strong interactions between signalling through these receptors. Whereas useful models to study these receptors in great detail in the murine and human system are now emerging, relatively little is known regarding these receptors in companion and farm animals. In this review, current knowledge regarding these receptors in species of veterinary relevance is summarised.