Pattern Recognition Receptors Signaling Pathways Research Articles

Cell-intrinsic C5a synergizes with Dectin-1 in macrophages to mediate fungal killing

The complement factor C5a is a core effector product of complement activation. C5a, acting through its receptors C5aR1 and C5aR2, exerts pleiotropic immunomodulatory functions in myeloid cells, which is vital for host defense against pathogens. Pattern-recognition receptors (PRRs) are similarly expressed by immune cells as detectors of pathogen-associated molecular patterns. Although there is evidence of cross talk between complement and PRR signaling pathways, knowledge of the full potential for C5a-PRR interaction is limited. In this study, we comprehensively investigated how C5a signaling through C5a receptors can modulate diverse PRR-mediated cytokine responses in human primary monocyte-derived macrophages and observed a powerful, concentration-dependent bidirectional effect of C5a on PRR activities. Unexpectedly, C5a synergized with Dectin-1, Mincle, and STING in macrophages to a much greater extent than TLRs. Notably, we also identified that selective Dectin-1 activation using depleted zymosan triggered macrophages to generate cell-intrinsic C5a, which acted on intracellular and cell surface C5aR1, to help sustain mitochondrial ROS generation, up-regulate TNFα production, and enhance fungal killing. This study adds further evidence to the holistic functions of C5a as a central immunomodulator and important orchestrator of pathogen sensing and killing by phagocytes.

The Role of TRIM Proteins in Antiviral Defense

The Tripartite motif (TRIM) protein family is classified among a cohort of E3 ubiquitin ligase families. A large percentage of TRIM proteins are E3 ubiquitin ligase active and take part in a number of cellular functions. By adding ubiquitin molecules to target proteins via a variety of techniques, it can change those proteins. The important role of the TRIM protein in controlling pattern recognition receptor signaling pathways and the defense mechanisms of mammals against viruses, with a focus on protecting the host from viral infections, has been clarified by recent study. In addition to triggering crucial cell-intrinsic defense mechanisms like autophagy and transcription-dependent antiviral responses, TRIM proteins can also exhibit direct antiviral effects by obstructing particular viral components via a variety of mechanisms. Regrettably, certain viruses have developed efficient mechanisms to evade the antiviral activities exerted by specific TRIM proteins, including SARS-CoV-2. Viruses has the capacity to exploit TRIMs and the ubiquitination process directly, hence enhancing the viral replication cycle and inducing heightened pathogenicity. In this article, I have delved into research that explores the molecular mechanisms responsible for the antiviral effects of TRIM proteins. Additionally, I have examined how TRIM proteins exert their influence on various viral entities, shedding light on their crucial role in the immune response against viral infections.

The game between host antiviral innate immunity and immune evasion strategies of senecavirus A - A cell biological perspective.

Innate immunity is the first line of the cellular host to defend against viral infection. Upon infection, viruses can be sensed by the cellular host's pattern recognition receptors (PRRs), leading to the activation of the signaling cascade and the robust production of interferons (IFNs) to restrict the infection and replication of the viruses. However, numerous cunning viruses have evolved strategies to evade host innate immunity. The senecavirus A (SVA) is a newly identified member of the Picornaviridae family, causing severe vesicular or ulcerative lesions on the oral mucosa, snout, coronary bands, and hooves of pigs of different ages. During SVA infection, the cellular host will launch the innate immune response and various physiological processes to restrict SVA. In contrast, SVA has evolved several strategies to evade the porcine innate immune responses. This review focus on the underlying mechanisms employed by SVA to evade pattern recognition receptor signaling pathways, type I interferon (IFN-α/β) receptor (IFNAR) signaling pathway, interferon-stimulated genes (ISGs) and autophagy, and stress granules. Deciphering the antiviral immune evasion mechanisms by SVA will enhance our understanding of SVA's pathogenesis and provide insights into developing antiviral strategies and improving vaccines.

Polystyrene nanoparticles enhance the adverse effects of di-(2-ethylhexyl) phthalate on male reproductive system in mice

Coexposure of nanoplastics (NPs) with other pollutants adsorbed from the surroundings has received extensive attention. Currently, the combined effects of NPs and plasticizers remain unclear. Di-(2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer that has raised much concern owing to its ubiquitous pollution and endocrine-disrupting potential. This study aimed to investigate the toxic effects on the male reproductive system upon coexposure to NPs and DEHP. The C57BL/6J mice were orally administrated with polystyrene nanoparticles (PSNPs), DEHP or both for 35 days to evaluate their effects on sperm quality, histology of testes and epididymides, testicular transcriptomic characteristics as well as expression of some important genes in the epididymides. The low-dose PSNPs used here did not induce significant changes in sperm quality, while DEHP alone or cotreatment with DEHP and PSNPs caused notable impairment, mainly manifesting as decreased sperm quality and aberrant structure of the testis and epididymis. Moreover, enhanced toxic effects were found in the cotreatment group when compared with the individual DEHP treatment group, as manifested by more obvious alterations in the sperm parameters as well as histological changes in the testis and epididymis. Testicular transcriptomic analysis revealed differential regulation of genes involved in immune response, cytoplasmic pattern recognition receptor signaling pathways, protein ubiquitination, oxidative stress, necrotic cell death, ATP synthesis and the cellular respiratory chain. RT-qPCR verified that the expression patterns of Cenpb, Crisp1 and Mars were changed in testes, and genes relevant to epididymal function including Aqp9 and Octn2 were downregulated in epididymides, particularly in the cotreatment group. Collectively, our results emphasize that DEHP at an environmentally relevant dose can induce male reproductive toxicity, and PSNPs may aggravate the toxic effects.

Molecular alterations in human milk in simulated maternal nasal mucosal infection with live attenuated influenza vaccination.

Breastfeeding protects against mucosal infections in infants. The underlying mechanisms through which immunity develops in human milk following maternal infection with mucosal pathogens are not well understood. We simulated nasal mucosal influenza infection through live attenuated influenza vaccination (LAIV) and compared immune responses in milk to inactivated influenza vaccination (IIV). Transcriptomic analysis was performed on RNA extracted from human milk cells to evaluate differentially expressed genes and pathways on days 1 and 7 post-vaccination. Both LAIV and IIV vaccines induced influenza-specific IgA that persisted for at least 6 months. Regulation of type I interferon production, toll-like receptor, and pattern recognition receptor signaling pathways were highly upregulated in milk on day 1 following LAIV but not IIV at any time point. Upregulation of innate immunity in human milk may provide timely protection against mucosal infections until antigen-specific immunity develops in the human milk-fed infant.

PRR-Mediated Immune Response and Intestinal Flora Profile in Soybean Meal-Induced Enteritis of Pearl Gentian Groupers, Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂.

Pattern recognition receptors (PRRs) can recognize microbial-specific pathogen-associated molecular patterns, initiate signal cascade transduction, activate the expressions of host immunity and proinflammatory genes, and, ultimately, trigger an immune response against identified pathogens. The present study focused on two outcomes of feeding pearl gentian groupers with high levels of soybean meal (SBM): (1) growth performance and (2) the intestinal environment, including tissue structure, flora profile, and immune responses. Some 720 groupers were randomly divided into three groups (n = 4): (1) controls, fed a 50% fish meal feed (FM), (2) with 20% of the FM substituted with SBM (SBM20), and (3) 40% of the FM substituted with SBM (SBM40). The fish were fed these iso-nitrogenous and iso-lipidic diets for 10 weeks. They were kept in containers with 1 m3 of water under natural light and temperature levels. The experimental results demonstrate that the SBM diets significantly degraded growth performance and intestinal physiology. Typical enteritis characteristics and immune fluctuations appeared, as reflected by the enzyme activities of total superoxide dismutase and lysozyme, and the contents of immunoglobulin M, complement 3, and complement 4. 16SrDNA high-throughput sequencing showed that the intestinal flora was significantly affected, with the abundance of harmful bacteria, such as Vibrio and Streptococcus, increasing with dietary SBM level. Based on “3 + 2” full-length transcriptome sequencing, three triggered PRRs were found in the intestine: the RIG-like receptor, NOD-like receptor, and Toll-like receptor signaling pathways. The intestinal flora variations were significantly correlated with the activation of the three PRR signaling pathways by canonical correlation analysis. These culminated in the transcriptome activation of NF-κB, IRFs, and costimulatory molecules, ultimately promoting the expressions of proinflammatory cytokines, interferons (IFNs), chemokines, and other molecules vital to the innate and/or adaptive immune responses. This study provides new information for diagnosing and preventing SBMIE in aquaculture fish.

Sepsis Management, Controversies, and Advancement in Nanotechnology: A Systematic Review.

Sepsis is a potentially dangerous infection that requires prompt identification and treatment. Emergency medicine physicians must grasp the clinical signs and laboratory results of direct and indirect organ failure, the source of infection management, and the criteria for treating sepsis and septic shock. The pathogenesis of sepsis is connected to inflammation and an excess of reactive oxygen and nitrogen species, which activate the pathogen-associated molecular pattern (PAMP)-pattern recognition receptor (PRR) and damage-associated molecular pattern (DAMP)-PRR signaling pathways. The development of rapid, sensitive, and precise techniques for sepsis diagnosis might be aided by nanotechnology, a part of nanomedicine. Nanoparticles (NPs) such as magnetic NPs, gold NPs, fluorescent (silica and quantum dots), and lipid-based NPs have all been discussed to contribute to the detection of sepsis-related microbial infections. Because of the intrinsic and unique features of these nano-sized systems, researchers are evaluating nanotechnology-based alternatives for sepsis control. Recent advances in nanotechnology-based technologies for sepsis detection and management are discussed in this study.Databases (PubMed, Medline, PMC, Google Scholar) were used to source various studies that were carried out on sepsis in terms of assessment, types, diagnosis, and treatment controversies, with more attention being given with a focus on the most recent data, principles, and management guidelines. Priority was also given to studies published within the last 11 years, using keywords such as "sepsis guidelines," "sepsis clinical," "septic risk factors," "sepsis and nano technology," "nano particles," "sepsis controversies," and "nano diagnostic" in the search. After a filtration process, the eight most relevant studies were selected to be included in this review. The filtration process included the use of both inclusion and exclusion criteria. The excluded studies were pediatric populations, obstetrical populations, and nanotechnology advancements dealing with other fields not relating to sepsis. The selected studies were also undertaken through a quality appraisal process using corresponding assessment tools. The selected articles were all highly informative about sepsis and the processes of diagnosis and treatment that are currently in use as well as those that are still being developed or implemented. Furthermore, we look at how nanomedicine in the application of nanomaterials can be employed to efficiently manage sepsis.

Innate immunity and inflammophagy: balancing the defence and immune homeostasis.

Extensive crosstalk exists between autophagy and innate immune signalling pathways. The stimuli that induce pattern recognition receptor (PRR)-mediated innate immune signalling pathways, also upregulate autophagy. The purpose of this increased autophagy is to eliminate the stimuli and/or suppress the inflammatory pathways by targeted degradation of PRRs or intermediary proteins (termed 'inflammophagy'). By executing these functions, autophagy dampens excess inflammation triggered by the innate immune signalling pathways. Thus, autophagy helps in the maintenance of the body's innate immune homeostasis to protect from inflammatory and autoimmune diseases. Many autophagy-dependent mechanisms that could control innate immune signalling have been studied over the last few years. However, still, the understanding is incomplete, and studies that are more systematic should be undertaken to delineate the mechanisms of inflammophagy. Here, we discuss the available knowledge of crosstalk between autophagy and PRR signalling pathways.

Evasion of Antiviral Innate Immunity by Porcine Reproductive and Respiratory Syndrome Virus

Innate immunity is the front line for antiviral immune responses and bridges adaptive immunity against viral infections. However, various viruses have evolved many strategies to evade host innate immunity. A typical virus is the porcine reproductive and respiratory syndrome virus (PRRSV), one of the most globally devastating viruses threatening the swine industry worldwide. PRRSV engages several strategies to evade the porcine innate immune responses. This review focus on the underlying mechanisms employed by PRRSV to evade pattern recognition receptors signaling pathways, type I interferon (IFN-α/β) receptor (IFNAR)-JAK-STAT signaling pathway, and interferon-stimulated genes. Deciphering the antiviral immune evasion mechanisms by PRRSV will enhance our understanding of PRRSV’s pathogenesis and help us to develop more effective methods to control and eliminate PRRSV.

Balancing selection in Pattern Recognition Receptor signalling pathways is associated with gene function and pleiotropy in a wild rodent.

Pathogen-mediated balancing selection is commonly considered to play an important role in the maintenance of genetic diversity, in particular in immune genes. However, the factors that may influence which immune genes are the targets of such selection are largely unknown. To address this, here we focus on Pattern Recognition Receptor (PRR) signalling pathways, which play a key role in innate immunity. We used whole-genome resequencing data from a population of bank voles (Myodes glareolus) to test for associations between balancing selection, pleiotropy and gene function in a set of 123 PRR signalling pathway genes. To investigate the effect of gene function, we compared genes encoding (a) receptors for microbial ligands versus downstream signalling proteins, and (b) receptors recognizing components of microbial cell walls, flagella and capsids versus receptors recognizing features of microbial nucleic acids. Analyses based on the nucleotide diversity of full coding sequences showed that balancing selection primarily targeted receptor genes with a low degree of pleiotropy. Moreover, genes encoding receptors recognizing components of microbial cell walls etc. were more important targets of balancing selection than receptors recognizing nucleic acids. Tests for localized signatures of balancing selection in coding and noncoding sequences showed that such signatures were mostly located in introns, and more evenly distributed among different functional categories of PRR pathway genes. The finding that signatures of balancing selection in full coding sequences primarily occur in receptor genes, in particular those encoding receptors for components of microbial cell walls etc., is consistent with the idea that coevolution between hosts and pathogens is an important cause of balancing selection on immune genes.

Pattern Recognition Receptors and Liver Failure.

Liver failure is a clinical syndrome with many causes, a complicated pathogenesis, diverse clinical manifestations, and very high mortality. No effective treatment is yet available. Main pathological processes of liver failure include direct damage to parenchymal and nonparenchymal liver cells that might be caused by viruses or drugs, immune-mediated indirect damage, inflammation, and ischemia-hypoxia injury that further strengthen liver damage and lead to endotoxemia. Among these causes, viral or bacterial components (called pathogen-associated and damage-associated molecular patterns) are released during tissue damage and cell death and may be recognized by pattern recognition receptors (PRRs) to induce secretion of inflammatory cytokines and chemokines and activate immune cells. This process is an important mechanism that underlies the progression of liver failure. Research concerning the roles of PRR signaling pathways in liver failure is expected to result in development of immunomodulatory drugs to target specific disease stages, immune cells, and signal transduction molecules. This article briefly introduces the research status of six main PRRs (Toll-like receptors, nucleotide-binding oligomerization domain-like receptors, retinoic-acid-inducible gene I-like receptors, cytosolic DNA sensors, C-type lectin receptors, and inflammasomes) in acute liver failure and acute-on-chronic liver failure and explores further research directions.

Identification and functional analysis of immune deficiency (IMD) from Scylla paramamosain: The first evidence of IMD signaling pathway involved in immune defense against bacterial infection in crab species

Immune deficiency (IMD) pathway, one of the most essential pattern recognition receptor signaling pathways, plays vital roles in innate immune responses to eliminate pathogen infection in invertebrates. In the present study, an immune deficiency (IMD) gene and two NF-κB family members, Relish and Dorsal, were identified and characterized in mud crab Scylla paramamosain for the first time. The deduced SpIMD, SpRelish and SpDorsal protein contained conserved death domain and classical NF-κB domains, respectively. Phylogenetic analysis suggested that SpIMD was classified into the invertebrate IMD branch, and SpRelish could be classified into the type I NF-κB class while SpDorsal could be grouped into the type II NF-κB class. Tissue distribution results showed these three genes were ubiquitously expressed in all tested tissues. The expression patterns of IMD signaling pathway and NF-κB genes, including SpIMD, SpIKKβ, SpIKKε, SpRelish and SpDorsal, were distinct when crabs were stimulated with Vibro alginolyticus, indicating that they might be involved in responding to bacterial infection. When SpIMD was silenced by in vivo RNA interference assay, the expression levels of IMD pathway and antimicrobial peptides (AMPs) genes, including SpIKKβ, SpRelish, SpALF1-6 and SpCrustin, were significantly down-regulated (p < 0.05). Correspondingly, the bacteria clearance ability of hemolymph was extremely impaired in IMD silenced crabs. Overall, the IMD played vital roles in innate immune response by regulating the expressions of its down-stream signaling genes and AMPs in S. paramamosain. These findings might pave the way for a better understanding of innate immune system and establish a fundamental network for the IMD signaling pathway in crustaceans.

MicroRNA repertoire and comparative analysis of Andrias davidianus infected with ranavirus using deep sequencing

Andrias davidianus is a large and economically important amphibian in China. Ranavirus infection causes serious losses in A. davidianus farming industry. MicroRNA mediated host-pathogen interactions are important in antiviral defense. In this study, five small-RNA libraries from ranavirus infected and non-infected A. davidianus spleens were sequenced using high throughput sequencing. The miRNA expression pattern, potential functions, and target genes were investigated. In total, 1356 known and 431 novel miRNAs were discovered. GO and KEGG analysis revealed that certain miRNA target genes are associated with apoptotic, signal pathway, and immune response categories. Analysis identified 82 downregulated and 9 upregulated differentially expressed miRNAs, whose putative target genes are involved in pattern-recognition receptor signaling pathways and immune response. These findings suggested miRNAs play key roles in A. davidianus's response to ranavirus and could provide a reference for further miRNA functional identification, leading to novel approaches to improve A. davidianus ranavirus resistance.

Enteric Virome Sensing-Its Role in Intestinal Homeostasis and Immunity.

Pattern recognition receptors (PRRs) sensing commensal microorganisms in the intestine induce tightly controlled tonic signaling in the intestinal mucosa, which is required to maintain intestinal barrier integrity and immune homeostasis. At the same time, PRR signaling pathways rapidly trigger the innate immune defense against invasive pathogens in the intestine. Intestinal epithelial cells and mononuclear phagocytes in the intestine and the gut-associated lymphoid tissues are critically involved in sensing components of the microbiome and regulating immune responses in the intestine to sustain immune tolerance against harmless antigens and to prevent inflammation. These processes have been mostly investigated in the context of the bacterial components of the microbiome so far. The impact of viruses residing in the intestine and the virus sensors, which are activated by these enteric viruses, on intestinal homeostasis and inflammation is just beginning to be unraveled. In this review, we will summarize recent findings indicating an important role of the enteric virome for intestinal homeostasis as well as pathology when the immune system fails to control the enteric virome. We will provide an overview of the virus sensors and signaling pathways, operative in the intestine and the mononuclear phagocyte subsets, which can sense viruses and shape the intestinal immune response. We will discuss how these might interact with resident enteric viruses directly or in context with the bacterial microbiome to affect intestinal homeostasis.

Mitochondrial DNA as an inflammatory mediator in cardiovascular diseases.

Mitochondria play a central role in multiple cellular functions, including energy production, calcium homeostasis, and cell death. Currently, growing evidence indicates the vital roles of mitochondria in triggering and maintaining inflammation. Chronic inflammation without microbial infection — termed sterile inflammation — is strongly involved in the development of heart failure. Sterile inflammation is triggered by the activation of pattern recognition receptors (PRRs) that sense endogenous ligands called damage-associated molecular patterns (DAMPs). Mitochondria release multiple DAMPs including mitochondrial DNA, peptides, and lipids, which induce inflammation via the stimulation of multiple PRRs. Among the mitochondrial DAMPs, mitochondrial DNA (mtDNA) is currently highlighted as the DAMP that mediates the activation of multiple PRRs, including Toll-like receptor 9, Nod-like receptors, and cyclic GMP–AMP synthetase/stimulator of interferon gene pathways. These PRR signalling pathways, in turn, lead to the activation of nuclear factor-κB and interferon regulatory factor, which enhances the transcriptional activity of inflammatory cytokines and interferons, and induces the recruitment of inflammatory cells. As the heart is an organ comprising abundant mitochondria for its ATP consumption (needed to maintain constant cyclic contraction and relaxation), the generation of massive amounts of mitochondrial radical oxygen species and mitochondrial DAMPs are predicted to occur and promote cardiac inflammation. Here, we will focus on the role of mtDNA in cardiac inflammation and review the mechanism and pathological significance of mtDNA-induced inflammatory responses in cardiac diseases.

Antiviral effects and mechanisms of Yinhuapinggan granule against H1N1 influenza virus infection in RAW264.7 cells.

Yinhuapinggan granule (YHPG), a modified prescription based on Ma-Huang-Tang (MHT), is used in traditional Chinese medicine (TCM) to treat influenza, cough, and viral pneumonia. In this study, we investigated the antiviral effects of YHPG by means of pre-, post-, and co-treatment, and its underlying mechanisms on regulating the levels of inflammatory-related cytokines, modulating the mRNA expressions of interferon-stimulated genes in influenza virus-infected murine macrophage cells (RAW264.7), and evaluating the protein expressions of key effectors in the Type I IFN and pattern recognition receptor (PRRs) signaling pathways. The results showed that YHPG markedly inhibited influenza virus (IFV) replication in pre-, post- and co-treatment assay, especially in post-treatment assay. Antiviral mechanisms studies revealed that YHPG (500 and 250μg/mL) significantly up-regulated levels of IFN-β, IFN-stimulated genes (Mx-1, ISG-15 and ISG-56) compared with the IFV control group, while the levels of IL-6 and TNF-α were significantly down-regulated. Furthermore, western blot analysis results revealed that the protein expressions of the phosphorylated forms of TBK1, IRF3, ERK1/2, P38 MAPK and NF-κB p65 were significantly down-regulated in RAW264.7 cells with the YHPG (500 and 250μg/mL) treatment, while the expression of the phosphorylated form of STAT1 was significantly enhanced. Based on these results, YHPG had antiviral effects in IFV-infected RAW264.7 cells, which might be associated with regulation of the inflammatory cytokines production, evaluation of the levels of IFN-stimulated genes, and modulation of the protein expressions of key effectors in the Type I IFN and PRRs signaling pathways.

Canonical Stimulation of the NLRP3 Inflammasome by Fungal Antigens Links Innate and Adaptive B-Lymphocyte Responses by Modulating IL-1β and IgM Production.

The NLRP3 inflammasome is activated in response to different bacterial, viral, and fungal pathogens and serves as modulator of different pattern recognition receptors signaling pathways. One of the main functions of NLRP3 is to participate in IL-1β maturation which is important in the host defense against Pneumocystis and other fungal infections. However, dysregulation of NLRP3 and IL-1β secretion are also implicated in the pathophysiology of many auto-inflammatory disorders. Often time’s inflammatory flares are preceded by infectious illnesses questioning the role of infection in autoimmune exacerbations. However, we still do not fully understand the exact role that infection or even colonization plays as a trigger of inflammation. Herein, we investigated the role of NLRP3 in circulating B-lymphocytes following activation with two major microbial antigens (β-glucan and CpG). NLRP3 was determined essential in two independent B-lymphocytes processes: pro-inflammatory cytokine secretion and antibody regulation. Our results show that the β-glucan fungal cell wall carbohydrate stimulated B-lymphocytes to secrete IL-1β in a process partially mediated by Dectin-1 activation via SYK and the transcription factors NF-κB and AP-1. This IL-1β secretion was regulated by the NLRP3 inflammasome and was dependent on potassium efflux and Caspase-1. Interestingly, B-lymphocytes activated by unmethylated CpG motifs, found in bacterial and fungal DNA, failed to induce IL-1β. However, B-lymphocyte stimulation by CpG resulted in NLRP3 and Caspase-1 activation and the production and secretion of IgM antibodies. Furthermore, CpG-stimulated IgM secretion, unlike β-glucan-mediated IL-1β production, was mediated by the mammalian target of rapamycin (mTOR). Inhibition of NLRP3 and the mTOR pathway in CpG activated B-lymphocytes resulted in impaired IgM secretion suggesting their participation in antibody regulation. In conclusion, this study describes a differential response of NLRP3 to β-glucan and CpG antigens and identifies the NLRP3 inflammasome of human circulating B-lymphocytes as a modulator of the innate and adaptive immune systems.

Pattern-recognition receptors: signaling pathways and dysregulation in canine chronic enteropathies-brief review.

Pattern-recognition receptors (PRRs) are expressed by innate immune cells and recognize pathogen-associated molecular patterns (PAMPs) as well as endogenous damage-associated molecular pattern (DAMP) molecules. With a large potential for synergism or convergence between their signaling pathways, PRRs orchestrate a complex interplay of cellular mediators and transcription factors, and thus play a central role in homeostasis and host defense. Aberrant activation of PRR signaling, mutations of the receptors and/or their downstream signaling molecules, and/or DAMP/PAMP complex-mediated receptor signaling can potentially lead to chronic auto-inflammatory diseases or development of cancer. PRR signaling pathways appear to also present an interesting new avenue for the modulation of inflammatory responses and to serve as potential novel therapeutic targets. Evidence for a dysregulation of the PRR toll-like receptor (TLR)2, TLR4, TLR5, and TLR9, nucleotide-binding oligomerization domain-containing protein (NOD)2, and the receptor of advanced glycation end products (RAGE) exists in dogs with chronic enteropathies. We describe the TLR, NOD2, and RAGE signaling pathways and evaluate the current veterinary literature-in comparison to human medicine-to determine the role of TLRs, NOD2, and RAGE in canine chronic enteropathies.

Tumour viruses and innate immunity.

Host cells sense viral infection through pattern recognition receptors (PRRs), which detect pathogen-associated molecular patterns (PAMPs) and stimulate an innate immune response. PRRs are localized to several different cellular compartments and are stimulated by viral proteins and nucleic acids. PRR activation initiates signal transduction events that ultimately result in an inflammatory response. Human tumour viruses, which include Kaposi's sarcoma-associated herpesvirus, Epstein-Barr virus, human papillomavirus, hepatitis C virus, hepatitis B virus, human T-cell lymphotropic virus type 1 and Merkel cell polyomavirus, are detected by several different PRRs. These viruses engage in a variety of mechanisms to evade the innate immune response, including downregulating PRRs, inhibiting PRR signalling, and disrupting the activation of transcription factors critical for mediating the inflammatory response, among others. This review will describe tumour virus PAMPs and the PRRs responsible for detecting viral infection, PRR signalling pathways, and the mechanisms by which tumour viruses evade the host innate immune system.This article is part of the themed issue 'Human oncogenic viruses'.

Visualising pattern recognition receptor signalling.

Signalling by pattern recognition receptors (PRRs) is critical for protecting the host against pathogens. Disruption of these signalling pathways has been implicated in many diseases ranging from infection susceptibility to cancer and autoimmune disease. Understanding how PRRs signal is of critical importance due to their potential as therapeutic targets to ameliorate symptoms of inflammatory diseases. The recent advances in microscopy, such as the discovery of fluorescent proteins and the breaking of the diffraction limit of light, offer a unique opportunity to visualise receptor signalling at a single protein level within living cells. Many different microscopy techniques have been developed and used for dissecting different aspects of PRR signalling pathways. This review will provide an overview of the main microscopy techniques used for dissecting these pathways with a focus on Toll-like receptor and NOD-like receptor signalling.