Lessons from Nod2 studies: towards a link between Crohn's disease and bacterial sensing

Crosstalk between NOD2 and TLR2 suppresses the development of TLR2-mediated experimental colitis

Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular sensor for muramyl dipeptide (MDP), a degradation product of bacterial cell wall peptidoglycan (PGN). PGN stimulates cell-surface Toll-like receptor 2 (TLR2) independently of NOD2, indicating the presence of crosstalk between extracellular TLR2 and intracellular NOD2 upon exposure to PGN. NOD2-deficient mice were sensitive, while TLR2-deficient mice were resistant to experimental colitis induced by intrarectal administration of PGN. Severe colitis in NOD2-deficient mice was accompanied by increased expression of nuclear factor-kappa B-dependent cytokines and decreased expression of autophagy-related 16-like 1 (ATG16L1). MDP activation of NOD2 enhanced autophagy mediated by TLR2 in human dendritic cells. mRNA expression of TLR2 tended to be higher in the colonic mucosa of patients with active ulcerative colitis compared to that of those in remission. Induction of remission was associated with increased mRNA expression of ATG16L1 in both ulcerative colitis and Crohn's disease patients. Conversely, mRNA expression of receptor-interacting serine/threonine-protein kinase 2 was higher in the inflammatory colonic mucosa of patients with active disease than in the non-inflamed mucosa of patients in remission, in both ulcerative colitis and Crohn's disease. These findings highlight the role of NOD2-TLR2 crosstalk in the immunopathogenesis of colitis.

The crosstalk between microbial sensors ELMO1 and NOD2 shape intestinal immune responses

Microbial sensors play an essential role in maintaining cellular homoeostasis. Our knowledge is limited on how microbial sensing helps in differential immune response and its link to inflammatory diseases. Recently we have confirmed that ELMO1 (Engulfment and Cell Motility Protein-1) present in cytosol is involved in pathogen sensing, engulfment, and intestinal inflammation. Here, we show that ELMO1 interacts with another sensor, NOD2 (Nucleotide-binding oligomerization domain-containing protein 2), that recognizes bacterial cell wall component muramyl dipeptide (MDP). The polymorphism of NOD2 is linked to Crohn's disease (CD) pathogenesis. Interestingly, we found that overexpression of ELMO1 and mutant NOD2 (L1007fs) were not able to clear the CD-associated adherent invasive E. coli (AIEC-LF82). The functional implications of ELMO1-NOD2 interaction in epithelial cells were evaluated by using enteroid-derived monolayers (EDMs) from ELMO1 and NOD2 KO mice. Subsequently we also assessed the immune response in J774 macrophages depleted of either ELMO1 or NOD2 or both. The infection of murine EDMs with AIEC-LF82 showed higher bacterial load in ELMO1-KO, NOD2 KO EDMs, and ELMO1 KO EDMs treated with NOD2 inhibitors. The murine macrophage cells showed that the downregulation of ELMO1 and NOD2 is associated with impaired bacterial clearance that is linked to reduce pro-inflammatory cytokines and reactive oxygen species. Our results indicated that the crosstalk between microbial sensors in enteric infection and inflammatory diseases impacts the fate of the bacterial load and disease pathogenesis.

Integration and implementation of precision medicine in the multifaceted inflammatory bowel disease

Inflammatory bowel disease (IBD) is a complex disease with variability in genetic, environmental, and lifestyle factors affecting disease presentation and course. Precision medicine has the potential to play a crucial role in managing IBD by tailoring treatment plans based on the heterogeneity of clinical and temporal variability of patients. Precision medicine is a population-based approach to managing IBD by integrating environmental, genomic, epigenomic, transcriptomic, proteomic, and metabolomic factors. It is a recent and rapidly developing medicine. The widespread adoption of precision medicine worldwide has the potential to result in the early detection of diseases, optimal utilization of healthcare resources, enhanced patient outcomes, and, ultimately, improved quality of life for individuals with IBD. Though precision medicine is promising in terms of better quality of patient care, inadequacies exist in the ongoing research. There is discordance in study conduct, and data collection, utilization, interpretation, and analysis. This review aims to describe the current literature on precision medicine, its multiomics approach, and future directions for its application in IBD.

The crosstalk between microbial sensors ELMO1 and NOD2 shape intestinal immune responses.. [DOI: 10.1101/2022.07.09.499433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Microbial sensors play an essential role in maintaining cellular homeostasis. Our knowledge is limited on how microbial sensing helps in differential immune response and its link to inflammatory diseases. Recently, we have shown that cytosolic sensor ELMO1 (Engulfment and Cell Motility Protein-1) binds to effectors from pathogenic bacteria and controls intestinal inflammation. Here, we show that ELMO1 interacts with another sensor, NOD2 (Nucleotide-binding oligomerization domain-containing protein 2), that recognizes bacterial cell wall component muramyl dipeptide (MDP). The polymorphism of NOD2 is linked to Crohn’s disease (CD) pathogenesis. Interestingly, we found that overexpression of ELMO1 and mutant NOD2 (L1007fs) were not able to clear the CD-associated adherent invasive E. coli (AIEC-LF82). To understand the interplay of microbial sensing of ELMO1-NOD2 in epithelial cells and macrophages, we used enteroid-derived monolayers (EDMs) from ELMO1 and NOD2 KO mice and ELMO1 and NOD2-depleted murine macrophage cell lines. The infection of murine EDMs with AIEC-LF82 showed higher bacterial load in ELMO1-KO, NOD2 KO EDMs, and ELMO1 KO EDMs treated with NOD2 inhibitors. The murine macrophage cells showed that the downregulation of ELMO1 and NOD2 is associated with impaired bacterial clearance that is linked to reduced pro-inflammatory cytokines and reactive oxygen species. Our results indicated that the crosstalk between microbial sensors in enteric infection and inflammatory diseases impacts the fate of the bacterial load and disease pathogenesis.

Insights into inflammasome regulation: cellular, molecular, and pathogenic control of inflammasome activation

Maintenance of immune homeostasis is an intricate process wherein inflammasomes play a pivotal role by contributing to innate and adaptive immune responses. Inflammasomes are ensembles of adaptor proteins that can trigger a signal following innate sensing of pathogens or non-pathogens eventuating in the inductions of IL-1β and IL-18. These inflammatory cytokines substantially influence the antigen-presenting cell's costimulatory functions and T helper cell differentiation, contributing to adaptive immunity. As acute and chronic disease conditions may accompany parallel tissue damage, we analyze the critical role of extracellular factors such as cytokines, amyloids, cholesterol crystals, etc., intracellular metabolites, and signaling molecules regulating inflammasome activation/inhibition. We develop an operative framework for inflammasome function and regulation by host cell factors and pathogens. While inflammasomes influence the innate and adaptive immune components' interplay modulating the anti-pathogen adaptive immune response, pathogens may target inflammasome inhibition as a survival strategy. As trapped between health and diseases, inflammasomes serve as promising therapeutic targets and their modus operandi serves as a scientific rationale for devising better therapeutic strategies.

Precision medicine in inflammatory bowel disease: concept, progress and challenges

Crohn's disease and ulcerative colitis are increasingly prevalent, relapsing and remitting inflammatory bowel diseases (IBDs) with variable disease courses and complications. Their aetiology remains unclear but current evidence shows an increasingly complex pathophysiology broadly centring on the genome, exposome, microbiome and immunome. Our increased understanding of disease pathogenesis is providing an ever-expanding arsenal of therapeutic options, but these can be expensive and patients can lose response or never respond to certain therapies. Therefore, there is now a growing need to personalise therapies on the basis of the underlying disease biology and a desire to shift our approach from "reactive" management driven by disease complications to "proactive" care with an aim to prevent disease sequelae. Precision medicine is the tailoring of medical treatment to the individual patient, encompassing a multitude of data-driven (and multi-omic) approaches to foster accurate clinical decision-making. In IBD, precision medicine would have significant benefits, enabling timely therapy that is both effective and appropriate for the individual. In this review, we summarise some of the key areas of progress towards precision medicine, including predicting disease susceptibility and its course, personalising therapies in IBD and monitoring response to therapy. We also highlight some of the challenges to be overcome in order to deliver this approach.

Immunoproteomics Methods and Techniques

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new, and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent progress in genomics and mass spectrometry have led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel-based, array-based, mass spectrometry-based, DNA-based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of protein antigens targeted by the immune system during disease.

Short communication: Uncovering quantitative trait loci associated with resistance to Mycobacterium avium ssp. paratuberculosis infection in Holstein cattle using a high-density single nucleotide polymorphism panel

Mycobacterium avium ssp. paratuberculosis (MAP) is the etiological agent of Johne's disease in cattle. Johne's disease is a disease of significant economic, animal welfare, and public health concern around the globe. Therefore, understanding the genetic architecture of resistance to MAP infection has great relevance to advance genetic selection methods to breed more resistant animals. The objectives of this study were to perform a genome-wide association study of previously analyzed 50K genotypes now imputed to a high-density single nucleotide polymorphism panel (777K), aiming to validate previously reported associations and potentially identify additional single nucleotide polymorphisms associated with antibody response to MAP infection. A principal component regression-based genome-wide association study revealed 15 putative quantitative trait loci (QTL) associated with the MAP infection phenotype (serum or milk ELISA tests) on 9 different chromosomes (Bos taurus autosomes 5, 6, 7, 10, 14, 15, 16, 20, and 21). These results validated previous findings and identified new QTL on Bos taurus autosomes 15, 16, 20, and 21. The positional candidate genes NLRP3, IFi47, TRIM41, TNFRSF18, and TNFRSF4 lying within these QTL were identified. Further functional validation of these genes is now warranted to investigate their roles in regulating the immune response and, consequently, cattle resistance to MAP infection.

Intestinal Barrier Interactions with Specialized CD8 T Cells

The trillions of microorganisms that reside in the gastrointestinal tract, essential for nutrient absorption, are kept under control by a single cell barrier and large amounts of immune cells. Intestinal epithelial cells (IECs) are critical in establishing an environment supporting microbial colonization and immunological tolerance. A large population of CD8⁺ T cells is in direct and constant contact with the IECs and the intraepithelial lymphocytes (IELs). Due to their location, at the interphase of the intestinal lumen and external environment and the host tissues, they seem ideally positioned to balance immune tolerance and protection to preserve the fragile intestinal barrier from invasion as well as immunopathology. IELs are a heterogeneous population, with a large innate-like contribution of unknown specificity, intercalated with antigen-specific tissue-resident memory T cells. In this review, we provide a comprehensive overview of IEL physiology and how they interact with the IECs and contribute to immune surveillance to preserve intestinal homeostasis and host-microbial relationships.

NOD2 dependent neutrophil recruitment is required for early protective immune responses against infectious Litomosoides sigmodontis L3 larvae

Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) recognizes muramyl dipeptide (MDP) of bacterial cell walls, triggering NFκB-induced pro-inflammation. As most human pathogenic filariae contain Wolbachia endobacteria that synthesize the MDP-containing cell wall precursor lipid II, NOD2’s role during infection with the rodent filaria Litomosoides sigmodontis was investigated. In NFκB reporter-cells, worm-extract containing Wolbachia induced NOD2 and NOD1. NOD2-deficient mice infected with L. sigmodontis had significantly more worms than wildtype controls early in infection. Increased worm burden was not observed after subcutaneous infection, suggesting that protective NOD2-dependent immune responses occur within the skin. Flow cytometry demonstrated that neutrophil recruitment to the skin was impaired in NOD2^−/− mice after intradermal injection of third stage larvae (L3), and blood neutrophil numbers were reduced after L. sigmodontis infection. PCR array supported the requirement of NOD2 for recruitment of neutrophils to the skin, as genes associated with neutrophil recruitment and activation were downregulated in NOD2^−/− mice after intradermal L3 injection. Neutrophil depletion before L. sigmodontis infection increased worm recovery in wildtype mice, confirming that neutrophils are essential against invading L3 larvae. This study indicates that NOD-like receptors are implemented in first-line protective immune responses against filarial nematodes.

Casting the critical regions in nucleotide binding oligomerization domain 2 protein: a signature mediated structural dynamics approach

Nucleotide binding oligomerization domain 2 (NOD2), a protein involved in the first line defence mechanism has a pivotal role in innate immunity. Impaired function of this protein is implicated in disorders such as Blau syndrome and Crohn's disease. Since an altered function is linked to protein's structure, we framed a systematic strategy to interpret the structure-function relationship of the protein. Initiated with mutation-based pattern prediction and identified a distant ortholog (DO) of NOD2 from which the intra-residue interaction network was elucidated. The network was used to identify hotspots that serve as critical points to maintain the stable architecture of the protein. Structural comparison of NOD2 domains with a DO revealed the minimal number of intra-protein interactions required by the protein to maintain the structural fold. In addition, the conventional molecular dynamics simulation emphasized the conformational transitions at hot spot residues between native NOD2 domains and its respective mutants (G116R, R42W and R54A) structures. The analysis of intra-protein interactions globally and the displacement of residues locally around the mutational site revealed loss of several critical bonds and residues vital for the protein's function. Conclusively we report, about 10 residues in leucine-rich repeat, 13 residues in NOD and 6 residues in CARD domain are required by the NOD2 to maintain its function. This protocol will help the researchers to achieve for more prospective studies to attest druggable site utility in discovering novel drug candidates.

The immune system of the gut and potential adverse effects of oral nanocarriers on its function

There is substantial effort in modern pharmacotherapy to use nanoparticle-based drug delivery systems (nDDS) for improving the oral absorption of drugs. An often neglected circumstance regarding this approach is that the gut is a major part of the immune system that may be vulnerable for immune-cell toxicity, or mediate humoral immune response against various components of nDDS, recognized as foreign. This review recapitulates the structure and function of gut-associated lymphoid tissue (GALT), i.e., the enteral section of mucosa-associated lymphoid tissue (MALT) and reminds how virus-like nDDS may potentially induce immunogenicity just as attenuated or killed viruses do in oral vaccines. Furthermore, we present examples for immune toxicities of emulsifiers and polymer-containing micelles, manifested in complement activation-related pseudoallergy (CARPA). A major message of the review is that early testing of immunogenicity or other adverse immune effects of nDDS in appropriate test systems or models may be prudent to recognize the risk of rare immune problems that may surface in late-stage clinical trials or after marketing of nDDS.

NOD-Like Receptor Signaling in Cholesteatoma

Background. Cholesteatoma is a destructive process of the middle ear resulting in erosion of the surrounding bony structures with consequent hearing loss, vestibular dysfunction, facial paralysis, or intracranial complications. The etiopathogenesis of cholesteatoma is controversial but is associated with recurrent ear infections. The role of intracellular innate immune receptors, the NOD-like receptors, and their associated signaling networks was investigated in cholesteatoma, since mutations in NOD-like receptor-related genes have been implicated in other chronic inflammatory disorders. Results. The expression of NOD2 mRNA and protein was significantly induced in cholesteatoma compared to the external auditory canal skin, mainly located in the epithelial layer of cholesteatoma. Microarray analysis showed significant upregulation for NOD2, not for NOD1, TLR2, or TLR4 in cholesteatoma. Moreover, regulation of genes in an interaction network of the NOD-adaptor molecule RIPK2 was detected. In addition to NOD2, NLRC4, and PYCARD, the downstream molecules IRAK1 and antiapoptotic regulator CFLAR showed significant upregulation, whereas SMAD3, a proapoptotic inducer, was significantly downregulated. Finally, altered regulation of inflammatory target genes of NOD signaling was detected. Conclusions. These results indicate that the interaction of innate immune signaling mediated by NLRs and their downstream target molecules is involved in the etiopathogenesis and growth of cholesteatoma.

Periodontal innate immune mechanisms relevant to atherosclerosis

Atherosclerosis is a common cardiovascular disease in the USA where it is a leading cause of illness and death. Atherosclerosis is the most common cause for heart attack and stroke. Most commonly, people develop atherosclerosis as a result of diabetes, genetic risk factors, high blood pressure, a high-fat diet, obesity, high blood cholesterol levels, and smoking. However, a sizable number of patients suffering from atherosclerosis do not harbor the classical risk factors. Ongoing infections have been suggested to play a role in this process. Periodontal disease is perhaps the most common chronic infection in adults with a wide range of clinical variability and severity. Research in the past decade has shed substantial light on both the initiating infectious agents and host immunological responses in periodontal disease. Up to 46% of the general population harbors the microorganism(s) associated with periodontal disease, although many are able to limit the progression of periodontal disease or even clear the organism(s) if infected. In the last decade, several epidemiological studies have found an association between periodontal infection and atherosclerosis. This review focuses on exploring the molecular consequences of infection by pathogens that exacerbate atherosclerosis, with the focus on infections by the periodontal bacterium Porphyromonas gingivalis as a running example.

Inflammation-associated adherent-invasive Escherichia coli are enriched in pathways for use of propanediol and iron and M-cell translocation

BACKGROUND

Perturbations of the intestinal microbiome, termed dysbiosis, are linked to intestinal inflammation. Isolation of adherent-invasive Escherichia coli (AIEC) from intestines of patients with Crohn's disease (CD), dogs with granulomatous colitis, and mice with acute ileitis suggests these bacteria share pathoadaptive virulence factors that promote inflammation.

METHODS

To identify genes associated with AIEC, we sequenced the genomes of phylogenetically diverse AIEC strains isolated from people with CD (4), dogs with granulomatous colitis (2), and mice with ileitis (2) and 1 non-AIEC strain from CD ileum and compared them with 38 genome sequences of E. coli and Shigella. We then determined the prevalence of AIEC-associated genes in 49 E. coli strains from patients with CD and controls and correlated genotype with invasion of intestinal epithelial cells, persistence within macrophages, AIEC pathotype, and growth in standardized conditions.

RESULTS

Genes encoding propanediol utilization (pdu operon) and iron acquisition (yersiniabactin, chu operon) were overrepresented in AIEC relative to nonpathogenic E. coli. PduC (propanediol dehydratase) was enriched in CD-derived AIEC, correlated with increased cellular invasion, and persistence in vitro and was increasingly expressed in fucose-containing media. Growth of AIEC required iron, and the presence of chuA (heme acquisition) correlated with persistence in macrophages. CD-associated AIEC with lpfA 154 (long polar fimbriae) demonstrated increased invasion of epithelial cells and translocation across M cells.

CONCLUSIONS

Our findings provide novel insights into the genetic basis of the AIEC pathotype, supporting the concept that AIEC are equipped to exploit and promote intestinal inflammation and reveal potential targets for intervention against AIEC and inflammation-associated dysbiosis.

Rectal microRNAs are perturbed in pediatric inflammatory bowel disease of the colon

BACKGROUND AND AIMS

Changes in intestinal microRNAs have been reported in adult patients with ulcerative colitis or Crohn's disease. The goal of this study was to identify changes in microRNA expression associated with colitis in children with inflammatory bowel disease.

METHODS

Rectal mucosal biopsies (n = 50) and blood samples (n = 47) were collected from patients with known or suspected inflammatory bowel disease undergoing endoscopy. Rectal and serum microRNA levels were profiled using the nCounter platform and the TaqMan low-density array platform, respectively. Significantly altered microRNAs were validated in independent sample sets via quantitative RT-PCR. In vitro luciferase reporter assays were performed in the human colorectal Caco-2 cell line to determine the effect of miR-192 on NOD2 expression.

RESULTS

Profiling of rectal RNA identified 21 microRNAs significantly altered between control, UC, and colonic CD sample groups. Nine of the ten microRNAs selected for validation were confirmed as significantly changed. Rectal miR-24 was increased 1.47-fold in UC compared to CD samples (p = 0.0052) and was the only microRNA altered between IBD subtypes. Three colitis-associated microRNAs were significantly altered in sera of disease patients and displayed diagnostic utility. However, no serum microRNAs were found to distinguish ulcerative colitis from Crohn's colitis. Finally, miR-192 inhibition did not affect luciferase reporter activity, suggesting that miR-192 does not regulate human NOD2.

CONCLUSION

This study has demonstrated that rectal and serum microRNAs are perturbed in pediatric inflammatory bowel disease. Future studies identifying targets of inflammatory bowel disease-associated microRNAs may lead to novel therapies.

Bacterial sensor Nod2 prevents inflammation of the small intestine by restricting the expansion of the commensal Bacteroides vulgatus

Nod2 has been extensively characterized as a bacterial sensor that induces an antimicrobial and inflammatory gene expression program. Therefore, it is unclear why Nod2 mutations that disrupt bacterial recognition are paradoxically among the highest risk factors for Crohn's disease, which involves an exaggerated immune response directed at intestinal bacteria. Here, we identified several abnormalities in the small-intestinal epithelium of Nod2(-/-) mice including inflammatory gene expression and goblet cell dysfunction, which were associated with excess interferon-γ production by intraepithelial lymphocytes and Myd88 activity. Remarkably, these abnormalities were dependent on the expansion of a common member of the intestinal microbiota Bacteroides vulgatus, which also mediated exacerbated inflammation in Nod2(-/-) mice upon small-intestinal injury. These results indicate that Nod2 prevents inflammatory pathologies by controlling the microbiota and support a multihit disease model involving specific gene-microbe interactions.

VIDEO ABSTRACT

Macrophages inhibit human osteosarcoma cell growth after activation with the bacterial cell wall derivative liposomal muramyl tripeptide in combination with interferon-γ

Background

In osteosarcoma, the presence of tumor-infiltrating macrophages positively correlates with patient survival in contrast to the negative effect of tumor-associated macrophages in patients with other tumors. Liposome-encapsulated muramyl tripeptide (L-MTP-PE) has been introduced in the treatment of osteosarcoma patients, which may enhance the potential anti-tumor activity of macrophages. Direct anti-tumor activity of human macrophages against human osteosarcoma cells has not been described so far. Hence, we assessed osteosarcoma cell growth after co-culture with human macrophages.

Methods

Monocyte-derived M1-like and M2-like macrophages were polarized with LPS + IFN-γ, L-MTP-PE +/− IFN-γ or IL-10 and incubated with osteosarcoma cells. Two days later, viable tumor cell numbers were analyzed. Antibody-dependent effects were investigated using the therapeutic anti-EGFR antibody cetuximab.

Results

M1-like macrophages inhibited osteosarcoma cell growth when activated with LPS + IFN-γ. Likewise, stimulation of M1-like macrophages with liposomal muramyl tripeptide (L-MTP-PE) inhibited tumor growth, but only when combined with IFN-γ. Addition of the tumor-reactive anti-EGFR antibody cetuximab did not further improve the anti-tumor activity of activated M1-like macrophages. The inhibition was mediated by supernatants of activated M1-like macrophages, containing TNF-α and IL-1β. However, specific blockage of these cytokines, nitric oxide or reactive oxygen species did not inhibit the anti-tumor effect, suggesting the involvement of other soluble factors released upon macrophage activation. While LPS + IFN-γ–activated M2-like macrophages had low anti-tumor activity, IL-10–polarized M2-like macrophages were able to reduce osteosarcoma cell growth in the presence of the anti-EGFR cetuximab involving antibody-dependent tumor cell phagocytosis.

Conclusion

This study demonstrates that human macrophages can be induced to exert direct anti-tumor activity against osteosarcoma cells. Our observation that the induction of macrophage anti-tumor activity by L-MTP-PE required IFN-γ may be of relevance for the optimization of L-MTP-PE therapy in osteosarcoma patients.

Periodontal innate immune mechanisms relevant to obesity

Obesity affects over 35% of the adult population of the USA, and obesity-related illnesses have emerged as the leading cause of preventable death worldwide, according to the World Health Organization. Obesity's secondary morbidities include increased risk of cardiovascular disease, type II diabetes, and cancer, in addition to increased occurrence and severity of infections. Sedentary lifestyle and weight gain caused by consumption of a high-fat diet contribute to the development of obesity, with individuals having a body mass index (BMI) score > 30 being considered obese. Genetic models of obesity (ob/ob mice, db/db mice, and fa/fa rats) have been insufficient to study human obesity because of the overall lack of genetic causes for obesity in human populations. To date, the diet-induced obese (DIO) mouse model best serves research studies relevant to human health. Periodontal disease presents with a wide range of clinical variability and severity. Research in the past decade has shed substantial light on both the initiating infectious agents and host immunological responses in periodontal disease. Up to 46% of the general population harbors the microorganism(s) associated with periodontal disease, although many are able to limit the progression of periodontal disease or even clear the organism(s) if infected. In the last decade, several epidemiological studies have found an association between obesity and increased incidence of periodontal disease. This review focuses on exploring the immunological consequences of obesity that exacerbate effects of infection by pathogens, with focus on infection by the periodontal bacterium Porphyromonas gingivalis as a running example.

Immunoproteomics: current technology and applications

The varied landscape of the adaptive immune response is determined by the peptides presented by immune cells, derived from viral or microbial pathogens or cancerous cells. The study of immune biomarkers or antigens is not new and classical methods such as agglutination, enzyme-linked immunosorbent assay, or Western blotting have been used for many years to study the immune response to vaccination or disease. However, in many of these traditional techniques, protein or peptide identification has often been the bottleneck. Recent advances in genomics and proteomics, has led to many of the rapid advances in proteomics approaches. Immunoproteomics describes a rapidly growing collection of approaches that have the common goal of identifying and measuring antigenic peptides or proteins. This includes gel based, array based, mass spectrometry, DNA based, or in silico approaches. Immunoproteomics is yielding an understanding of disease and disease progression, vaccine candidates, and biomarkers. This review gives an overview of immunoproteomics and closely related technologies that are used to define the full set of antigens targeted by the immune system during disease.

Pathogen recognition and activation of the innate immune response in zebrafish

The zebrafish has proven itself as an excellent model to study vertebrate innate immunity. It presents us with possibilities for in vivo imaging of host-pathogen interactions which are unparalleled in mammalian model systems. In addition, its suitability for genetic approaches is providing new insights on the mechanisms underlying the innate immune response. Here, we review the pattern recognition receptors that identify invading microbes, as well as the innate immune effector mechanisms that they activate in zebrafish embryos. We compare the current knowledge about these processes in mammalian models and zebrafish and discuss recent studies using zebrafish infection models that have advanced our general understanding of the innate immune system. Furthermore, we use transcriptome analysis of zebrafish infected with E. tarda, S. typhimurium, and M. marinum to visualize the gene expression profiles resulting from these infections. Our data illustrate that the two acute disease-causing pathogens, E. tarda and S. typhimurium, elicit a highly similar proinflammatory gene induction profile, while the chronic disease-causing pathogen, M. marinum, induces a weaker and delayed innate immune response.

Genetic and pharmacological targeting of TPL-2 kinase ameliorates experimental colitis: a potential target for the treatment of Crohn's disease?

Inflammatory bowel disease is characterized by dysregulated immune responses against intestinal microflora leading to marked activation of nuclear factor-κB (NF-κB) with subsequent production of pro-inflammatory cytokines. Besides NF-κB, the tumor progression locus 2 (TPL-2)/extracellular signal-regulated kinase (ERK) pathway also regulates inflammatory cytokines such as interleukin-1β and tumor necrosis factor-α, but its role during intestinal inflammation is incompletely understood. We analyzed the impact of TPL-2 in the dextran sulfate sodium-induced experimental colitis model. Despite normal activation of NF-κB, animals lacking TPL-2 developed only mild colitis with reduced synthesis of inflammatory cytokines. Further, pharmacological inhibition of the TPL-2 kinase was similarly effective in ameliorating colitis as TPL-2 deficiency without obvious side effects. Because increased TPL-2/ERK activation was seen in patients with Crohn's disease (CD) but not ulcerative colitis, our findings encourage further investigation of TPL-2 kinase as potential target for the treatment of CD patients.

Polymorphisms of NOD2 and the risk of tuberculosis: a validation study in the Chinese population

A genome-wide association study (GWAS) of leprosy reported four specific genetic polymorphisms of NOD2 that were associated with susceptibility to Mycobacterium leprae in China. Considering the role of NOD2 in innate immune defence, we performed a study in a Chinese population to determine whether the same SNPs of NOD2 that were associated with disease caused by M. leprae were also associated with disease caused by Mycobacterium tuberculosis. We performed a frequency-matched case-control study in 1043 patients with pulmonary tuberculosis and 808 unaffected controls. All subjects were >15 years old and were Han Chinese from Jiangsu Province. We extracted DNA from a blood sample from each study participant. SNPs of rs3135499, rs7194886, rs8057341 and rs9302752 in the NOD2 gene were genotyped using a TaqMan-based allelic discrimination system. Using all possible patients with tuberculosis as cases, no significant association was found between the four specific SNPs and the risk of tuberculosis. In a subgroup analysis restricted to cases with bacteriologically confirmed tuberculosis (sputum culture positive), the variant genotype of rs7194886 was significantly associated with an altered risk of tuberculosis. Compared with the CC genotype, individuals carrying the CT/TT genotype of rs7194886 had an increased risk [odds ratio (OR) 1.35, 95% confidence interval (CI) (1.05-1.72)]. The association was stronger among tobacco smokers and males. By haplotype analysis, rs9302752C-rs7194886T was associated with an increased risk of bacteriologically confirmed tuberculosis (sputum culture positive) (P = 0.039), but it was not significant after correcting for multiple comparisons. In summary, genetic polymorphisms of the SNP rs7194886 in the NOD2 gene, which were discovered in the GWAS of leprosy, might also be associated with the pulmonary tuberculosis in the Chinese population.

Inflammatory bowel disease: is it a primary immunodeficiency?

Inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease are chronic and relapsing conditions, characterized by abdominal pain, diarrhea, bleeding and malabsorption. IBD has been considered a hyperinflammatory state due to disturbed interactions between the immune system and the commensal bacterial flora of the gut. However, there is evidence that Crohn's disease might be the consequence of a reduced release of pro-inflammatory cytokines and an impaired acute inflammatory response, thereby suggesting that IBD might be an immunodeficiency rather than an excessive inflammatory reaction. This theory has been supported by observations in patients with primary immunodeficiencies such as the Wiskott-Aldrich syndrome and IPEX (immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome). In contrary, defects in the anti-inflammatory down-regulation of the immune response as they are seen in patients with Mendelian defects in the IL10 signaling pathway support the hyper-inflammatory theory. In this review, we describe and discuss primary immunodeficiencies associated with IBD and show that the bowel is a highly sensitive indicator of dysregulations, making IBD a model disease to study and identify key regulators required to balance the human mucosal immune system.

Interactions between microbes and the gut epithelium

Gut microbes interact with the epithelium through cell surface components, fermentation products, and extracellular secreted proteins. Host-microbial interactions primarily involve TLRs (toll-like receptors) and NLR (nucleotide-binding oligomerization domain and leucine-rich repeat containing proteins). In a strain and dose-dependent manner, several probiotic strains directly alter tight junction protein expression and/or localization in gut epithelial cells through the release of secreted compounds. Interactions between gut microbes and intestinal epithelial and immune cells are necessary for the development and maintenance of intestinal homeostasis.

Intrinsic and extrinsic regulation of innate immune receptors

Pattern recognition receptors (PRRs) in innate immune cells play a pivotal role in the first line of host defense system. PRRs recognize pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs) to initiate and regulate innate and adaptive immune responses. PRRs include Toll-like receptors (TLRs), RIG-I-like receptors (RLRs) and NOD-like receptors (NLRs), which have their own features in ligand recognition and cellular location. Activated PRRs deliver signals to adaptor molecules (MyD88, TRIF, MAL/TIRAP, TRAM, IPS-1) which act as important messengers to activate downstream kinases (IKK complex, MAPKs, TBK1, RIP-1) and transcription factors (NF-κB, AP-1, IRF3), which produce effecter molecules including cytokines, chemokines, inflammatory enzymes, and type I interferones. Since excessive PRR activation is closely linked to the development of chronic inflammatory diseases, the role of intrinsic and extrinsic regulators in the prevention of over- or unnecessary activation of PRRs has been widely studied. Intracellular regulators include MyD88s, SOCS1, TOLLIP, A20, and CYLD. Extrinsic regulators have also been identified with their molecular targets in PRR signaling pathways. TLR dimerization has been suggested as an inhibitory target for small molecules such as curcumin, cinnamaldehyde, and sulforaphane. TBK1 kinase can be a target for certain flavonoids such as EGCG, luteolin, quercetin, chrysin, and eriodictyol to regulate TRIF-dependent TLR pathways. This review focuses on the features of PRR signaling pathways and the therapeutic targets of intrinsic and extrinsic regulators in order to provide beneficial strategies for controlling the activity of PRRs and the related inflammatory diseases and immune disorders.

[A protein interaction network and cell signaling pathways activated by muramyl peptides]

Review is devoted to studying the interaction muramyl peptides with protein components of immune system cells. Systems analysis of published results may be useful to select not only the strategy to further explore the function of this class of glycopeptides, but their use in clinical practice.

Detection of Mycobacterium avium ss. Paratuberculosis in Blau Syndrome Tissues

Background and Aim of the Work. Blau syndrome is an inherited granulomatous inflammatory disorder with clinical findings of uveitis, arthritis, and dermatitis. Although rare, Blau syndrome shares features with the more common diseases sarcoidosis and Crohn's disease. The clinical findings of Blau syndrome are indistinguishable from juvenile sarcoidosis; the mutations of Blau syndrome are on the same gene of chromosome 16 (CARD15) that confers susceptibility to Crohn's disease. The product of this gene is part of the innate immune system. Mycobacterium avium ss. paratuberculosis (MAP) is the putative cause of Crohn's disease and has been implicated as a causative agent of sarcoidosis. Methods. Archival tissues of individuals with Blau syndrome were tested for the presence of MAP. Results. DNA evidence of MAP was detected in all of the tissues. Conclusions. This article finds that MAP is present in Blau syndrome tissue and postulates that it has a causal role. The presence of MAP in Blau syndrome—an autosomal dominant, systemic inflammatory disease—connects genetic and environmental aspects of “autoimmune” disease.

The pathogen recognition receptor NOD2 regulates human FOXP3+ T cell survival

The expression of pathogen recognition receptors in human FOXP3+ T regulatory cells is established, yet the function of these receptors is currently obscure. In the process of studying the function of both peripheral and lamina propria FOXP3+ lymphocytes in patients with the human inflammatory bowel disease Crohn's disease, we observed a clear deficiency in the quantity of FOXP3+ lymphocytes in patients with disease-associated polymorphisms in the pathogen recognition receptor gene NOD2. Subsequently, we determined that the NOD2 ligand, muramyl dipeptide (MDP), activates NF-kappaB in primary human FOXP3+ T cells. This activation is functionally relevant, as MDP-stimulated human FOXP3+ T cells are protected from death receptor Fas-mediated apoptosis. Importantly, apoptosis protection was not evident in MDP-stimulated FOXP3+ T cells isolated from a patient with the disease-associated polymorphism. Thus, we propose that one function of pathogen recognition receptors in human T regulatory cells is the protection against death receptor-mediated apoptosis in a Fas ligand-rich environment, such as that of the inflamed intestinal subepithelial space.

Expression of NOD2 is increased in inflamed human dental pulps and lipoteichoic acid-stimulated odontoblast-like cells

Human odontoblasts trigger immune response s to oral bacteria that invade dental tissues during the caries process. To date, their ability to regulate the expression of the nucleotide-binding domain leucine-rich repeat containing receptor NOD2 when challenged by Gram-positive bacteria is unknown. In this study, we investigated NOD2 expression in healthy and inflamed human dental pulps challenged by bacteria, and in cultured odontoblast-like cells stimulated with lipoteichoic acid (LTA), a Toll-like receptor (TLR) 2 agonist which is specific for Gram-positive bacteria. We found that NOD2 gene expression was significantly up-regulated in pulps with acute inflammation compared to healthy ones. In vitro, LTA augmented NOD2 gene expression and protein level in odontoblast-like cells. The increase was more pronounced in odontoblast-like cells compared to dental pulp fibroblasts. Blocking experiments in odontoblast-like cells with anti-TLR2 antibody strongly reduced the NOD2 gene expression increase, whereas stimulation with the synthetic TLR2 ligand Pam2CSK4 confirmed NOD2 gene up-regulation following TLR2 engagement. These data suggest that NOD2 up-regulation is part of the odontoblast immune response to Gram-positive bacteria and might be important in protecting human dental pulp from the deleterious effects of cariogenic pathogens.

Intestinal macrophages: differentiation and involvement in intestinal immunopathologies

Intestinal macrophages, preferentially located in the subepithelial lamina propria, represent the largest pool of tissue macrophages in humans. As an adaptation to the local antigen- and bacteria-rich environment, intestinal macrophages exhibit several distinct phenotypic and functional characteristics. Notably, microbe-associated molecular pattern receptors, including the lipopolysaccharide (LPS) receptors CD14 and TLR4, and also the Fc receptors for IgA and IgG are absent on most intestinal macrophages under homeostatic conditions. Moreover, while macrophages in the intestinal mucosa are refractory to the induction of proinflammatory cytokine secretion, they still display potent phagocytic activity. These adaptations allow intestinal macrophages to comply with their main task, i.e., the efficient removal of microbes while maintaining local tissue homeostasis. In this paper, we review recent findings on the functional differentiation of monocyte subsets into distinct macrophage populations and on the phenotypic and functional adaptations that have evolved in intestinal macrophages in response to their antigen-rich environment. Furthermore, the involvement of intestinal macrophages in the pathogenesis of celiac disease and inflammatory bowel diseases is discussed.

Clustering of (auto)immune diseases with early-onset and complicated inflammatory bowel disease

Studies in adult inflammatory bowel disease (IBD) patients have highlighted associations with genetic and serologic markers and suggest an association with disease location, behaviour and natural history. Data on patients with Crohn's disease (CD, n=80), ulcerative colitis (UC, n=15) and indeterminate colitis (n=4) were collected. All individuals were analysed for CARD15 R702W, G908R and L1007fs for toll-like receptor 4 (TLR4) Asp299Gly and for anti-Saccharomyces cerevisiae antibodies (ASCA) and atypical perinuclear antineutrophil cytoplasmatic antibodies (pANCA). After a mean of 10.7 years of follow up, the disease behaviour changed in 45% of CD patients, in contrast to disease location, where only 12.5% had a change (p<0.001). The younger the age at diagnosis, the more patients presented with colonic disease (p=0.021). Also, more TLR4 Asp299 Gly variants were found when the age at onset was younger (p=0.018). A large number of concomitant diseases were observed. There was no difference in the prevalence of TLR4 variants nor ASCA or pANCA between the patients with or without concomitant diseases. Patients who progressed more often needed surgery as compared to patients who remained free of stenosing or fistulising disease (27/32 or 84% versus 3/35 or 8.6%, respectively, p<0.0001) and more often had concomitant immune-mediated diseases and a trend for more seroreactivity towards ASCA.

Pathogen recognition in the innate immune response

Immunity against microbial pathogens primarily depends on the recognition of pathogen components by innate receptors expressed on immune and non-immune cells. Innate receptors are evolutionarily conserved germ-line-encoded proteins and include TLRs (Toll-like receptors), RLRs [RIG-I (retinoic acid-inducible gene-I)-like receptors] and NLRs (Nod-like receptors). These receptors recognize pathogens or pathogen-derived products in different cellular compartments, such as the plasma membrane, the endosomes or the cytoplasm, and induce the expression of cytokines, chemokines and co-stimulatory molecules to eliminate pathogens and instruct pathogen-specific adaptive immune responses. In the present review, we will discuss the recent progress in the study of pathogen recognition by TLRs, RLRs and NLRs and their signalling pathways.

Interactions among genes influencing bacterial recognition increase IBD risk in a population-based New Zealand cohort

Bacterial sensing is crucial for appropriate response by the innate and adaptive immune system against invading microorganisms. Single nucleotide polymorphisms (SNPs) in genes involved in bacterial recognition, CARD15 and TLR4, increased the risk of inflammatory bowel disease (IBD) in a New Zealand Caucasian case-control cohort. We now consider the effects of SNPs in CD14, TLR9, and BPI, analyzed individually, in association with one another, and with SNPs in CARD15 or TLR4 in this same population group. SNPs in CD14 (c.-159 C>T), TLR9 (c.-1237T>C) and BPI (c.645A>G) showed no significant allele or genotype frequency differences between IBD cases and controls. Genotype-phenotype mapping reveals an association with BPI and ileocolonic Crohn's disease (CD) as well as an association with CD14 and early-onset ulcerative colitis (UC). Genotype interaction analyses using three different statistical approaches provided significant evidence of interaction for the following combinations: CARD15/TLR4 (CD and UC), CARD15/CD14 (CD and UC), CD14/TLR4 (UC only), and CD14/BPI (UC only). A trend for an association between BPI and TLR4 was observed in UC patients, but failed to reach statistical significance. Our findings support the idea of gene-gene interactions for genes involved in closely related pathways (i.e. bacterial detection). There is evidence that carrying two SNPs in genes may lead to statistical significance for genes and SNPs that do not otherwise confirm as risk alleles for disease aetiology when analysed alone.

Hyperexpression of NOD2 in intestinal mast cells of Crohn's disease patients: preferential expression of inflammatory cell-recruiting molecules via NOD2 in mast cells

NOD2, an intracellular sensor of bacteria-derived muramyl dipeptide (MDP) has been implicated as a key player in intestinal immune health and disease. Mast cells (MCs) have been reported to be increased in the gut of patients with inflammatory bowel disease. However, NOD2 expression and its role in human primary MCs are unknown. The number of NOD2(+) intestinal MCs was significantly increased in the Crohn's disease (CD) specimens compared to Ulcerative colitis (UC) specimens and controls. IFN-gamma upregulated NOD2 expression in MCs. CXCL10 and urokinase-type plasminogen activator (uPA) upregulation was specific to MCs activated by MDP compared to MCs activated by LPS and IgE/anti-IgE. MDP-induced upregulation of ICAM-1, VCAM-1, and uPA was specific to MCs compared to mononuclear cells. The number of CXCL10(+)NOD2(+) intestinal MCs was significantly increased in the CD patients. Our results suggest that NOD2(+) MCs have specific pathogenic roles that involve the recruitment of inflammatory cells in CD.

Muramyldipeptide modulates CXCL-8 release of BEAS-2B cells via NOD2

Chronic inflammation and acute exacerbations are pathophysiological features of chronic obstructive pulmonary disease (COPD). An impaired immune response to bacterial pathogens can contribute to both of them. Nucleotide oligomerization domain 2 (NOD2) is an intracellular receptor of innate immunity for muramyldipeptide (MDP). Mutations of the NOD2 gene followed by decreased recognition of MDP are associated with chronic intestinal inflammation and pulmonary complications of patients with allogenic stem cell transplant and sepsis. Our study provides evidence that NOD2, toll-like receptor 4 (TLR4) and the adapter protein receptor-interacting protein 2 (RIP2) are induced by tumor-necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in the bronchial epithelial cell line BEAS-2B. We also demonstrate that lipopolysaccharide (LPS) can further increase NOD2 transcription in a TNF-alpha and IFN-gamma-induced activation state. In addition, we show that, while MDP fails to enhance CXCL-8 release from otherwise unstimulated BEAS-2B cells, a 12 h prestimulation period with TNF-alpha and IFN-gamma primes the cells for an additional increase of CXCL-8 secretion via induction of NOD2 and RIP2. LPS itself significantly augments CXCL-8 production and co-administration of MDP further increases cytokine secretion. Finally, overexpression of an SNP13 mutant decreased MDP-induced chemokine production in BEAS-2B cells compared with NOD2 wild type overexpression. Taken together, our work indicates that MDP and NOD2 play an important role for CXCL-8 release of BEAS-2B cells following LPS-challenge via synergistic interactions between MDP and LPS.

NOD2, the gene responsible for familial granulomatous uveitis, in a mouse model of uveitis

PURPOSE

NOD2 plays an important role in the recognition of intracellular bacteria through its ability to sense the components of bacterial peptidoglycan (PGN), namely muramyl dipeptide (MDP) and muramyl tripeptide (MTP). Specific mutations in the human NOD2 gene cause Blau syndrome, an autosomal dominant form of uveitis, arthritis, and dermatitis. As a first step toward understanding the role of NOD2 in the pathogenesis of uveitis, the authors developed a mouse model of MDP-dependent uveitis.

METHODS

BALB/c mice and mice deficient in L-selectin or NOD2 received intravitreal injection of MDP, MTP, or PGN. The intravascular response within the iris and cellular infiltration was quantified by intravital microscopy and histologic assessment.

RESULTS

MDP induced an acute, ocular inflammatory response, wherein rolling and adhering leukocytes within the vasculature were significantly increased within 6 hours after MDP treatment. A minor increase in cellular infiltration occurred at 12 hours after MDP treatment. The adhesion molecule L-selectin participated in MDP-induced vascular inflammation because L-selectin knockout mice showed a significant decrease in the number of rolling cells. Importantly, NOD2 plays an essential role in ocular inflammation induced by MDP, as indicated by the fact that uveitis did not develop in Nod2 knockout mice in response to MDP. Nod2 knockout mice also showed abolished ocular inflammation in response to MTP but not to PGN treatment.

CONCLUSIONS

These findings demonstrate a novel mouse model of uveitis, wherein NOD2 plays an essential role in inflammation induced by the minimal components of PGN. Thus, innate immune responses mediated by NOD2 may participate in the development of uveitis in response to bacterial products.

Development of inflammatory bowel disease in Long-Evans Cinnamon rats based on CD4+CD25+Foxp3+ regulatory T cell dysfunction

A mutant strain with defective thymic selection of the Long-Evans Cinnamon (LEC) rat was found to spontaneously develop inflammatory bowel disease (IBD)-like colitis. The secretion of Th1-type cytokines including IFN-gamma and IL-2 from T cells of mesenteric lymph node cells (MLNs) and lamina propria mononuclear cells, but not spleen cells, in LEC rats was significantly increased more than that of the control Long-Evans Agouti rats through up-regulated expression of T-bet and phosphorylation of STAT-1 leading to NF-kappaB activation. In addition, the number of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells of the thymus, MLNs, and lamina propria mononuclear cells from LEC rats was significantly reduced, comparing with that of the control rats. Moreover, bone marrow cell transfer from LEC rats into irradiated control rats revealed significantly reduced CD25(+)Foxp3(+) Treg cells in thymus, spleen, and MLNs compared with those from control rats. Indeed, adoptive transfer with T cells of MLNs, not spleen cells, from LEC rats into SCID mice resulted in the development of inflammatory lesions resembling the IBD-like lesions observed in LEC rats. These results indicate that the dysfunction of the regulatory system controlled by Treg cells may play a crucial role in the development of IBD-like lesions through up-regulated T-bet, STAT-1, and NF-kappaB activation of peripheral T cells in LEC rats.

Role of Sp1 and HNF1 transcription factors in SGLT1 regulation during chronic intestinal inflammation

In a rabbit model of chronic intestinal inflammation, we previously demonstrated that the activity of Na-glucose cotransporter (SGLT1), SLC5A1, is inhibited. This inhibition is secondary to a decrease in the number of cotransporters, indicating that the regulation of SGLT1 during chronic inflammation is at the level of transcription. However, the regulation of SGLT1 expression and the transcription factors involved in the regulation are not yet known. In this report, we describe the cloning and characterization of rabbit SGLT1 promoter and the identification of transcription factors affected in villus cells during chronic intestinal inflammation. The promoter sequence for SGLT1 gene was identified by using the publicly available rabbit genomic sequence. Even though rabbit SGLT1 promoter did not have considerable overall homology with other mammalian SGLT1 promoters, two specificity protein 1 (Sp1) and a hepatocyte nuclear factor 1 (HNF1) binding sites were highly conserved among the species. Rabbit SGLT1 cDNA was encoded by 15 exons. Minimal promoter region determination showed that 196 nucleotides upstream of the transcription start site were sufficient for optimal promoter activity. This region encompassed two transcription factor binding sites, Sp1 and HNF1. For maximal SGLT1 promoter activity, these two transcription factor binding sites were essential, and their effect was synergistic, indicating that two separate regulatory pathways might be involved in their regulation. Using mobility shift assays, we further demonstrated that the binding of both Sp1 and HNF1 transcription factors to SGLT1 promoter regions were affected during chronic intestinal inflammation. Thus this report demonstrates that Sp1 and HNF1 transcription factors act in concert to regulate SGLT1 transcription in the chronically inflamed intestine.

Incidence of Mycobacterium avium subspecies paratuberculosis in a population-based cohort of patients with Crohn's disease and control subjects

OBJECTIVE

To define the incidence of Mycobacterium avium subspecies paratuberculosis (MAP) in patients with Crohn's disease (CD) and in control subjects.

METHODS

Blood samples from 361 CD patients from a previously described population-based inflammatory bowel disease (IBD) cohort and 200 blood donor controls, of known NOD2 genotype, were screened by PCR for MAP-specific IS900 DNA. These results were correlated with NOD2 genotype.

RESULTS

The PCR assay was capable of detecting 20 fg of purified MAP DNA, equivalent to roughly 100 MAP cells/mL of blood. MAP-specific IS900 DNA was detected in 33.8% of CD cases and 21.5% of controls (OR 1.86, 95% CI 1.247-2.785, P= 0.002). All study participants were genotyped for the NOD2 mutations 2104C>T (R702W), 2722G>C (G908R), and 3020insC (1007fs). Carriage of one or two NOD2 mutations was not associated with a significantly higher risk of CD (OR 0.75, 95% CI 0.465-1.207, P= 0.234). No significant association was seen in the CD cohort for carriage of one or two NOD2 mutations and MAP status (OR 0.883, 95% CI 0.494-1.579, P= 0.675).

CONCLUSIONS

Screening peripheral blood using IS900 PCR indicated that MAP DNA could be detected in a significant proportion of CD cases from a large population-based cohort, and also, in control subjects. The over-representation of MAP DNA in CD suggests either a role or a probable role for MAP in the etiology of CD.

Colitis and cancer: a tale of inflammatory cells and their cytokines

Chronic inflammatory disorders are often associated with an increased cancer risk. A particularly striking example of the chronic inflammation-cancer link is seen in inflammatory bowel disease, in which chronic colitis or persistent inflammation in the colon is associated with elevated risk of colorectal cancer. Animal models exploring the mechanisms by which inflammation increases the risk of colon cancer have shown that inflammatory cells, through the effects of the cytokines they produce, have a major role in promoting neoplastic transformation. In this issue of the JCI, Popivanova and colleagues demonstrate that TNF-alpha, through its effects on the immune system, plays a critical role in promoting neoplastic transformation in this setting (see the related article beginning on page 560). Importantly, the study also provides evidence that anti-TNF-alpha therapies, which are currently in clinical use, may interrupt the process.

Distinct TLR- and NLR-mediated transcriptional responses to an intracellular pathogen

How the innate immune system tailors specific responses to diverse microbial infections is not well understood. Cells use a limited number of host receptors and signaling pathways to both discriminate among extracellular and intracellular microbes, and also to generate responses commensurate to each threat. Here, we have addressed these questions by using DNA microarrays to monitor the macrophage transcriptional response to the intracellular bacterial pathogen Listeria monocytogenes. By utilizing combinations of host and bacterial mutants, we have defined the host transcriptional responses to vacuolar and cytosolic bacteria. These compartment-specific host responses induced significantly different sets of target genes, despite activating similar transcription factors. Vacuolar signaling was entirely MyD88-dependent, and induced the transcription of pro-inflammatory cytokines. The IRF3-dependent cytosolic response induced a distinct set of target genes, including IFNβ. Many of these cytosolic response genes were induced by secreted cytokines, so we further identified those host genes induced independent of secondary signaling. The host response to cytosolic bacteria was reconstituted by the cytosolic delivery of L. monocytogenes genomic DNA, but we observed an amplification of this response by NOD2 signaling in response to MDP. Correspondingly, the induction of IFNβ was reduced in nod2^−/− macrophages during infection with either L. monocytogenes or Mycobacterium tuberculosis. Combinatorial control of IFNβ induction by recognition of both DNA and MDP may highlight a mechanism by which the innate immune system integrates the responses to multiple ligands presented in the cytosol by intracellular pathogens.

Macrophages are critical cells of the innate immune system, contributing to immediate and robust defense against microbial infections. Macrophages detect pathogens using host receptors located on the cell surface, in phagosomal vacuoles, and in the cytosol. While fundamental to innate immunity, it is not clear if these different receptors merely provide redundant mechanisms for sensing microbial infection, or if instead they induce distinct gene expression programs that may allow for threat-specific host responses. We addressed this question by dissecting the macrophage transcriptional responses to the model intracellular bacterial pathogen Listeria monocytogenes. Using genetic and genomic approaches, we found that the macrophage response to L. monocytogenes trapped in phagosomal compartments was distinct and separable from the response to live bacteria replicating in the host cytosol. The macrophage response to cytosolic bacteria was recapitulated by bacterial nucleic acid and cell wall fragments, and induced surprisingly few primary response genes. These findings highlight a mechanism by which the innate immune system may specifically sense intracellular bacteria, as the macrophage response to Mycobacterium tuberculosis was similarly regulated.

Cutting edge: The IkappaB kinase (IKK) inhibitor, NEMO-binding domain peptide, blocks inflammatory injury in murine colitis

Inflammatory mediators such as TNF-alpha, IL-6, and IL-1 are important in the pathogenesis of inflammatory bowel diseases and are regulated by the activation of NF-kappaB. The aim of the present study was to investigate whether the NF-kappaB essential modulator (NEMO)-binding domain (NBD) peptide, which has been shown to block the association of NEMO with the IkappaB kinasebeta subunit (IKKbeta) and inhibit NF-kappaB activity, reduces inflammatory injury in mice with colitis. Two colitis models were established by the following: 1) inclusion of dextran sulfate sodium salt (DSS) in the drinking water of the mice; and 2) a trinitrobenzene sulfonic acid enema. Marked NF-kappaB activation and expression of proinflammatory cytokines were observed in colonic tissues. The NBD peptide ameliorated colonic inflammatory injury through the down-regulation of proinflammatory cytokines mediated by NF-kappaB inhibition in both models. These results indicate that an IKKbeta-targeted NF-kappaB blockade using the NBD peptide could be an attractive therapeutic approach for inflammatory bowel disease.

Primary immunodeficiencies: a field in its infancy

A paradigm shift is occurring in the field of primary immunodeficiencies, with revision of the definition of these conditions and a considerable expansion of their limits. Inborn errors of immunity were initially thought to be confined to a few rare, familial, monogenic, recessive traits impairing the development or function of one or several leukocyte subsets and resulting in multiple, recurrent, opportunistic, and fatal infections in infancy. A growing number of exceptions to each of these conventional qualifications have gradually accumulated. It now appears that most individuals suffer from at least one of a multitude of primary immunodeficiencies, the dissection of which is helping to improve human medicine while describing immunity in natura.

Progress in basic inflammatory bowel disease research

A modern approach to inflammatory bowel disease (IBD) research has been under way for little over one-half century, but only during the last two decades has progress accelerated and finally generated tangible results that have been translated into practical and better therapeutic strategies. The areas where progress has been more evident are those currently believed to be the key components of IBD pathogenesis, and include the environment, genetics, enteric microbiology, and immune reactivity. Progress in these different areas has been somewhat uneven, yielding a better understanding of the mechanisms behind gut inflammation and tissue injury rather than of specific etiological agents or predisposing factors. However, with the rapidly increasing utilization of novel methodological approaches like genetics, genomics, proteomics, and pharmacogenomics, it is reasonable to anticipate that the etiopathogenesis of IBD will be unveiled in the next couple of decades and more definitive, perhaps disease-modifying, approaches will be uncovered and implemented.

hPepT1 selectively transports muramyl dipeptide but not Nod1-activating muramyl peptides

Muramyl peptides derived from bacterial peptidoglycan are detected intracellularly by Nod1 and Nod2, 2 members of the newly characterized nod-like receptor (NLR) family of pattern recognition molecules. In the absence of bacterial invasion into the host cytosolic compartment, it remains unclear whether muramyl peptides can cross the plasma membrane and localize into the cytosol. We have recently demonstrated that the plasma membrane transporter, hPepT1, was able to efficiently translocate muramyl dipeptide (MDP), a specific Nod2-activating molecule, into host cells. We aimed to characterize the transport properties of hPepT1 towards a spectrum of muramyl peptides, including Nod1-activating molecules. To do so, we designed an original procedure based on the ectopic expression of hPepT1 in oocytes from Xenopus laevis. Our results demonstrated that hPepT1 transports MDP but no other Nod2-activating molecule. Moreover, we observed that Nod1-stimulating muramyl peptides were not transported by hPepT1. Since hPepT1 expression is strongly associated with intestinal epithelial cells, where Nod1 and Nod2 have been shown to play a key role, these observations suggest a distinct contribution of Nod1 and Nod2 in mucosal homeostasis following the cellular uptake of muramyl peptides by hPepT1.

Angiogenesis and chronic inflammation: cause or consequence?

Evidence has been gathered regarding the association between angiogenesis and inflammation in pathological situations. These two phenomena have long been coupled together in many chronic inflammatory disorders with distinct etiopathogenic origin, including psoriasis, rheumatoid arthritis, Crohn's disease, diabetes, and cancer. Lately, this concept has further been substantiated by the finding that several previously established non-inflammatory disorders, such as osteoarthritis and obesity, display both inflammation and angiogenesis in an exacerbated manner. In addition, the interplay between inflammatory cells, endothelial cells and fibroblasts in chronic inflammation sites, together with the fact that inflammation and angiogenesis can actually be triggered by the same molecular events, further strengthen this association. Therefore, elucidating the underlying cellular and molecular mechanisms that gather together the two processes is mandatory in order to understand their synergistic effect, and to develop new therapeutic approaches for the management of these disorders that cause a great deal of discomfort, disability, and in some cases death.