Mathias W Hornef

Université Paris Diderot - Paris 7, Paris, Ile-de-France, France

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Publications (24)231.63 Total impact

  • Article: MicroRNA-146a-mediated downregulation of IRAK1 protects mouse and human small intestine against ischemia/reperfusion injury.
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    ABSTRACT: Intestinal ischemia/reperfusion (I/R) injury causes inflammation and tissue damage and is associated with high morbidity and mortality. Uncontrolled activation of the innate immune system through toll-like receptors (Tlr) plays a key role in I/R-mediated tissue damage but the underlying mechanisms have not been fully resolved. Here, we identify post-transcriptional upregulation of the essential Tlr signalling molecule interleukin 1 receptor-associated kinase (Irak) 1 as the causative mechanism for post-ischemic immune hyper-responsiveness of intestinal epithelial cells. Increased Irak1 protein levels enhanced epithelial ligand responsiveness, chemokine secretion, apoptosis and mucosal barrier disruption in an experimental intestinal I/R model using wild-type, Irak1(-/-) and Tlr4(-/-) mice and ischemic human intestinal tissue. Irak1 accumulation under hypoxic conditions was associated with reduced K48 ubiquitination and enhanced Senp1-mediated deSUMOylation of Irak1. Importantly, administration of microRNA (miR)-146a or induction of miR-146a by the phytochemical diindolylmethane controlled Irak1 upregulation and prevented immune hyper-responsiveness in mouse and human tissue. These findings indicate that Irak1 accumulation triggers I/R-induced epithelial immune hyper-responsiveness and suggest that the induction of miR-146a offers a promising strategy to prevent I/R tissue injury.
    EMBO Molecular Medicine 11/2012; · 10.33 Impact Factor
  • Article: The mammalian intestinal epithelium as integral player in the establishment and maintenance of host-microbial homeostasis.
    Claudia U Duerr, Mathias W Hornef
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    ABSTRACT: Only one single layer of epithelial cells separates the densely colonized and environmentally exposed intestinal lumen from the largely sterile subepithelial tissue. Together with the overlaying mucus and the subepithelial mucosal immune system the epithelium has evolved to maintain homeostasis in the presence of the enteric microbiota. It also contributes to rapid and efficient antimicrobial host defence in the event of infection with pathogenic microorganisms. Both, epithelial antimicrobial host defence and homeostasis rely on signalling pathways induced by innate immune receptors demonstrating the active role of epithelial cells in the host-microbial interplay. The interaction of epithelial cells with professional immune cells illustrates the integrated function within the mucosal tissue. In the present review we focus on structural and functional changes of the intestinal epithelium during the fetal-neonatal transition and infancy and try to delineate its role in the induction and maintenance of host-microbial homeostasis. We also address factors that impair epithelial functions and may lead to disruption of the mucosal barrier, tissue damage and the development of symptomatic disease.
    Seminars in Immunology 12/2011; 24(1):25-35. · 6.39 Impact Factor
  • Article: Between vigilance and tolerance: the immune function of the intestinal epithelium.
    Cécilia Chassin, Mathias W Hornef
    Cellular and Molecular Life Sciences CMLS 11/2011; 68(22):3619-21. · 6.57 Impact Factor
  • Article: Establishment of intestinal homeostasis during the neonatal period.
    Silvia Stockinger, Mathias W Hornef, Cécilia Chassin
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    ABSTRACT: The intestinal mucosa faces the challenge of regulating the balance between immune tolerance towards commensal bacteria, environmental stimuli and food antigens on the one hand, and induction of efficient immune responses against invading pathogens on the other hand. This regulatory task is of critical importance to prevent inappropriate immune activation that may otherwise lead to chronic inflammation, tissue disruption and organ dysfunction. The most striking example for the efficacy of the adaptive nature of the intestinal mucosa is birth. Whereas the body surfaces are protected from environmental and microbial exposure during fetal life, bacterial colonization and contact with potent immunostimulatory substances start immediately after birth. In the present review, we summarize the current knowledge on the mechanisms underlying the transition of the intestinal mucosa during the neonatal period leading to the establishment of a stable, life-long host-microbial homeostasis. The environmental exposure and microbial colonization during the neonatal period, and also the influence of maternal milk on the immune protection of the mucosa and the role of antimicrobial peptides, are described. We further highlight the molecular mechanisms of innate immune tolerance in neonatal intestinal epithelium. Finally, we link the described immunoregulatory mechanisms to the increased susceptibility to inflammatory and infectious diseases during the neonatal period.
    Cellular and Molecular Life Sciences CMLS 09/2011; 68(22):3699-712. · 6.57 Impact Factor
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    Article: IFN-lambda determines the intestinal epithelial antiviral host defense.
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    ABSTRACT: Type I and type III IFNs bind to different cell-surface receptors but induce identical signal transduction pathways, leading to the expression of antiviral host effector molecules. Despite the fact that type III IFN (IFN-λ) has been shown to predominantly act on mucosal organs, in vivo infection studies have failed to attribute a specific, nonredundant function. Instead, a predominant role of type I IFN was observed, which was explained by the ubiquitous expression of the type I IFN receptor. Here we comparatively analyzed the role of functional IFN-λ and type I IFN receptor signaling in the innate immune response to intestinal rotavirus infection in vivo, and determined viral replication and antiviral gene expression on the cellular level. We observed that both suckling and adult mice lacking functional receptors for IFN-λ were impaired in the control of oral rotavirus infection, whereas animals lacking functional receptors for type I IFN were similar to wild-type mice. Using Mx1 protein accumulation as marker for IFN responsiveness of individual cells, we demonstrate that intestinal epithelial cells, which are the prime target cells of rotavirus, strongly responded to IFN-λ but only marginally to type I IFN in vivo. Systemic treatment of suckling mice with IFN-λ repressed rotavirus replication in the gut, whereas treatment with type I IFN was not effective. These results are unique in identifying a critical role of IFN-λ in the epithelial antiviral host defense.
    Proceedings of the National Academy of Sciences 05/2011; 108(19):7944-9. · 9.68 Impact Factor
  • Article: miR-146a mediates protective innate immune tolerance in the neonate intestine.
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    ABSTRACT: After birth, the intestinal mucosa undergoes a dramatic transition from a sterile protected site to an environmentally exposed and permanently colonized surface. The mechanisms that facilitate this transition are ill defined. Here, we demonstrate that microRNA-146a-mediated translational repression and proteolytic degradation of the essential Toll-like receptor (TLR) signaling molecule interleukin 1 receptor associated kinase 1 (IRAK1) is sufficient to induce intestinal epithelial innate immune tolerance and provide protection from bacteria-induced epithelial damage in neonates. Despite low IRAK1 protein levels, continuous TLR4- and IRAK1-dependent signal transduction induced by intraepithelial endotoxin persistence during the neonatal period maintains tolerance through sustained miR-146a expression. Strikingly, it additionally facilitates transcription of a distinct set of genes involved in cell survival, differentiation, and homeostasis. Thus, our results identify the underlying molecular mechanisms of intestinal epithelial innate immune tolerance during the neonatal period and characterize tolerance as an active condition involved in the establishment of intestinal mucosal homeostasis.
    Cell host & microbe 10/2010; 8(4):358-68. · 13.02 Impact Factor
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    Article: Cesarean delivery is associated with celiac disease but not inflammatory bowel disease in children.
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    ABSTRACT: The aim of this study was to analyze a possible association between cesarean delivery and enteric inflammatory diseases in children. A retrospective, multicenter, case-control study that included 1950 children was performed in cooperation with 26 university and 16 nonacademic children's hospitals. Information on intestinal disease manifestation, together with mode of delivery and gestational age at birth, postnatal complications, and breastfeeding, was collected by the attending physician from children and their parents who were visiting a gastrointestinal outpatient clinic for Crohn disease (CD; 516 cases), ulcerative colitis (250 cases), celiac disease (157 cases), and other gastrointestinal diseases (165 cases) and control subjects who were visiting ophthalmologic, orthodontic, and dental outpatient clinics (862 cases). Whereas the rate of cesarean delivery of children with Crohn disease or ulcerative colitis was similar to that of control subjects, a significantly enhanced likelihood of being born by cesarean delivery was found in children with celiac disease compared with control subjects (odds ratio: 1.8 [95% confidence interval: 1.13-2.88]; P = .014). The mode of delivery and associated alterations in the development of the enteric homeostasis during the neonatal period might influence the incidence of celiac disease.
    PEDIATRICS 06/2010; 125(6):e1433-40. · 4.47 Impact Factor
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    Article: Potentiation of epithelial innate host responses by intercellular communication.
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    ABSTRACT: The epithelium efficiently attracts immune cells upon infection despite the low number of pathogenic microbes and moderate levels of secreted chemokines per cell. Here we examined whether horizontal intercellular communication between cells may contribute to a coordinated response of the epithelium. Listeria monocytogenes infection, transfection, and microinjection of individual cells within a polarized intestinal epithelial cell layer were performed and activation was determined at the single cell level by fluorescence microscopy and flow cytometry. Surprisingly, chemokine production after L. monocytogenes infection was primarily observed in non-infected epithelial cells despite invasion-dependent cell activation. Whereas horizontal communication was independent of gap junction formation, cytokine secretion, ion fluxes, or nitric oxide synthesis, NADPH oxidase (Nox) 4-dependent oxygen radical formation was required and sufficient to induce indirect epithelial cell activation. This is the first report to describe epithelial cell-cell communication in response to innate immune activation. Epithelial communication facilitates a coordinated infectious host defence at the very early stage of microbial infection.
    PLoS Pathogens 01/2010; 6(11):e1001194. · 9.13 Impact Factor
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    Article: O-antigen delays lipopolysaccharide recognition and impairs antibacterial host defense in murine intestinal epithelial cells.
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    ABSTRACT: Although Toll-like receptor (TLR) 4 signals from the cell surface of myeloid cells, it is restricted to an intracellular compartment and requires ligand internalization in intestinal epithelial cells (IECs). Yet, the functional consequence of cell-type specific receptor localization and uptake-dependent lipopolysaccharide (LPS) recognition is unknown. Here, we demonstrate a strikingly delayed activation of IECs but not macrophages by wildtype Salmonella enterica subsp. enterica sv. (S.) Typhimurium as compared to isogenic O-antigen deficient mutants. Delayed epithelial activation is associated with impaired LPS internalization and retarded TLR4-mediated immune recognition. The O-antigen-mediated evasion from early epithelial innate immune activation significantly enhances intraepithelial bacterial survival in vitro and in vivo following oral challenge. These data identify O-antigen expression as an innate immune evasion mechanism during apical intestinal epithelial invasion and illustrate the importance of early innate immune recognition for efficient host defense against invading Salmonella.
    PLoS Pathogens 10/2009; 5(9):e1000567. · 9.13 Impact Factor
  • Article: Internalization-dependent recognition of Mycobacterium avium ssp. paratuberculosis by intestinal epithelial cells.
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    ABSTRACT: Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of Johne's disease, a highly prevalent chronic intestinal infection in domestic and wildlife ruminants. The microbial pathogenesis of MAP infection has attracted additional attention due to an association with the human enteric inflammatory Crohn's disease. MAP is acquired by the faecal-oral route prompting us to study the interaction with differentiated intestinal epithelial cells. MAP was rapidly internalized and accumulated in a late endosomal compartment. In contrast to other opportunistic mycobacteria or M. bovis, MAP induced significant epithelial activation as indicated by a NF-kappaB-independent but Erk-dependent chemokine secretion. Surprisingly, MAP-induced chemokine production was completely internalization-dependent as inhibition of Rac-dependent bacterial uptake abolished epithelial activation. In accordance, innate immune recognition of MAP by differentiated intestinal epithelial cells occurred through the intracellularly localized pattern recognition receptors toll-like receptor 9 and NOD1 with signal transduction via the adaptor molecules MyD88 and RIP2. The internalization-dependent innate immune activation of intestinal epithelial cells is in contrast to the stimulation of professional phagocytes by extracellular bacterial constituents and might significantly contribute to the histopathological changes observed during enteric MAP infection.
    Cellular Microbiology 09/2009; 11(12):1802-15. · 5.46 Impact Factor
  • Article: TLR4 facilitates translocation of bacteria across renal collecting duct cells.
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    ABSTRACT: Uropathogenic Escherichia coli (UPEC) are the most frequent causes of urinary tract infections and pyelonephritis. Renal medullary collecting duct (MCD) cells are the intrarenal site to which UPEC strains prefer to adhere and initiate an inflammatory response, but the ability of UPEC strains to translocate across impermeant MCD cells has not been demonstrated definitively. Here, several UPEC strains adhered to the apical surface and translocated across confluent murine inner MCD cells grown on filters. UPEC strains expressing cytolytic and vacuolating cytotoxins disrupted the integrity of cell layers, whereas noncytolytic UPEC strains passed through the cell layers without altering tight junctions. Apical-to-basal transcellular translocation was dramatically reduced after extinction of Toll-like receptor 4 (TLR4) and the lipid raft marker caveolin-1 by small interfering RNA. Furthermore, disruption of lipid raft integrity by filipin III and methyl-beta-cyclodextrin significantly reduced both the transcellular translocation of UPEC across murine inner MCD cell layers and the stimulation of proinflammatory mediators. Bacterial translocation was also significantly reduced in primary cultures of TLR4-deficient mouse MCD cells compared with MCD cells from wild-type mice. Benzyl alcohol, an anesthetic that enhances membrane fluidity, favored the recruitment of caveolin-1 in lipid rafts and increased the translocation of UPEC across cultured TLR4-deficient MCD cells. These findings demonstrate that the transcellular translocation of UPEC strains across impermeant layers of MCD cells may occur through lipid rafts via a TLR4-facilitated process.
    Journal of the American Society of Nephrology 09/2008; 19(12):2364-74. · 9.66 Impact Factor
  • Article: The function and biological role of toll-like receptors in infectious diseases: an update.
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    ABSTRACT: The present review summarizes exciting new findings and reports recent advances in the understanding of the role of toll-like receptors in health and disease. It intends to provide a rough survey on topics discussed by researchers in the field and to stimulate discussion on new aspects of the complex processes involved in innate host defence. Novel findings have been reported on the many aspects of toll-like receptors biology, namely the receptor structure and the molecular process of ligand recognition, receptor assembly, cellular localization and trafficking, downstream signaling and the regulatory factors involved, genetic polymorphisms within receptor genes and their linkage to human diseases, and the functional role of toll-like receptors in immune defence and host-microbe homeostasis. Recent advances have allowed a more detailed picture not only of the processes involved in microbial recognition and host defence but also revealed unexpected insights into the cause of inflammatory processes and the close interrelationship between the vertebrate host and the microbially colonized environment.
    Current Opinion in Infectious Diseases 07/2008; 21(3):304-12. · 4.93 Impact Factor
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    Article: Developmental switch of intestinal antimicrobial peptide expression.
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    ABSTRACT: Paneth cell-derived enteric antimicrobial peptides provide protection from intestinal infection and maintenance of enteric homeostasis. Paneth cells, however, evolve only after the neonatal period, and the antimicrobial mechanisms that protect the newborn intestine are ill defined. Using quantitative reverse transcription-polymerase chain reaction, immunohistology, reverse-phase high-performance liquid chromatography, and mass spectrometry, we analyzed the antimicrobial repertoire in intestinal epithelial cells during postnatal development. Surprisingly, constitutive expression of the cathelin-related antimicrobial peptide (CRAMP) was observed, and the processed, antimicrobially active form was identified in neonatal epithelium. Peptide synthesis was limited to the first two weeks after birth and gradually disappeared with the onset of increased stem cell proliferation and epithelial cell migration along the crypt-villus axis. CRAMP conferred significant protection from intestinal bacterial growth of the newborn enteric pathogen Listeria monocytogenes. Thus, we describe the first example of a complete developmental switch in innate immune effector expression and anatomical distribution. Epithelial CRAMP expression might contribute to bacterial colonization and the establishment of gut homeostasis, and provide protection from enteric infection during the postnatal period.
    Journal of Experimental Medicine 02/2008; 205(1):183-93. · 13.85 Impact Factor
  • Article: Cytokine-mediated control of lipopolysaccharide-induced activation of small intestinal epithelial cells.
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    ABSTRACT: Cytokines with anti-inflammatory properties have been implicated in the prevention of inappropriate immune activation by commensal bacteria in the intestinal tract. Here, we analysed receptor expression, cellular signalling, and the inhibitory activity of interleukin (IL)-4, -10, -11, and -13 as well as of transforming growth factor-beta on lipopolysaccharide-mediated small intestinal epithelial cell activation. Only IL-4 and IL-13 had a significant inhibitory effect on chemokine secretion and nitric oxide (NO) production in differentiated and polarized cells. Reverse transcription-polymerase chain reaction of primary intestinal epithelial cells obtained by laser-microdissection confirmed expression of the type II IL-4 receptor consisting of the IL-4 receptor alpha and the IL-13 receptor alpha1. Also, IL-4 or IL-13 led to rapid signal transducer and activator of transcription 6 phosphorylation, diminished inducible NO synthase expression, and enhanced the antagonistic arginase 1 activity. In conclusion, cytokines such as IL-4 and IL-13 affect intestinal epithelial cells and exhibit a modulating activity on Toll-like receptor-4-mediated epithelial cell activation.
    Immunology 12/2007; 122(3):306-15. · 3.32 Impact Factor
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    Article: Hormonal control of the renal immune response and antibacterial host defense by arginine vasopressin.
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    ABSTRACT: Ascending urinary tract infection (UTI) and pyelonephritis caused by uropathogenic Escherichia coli (UPEC) are very common infections that can cause severe kidney damage. Collecting duct cells, the site of hormonally regulated ion transport and water absorption controlled by vasopressin, are the preferential intrarenal site of bacterial adhesion and initiation of inflammatory response. We investigated the effect of the potent V2 receptor (V2R) agonist deamino-8-D-arginine vasopressin (dDAVP) on the activation of the innate immune response using established and primary cultured collecting duct cells and an experimental model of ascending UTI. dDAVP inhibited Toll-like receptor 4-mediated nuclear factor kappaB activation and chemokine secretion in a V2R-specific manner. The dDAVP-mediated suppression involved activation of protein phosphatase 2A and required an intact cystic fibrosis transmembrane conductance regulator Cl- channel. In vivo infusion of dDAVP induced a marked fall in proinflammatory mediators and neutrophil recruitment, and a dramatic rise in the renal bacterial burden in mice inoculated with UPECs. Conversely, administration of the V2R antagonist SR121463B to UPEC-infected mice stimulated both the local innate response and the antibacterial host defense. These findings evidenced a novel hormonal regulation of innate immune cellular activation and demonstrate that dDAVP is a potent modulator of microbial-induced inflammation in the kidney.
    Journal of Experimental Medicine 12/2007; 204(12):2837-52. · 13.85 Impact Factor
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    Article: Postnatal acquisition of endotoxin tolerance in intestinal epithelial cells.
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    ABSTRACT: The role of innate immune recognition by intestinal epithelial cells (IECs) in vivo is ill-defined. Here, we used highly enriched primary IECs to analyze Toll-like receptor (TLR) signaling and mechanisms that prevent inappropriate stimulation by the colonizing microflora. Although the lipopolysaccharide (LPS) receptor complex TLR4/MD-2 was present in fetal, neonatal, and adult IECs, LPS-induced nuclear factor kappaB (NF-kappaB) activation and chemokine (macrophage inflammatory protein 2 [MIP-2]) secretion was only detected in fetal IECs. Fetal intestinal macrophages, in contrast, were constitutively nonresponsive to LPS. Acquisition of LPS resistance was paralleled by a spontaneous activation of IECs shortly after birth as illustrated by phosphorylation of IkappaB-alpha and nuclear translocation of NF-kappaB p65 in situ as well as transcriptional activation of MIP-2. Importantly, the spontaneous IEC activation occurred in vaginally born mice but not in neonates delivered by Caesarean section or in TLR4-deficient mice, which together with local endotoxin measurements identified LPS as stimulatory agent. The postnatal loss of LPS responsiveness of IECs was associated with a posttranscriptional down-regulation of the interleukin 1 receptor-associated kinase 1, which was essential for epithelial TLR4 signaling in vitro. Thus, unlike intestinal macrophages, IECs acquire TLR tolerance immediately after birth by exposure to exogenous endotoxin to facilitate microbial colonization and the development of a stable intestinal host-microbe homeostasis.
    Journal of Experimental Medicine 05/2006; 203(4):973-84. · 13.85 Impact Factor
  • Article: Bacterial evasion of innate defense at epithelial linings.
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    ABSTRACT: The evolution of multicellular organisms has been, and continues to be, paralleled by the evolution of the surrounding microbial flora. This intimate coexistence between higher host organisms and microbes has generated a myriad of adaptation strategies at both sides to cope with, or even benefit from the given conditions. On the host side, the development of an effective immune defence system allowed the maintenance of an astonishingly stable homeostasis on many body sites, and even the establishment of sterile surfaces at vulnerable anatomical sites. On the other hand, microbial diversity has led to the establishment of a large number of microbial life styles that allow persistence and proliferation in the presence of host defense mechanisms. The following review describes bacterial strategies to circumvent or modify host defenses that operate at the epithelial lining. It illustrates the enormous diversity of mechanisms that are part of the complex interplay between microbial organisms and the host. It also reflects the dramatic progress made in the understanding of the mammalian immune defense system which many times has been initiated by the surprising results from the study of microbial pathogenesis.
    Chemical immunology and allergy 02/2005; 86:72-98.
  • Article: The role of epithelial Toll-like receptor expression in host defense and microbial tolerance.
    Mathias W Hornef, Christian Bogdan
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    ABSTRACT: The recognition of microbial structures by Toll-like receptors (TLRs) on professional immune cells situated at sterile internal body sites occurs during invasive microbial infection. It indicates infectious non-self and thereby represents the adequate co-stimulatory signal to initiate activation of the adaptive immune system against the invading pathogen. In contrast, most epithelial body surfaces are permanently colonized by microbial organisms of the normal flora and thus TLR ligands are present under physiological conditions. In the following, we discuss the characteristics of TLR-mediated recognition by epithelial cells, the subsequent activation of the host immune system, and protective mechanisms that might help to avoid inadequate stimulation and allow differentiation between commensal or pathogenic micro-organisms. Recent findings suggest that the role of epithelial cells in the maintenance of stable microbial colonization of host surfaces and the immediate host response to infectious challenges might have to be revised.
    Journal of Endotoxin Research 02/2005; 11(2):124-8. · 3.06 Impact Factor
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    Article: Increased diversity of intestinal antimicrobial peptides by covalent dimer formation.
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    ABSTRACT: Antimicrobial peptides are essential effector molecules of the innate immune system. Here we describe the structure, function and diversity of cryptdin-related sequence (CRS) peptides, a large family of antimicrobial molecules. We identified the peptides as covalent dimers in mouse intestinal tissue in amounts comparable to those of Paneth cell-derived enteric alpha-defensins. CRS peptides caused rapid and potent killing of commensal and pathogenic bacteria. The CRS peptides formed homo- and heterodimers in vivo, thereby expanding the repertoire of antimicrobial peptides and increasing the peptide diversity of Paneth cell secretions. CRS peptides might therefore be important in the maintenance of the microbial homeostasis within the intestinal tract.
    Nature Immunology 09/2004; 5(8):836-43. · 26.01 Impact Factor
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    Article: Growth control of small-colony variants by genetic regulation of the hemin uptake system.
    Andreas Roggenkamp, Harald Hoffmann, Mathias W Hornef
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    ABSTRACT: Small-colony variants (SCVs) are slow-growing variants of human bacterial pathogens. They are associated with chronic persistent infections, and their biochemical identification and antimicrobial treatment are impaired by altered metabolic properties. To contribute to the understanding of SCV-mediated infections, we analyzed a clinical SCV isolate derived from a chronic prosthetic hip infection. A sequence analysis of housekeeping genes identified an Enterobacter hormaechei-like organism. The SCV phenotype, with growth as microcolonies, was caused by a block within the heme biosynthesis pathway through deletion of the hemB locus, as shown by hybridization and complementation experiments. At a low frequency, large-colony variants (LCVs) arose that were dependent on exogenous hemin. To investigate this phenomenon, we cloned and sequenced the 5.8-kb hemin uptake system, denoted ehu. Gene expression analysis indicated regulation of this locus in wild-type bacteria by the global iron regulator Fur. Inactivation of Fur in LCVs caused the derepression of ehu expression and facilitated bacterial growth. Genetic alterations of the fur locus in LCVs were identified as insertions of IS1A elements and point mutations. In contrast, SCVs could utilize exogenous hemin only in the absence of iron. Thus, we provide the first molecular characterization of the growth properties of a clinical SCV isolate, which may help to improve the diagnostic and therapeutic management of patients with chronic persistent infections.
    Infection and Immunity 05/2004; 72(4):2254-62. · 4.16 Impact Factor

Institutions

  • 2012
    • Université Paris Diderot - Paris 7
      Paris, Ile-de-France, France
  • 2008–2011
    • Medizinische Hochschule Hannover
      • Institute for Medical Microbiology and Hospital Epidemiology
      Hannover, Lower Saxony, Germany
  • 2002–2008
    • Karolinska Institute
      Stockholm, Stockholm, Sweden
  • 2004–2007
    • Universität Freiburg
      • Institute of Medical Microbiology and Hygiene
      Freiburg, Lower Saxony, Germany
    • Ludwig-Maximilian-University of Munich
      • Max-von-Pettenkofer Institute for Hygiene and Medical Microbiology
      München, Bavaria, Germany
  • 2003
    • Swedish Institute for Communicable Disease Control
      Stockholm, Stockholm, Sweden