17 results found
Clarke TB, Brown RL, Sequeira RL, The microbiota protects against respiratory infection via GM-CSF signaling, Nature Communications, ISSN: 2041-1723
Brown RL, Clarke TB, 2017, The regulation of host defences to infection by the microbiota, IMMUNOLOGY, Vol: 150, Pages: 1-6, ISSN: 0019-2805
Dominguez-Huettinger E, Boon NJ, Clarke TB, et al., 2017, Mathematical Modeling of Streptococcus pneumoniae Colonization, Invasive Infection and Treatment, FRONTIERS IN PHYSIOLOGY, Vol: 8, ISSN: 1664-042X
Pader V, Hakim S, Painter KL, et al., 2017, Staphylococcus aureus inactivates daptomycin by releasing membrane phospholipids, NATURE MICROBIOLOGY, Vol: 2, ISSN: 2058-5276
Hergott CB, Roche AM, Tamashiro E, et al., 2016, Peptidoglycan from the gut microbiota governs the lifespan of circulating phagocytes at homeostasis, BLOOD, Vol: 127, Pages: 2460-2471, ISSN: 0006-4971
Clarke TB, 2014, Early Innate Immunity to Bacterial Infection in the Lung Is Regulated Systemically by the Commensal Microbiota via Nod-Like Receptor Ligands, INFECTION AND IMMUNITY, Vol: 82, Pages: 4596-4606, ISSN: 0019-9567
Clarke TB, 2014, Microbial Programming of Systemic Innate Immunity and Resistance to Infection, PLOS PATHOGENS, Vol: 10, ISSN: 1553-7366
Dominguez-Huttinger E, Clarke TB, Tanaka RJ, 2014, Mathematical modelling of host pathogen interactions at mucosal surfaces reveals the dual role of the epithelial barrier in determining the outcome of infectious processes, IMMUNOLOGY, Vol: 143, Pages: 150-150, ISSN: 0019-2805
Clarke TB, Francella N, Huegel A, et al., 2011, Invasive bacterial pathogens exploit TLR-mediated downregulation of tight junction components to facilitate translocation across the epithelium., Cell Host Microbe, Vol: 9, Pages: 404-414
Streptococcus pneumoniae and Haemophilus influenzae are members of the normal human nasal microbiota with the ability to cause invasive infections. Bacterial invasion requires translocation across the epithelium; however, mechanistic understanding of this process is limited. Examining the epithelial response to murine colonization by S. pneumoniae and H. influenzae, we observed the TLR-dependent downregulation of claudins 7 and 10, tight junction components key to the maintenance of epithelial barrier integrity. When modeled in vitro, claudin downregulation was preceded by upregulation of SNAIL1, a transcriptional repressor of tight junction components, and these phenomena required p38 MAPK and TGF-β signaling. Consequently, downregulation of SNAIL1 expression inhibited bacterial translocation across the epithelium. Furthermore, disruption of epithelial barrier integrity by claudin 7 inhibition in vitro or TLR stimulation in vivo promoted bacterial translocation. These data support a general mechanism for epithelial opening exploited by invasive pathogens to facilitate movement across the epithelium to initiate disease.
Clarke TB, Weiser JN, 2011, Intracellular sensors of extracellular bacteria., Immunol Rev, Vol: 243, Pages: 9-25
Initial recognition of bacteria by the innate immune system is thought to occur primarily by germline-encoded pattern recognition receptors (PRRs). These receptors are present in multiple compartments of host cells and are thus capable of surveying both the intracellular and extracellular milieu for bacteria. It has generally been presumed that the cellular location of these receptors dictates what type of bacteria they respond to: extracellular bacteria being recognized by cell surface receptors, such as certain Toll-like receptors, and bacteria that are capable of breaching the plasma membrane and entering the cytoplasm, being sensed by cytoplasmic receptors, including the Nod-like receptors (NLRs). Increasingly, it is becoming apparent that this is a false dichotomy and that extracellular bacteria can be sensed by cytoplasmic PRRs and this is crucial for controlling the levels of these bacteria. In this review, we discuss the role of two NLRs, Nod1 and Nod2, in the recognition of and response to extracellular bacteria.
Clarke TB, Davis KM, Lysenko ES, et al., 2010, Recognition of peptidoglycan from the microbiota by Nod1 enhances systemic innate immunity., Nat Med, Vol: 16, Pages: 228-231
Humans are colonized by a large and diverse bacterial flora (the microbiota) essential for the development of the gut immune system. A broader role for the microbiota as a major modulator of systemic immunity has been proposed; however, evidence and a mechanism for this role have remained elusive. We show that the microbiota are a source of peptidoglycan that systemically primes the innate immune system, enhancing killing by bone marrow-derived neutrophils of two major pathogens: Streptococcus pneumoniae and Staphylococcus aureus. This requires signaling via the pattern recognition receptor nucleotide-binding, oligomerization domain-containing protein-1 (Nod1, which recognizes meso-diaminopimelic acid (mesoDAP)-containing peptidoglycan found predominantly in Gram-negative bacteria), but not Nod2 (which detects peptidoglycan found in Gram-positive and Gram-negative bacteria) or Toll-like receptor 4 (Tlr4, which recognizes lipopolysaccharide). We show translocation of peptidoglycan from the gut to neutrophils in the bone marrow and show that peptidoglycan concentrations in sera correlate with neutrophil function. In vivo administration of Nod1 ligands is sufficient to restore neutrophil function after microbiota depletion. Nod1(-/-) mice are more susceptible than wild-type mice to early pneumococcal sepsis, demonstrating a role for Nod1 in priming innate defenses facilitating a rapid response to infection. These data establish a mechanism for systemic immunomodulation by the microbiota and highlight potential adverse consequences of microbiota disruption by broad-spectrum antibiotics on innate immune defense to infection.
Kawai F, Clarke TB, Roper DI, et al., 2010, Crystal Structures of Penicillin-Binding Proteins 4 and 5 from Haemophilus influenzae, Journal of Molecular Biology, Vol: 396, Pages: 634-645, ISSN: 0022-2836
Clarke TB, Kawai F, Park S-Y, et al., 2009, Mutational analysis of the substrate specificity of Escherichia coli penicillin binding protein 4., Biochemistry, Vol: 48, Pages: 2675-2683
Escherichia coli PBP4 is the archetypal class C, low molecular mass penicillin binding protein (LMM-PBP) and possesses both dd-carboxypeptidase and dd-endopeptidase activity. In contrast to other classes of PBP, class C LMM-PBPs show high dd-carboxypeptidase activity and rapidly hydrolyze synthetic fragments of peptidoglycan. The recently solved X-ray crystal structures of three class C LMM-PBPs (E. coli PBP4, Bacillus subtilis PBP4a, and Actinomadura R39 dd-peptidase) have identified several residues that form a pocket in the active site unique to this class of PBP. The X-ray cocrystal structure of the Actinomadura R39 DD-peptidase with a cephalosporin bearing a peptidoglycan-mimetic side chain showed that residues of this pocket interact with the third position meso-2,6-diaminopimelic acid residue of the peptidoglycan stem peptide. Equivalent residues of E. coli PBP4 (Asp155, Phe160, Arg361, and Gln422) were mutated, and the effect on both DD-carboxypeptidase and DD-endopeptidase activities was determined. Using N-acetylmuramyl-L-alanyl-gamma-D-glutamyl-meso-2,6-diaminopimelyl-D-alanyl-D-alanine as substrate, mutation of Asp155, Phe160, Arg361, and Gln422 to alanine reduced k(cat)/K(m) by 12.7-, 1.9-, 24.5-, and 13.8-fold, respectively. None of the k(cat) values deviated significantly from wild-type PBP4. PBP4 DD-endopeptidase activity was also affected, with substitution of Asp155, Arg361, and Gln422 reducing specific activity by 22%, 56%, and 40%, respectively. This provides the first direct demonstration of the importance of residues forming a subsite to accommodate meso-2,6-diaminopimelic acid in both the DD-carboxypeptidase and DD-endopeptidase activities of a class C LMM-PBP.
Paradis-Bleau C, Lloyd A, Sanschagrin F, et al., 2009, Pseudomonas aeruginosa MurE amide ligase: enzyme kinetics and peptide inhibitor, Biochemical Journal, Vol: 421, Pages: 263-272, ISSN: 0264-6021
Zhang Z, Clarke TB, Weiser JN, 2009, Cellular effectors mediating Th17-dependent clearance of pneumococcal colonization in mice., J Clin Invest, Vol: 119, Pages: 1899-1909
Microbial colonization of mucosal surfaces may be an initial event in the progression to disease, and it is often a transient process. For the extracellular pathogen Streptococcus pneumoniae studied in a mouse model, nasopharyngeal carriage is eliminated over a period of weeks and requires cellular rather than humoral immunity. Here, we demonstrate that primary infection led to TLR2-dependent recruitment of monocyte/macrophages into the upper airway lumen, where they engulfed pneumococci. Pharmacologic depletion of luminal monocyte/macrophages by intranasal instillation of liposomal clodronate diminished pneumococcal clearance. Efficient clearance of colonization required TLR2 signaling to generate a population of pneumococcal-specific IL-17-expressing CD4+ T cells. Depletion of either IL-17A or CD4+ T cells was sufficient to block the recruitment of monocyte/macrophages that allowed for effective late pneumococcal clearance. In contrast with naive mice, previously colonized mice showed enhanced early clearance that correlated with a more robust influx of luminal neutrophils. As for primary colonization, these cellular responses required Th17 immunity. Our findings demonstrate that monocyte/macrophages and neutrophils recruited to the mucosal surface are key effectors in clearing primary and secondary bacterial colonization, respectively.
Paradis-Bleau C, Lloyd A, Sanschagrin F, et al., 2008, Phage display-derived inhibitor of the essential cell wall biosynthesis enzyme MurF, BMC Biochemistry, Vol: 9, Pages: 33-33, ISSN: 1471-2091
Lysenko ES, Clarke TB, Shchepetov M, et al., 2007, Nod1 signaling overcomes resistance of S. pneumoniae to opsonophagocytic killing., PLoS Pathog, Vol: 3
Airway infection by the Gram-positive pathogen Streptococcus pneumoniae (Sp) leads to recruitment of neutrophils but limited bacterial killing by these cells. Co-colonization by Sp and a Gram-negative species, Haemophilus influenzae (Hi), provides sufficient stimulus to induce neutrophil and complement-mediated clearance of Sp from the mucosal surface in a murine model. Products from Hi, but not Sp, also promote killing of Sp by ex vivo neutrophil-enriched peritoneal exudate cells. Here we identify the stimulus from Hi as its peptidoglycan. Enhancement of opsonophagocytic killing was facilitated by signaling through nucleotide-binding oligomerization domain-1 (Nod1), which is involved in recognition of gamma-D-glutamyl-meso-diaminopimelic acid (meso-DAP) contained in cell walls of Hi but not Sp. Neutrophils from mice treated with Hi or compounds containing meso-DAP, including synthetic peptidoglycan fragments, showed increased Sp killing in a Nod1-dependent manner. Moreover, Nod1(-/-) mice showed reduced Hi-induced clearance of Sp during co-colonization. These observations offer insight into mechanisms of microbial competition and demonstrate the importance of Nod1 in neutrophil-mediated clearance of bacteria in vivo.
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