Publications by authors named "Simon J Cleary"

19 Publications

  • Page 1 of 1

Platelets Independently Recruit into Asthmatic Lungs and Models of Allergic Inflammation via CCR3.

Am J Respir Cell Mol Biol 2021 Feb 8. Epub 2021 Feb 8.

King's College London, Pharmaceutical Sciences, London, United Kingdom of Great Britain and Northern Ireland;

Platelet activation and pulmonary recruitment occur in patients with asthma and in animal models of allergic asthma, where leukocyte infiltration, airway remodelling, and hyperresponsiveness are suppressed by experimental platelet depletion. These observations suggest the importance of platelets to various characteristics of allergic disease, but the mechanisms of platelet migration and location are not understood. To assess the mechanism of platelet recruitment to extravascular compartments of lungs from asthmatic patients, and following allergen challenge of house dust mite (HDM, containing the DerP1 allergen) sensitized mice; additionally we assessed the role of chemokines in this process. Lung sections were immunohistochemically stained for CD42b+ platelets. Intravital microscopy in allergic mice visualised platelets tagged with an anti-mouse CD49b-PE antibody. Platelet-endothelial interactions were measured in response to HDM (DerP1) exposure in the presence of antagonists to CCR3, CCR4, and CXCR4. Extravascular CD42b+ platelets were detected in the epithelium and submucosa in bronchial biopsies taken from subjects with steroid naïve mild asthma. Platelets were significantly raised in lung parenchyma from patients with fatal asthma compared with post mortem control lung tissue. Furthermore, in DerP1-sensitized mice, subsequent HDM exposure induced endothelial rolling, adhesion; and recruitment of platelets into airway walls compared with sham-sensitized mice, via a CCR3-dependent mechanism in the absence of aggregation or interactions with leukocytes. Localization of singular non-aggregated platelets occurs in lungs of asthmatic patients. In allergic mice, platelet recruitment occurs via recognised vascular adhesive and migratory events, independently of leukocytes via a CCR3 dependent mechanism.
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http://dx.doi.org/10.1165/rcmb.2020-0425OCDOI Listing
February 2021

Chewing the fat on TRALI.

Blood 2021 Feb;137(5):586-587

University of California, San Francisco.

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http://dx.doi.org/10.1182/blood.2020010034DOI Listing
February 2021

β2M Signals Monocytes Through Non-Canonical TGFβ Receptor Signal Transduction.

Circ Res 2021 Jan 29. Epub 2021 Jan 29.

Aab Cardiovascular Research Institute, University of Rochester School of Medicine and Dentistry, UNITED STATES.

Circulating monocytes can have pro-inflammatory or pro-reparative phenotypes. The endogenous signaling molecules and pathways that regulate monocyte polarization in vivo are poorly understood. We have shown that platelet derived beta-2 microglobulin (β2M) and transforming growth factor beta (TGFβ) have opposing effects on monocytes by inducing inflammatory and reparative phenotypes respectively, but each bind and signal through the same receptor. We now define the signaling pathways involved. To determine the molecular mechanisms and signal transduction pathways by which β2M and TGFβ regulate monocyte responses both in vitro and in vivo. Wild-type (WT) and platelet specific β2M knockout (Plt-β2M) mice were treated intravenously with either β2M or TGFβ to increase plasma concentrations to those in cardiovascular diseases. Elevated plasma β2M increased pro-inflammatory monocytes, while increased plasma TGFβ increased pro-reparative monocytes. TGFβ receptor (TGFβR) inhibition blunted monocyte responses to both β2M and TGFβ in vivo. Using imaging flow cytometry, we found that β2M decreased monocyte SMAD2/3 nuclear localization, while TGFβ promoted SMAD nuclear translocation, but decreased non-canonical/inflammatory (JNK and NFκB nuclear localization). This was confirmed in vitro using both imaging flow cytometry and immunoblots. β2M, but not TGFβ, promoted ubiquitination of SMAD3 and SMAD4, that inhibited their nuclear trafficking. Inhibition of ubiquitin ligase activity blocked non-canonical SMAD-independent monocyte signaling and skewed monocytes towards a pro-reparative monocyte response. Our findings indicate that elevated plasma β2M and TGFβ dichotomously polarize monocytes. Furthermore, these immune molecules share a common receptor, but induce SMAD-dependent canonical signaling (TGFβ) versus non-canonical SMAD-independent signaling (β2M) in a ubiquitin ligase dependent manner. This work has broad implications as β2M is increased in several inflammatory conditions, while TGFβ is increased in fibrotic diseases.
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http://dx.doi.org/10.1161/CIRCRESAHA.120.317119DOI Listing
January 2021

Global absence and targeting of protective immune states in severe COVID-19.

Nature 2021 03 25;591(7848):124-130. Epub 2021 Jan 25.

Department of Pathology, University of California San Francisco, San Francisco, CA, USA.

Although infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has pleiotropic and systemic effects in some individuals, many others experience milder symptoms. Here, to gain a more comprehensive understanding of the distinction between severe and mild phenotypes in the pathology of coronavirus disease 2019 (COVID-19) and its origins, we performed a whole-blood-preserving single-cell analysis protocol to integrate contributions from all major immune cell types of the blood-including neutrophils, monocytes, platelets, lymphocytes and the contents of the serum. Patients with mild COVID-19 exhibit a coordinated pattern of expression of interferon-stimulated genes (ISGs) across every cell population, whereas these ISG-expressing cells are systemically absent in patients with severe disease. Paradoxically, individuals with severe COVID-19 produce very high titres of anti-SARS-CoV-2 antibodies and have a lower viral load compared to individuals with mild disease. Examination of the serum from patients with severe COVID-19 shows that these patients uniquely produce antibodies that functionally block the production of the ISG-expressing cells associated with mild disease, by activating conserved signalling circuits that dampen cellular responses to interferons. Overzealous antibody responses pit the immune system against itself in many patients with COVID-19, and perhaps also in individuals with other viral infections. Our findings reveal potential targets for immunotherapies in patients with severe COVID-19 to re-engage viral defence.
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http://dx.doi.org/10.1038/s41586-021-03234-7DOI Listing
March 2021

Red Blood Cells Elicit Platelet-Dependent Neutrophil Recruitment into Lung Airspaces.

Shock 2020 Dec 9. Epub 2020 Dec 9.

Sackler Institute of Pulmonary Pharmacology, Institute of Pharmaceutical Science, King's College London, London, UK.

Haemolysis that occurs in intravascular haemolytic disorders, such as sickle cell disease and malaria, is associated with inflammation and platelet activation. Alveolar haemorrhage, for example following primary blast lung injury (PBLI) or acute respiratory distress syndrome (ARDS), results in the escape of erythrocytes (RBCs) into alveolar spaces, where they subsequently lyse and release their intracellular contents. However, the inflammatory effects of RBCs in the airways are not fully understood. We hypothesized that RBCs in the airway induce an inflammatory response, associated with platelet activation. By instilling whole RBCs or lysed RBCs into the airways of mice, we have demonstrated that whole RBCs elicit macrophage accumulation in the lung. However, lysed RBCs induce significant inflammatory cell recruitment, particularly neutrophils and this was associated with a 50% increase in circulating platelet neutrophil complexes (PNCs). Platelet depletion prior to lysed RBC exposure in the lung resulted in reduced neutrophil recruitment, suggesting that the presence of intracellular RBC components in the airways can elicit inflammation that is platelet dependent. To identify specific platelet dependent signalling pathways involved in neutrophil recruitment, anti-P-selectin ligand and anti-PSGL1 blocking antibodies were tested, however neither affected neutrophil recruitment. These findings implicate an involvement for other, as yet unidentified platelet-dependent signalling and adhesion mechanisms. Further understanding of how platelets contribute to lung inflammation induced by the presence of RBCs could offer novel therapeutic approaches to attenuate inflammation that occurs in conditions associated with alveolar haemorrhage.
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http://dx.doi.org/10.1097/SHK.0000000000001705DOI Listing
December 2020

Natural killer cells activated through NKG2D mediate lung ischemia-reperfusion injury.

J Clin Invest 2021 Feb;131(3)

Department of Medicine, University of California, San Francisco, California.

Pulmonary ischemia-reperfusion injury (IRI) is a clinical syndrome of acute lung injury that occurs after lung transplantation or remote organ ischemia. IRI causes early mortality and has no effective therapies. While NK cells are innate lymphocytes capable of recognizing injured cells, their roles in acute lung injury are incompletely understood. Here, we demonstrated that NK cells were increased in frequency and cytotoxicity in 2 different IRI mouse models. We showed that NK cells trafficked to the lung tissue from peripheral reservoirs and were more mature within lung tissue. Acute lung ischemia-reperfusion injury was blunted in a NK cell-deficient mouse strain but restored with adoptive transfer of NK cells. Mechanistically, NK cell NKG2D receptor ligands were induced on lung endothelial and epithelial cells following IRI, and antibody-mediated NK cell depletion or NKG2D stress receptor blockade abrogated acute lung injury. In human lung tissue, NK cells were increased at sites of ischemia-reperfusion injury and activated NK cells were increased in prospectively collected human bronchoalveolar lavage in subjects with severe IRI. These data support a causal role for recipient peripheral NK cells in pulmonary IRI via NK cell NKG2D receptor ligation. Therapies targeting NK cells may hold promise in acute lung injury.
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http://dx.doi.org/10.1172/JCI137047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7852842PMC
February 2021

Update on animal models for COVID-19 research.

Br J Pharmacol 2020 12 2;177(24):5679-5681. Epub 2020 Nov 2.

Sackler Institute of Pulmonary Pharmacology, King's College London, London, UK.

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http://dx.doi.org/10.1111/bph.15266DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7707085PMC
December 2020

Global Absence and Targeting of Protective Immune States in Severe COVID-19.

bioRxiv 2020 Oct 29. Epub 2020 Oct 29.

While SARS-CoV-2 infection has pleiotropic and systemic effects in some patients, many others experience milder symptoms. We sought a holistic understanding of the severe/mild distinction in COVID-19 pathology, and its origins. We performed a whole-blood preserving single-cell analysis protocol to integrate contributions from all major cell types including neutrophils, monocytes, platelets, lymphocytes and the contents of serum. Patients with mild COVID-19 disease display a coordinated pattern of interferon-stimulated gene (ISG) expression across every cell population and these cells are systemically absent in patients with severe disease. Severe COVID-19 patients also paradoxically produce very high anti-SARS-CoV-2 antibody titers and have lower viral load as compared to mild disease. Examination of the serum from severe patients demonstrates that they uniquely produce antibodies with multiple patterns of specificity against interferon-stimulated cells and that those antibodies functionally block the production of the mild disease-associated ISG-expressing cells. Overzealous and auto-directed antibody responses pit the immune system against itself in many COVID-19 patients and this defines targets for immunotherapies to allow immune systems to provide viral defense.

One Sentence Summary: In severe COVID-19 patients, the immune system fails to generate cells that define mild disease; antibodies in their serum actively prevents the successful production of those cells.
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http://dx.doi.org/10.1101/2020.10.28.359935DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7605559PMC
October 2020

Global Absence and Targeting of Protective Immune States in Severe COVID-19.

Res Sq 2020 Oct 28. Epub 2020 Oct 28.

Department of Pathology, San Francisco, 513 Parnassus Ave, HSW512, San Francisco, CA 94143-0511, USA.

While SARS-CoV-2 infection has pleiotropic and systemic effects in some patients, many others experience milder symptoms. We sought a holistic understanding of the severe/mild distinction in COVID-19 pathology, and its origins. We performed a wholeblood preserving single-cell analysis protocol to integrate contributions from all major cell types including neutrophils, monocytes, platelets, lymphocytes and the contents of serum. Patients with mild COVID-19 disease display a coordinated pattern of interferonstimulated gene (ISG) expression across every cell population and these cells are systemically absent in patients with severe disease. Severe COVID-19 patients also paradoxically produce very high anti-SARS-CoV-2 antibody titers and have lower viral load as compared to mild disease. Examination of the serum from severe patients demonstrates that they uniquely produce antibodies with multiple patterns of specificity against interferon-stimulated cells and that those antibodies functionally block the production of the mild disease-associated ISG-expressing cells. Overzealous and autodirected antibody responses pit the immune system against itself in many COVID-19 patients and this defines targets for immunotherapies to allow immune systems to provide viral defense.
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http://dx.doi.org/10.21203/rs.3.rs-97042/v1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7605560PMC
October 2020

Lung megakaryocytes are immune modulatory cells.

J Clin Invest 2021 Jan;131(1)

Aab Cardiovascular Research Institute and.

Although platelets are the cellular mediators of thrombosis, they are also immune cells. Platelets interact both directly and indirectly with immune cells, impacting their activation and differentiation, as well as all phases of the immune response. Megakaryocytes (Mks) are the cell source of circulating platelets, and until recently Mks were typically only considered bone marrow-resident (BM-resident) cells. However, platelet-producing Mks also reside in the lung, and lung Mks express greater levels of immune molecules compared with BM Mks. We therefore sought to define the immune functions of lung Mks. Using single-cell RNA sequencing of BM and lung myeloid-enriched cells, we found that lung Mks, which we term MkL, had gene expression patterns that are similar to antigen-presenting cells. This was confirmed using imaging and conventional flow cytometry. The immune phenotype of Mks was plastic and driven by the tissue immune environment, as evidenced by BM Mks having an MkL-like phenotype under the influence of pathogen receptor challenge and lung-associated immune molecules, such as IL-33. Our in vitro and in vivo assays demonstrated that MkL internalized and processed both antigenic proteins and bacterial pathogens. Furthermore, MkL induced CD4+ T cell activation in an MHC II-dependent manner both in vitro and in vivo. These data indicated that MkL had key immune regulatory roles dictated in part by the tissue environment.
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http://dx.doi.org/10.1172/JCI137377DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7773372PMC
January 2021

Complement activation on endothelium initiates antibody-mediated acute lung injury.

J Clin Invest 2020 11;130(11):5909-5923

Department of Medicine, UCSF, San Francisco, California, USA.

Antibodies targeting human leukocyte antigen (HLA)/major histocompatibility complex (MHC) proteins limit successful transplantation and transfusion, and their presence in blood products can cause lethal transfusion-related acute lung injury (TRALI). It is unclear which cell types are bound by these anti-leukocyte antibodies to initiate an immunologic cascade resulting in lung injury. We therefore conditionally removed MHC class I (MHC I) from likely cellular targets in antibody-mediated lung injury. Only the removal of endothelial MHC I reduced lung injury and mortality, related mechanistically to absent endothelial complement fixation and lung platelet retention. Restoration of endothelial MHC I rendered MHC I-deficient mice susceptible to lung injury. Neutrophil responses, including neutrophil extracellular trap (NET) release, were intact in endothelial MHC I-deficient mice, whereas complement depletion reduced both lung injury and NETs. Human pulmonary endothelial cells showed high HLA class I expression, and posttransfusion complement activation was increased in clinical TRALI. These results indicate that the critical source of antigen for anti-leukocyte antibodies is in fact the endothelium, which reframes our understanding of TRALI as a rapid-onset vasculitis. Inhibition of complement activation may have multiple beneficial effects of reducing endothelial injury, platelet retention, and NET release in conditions where antibodies trigger these pathogenic responses.
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http://dx.doi.org/10.1172/JCI138136DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7598054PMC
November 2020

Animal models of mechanisms of SARS-CoV-2 infection and COVID-19 pathology.

Br J Pharmacol 2020 11 19;177(21):4851-4865. Epub 2020 Jul 19.

Sackler Institute of Pulmonary Pharmacology, Institute of Pharmaceutical Science, School of Cancer and Pharmaceutical Sciences, King's College London, London, UK.

The coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 infections has led to a substantial unmet need for treatments, many of which will require testing in appropriate animal models of this disease. Vaccine trials are already underway, but there remains an urgent need to find other therapeutic approaches to either target SARS-CoV-2 or the complications arising from viral infection, particularly the dysregulated immune response and systemic complications which have been associated with progression to severe COVID-19. At the time of writing, in vivo studies of SARS-CoV-2 infection have been described using macaques, cats, ferrets, hamsters, and transgenic mice expressing human angiotensin I converting enzyme 2 (ACE2). These infection models have already been useful for studies of transmission and immunity, but to date only partly model the mechanisms involved in human severe COVID-19. There is therefore an urgent need for development of animal models for improved evaluation of efficacy of drugs identified as having potential in the treatment of severe COVID-19. These models need to reproduce the key mechanisms of COVID-19 severe acute respiratory distress syndrome and the immunopathology and systemic sequelae associated with this disease. Here, we review the current models of SARS-CoV-2 infection and COVID-19-related disease mechanisms and suggest ways in which animal models can be adapted to increase their usefulness in research into COVID-19 pathogenesis and for assessing potential treatments. LINKED ARTICLES: This article is part of a themed issue on The Pharmacology of COVID-19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc.
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http://dx.doi.org/10.1111/bph.15143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7283621PMC
November 2020

Mitochondrial DNA Stimulates TLR9-Dependent Neutrophil Extracellular Trap Formation in Primary Graft Dysfunction.

Am J Respir Cell Mol Biol 2020 03;62(3):364-372

Department of Medicine.

The immune system is designed to robustly respond to pathogenic stimuli but to be tolerant to endogenous ligands to not trigger autoimmunity. Here, we studied an endogenous damage-associated molecular pattern, mitochondrial DNA (mtDNA), during primary graft dysfunction (PGD) after lung transplantation. We hypothesized that cell-free mtDNA released during lung ischemia-reperfusion triggers neutrophil extracellular trap (NET) formation via TLR9 signaling. We found that mtDNA increases in the BAL fluid of experimental PGD (prolonged cold ischemia followed by orthotopic lung transplantation) and not in control transplants with minimal warm ischemia. The adoptive transfer of mtDNA into the minimal warm ischemia graft immediately before lung anastomosis induces NET formation and lung injury. TLR9 deficiency in neutrophils prevents mtDNA-induced NETs, and TLR9 deficiency in either the lung donor or recipient decreases NET formation and lung injury in the PGD model. Compared with human lung transplant recipients without PGD, severe PGD was associated with high levels of BAL mtDNA and NETs, with evidence of relative deficiency in DNaseI. We conclude that mtDNA released during lung ischemia-reperfusion triggers TLR9-dependent NET formation and drives lung injury. In PGD, DNaseI therapy has a potential dual benefit of neutralizing a major NET trigger (mtDNA) in addition to dismantling pathogenic NETs.
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http://dx.doi.org/10.1165/rcmb.2019-0140OCDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7055700PMC
March 2020

LPS-induced Lung Platelet Recruitment Occurs Independently from Neutrophils, PSGL-1, and P-Selectin.

Am J Respir Cell Mol Biol 2019 08;61(2):232-243

1Sackler Institute of Pulmonary Pharmacology, Institute of Pharmaceutical Science and.

Platelets are recruited to inflammatory foci and contribute to host defense and inflammatory responses. Compared with platelet recruitment in hemostasis and thrombosis, the mechanisms of platelet recruitment in inflammation and host defense are poorly understood. Neutrophil recruitment to lung airspaces after inhalation of bacterial LPS requires platelets and PSGL-1 in mice. Given this association between platelets and neutrophils, we investigated whether recruitment of platelets to lungs of mice after LPS inhalation was dependent on PSGL-1, P-selectin, or interaction with neutrophils. BALB/c mice were administered intranasal LPS (O55:B5, 5 mg/kg) and, 48 hours later, lungs were collected and platelets and neutrophils quantified in tissue sections by immunohistochemistry. The effects of functional blocking antibody treatments targeting the platelet-neutrophil adhesion molecules, P-selectin or PSGL-1, or treatment with a neutrophil-depleting antibody targeting Ly6G, were tested on the extent of LPS-induced lung platelet recruitment. Separately in Pf4-Cre × mTmG mice, two-photon intravital microscopy was used to image platelet adhesion in live lungs. Inhalation of LPS caused both platelet and neutrophil recruitment to the lung vasculature. However, decreasing lung neutrophil recruitment by blocking PSGL-1, P-selectin, or depleting blood neutrophils had no effect on lung platelet recruitment. Lung intravital imaging revealed increased adhesion of platelets in the lung microvasculature which was not associated with thrombus formation. In conclusion, platelet recruitment to lungs in response to LPS occurs through mechanisms distinct from those mediating neutrophil recruitment, or the occurrence of pulmonary emboli.
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http://dx.doi.org/10.1165/rcmb.2018-0182OCDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6670039PMC
August 2019

Gustav Born: pioneer in imaging platelet and leukocyte biology.

Platelets 2018 Dec 9;29(8):766-770. Epub 2018 Nov 9.

a Sackler Institute of Pulmonary Pharmacology, Institute of Pharmaceutical Science , King's College London , London , UK.

Gustav Born achieved scientific fame for his application of light transmission aggregometry to the study of platelet function, but also led interdisciplinary research teams in pioneering quantitative in vivo imaging studies of platelet aggregation and leukocyte adhesion, and in conducting the first research into the biomechanical factors underlying atherosclerotic plaque rupture. Gus Born also communicated both current research findings and an integrated understanding of cardiovascular biology to a wide audience through acting as scientific advisor on several television productions. Using footage from two of these films, we discuss Gustav Born's scientific achievements and legacy.
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http://dx.doi.org/10.1080/09537104.2018.1535001DOI Listing
December 2018

Sensory nerves mediate spontaneous behaviors in addition to inflammation in a murine model of psoriasis.

FASEB J 2019 02 11;33(2):1578-1594. Epub 2018 Sep 11.

British Heart Foundation (BHF) Cardiovascular Centre of Research Excellence, Vascular Biology and Inflammation Section, King's College London, London, United Kingdom.

Psoriasis is characterized by keratinocyte hyperproliferation, erythema, as well as a form of pruritus, involving cutaneous discomfort. There is evidence from both clinical and murine models of psoriasis that chemical or surgical depletion of small-diameter sensory nerves/nociceptors benefits the condition, but the mechanisms are unclear. Hence, we aimed to understand the involvement of sensory nerve mediators with a murine model of psoriasis and associated spontaneous behaviors, indicative of cutaneous discomfort. We have established an Aldara model of psoriasis in mice and chemically depleted the small-diameter nociceptors in a selective manner. The spontaneous behaviors, in addition to the erythema and skin pathology, were markedly improved. Attenuated inflammation was associated with reduced dermal macrophage influx and production of reactive oxygen/nitrogen species (peroxynitrite and protein nitrosylation). Subsequently, this directly influenced observed behavioral responses. However, the blockade of common sensory neurogenic mechanisms for transient receptor potential (TRP)V1, TRPA1, and neuropeptides (substance P and calcitonin gene-related peptide) using genetic and pharmacological approaches inhibited the behaviors but not the inflammation. Thus, a critical role of the established sensory TRP-neuropeptide pathway in influencing cutaneous discomfort is revealed, indicating the therapeutic potential of agents that block that pathway. The ongoing inflammation is mediated by a distinct sensory pathway involving macrophage activation.-Kodji, X., Arkless, K. L., Kee, Z., Cleary, S. J., Aubdool, A. A., Evans, E., Caton, P., Pitchford, S. C., Brain, S. D. Sensory nerves mediate spontaneous behaviors in addition to inflammation in a murine model of psoriasis.
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http://dx.doi.org/10.1096/fj.201800395RRDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6338626PMC
February 2019

Platelets Play a Central Role in Sensitization to Allergen.

Am J Respir Cell Mol Biol 2018 07;59(1):96-103

Sackler Institute of Pulmonary Pharmacology, Institute of Pharmaceutical Science, King's College London, London, United Kingdom.

Platelet activation occurs in patients with allergic inflammation, and platelets can be activated directly by allergen via an IgE-dependent process. Platelets have been shown to activate APCs such as CD11c dendritic cells in vitro. Although CD11c dendritic cells are a requisite for allergen sensitization, the role of platelets in this process is unknown. In this study, we investigated whether platelets were necessary for allergen sensitization. Balb/c mice sensitized to ovalbumin were exposed to subsequent aerosolized allergen (ovalbumin challenge). We analyzed lung CD11c cell activation, colocalization with platelets, and some other indices of inflammation. The role of platelets at the time of allergen sensitization was assessed through platelet depletion experiments restricted to the period of sensitization. Platelets colocalized with airway CD11c cells, and this association increased after allergen sensitization as well as after subsequent allergen exposure. Temporary platelet depletion (>95%) at the time of allergen sensitization led to a suppression of IgE and IL-4 synthesis and to a decrease in the pulmonary recruitment of eosinophils, macrophages, and lymphocytes after subsequent allergen exposure. Furthermore, in mice previously depleted of platelets at the time of sensitization, the recovered platelet population was shown to have reduced expression of FcεRI. Pulmonary CD11c cell recruitment was suppressed in these mice after allergen challenge, suggesting that the migration of CD11c cells in vivo may be dependent on direct platelet recognition of allergen. We conclude that platelets are necessary for efficient host sensitization to allergen. This propagates the subsequent inflammatory response during secondary allergen exposure and increases platelet association with airway CD11c cells.
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http://dx.doi.org/10.1165/rcmb.2017-0401OCDOI Listing
July 2018

Platelet Depletion Impairs Host Defense to Pulmonary Infection with Pseudomonas aeruginosa in Mice.

Am J Respir Cell Mol Biol 2018 03;58(3):331-340

1 Sackler Institute of Pulmonary Pharmacology, Institute of Pharmaceutical Science and.

Platelets have been implicated in pulmonary inflammatory cell recruitment after exposure to allergic and nonallergic stimuli, but little is known about the role of platelets in response to pulmonary infection with Pseudomonas aeruginosa. In this study, we have investigated the impact of the experimental depletion of circulating platelets on a range of inflammatory and bacterial parameters, and their subsequent impact on mortality in a murine model of pulmonary infection with P. aeruginosa. P. aeruginosa infection in mice induced a mild, but significant, state of peripheral thrombocytopenia in addition to pulmonary platelet accumulation. Increased platelet activation was detected in infected mice through increased levels of the platelet-derived mediators, platelet factor-4 and β-thromboglobulin, in BAL fluid and blood plasma. In mice depleted of circulating platelets, pulmonary neutrophil recruitment was significantly reduced 24 hours after infection, whereas the incidence of systemic dissemination of bacteria was significantly increased compared with non-platelet-depleted control mice. Furthermore, mortality rates were increased in bacterial-infected mice depleted of circulating platelets. This work demonstrates a role for platelets in the host response toward a gram-negative bacterial respiratory infection.
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http://dx.doi.org/10.1165/rcmb.2017-0083OCDOI Listing
March 2018

P-Rex and Vav Rac-GEFs in platelets control leukocyte recruitment to sites of inflammation.

Blood 2015 Feb 23;125(7):1146-58. Epub 2014 Dec 23.

Signalling Programme, Babraham Institute, Cambridge, United Kingdom; and.

The small GTPase Rac is required for neutrophil recruitment during inflammation, but its guanine-nucleotide exchange factor (GEF) activators seem dispensable for this process, which led us to investigate the possibility of cooperation between Rac-GEF families. Thioglycollate-induced neutrophil recruitment into the peritoneum was more severely impaired in P-Rex1(-/-) Vav1(-/-) (P1V1) or P-Rex1(-/-) Vav3(-/-) (P1V3) mice than in P-Rex null or Vav null mice, suggesting cooperation between P-Rex and Vav Rac-GEFs in this process. Neutrophil transmigration and airway infiltration were all but lost in P1V1 and P1V3 mice during lipopolysaccharide (LPS)-induced pulmonary inflammation, with altered intercellular adhesion molecule 1-dependent slow neutrophil rolling and strongly reduced L- and E-selectin-dependent adhesion in airway postcapillary venules. Analysis of adhesion molecule expression, neutrophil adhesion, spreading, and migration suggested that these defects were only partially neutrophil-intrinsic and were not obviously involving vascular endothelial cells. Instead, P1V1 and P1V3 platelets recapitulated the impairment of LPS-induced intravascular neutrophil adhesion and recruitment, showing P-Rex and Vav expression in platelets to be crucial. Similarly, during ovalbumin-induced allergic inflammation, pulmonary recruitment of P1V1 and P1V3 eosinophils, monocytes, and lymphocytes was compromised in a platelet-dependent manner, and airway inflammation was essentially abolished, resulting in improved airway responsiveness. Therefore, platelet P-Rex and Vav family Rac-GEFs play important proinflammatory roles in leukocyte recruitment.
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http://dx.doi.org/10.1182/blood-2014-07-591040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4326774PMC
February 2015