Mechanical ventilation modulates Toll-like receptor-3-induced lung inflammation via a MyD88-dependent, TLR4-independent pathway: a controlled animal study

<p>Abstract</p> <p>Background</p> <p>Mechanical ventilation augments lung inflammation resulting from exposure to microbial products. The objective of this study was to test the hypothesis that ventilator-associated immune modulation requires MyD88-dependent signaling. Because MyD88 is a critical adapter protein utilized for pro-inflammatory signaling by all Toll-like receptors (TLRs), with the exception of TLR3, as well as by the IL-1 and IL-18 receptors, MyD88 dependence would implicate generation of an endogenous soluble ligand recognized by one or more of these receptors during mechanical ventilation and would provide an opportunity for a potential future therapeutic intervention.</p> <p>Methods</p> <p>We compared the effect of mechanical ventilation on lung inflammation and permeability between poly(I:C) exposed mice with or without expression of MyD88. Poly(I:C) is a synthetic ligand for TLR3, the only MyD88-independent TLR, allowing isolation of the effect of MyD88 deletion on ventilator-augmentation of lung inflammation. Lung inflammation was assessed by cytokine concentration in lung tissue homogenate and polymorphonuclear cell (PMN) number in bronchoalveolar lavage fluid (BALF). Lung permeability was assessed by total protein, IgM, and intravenously injected FITC-dextran concentrations in BALF.</p> <p>Results</p> <p>We found that MyD88 was required for mechanical ventilation augmentation of TLR3-induced lung inflammation and permeability. Because TLR4 is the most commonly reported receptor for endogenous ligands generated during tissue injury, we performed a second experiment comparing wildtype and TLR4-/- mice. We found that mechanical ventilation increased TLR3-mediated inflammation and permeability independent of TLR4.</p> <p>Conclusion</p> <p>These data support the hypothesis that mechanical ventilation with moderate tidal volumes generates an endogenous ligand(s) recognized by MyD88-dependent receptor(s) other than TLR4, and that this mechanism can contribute to the development of ventilator-associated lung inflammation and injury. Identification of these ligands and/or receptors could lead to new pharmacological treatments for ARDS.</p

Mechanical ventilation interacts with endotoxemia to induce extrapulmonary organ dysfunction

INTRODUCTION: Multiple organ dysfunction syndrome (MODS) is a common complication of sepsis in mechanically ventilated patients with acute respiratory distress syndrome, but the links between mechanical ventilation and MODS are unclear. Our goal was to determine whether a minimally injurious mechanical ventilation strategy synergizes with low-dose endotoxemia to induce the activation of pro-inflammatory pathways in the lungs and in the systemic circulation, resulting in distal organ dysfunction and/or injury. METHODS: We administered intraperitoneal Escherichia coli lipopolysaccharide (LPS; 1 μg/g) to C57BL/6 mice, and 14 hours later subjected the mice to 6 hours of mechanical ventilation with tidal volumes of 10 ml/kg (LPS + MV). Comparison groups received ventilation but no LPS (MV), LPS but no ventilation (LPS), or neither LPS nor ventilation (phosphate-buffered saline; PBS). RESULTS: Myeloperoxidase activity and the concentrations of the chemokines macrophage inflammatory protein-2 (MIP-2) and KC were significantly increased in the lungs of mice in the LPS + MV group, in comparison with mice in the PBS group. Interestingly, permeability changes across the alveolar epithelium and histological changes suggestive of lung injury were minimal in mice in the LPS + MV group. However, despite the minimal lung injury, the combination of mechanical ventilation and LPS resulted in chemical and histological evidence of liver and kidney injury, and this was associated with increases in the plasma concentrations of KC, MIP-2, IL-6, and TNF-α. CONCLUSION: Non-injurious mechanical ventilation strategies interact with endotoxemia in mice to enhance pro-inflammatory mechanisms in the lungs and promote extra-pulmonary end-organ injury, even in the absence of demonstrable acute lung injury

A point mutation in the murine Hem1 gene reveals an essential role for Hematopoietic Protein 1 in lymphopoiesis and innate immunity

Hem1 (Hematopoietic protein 1) is a hematopoietic cell-specific member of the Hem family of cytoplasmic adaptor proteins. Orthologues of Hem1 in Dictyostelium discoideum, Drosophila melanogaster, and Caenorhabditis elegans are essential for cytoskeletal reorganization, embryonic cell migration, and morphogenesis. However, the in vivo functions of mammalian Hem1 are not known. Using a chemical mutagenesis strategy in mice to identify novel genes involved in immune cell functions, we positionally cloned a nonsense mutation in the Hem1 gene. Hem1 deficiency results in defective F-actin polymerization and actin capping in lymphocytes and neutrophils caused by loss of the Rac-controlled actin-regulatory WAVE protein complex. T cell development is disrupted in Hem1-deficient mice at the CD4−CD8− (double negative) to CD4+CD8+ (double positive) cell stages, whereas T cell activation and adhesion are impaired. Hem1-deficient neutrophils fail to migrate in response to chemotactic agents and are deficient in their ability to phagocytose bacteria. Remarkably, some Rac-dependent functions, such as Th1 differentiation and nuclear factor κB (NF-κB)–dependent transcription of proinflammatory cytokines proceed normally in Hem1-deficient mice, whereas the production of Th17 cells are enhanced. These results demonstrate that Hem1 is essential for hematopoietic cell development, function, and homeostasis by controlling a distinct pathway leading to cytoskeletal reorganization, whereas NF-κB–dependent transcription proceeds independently of Hem1 and F-actin polymerization

Differentiation of Gram-Negative Bacterial Aerosol Exposure Using Detected Markers in Bronchial-Alveolar Lavage Fluid

The identification of biosignatures of aerosol exposure to pathogens has the potential to provide useful diagnostic information. In particular, markers of exposure to different types of respiratory pathogens may yield diverse sets of markers that can be used to differentiate exposure. We examine a mouse model of aerosol exposure to known Gram negative bacterial pathogens, Francisella tularensis novicida and Pseudomonas aeruginosa. Mice were subjected to either a pathogen or control exposure and bronchial alveolar lavage fluid (BALF) was collected at four and twenty four hours post exposure. Small protein and peptide markers within the BALF were detected by matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS) and analyzed using both exploratory and predictive data analysis methods; principle component analysis and degree of association. The markers detected were successfully used to accurately identify the four hour exposed samples from the control samples. This report demonstrates the potential for small protein and peptide marker profiles to identify aerosol exposure in a short post-exposure time frame

East Coast Fever Caused by Theileria parva Is Characterized by Macrophage Activation Associated with Vasculitis and Respiratory Failure

Respiratory failure and death in East Coast Fever (ECF), a clinical syndrome of African cattle caused by the apicomplexan parasite Theileria parva, has historically been attributed to pulmonary infiltration by infected lymphocytes. However, immunohistochemical staining of tissue from T. parva infected cattle revealed large numbers of CD3- and CD20-negative intralesional mononuclear cells. Due to this finding, we hypothesized that macrophages play an important role in Theileria parva disease pathogenesis. Data presented here demonstrates that terminal ECF in both Holstein and Boran cattle is largely due to multisystemic histiocytic responses and resultant tissue damage. Furthermore, the combination of these histologic changes with the clinical findings, including lymphadenopathy, prolonged pyrexia, multi-lineage leukopenia, and thrombocytopenia is consistent with macrophage activation syndrome. All animals that succumbed to infection exhibited lymphohistiocytic vasculitis of small to medium caliber blood and lymphatic vessels. In pulmonary, lymphoid, splenic and hepatic tissues from Holstein cattle, the majority of intralesional macrophages were positive for CD163, and often expressed large amounts of IL-17. These data define a terminal ECF pathogenesis in which parasite-driven lymphoproliferation leads to secondary systemic macrophage activation syndrome, mononuclear vasculitis, pulmonary edema, respiratory failure and death. The accompanying macrophage phenotype defined by CD163 and IL-17 is presented in the context of this pathogenesis

Animal models of acute lung injury

Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury