Dr Steven Maltby

Background: Acute exacerbations of asthma represent a major burden of disease and are often caused by respiratory infections. Viral infections are recognized as significant triggers of exacerbations; however, less is understood about the how microbial bioproducts such as the endotoxin (lipopolysaccharide (LPS)) trigger episodes. Indeed, increased levels of LPS have been linked to asthma onset, severity and steroid resistance. Objective: The goal of this study was to identify mechanisms underlying bacterial-induced exacerbations by employing LPS as a surrogate for infection. Methods: We developed a mouse model of LPS-induced exacerbation on the background of pre-existing type-2 allergic airway disease (AAD). Results: LPS-induced exacerbation was characterized by steroid-resistant airway hyperresponsiveness (AHR) and an exaggerated inflammatory response distinguished by increased numbers of infiltrating neutrophils/macrophages and elevated production of lung inflammatory cytokines, including TNFa, IFN¿, IL-27 and MCP-1. Expression of the type-2 associated inflammatory factors such as IL-5 and IL-13 were elevated in AAD but not altered by LPS exposure. Furthermore, AHR and airway inflammation were no longer suppressed by corticosteroid (dexamethasone) treatment after LPS exposure. Depletion of pulmonary macrophages by administration of 2-chloroadenosine into the lungs suppressed AHR and reduced IL-13, TNFa and IFN¿ expression. Blocking IL-13 function, through either IL-13-deficiency or administration of specific blocking antibodies, also suppressed AHR and airway inflammation. Conclusions & Clinical Relevance: We present evidence that IL-13 and innate immune pathways (in particular pulmonary macrophages) contribute to LPS-induced exacerbation of pre-existing AAD and provide insight into the complex molecular processes potentially underlying microbial-induced exacerbations.

Extra-intestinal manifestations (EIM) are common in inflammatory bowel disease (IBD). One such EIM is sub-clinical pulmonary inflammation, which occurs in up to 50% of IBD patients. In animal models of colitis, pulmonary inflammation is driven by neutrophilic infiltrations, primarily in response to the systemic bacteraemia and increased bacterial load in the lungs. Platelet activating factor receptor (PAFR) plays a critical role in regulating pulmonary responses to infection in conditions, such as chronic obstructive pulmonary disease and asthma. We investigated the role of PAFR in pulmonary EIMs of IBD, using dextran sulfate sodium (DSS) and anti-CD40 murine models of colitis. Both models induced neutrophilic inflammation, with increased TNF and IL-1ß levels, bacterial load and PAFR protein expression in mouse lungs. Antagonism of PAFR decreased lung neutrophilia, TNF, and IL-1ß in an NLRP3 inflammasome-dependent manner. Lipopolysaccharide from phosphorylcholine (ChoP)-positive bacteria induced NLRP3 and caspase-1 proteins in human alveolar epithelial cells, however antagonism of PAFR prevented NLRP3 activation by ChoP. Amoxicillin reduced bacterial populations in the lungs and reduced NLRP3 inflammasome protein levels, but did not reduce PAFR. These data suggest a role for PAFR in microbial pattern recognition and NLRP3 inflammasome signaling in the lung.

Inflammatory bowel disease (IBD) is associated with several immune-mediated extraintestinal manifestations. More than half of all IBD patients have some form of respiratory pathology, most commonly neutrophil-mediated diseases, such as bronchiectasis and chronic bronchitis. Using murine models of colitis, we aimed to identify the immune mechanisms driving pulmonary manifestations of IBD. We found increased neutrophil numbers in lung tissue associated with the pulmonary vasculature in both trinitrobenzenesulfonic acid¿ and dextran sulfate sodium¿induced models of colitis. Analysis of systemic inflammation identified that neutrophilia was associated with bacteremia and pyrexia in animal models of colitis. We further identified IL-6 as a systemic mediator of neutrophil recruitment from the bone marrow of dextran sulfate sodium animals. Functional inhibition of IL-6 led to reduced systemic and pulmonary neutrophilia, but it did not attenuate established colitis pathology. These data suggest that systemic bacteremia and pyrexia drive IL-6 secretion, which is a critical driver for pulmonary manifestation of IBD. Targeting IL-6 may reduce neutrophil-associated extraintestinal manifestations in IBD patients.

A link between inflammatory disease and bone loss is now recognized. However, limited data exist on the impact of virus infection on bone loss and regeneration. Bone loss results from an imbalance in remodeling, the physiological process whereby the skeleton undergoes continual cycles of formation and resorption. The specific molecular and cellular mechanisms linking virus-induced inflammation to bone loss remain unclear. In the current study, we provide evidence that infection of mice with either lymphocytic choriomeningitis virus (LCMV) or pneumonia virus of mice (PVM) resulted in rapid and substantial loss of osteoblasts from the bone surface. Osteoblast ablation was associated with elevated levels of circulating inflammatory cytokines, including TNF-a, IFN-g, IL-6, and CCL2. Both LCMV and PVM infections resulted in reduced osteoblast-specific gene expression in bone, loss of osteoblasts, and reduced serum markers of bone formation, including osteocalcin and procollagen type 1 N propeptide. Infection of Rag-1-deficient mice (which lack adaptive immune cells) or specific depletion of CD8+ T lymphocytes limited osteoblast loss associated with LCMV infection. By contrast, CD8+ T cell depletion had no apparent impact on osteoblast ablation in association with PVM infection. In summary, our data demonstrate dramatic loss of osteoblasts in response to virus infection and associated systemic inflammation. Further, the inflammatory mechanisms mediating viral infection-induced bone loss depend on the specific inflammatory condition.

Experimental stroke leads to microglia activation and progressive neuronal loss at sites of secondary neurodegeneration (SND). These lesions are remote from, but synaptically connected to, primary infarction sites. Previous studies have demonstrated that immune cells are present in sites of infarction in the first hours and days after stroke, and are associated with increased neurodegeneration in peri-infarct regions. However, it is not known whether immune cells are also present in more distal sites where SND occurs. Our study aimed to investigate whether immune cells are present in sites of SND and, if so, how these cell populations compare to those in the peri-infarct zone. Cells were isolated from the thalamus, the main site of SND, and remaining brain tissue 14 days post-stroke. Analysis was performed using flow cytometry to quantify microglia, myeloid cell and lymphocyte numbers. We identified a substantial infiltration of immune cells in the ipsilateral (stroked) compared to the contralateral (control) thalamus, with a significant increase in the percentage of CD4+ and CD8+ T cells. This result was further quantified using immunofluorescent labelling of fixed tissue. In the remaining ipsilateral hemisphere tissue, there were significant increases in the frequency of CD4+ and CD8+ T lymphocytes, B lymphocytes, Ly6G+ neutrophils and both Ly6G-Ly6CLO and Ly6G-Ly6CHI monocytes. Our results indicate that infiltrating immune cells persist in ischemic tissue after the acute ischemic phase, and are increased in sites of SND. Importantly, immune cells have been shown to play pivotal roles in both damage and repair processes after stroke. Our findings indicate that immune cells may also be involved in the pathogenesis of SND and further clinical studies are warranted to characterise the nature of inflammatory cell infiltrates in human disease.

Respiratory syncytial virus (RSV) infection induces asthma exacerbations, which leads to worsening of clinical symptoms and may result in a sustained decline in lung function. Exacerbations are the main cause of morbidity and mortality associated with asthma, and significantly contribute to asthma-associated healthcare costs. Although glucocorticoids are used to manage exacerbations, some patients respond to them poorly. The underlying mechanisms associated with steroid-resistant exacerbations remain largely unknown. We have previously established a mouse model of RSV-induced exacerbation of allergic airways disease, which mimics hallmark clinical features of asthma. In this study, we have identified key roles for macrophage IFN-¿ and IL-27 in the regulation of RSV-induced exacerbation of allergic airways disease. Production of IFN-¿ and IL-27 was steroid-resistant, and neutralization of IFN-¿ or IL-27 significantly suppressed RSV-induced steroid-resistant airway hyperresponsiveness and airway inflammation. We have previously implicated activation of pulmonary macrophage by TNF-a and/or MCP-1 in the mechanisms of RSV-induced exacerbation. Stimulation of pulmonary macrophages with TNF-a and/or MCP-1 induced expression of both IFN-¿ and IL-27. Our findings highlight critical roles for IFN-¿ and IL-27, downstream of TNF-a and MCP-1, in the mechanism of RSV-induced exacerbation. Thus, targeting the pathways that these factors activate may be a potential therapeutic approach for virus-induced asthma exacerbations.

Asthma is a chronic respiratory disease characterized by respiratory symptoms, airway inflammation, airway obstruction and airway hyper-responsiveness. Asthma is common and directly affects 10% of Australians, 1¿5% of adults in Asia and 300 million people worldwide. It is a heterogeneous disorder with many clinical, molecular, biological and pathophysiological phenotypes. Current management strategies successfully treat the majority of patients with asthma who have access to them. However, there is a subset of an estimated 5¿10% of patients with asthma who have severe disease and are disproportionately impacted by symptoms, exacerbations and overall illness burden. The care required for this relatively small proportion of patients is also significant and has a major impact on the healthcare system. A number of new therapies that hold promise for severe asthma are currently in clinical trials or are entering the Australian and international market. However, recognition of severe asthma in clinical practice is variable, and there is little consensus on the best models of care or how to integrate emerging and often costly therapies into current practice. In this article, we report on roundtable discussions held with severe asthma experts from around Australia, and make recommendations about approaches for better patient diagnosis and assessment. We assess current models of care for patient management and discuss how approaches may be optimized to improve patient outcomes. Finally, we propose mechanisms to assess new therapies and how to best integrate these approaches into future treatment.

Background Asthma and COPD are common airway diseases. Individuals with overlapping asthma and COPD experience increased health impairment and severe disease exacerbations. Efficacious treatment options are required for this population. Omalizumab (anti-IgE) therapy is effective in patients with severe persistent asthma, but limited data are available on efficacy in populations with overlapping asthma and COPD. Methods Data from the Australian Xolair Registry were used to compare treatment responses in individuals with asthma-COPD overlap with responses in patients with severe asthma alone. Participants were assessed at baseline and after 6¿months of omalizumab treatment. We used several different definitions of asthma-COPD overlap. First, we compared participants with a previous physician diagnosis of COPD to participants with no COPD diagnosis. We then made¿comparisons based on baseline lung function, comparing participants with an FEV1 <¿80%¿predicted to those with an FEV1 > 80%¿predicted after bronchodilator use. In the population with an FEV1< 80%, analysis was further stratified based on smoking history. Results Omalizumab treatment markedly improved asthma control and health-related quality of life in all populations assessed based on the Asthma Control Questionnaire and Asthma Quality of Life Questionnaire scores. Omalizumab treatment did not improve lung function (FEV1, FVC, or FEV1/FVC ratio) in populations that were enriched for asthma-COPD overlap (diagnosis of COPD or FEV1¿< 80%/ever smokers). Conclusions Our study suggests that omalizumab improves asthma control and health-related quality of life in individuals with severe allergic asthma and overlapping COPD. These findings provide real-world efficacy data for this patient population and suggest that omalizumab is useful in the management of severe asthma with COPD overlap.

Viral respiratory infections trigger severe exacerbations of asthma, worsen disease symptoms, and impair lung function. To investigate the mechanisms underlying viral exacerbation, we established a mouse model of respiratory syncytial virus (RSV)-induced exacerbation after allergen sensitization and challenge. RSV infection of OVA-sensitized/challenged BALB/c mice resulted in significantly increased airway hyperresponsiveness (AHR) and macrophage and neutrophil lung infiltration. Exacerbation was accompanied by increased levels of inflammatory cytokines (including TNF-a, MCP-1, and keratinocyte-derived protein chemokine [KC]) compared with uninfected OVA-treated mice or OVA-treated mice exposed to UV-inactivated RSV. Dexamethasone treatment completely inhibited all features of allergic disease, including AHR and eosinophil infiltration, in uninfected OVAsensitized/challenged mice. Conversely, dexamethasone treatment following RSV-induced exacerbation only partially suppressed AHR and failed to dampen macrophage and neutrophil infiltration or inflammatory cytokine production (TNF-a, MCP-1, and KC). This mimics clinical observations in patients with exacerbations, which is associated with increased neutrophils and often poorly responds to corticosteroid therapy. Interestingly, we also observed increased TNF-a levels in sputum samples from patients with neutrophilic asthma. Although RSV-induced exacerbation was resistant to steroid treatment, inhibition of TNF-a and MCP-1 function or depletion of macrophages suppressed features of disease, including AHR and macrophage and neutrophil infiltration. Our findings highlight critical roles for macrophages and inflammatory cytokines (including TNF-a and MCP-1) in viral-induced exacerbation of asthma and suggest examination of these pathways as novel therapeutic approaches for disease management.

Background Steroid-resistant asthma is a major clinical problem that is linked to activation of innate immune cells. Levels of IFN-¿ and LPS are often increased in these patients. Cooperative signaling between IFN-¿/LPS induces macrophage-dependent steroid-resistant airway hyperresponsiveness (AHR) in mouse models. MicroRNAs (miRs) are small noncoding RNAs that regulate the function of innate immune cells by controlling mRNA stability and translation. Their role in regulating glucocorticoid responsiveness and AHR remains unexplored. Objective IFN-¿ and LPS synergistically increase the expression of miR-9 in macrophages and lung tissue, suggesting a role in the mechanisms of steroid resistance. Here we demonstrate the role of miR-9 in IFN-¿/LPS-induced inhibition of dexamethasone (DEX) signaling in macrophages and in induction of steroid-resistant AHR. Methods MiRNA-9 expression was assessed by means of quantitative RT-PCR. Putative miR-9 targets were determined in silico and confirmed in luciferase reporter assays. miR-9 function was inhibited with sequence-specific antagomirs. The efficacy of DEX was assessed by quantifying glucocorticoid receptor (GR) cellular localization, protein phosphatase 2A (PP2A) activity, and AHR. Results Exposure of pulmonary macrophages to IFN-¿/LPS synergistically induced miR-9 expression; reduced levels of its target transcript, protein phosphatase 2 regulatory subunit B (B56) d isoform; attenuated PP2A activity; and inhibited DEX-induced GR nuclear translocation. Inhibition of miR-9 increased both PP2A activity and GR nuclear translocation in macrophages and restored steroid sensitivity in multiple models of steroid-resistant AHR. Pharmacologic activation of PP2A restored DEX efficacy and inhibited AHR. MiR-9 expression was increased in sputum of patients with neutrophilic but not those with eosinophilic asthma. Conclusion MiR-9 regulates GR signaling and steroid-resistant AHR. Targeting miR-9 function might be a novel approach for the treatment of steroid-resistant asthma.

Pathogenic bacterial infections of the lung are life threatening and underpin chronic lung diseases. Current treatments are often ineffective potentially due to increasing antibiotic resistance and impairment of innate immunity by disease processes and steroid therapy. Manipulation miRNA directly regulating anti-microbial machinery of the innate immune system may boost host defence responses. Here we demonstrate that miR-328 is a key element of the host response to pulmonary infection with non-typeable haemophilus influenzae and pharmacological inhibition in mouse and human macrophages augments phagocytosis, the production of reactive oxygen species, and microbicidal activity. Moreover, inhibition of miR-328 in respiratory models of infection, steroid-induced immunosuppression, and smoke-induced emphysema enhances bacterial clearance. Thus, miRNA pathways can be targeted in the lung to enhance host defence against a clinically relevant microbial infection and offer a potential new anti-microbial approach for the treatment of respiratory diseases.

Chronic inflammatory diseases (e.g. asthma and chronic obstructive pulmonary disease) are leading causes of morbidity and mortality world-wide and effective treatments are limited. These disorders can often be attributed to abnormal immune responses to environmental stimuli and infections. Mechanisms leading to inflammation are complex, resulting from interactions of structural cells and activation of both the adaptive and innate arms of the immune system. The activation of structural and immune cells involves both temporary and permanent changes in gene expression in these cells, which underpin chronic inflammation and tissue dysfunction. miRNAs are small non-coding RNAs increasingly being recognized to play important roles in the post-transcriptional regulation of gene expression in mammalian cells by regulating translation. Individual miRNAs can exert their effects by directly inhibiting the translation or stability of multiple mRNAs simultaneously. Thus, the expression or blockade of function of a single miRNA (miR) can result in pronounced alterations in protein expression within a given cell. Dysregulation of miRNA expression may subsequently alter cellular function, and in certain situations predispose to disease. Our current understanding of the role of miRNA in the regulation of inflammatory disease (e.g. allergic diseases) remains limited. In this review, we provide an overview of the current understanding of miRNA biogenesis and function, the roles miRNA play in the regulation of immune cell function and their potential contribution to inflammatory diseases. We also highlight strategies to alter miRNA function for experimental or therapeutic gain, and discuss the potential utility and limitations of targeting these molecules as anti-inflammatory strategies. © 2013 John Wiley & Sons Ltd.