House Dust Mite Aeroallergen Suppresses Leukocyte Phagocytosis and Netosis Initiated by Pneumococcal Lung Infection.

Asthmatics are highly susceptible to developing lower respiratory tract infections caused by Streptococcus pneumoniae (SPN, the pneumococcus). It has recently emerged that underlying allergic airway disease creates a lung microenvironment that is defective in controlling pneumococcal lung infections. In the present study, we examined how house dust mite (HDM) aeroallergen exposure altered immunity to acute pneumococcal lung infection. Alveolar macrophage (AM) isolated from HDM-exposed mice expressed alternatively activated macrophage (AAM) markers including YM1, FIZZ1, IL-10, and ARG-1. In vivo, prior HDM exposure resulted in accumulation of AAMs in the lungs and 2-log higher bacterial titres in the bronchoalveolar (BAL) fluid of SPN-infected mice (Day 2). Acute pneumococcal infection further increased the expression of IL-10 and ARG1 in the lungs of HDM-exposed mice. Moreover, prior HDM exposure attenuated neutrophil extracellular traps (NETs) formation in the lungs and dsDNA levels in the BAL fluid of SPN-infected mice. In addition, HDM-SPN infected animals had significantly increased BAL fluid cellularity driven by an influx of macrophages/monocytes, neutrophils, and eosinophils. Increased lung inflammation and mucus production was also evident in HDM-sensitised mice following acute pneumococcal infection, which was associated with exacerbated airway hyperresponsiveness. Of note, PCV13 vaccination modestly reduced pneumococcal titres in the BAL fluid of HDM-exposed animals and did not prevent BAL inflammation. Our findings provide new insights on the relationship between pneumococcal lung infections and allergic airways disease, where defective AM phagocytosis and NETosis are implicated in increased susceptibility to pneumococcal infection.

G-CSFR antagonism reduces mucosal injury and airways fibrosis in a virus-dependent model of severe asthma.

BACKGROUND AND PURPOSE: Asthma is a chronic disease that displays heterogeneous clinical and molecular features. A phenotypic subset of late-onset severe asthmatics has debilitating fixed airflow obstruction, increased neutrophilic inflammation and a history of pneumonia. Influenza A virus (IAV) is an important viral cause of pneumonia and asthmatics are frequently hospitalised during IAV epidemics. This study aims to determine whether antagonising granulocyte colony stimulating factor receptor (G-CSFR) prevents pneumonia-associated severe asthma. EXPERIMENTAL APPROACH: Mice were sensitised to house dust mite (HDM) to establish allergic airway inflammation and subsequently infected with IAV (HKx31/H3N2 subtype). A neutralising monoclonal antibody against G-CSFR was therapeutically administered. KEY RESULTS: In IAV-infected mice with prior HDM sensitisation, a significant increase in airway fibrotic remodelling and airways hyper-reactivity was observed. A mixed granulocytic inflammatory profile consisting of neutrophils, macrophages and eosinophils was prominent and at a molecular level, G-CSF expression was significantly increased in HDMIAV-treated mice. Blockage of G-CSFR reduced neutrophilic inflammation in the bronchoalveolar and lungs by over 80% in HDMIAV-treated mice without altering viral clearance. Markers of NETosis (dsDNA and myeloperoxidase in bronchoalveolar), tissue injury (LDH activity in bronchoalveolar) and oedema (total bronchoalveolar-fluid protein) were also significantly reduced with anti-G-CSFR treatment. In addition, anti-G-CSFR antagonism significantly reduced bronchoalveolar gelatinase activity, active TFGß lung levels, collagen lung expression, airways fibrosis and airways hyper-reactivity in HDMIAV-treated mice. CONCLUSIONS AND IMPLICATIONS: We have shown that antagonising G-CSFR-dependent neutrophilic inflammation reduced pathological disruption of the mucosal barrier and airways fibrosis in an IAV-induced severe asthma model.

Novel Therapies for Pneumonia-Associated Severe Asthma Phenotypes.

Distinct asthma phenotypes are emerging from well-defined cohort studies and appear to be associated with a history of pneumonia. Asthmatics are more susceptible to infections caused by Streptococcus pneumoniae; however, the mechanisms that underlie defective immunity to this pathogen are still being elucidated. Here, we discuss how alternatively activated macrophages (AAMs) in asthmatics are defective in bacterial phagocytosis and how respiratory viruses disrupt essential host immunity to cause bacterial dispersion deeper into the lungs. We also describe how respiratory pathogens instigate neutrophilic inflammation and amplify type-2 inflammation in asthmatics. Finally, we propose novel dual-acting strategies including granulocyte-colony-stimulating factor receptor (G-CSFR) antagonism and specialised pro-resolving mediators (SPMs) to suppress type-2 and neutrophilic inflammation without compromising pathogen clearance.

Excessive Reactive Oxygen Species Inhibit IL-17A+ γδ T Cells and Innate Cellular Responses to Bacterial Lung Infection.

Aims: Excessive reactive oxygen species (ROS) are detrimental to immune cellular functions that control pathogenic microbes; however, the mechanisms are poorly understood. Our aim was to determine the immunological consequences of increased ROS levels during acute bacterial infection. Results: We used a model of Streptococcus pneumoniae (Spn) lung infection and superoxide dismutase 3-deficient (SOD3-/-) mice, as SOD3 is a major antioxidant enzyme that catalyses the dismutation of superoxide radicals. First, we observed that in vitro, macrophages from SOD3-/- mice generated excessive phagosomal ROS during acute bacterial infection. In vivo, there was a significant reduction in infiltrating neutrophils in the bronchoalveolar lavage fluid and reduced peribronchial and alveoli inflammation in SOD3-/- mice 2 days after Spn infection. Annexin V/propidium iodide staining revealed enhanced apoptosis in neutrophils from Spn-infected SOD3-/- mice. In addition, SOD3-/- mice showed an altered macrophage phenotypic profile, with markedly diminished recruitment of monocytes (CD11clo, CD11bhi) in the airways. Further investigation revealed significantly lower levels of the monocyte chemokine CCL-2, and cytokines IL-23, IL-1ß, and IL-17A in Spn-infected SOD3-/- mice. There were also significantly fewer IL-17A-expressing gamma-delta T cells (γδ T cells) in the lungs of Spn-infected SOD3-/- mice. Innovation: Our data demonstrate that SOD3 deficiency leads to an accumulation of phagosomal ROS levels that initiate early neutrophil apoptosis during pneumococcal infection. Consequent to these events, there was a failure to initiate innate γδ T cell responses. Conclusion: These studies offer new cellular and mechanistic insights into how excessive ROS can regulate innate immune responses to bacterial infection.

The transcriptomic response of Streptococcus pneumoniae following exposure to cigarette smoke extract.

Exposure to cigarette smoke is a risk factor for respiratory diseases. Although most research has focused on its effects on the host, cigarette smoke can also directly affect respiratory pathogens, in some cases enhancing virulence. Streptococcus pneumoniae (the pneumococcus) is a leading cause of community-acquired pneumonia worldwide, however data on the effects of cigarette smoke on the pneumococcus are sparse. Using RNA-seq, we show that pneumococci exposed to cigarette smoke extract in a concentrated acute exposure in vitro model initiate a 'survival' transcriptional response including the upregulation of detoxification enzymes, efflux pumps and osmoregulator transporters, as well as the downregulation of fatty acid and D-alanyl lipoteichoic acid biosynthesis genes. Except for the downregulation of the pneumolysin gene, there were no changes in the expression of major virulence factors following exposure to cigarette smoke. Compared to unexposed pneumococci, smoke-exposed pneumococci did not exhibit any changes in viability, adherence, hydrophobicity or cell lysis susceptibility. In this study, we demonstrate that pneumococci adapt to acute noxious cigarette smoke exposure by inducing a gene expression signature that allows the bacteria to resist its harmful effects.