Immunological basis of reversible and fixed airways disease

Ageing mechanisms that contribute to tissue remodeling in lung disease

Age is a major risk factor for chronic respiratory diseases such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD) and certain phenotypes of asthma. The recent COVID-19 pandemic also highlights the increased susceptibility of the elderly to acute respiratory distress syndrome (ARDS), a diffuse inflammatory lung injury with often long-term effects (ie parenchymal fibrosis). Collectively, these lung conditions are characterized by a pathogenic reparative process that, rather than restoring organ function, contributes to structural and functional tissue decline. In the ageing lung, the homeostatic control of wound healing following challenge or injury has an increased likelihood of being perturbed, increasing susceptibility to disease. This loss of fidelity is a consequence of a diverse range of underlying ageing mechanisms including senescence, mitochondrial dysfunction, proteostatic stress and diminished autophagy that occur within the lung, as well as in other tissues, organs and systems of the body. These ageing pathways are highly interconnected, involving localized and systemic increases in inflammatory mediators and damage associated molecular patterns (DAMPs); along with corresponding changes in immune cell function, metabolism and composition of the pulmonary and gut microbiomes. Here we comprehensively review the roles of ageing mechanisms in the tissue remodeling of lung disease.

Revisiting Type 2-high and Type 2-low airway inflammation in asthma: current knowledge and therapeutic implications

Asthma is a complex respiratory disorder characterized by marked heterogeneity in individual patient disease triggers and response to therapy. Several asthma phenotypes have now been identified, each defined by a unique interaction between genetic and environmental factors, including inflammatory, clinical and trigger-related phenotypes. Endotypes further describe the functional or pathophysiologic mechanisms underlying the patient's disease. type 2-driven asthma is an emerging nomenclature for a common subtype of asthma and is characterized by the release of signature cytokines IL-4, IL-5 and IL-13 from cells of both the innate and adaptive immune systems. A number of well-recognized biomarkers have been linked to mechanisms involved in type 2 airway inflammation, including fractional exhaled nitric oxide, serum IgE, periostin, and blood and sputum eosinophils. These type 2 cytokines are targets for pharmaceutical intervention, and a number of therapeutic options are under clinical investigation for the management of patients with uncontrolled severe asthma. Anticipating and understanding the heterogeneity of asthma and subsequent improved characterization of different phenotypes and endotypes must guide the selection of treatment to meet individual patients' needs.

Peripheral killer cells do not differentiate between asthma patients with or without fixed airway obstruction

OBJECTIVE

The three main types of killer cells - CD8⁺ T cells, NK cells and NKT cells - have been linked to asthma and chronic obstructive pulmonary disease (COPD). However, their role in a small subset of asthma patients displaying fixed airway obstruction (FAO), similar to that seen in COPD, has not been explored. The objective of the present study was to investigate killer cell numbers, phenotype and function in peripheral blood from asthma patients with FAO, asthma patients without FAO, and healthy individuals.

METHODS

Peripheral CD8⁺ T cells (CD8⁺CD3⁺CD56^-), NK cells (CD56⁺CD3^-) and NKT-like cells (CD56⁺CD3⁺) of 14 asthma patients with FAO (post-bronchodilator FEV/FVC <0.7, despite clinician-optimised treatment), 7 asthma patients without FAO (post-bronchodilator FEV/FVC ≥ 0.7), and 9 healthy individuals were studied.

RESULTS

No significant differences were seen between the number, receptor expression, MAPK signalling molecule expression, cytotoxic mediator expression, and functional cytotoxicity of peripheral killer cells from asthma patients with FAO, asthma patients without FAO and healthy individuals.

CONCLUSIONS

Peripheral killer cell numbers or functions do not differentiate between asthma patients with or without fixed airway obstruction.

The Coagulant Factor Xa Induces Protease-Activated Receptor-1 and Annexin A2-Dependent Airway Smooth Muscle Cytokine Production and Cell Proliferation

During asthma exacerbation, plasma circulating coagulant factor X (FX) enters the inflamed airways and is activated (FXa). FXa may have an important role in asthma, being involved in thrombin activation and an agonist of protease-activated receptor-1 (PAR-1). Extracellular annexin A2 and integrins are also implicated in PAR-1 signaling. In this study, the potential role of PAR-1 in mediating the effects of FXa on human airway smooth muscle (ASM) cell cytokine production and proliferation was investigated. FXa (5-50 nM), but not FX, stimulated increases in ASM IL-6 production and cell number after 24- and 48-hour incubation, respectively (P < 0.05; n = 5). FXa (15 nM) also stimulated increases in the levels of mRNA for cytokines (IL-6), cell cycle-related protein (cyclin D1), and proremodeling proteins (FGF-2, PDGF-B, CTGF, SM22, and PAI-1) after 3-hour incubation (P < 0.05; n = 4). The actions of FXa were insensitive to inhibition by hirudin (1 U/ml), a selective thrombin inhibitor, but were attenuated by SCH79797 (100 nM), a PAR-1 antagonist, or Cpd 22 (1 μM), an inhibitor of integrin-linked kinase. The selective targeting of PAR-1, annexin A2, or β1-integrin by small interfering RNA and/or by functional blocking antibodies also attenuated FXa-evoked responses. In contrast, the targeting of annexin A2 did not inhibit thrombin-stimulated ASM function. In airway biopsies of patients with asthma, FXa and annexin A2 were detected in the ASM bundle by immunohistochemistry. These findings establish FXa as a potentially important asthma mediator, stimulating ASM function through actions requiring PAR-1 and annexin A2 and involving integrin coactivation.

NF-kappaB Signaling in Chronic Inflammatory Airway Disease

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive airway disorders which differ in their underlying causes and phenotypes but overlap in patterns of pharmacological treatments. In both asthma and COPD, oxidative stress contributes to airway inflammation by inducing inflammatory gene expression. The redox-sensitive transcription factor, nuclear factor (NF)-kappaB (NF-κB), is an important participant in a broad spectrum of inflammatory networks that regulate cytokine activity in airway pathology. The anti-inflammatory actions of glucocorticoids (GCs), a mainstay treatment for asthma, involve inhibition of NF-κB induced gene transcription. Ligand bound GC receptors (GRs) bind NF-κB to suppress the transcription of NF-κB responsive genes (i.e., transrepression). However, in severe asthma and COPD, the transrepression of NF-κB by GCs is negated as a consequence of post-translational changes to GR and histones involved in chromatin remodeling. Therapeutics which target NF-κB activation, including inhibitors of IκB kinases (IKKs) are potential treatments for asthma and COPD. Furthermore, reversing GR/histone acetylation shows promise as a strategy to treat steroid refractory airway disease by augmenting NF-κB transrepression. This review examines NF-κB signaling in airway inflammation and its potential as target for treatment of asthma and COPD.

Non-eosinophilic airway hyper-reactivity in mice, induced by IFN-γ producing CD4(+) and CD8(+) lung T cells, is responsive to steroid treatment

Non-eosinophilic asthma is characterized by infiltration of neutrophils into the lung and variable responsiveness to glucocorticoids. The pathophysiological mechanisms have not been characterized in detail. Here, we present an experimental asthma model in mice associated with non-eosinophilic airway inflammation and airway hyper-responsiveness (AHR). For this, BALB/c mice were sensitized by biolistic DNA immunization with a plasmid encoding the model antigen β-galactosidase (pFascin-βGal mice). For comparison, eosinophilic airway inflammation was induced by subcutaneous injection of βGal protein (βGal mice). Intranasal challenge of mice in both groups induced AHR to a comparable extent as well as recruitment of inflammatory cells into the airways. In contrast to βGal mice, which exhibited extensive eosinophilic infiltration in the lung, goblet cell hyperplasia and polarization of CD4(+) T cells into Th2 and Th17 cells, pFascin-βGal mice showed considerable neutrophilia, but no goblet cell hyperplasia and a predominance of Th1 and Tc1 cells in the airways. Depletion studies in pFascin-βGal mice revealed that CD4(+) and CD8(+) cells cooperated to induce maximum inflammation, but that neutrophilic infiltration was not a prerequisite for AHR induction. Treatment of pFascin-βGal mice with dexamethasone before intranasal challenge did not affect neutrophilic infiltration, but significantly reduced AHR, infiltration of monocytes and lymphocytes as well as content of IFN-γ in the bronchoalveolar fluid. Our results suggest that non-eosinophilic asthma associated predominantly with Th1/Tc1 cells is susceptible to glucocorticoid treatment. pFascin-βGal mice might represent a mouse model to study pathophysiological mechanisms proceeding in the subgroup of asthmatics with non-eosinophilic asthma that respond to inhaled steroids.

LAPCs contribute to the pathogenesis of allergen-induced allergic airway inflammation in mice

BACKGROUND

The inflammatory immune response associated with allergic airway inflammation in asthma involves T helper type 2 (Th2) immunity. Given the data that a newly described late activator antigen-presenting cell (LAPC) population promotes Th2 immunity in viral infections, we undertook studies to investigate whether LAPCs have a pathogenic role in allergic airway inflammation.

METHODS

We employed acute ovalbumin (OVA) and house dust mite (HDM) sensitization and challenge models to establish allergic airway inflammation in mice, followed by the analysis of lungs and draining lymph node (DLN) cell infiltrates, immunoglobulin E (IgE) production, and airway hyper-responsiveness (AHR). We tested whether adoptive transfer of LAPCs isolated from mice with established allergic airway inflammation augments the development of sensitization in naïve mice.

RESULTS

We provide evidence that in both OVA and HDM mouse models of allergic inflammation, LAPCs accumulate in the lungs and draining lymph nodes (DLNs), concomitant with the onset of lung pathology, allergen-specific IgE production, eosinophilia, and Th2 cytokine production. Adoptive transfer experiments using OVA-activated LAPCs reveal exacerbation of disease pathology with an increase in lung inflammatory cells, eosinophilia, circulating IgE, Th2 cytokine production, and a worsening of AHR. OVA-activated LAPCs preferentially increased GATA-3 induction in naïve CD4(+) T cells.

CONCLUSIONS

Together, these data suggest an important role for LAPCs in polarizing the Th2 response in mouse models of allergic airway inflammation.

Regulation of pulmonary inflammation by mesenchymal cells

Pulmonary inflammation and tissue remodelling are common elements of chronic respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and pulmonary hypertension (PH). In disease, pulmonary mesenchymal cells not only contribute to tissue remodelling, but also have an important role in pulmonary inflammation. This review will describe the immunomodulatory functions of pulmonary mesenchymal cells, such as airway smooth muscle (ASM) cells and lung fibroblasts, in chronic respiratory disease. An important theme of the review is that pulmonary mesenchymal cells not only respond to inflammatory mediators, but also produce their own mediators, whether pro-inflammatory or pro-resolving, which influence the quantity and quality of the lung immune response. The notion that defective pro-inflammatory or pro-resolving signalling in these cells potentially contributes to disease progression is also discussed. Finally, the concept of specifically targeting pulmonary mesenchymal cell immunomodulatory function to improve therapeutic control of chronic respiratory disease is considered.

Could FEV₁ decline have a role in daily clinical practice for asthma monitoring?

OBJECTIVE

The aim of this review was to understand whether FEV1 decline measured during the follow-up of asthmatic subjects (FEV1 variation between two different measurements at a distance of at least 5 years) may have a role in their management.

METHODS

Articles, commentaries and reviews relating to the topic were searched in PubMed.

RESULTS

Patients with an accelerated FEV1 decline (>30 ml/year) may be either steroid-resistant/difficult-to-treat asthmatics or not adequately treated because they are either under-perceivers or poorly adherent to their therapy. Sometimes they may be unable to use devices correctly. Untreated rhinitis and incorrect lifestyle (obesity status, a high-fat diet and lack of exercise) must be considered when facing a pulmonary function decline. Identifying asthmatics with an accelerated FEV1 decline, even with well controlled symptoms, may allow us to make possible treatment adjustments or to remove potentially harmful environmental exposure and suggest a correct lifestyle. Depending on FEV1 decline severity, we may detect different asthma phenotypes. One type is characterized by no/low lung function reduction. Among moderate/severe 'declining' subjects, there may be a group that might be responsive to treatment and a second one with a quicker loss in lung function that may be unresponsive to therapy.

CONCLUSION

FEV1 decline calculation should be assessed early in clinical practice over the course of time in order to make all possible variations in treatment, environmental exposure and lifestyle more efficacious overall for declining subjects responsive to anti-inflammatory therapy. Further studies are necessary to validate this approach to asthma.

The Th17 pathway and inflammatory diseases of the intestines, lungs, and skin

The recent discovery of a new CD4+ T cell subset, Th17, has transformed our understanding of the pathogenetic basis of an increasing number of chronic immune-mediated diseases. Particularly in tissues that interface with the microbial environment-such as the intestinal and respiratory tracts and the skin-where most of the Th17 cells in the body reside, dysregulated immunity to self (or the extended self, the diverse microbiota that normally colonize these tissues) can result in chronic inflammatory disease. In this review, we focus on recent advances in the biology of the Th17 pathway and on genome-wide association studies that implicate this immune pathway in human disease involving these tissues.

Antibiotics as immunomodulant agents in COPD

It is widely accepted that some antibiotics have activities beyond their direct antibacterial effects. Macrolide is the antibiotic class with more convincing studies and evidence on its immunomodulatory and anti-inflammatory activities. Different clinical studies have shown that macrolide prophylaxis in patients with moderate-severe chronic obstructive pulmonary disease (COPD) can have a significant impact on the exacerbation rate reducing morbidity and, potentially, mortality of the disease. Other antibiotics, such as fluoroquinolones, demonstrate a variety of immunomodulatory effects but only few clinical data are available in COPD. New macrolide derivatives devoid of antibacterial activity have been synthetized. This review analyses the relevance of immunomodulatory and anti-inflammatory effects of antibiotics in the management of COPD.