Paucigranulocytic asthma: Do sputum macrophages matter?

Macrophages Orchestrate Airway Inflammation, Remodeling, and Resolution in Asthma

Asthma is a heterogenous chronic inflammatory lung disease with endotypes that manifest different immune system profiles, severity, and responses to current therapies. Regardless of endotype, asthma features increased immune cell infiltration, inflammatory cytokine release, and airway remodeling. Lung macrophages are also heterogenous in that there are separate subsets and, depending on the environment, different effector functions. Lung macrophages are important in recruitment of immune cells such as eosinophils, neutrophils, and monocytes that enhance allergic inflammation and initiate T helper cell responses. Persistent lung remodeling including mucus hypersecretion, increased airway smooth muscle mass, and airway fibrosis contributes to progressive lung function decline that is insensitive to current asthma treatments. Macrophages secrete inflammatory mediators that induce airway inflammation and remodeling. Additionally, lung macrophages are instrumental in protecting against pathogens and play a critical role in resolution of inflammation and return to homeostasis. This review summarizes current literature detailing the roles and existing knowledge gaps for macrophages as key inflammatory orchestrators in asthma pathogenesis. We also raise the idea that modulating inflammatory responses in lung macrophages is important for alleviating asthma.

Delineating asthma according to inflammation phenotypes with a focus on paucigranulocytic asthma

ABSTRACT

Asthma is characterized by chronic airway inflammation and airway hyper-responsiveness. However, the differences in pathophysiology and phenotypic symptomology make a diagnosis of "asthma" too broad hindering individualized treatment. Four asthmatic inflammatory phenotypes have been identified based on inflammatory cell profiles in sputum: eosinophilic, neutrophilic, paucigranulocytic, and mixed-granulocytic. Paucigranulocytic asthma may be one of the most common phenotypes in stable asthmatic patients, yet it remains much less studied than the other inflammatory phenotypes. Understanding of paucigranulocytic asthma in terms of phenotypic discrimination, distribution, stability, surrogate biomarkers, underlying pathophysiology, clinical characteristics, and current therapies is fragmented, which impedes clinical management of patients. This review brings together existing knowledge and ongoing research about asthma phenotypes, with a focus on paucigranulocytic asthma, in order to present a comprehensive picture that may clarify specific inflammatory phenotypes and thus improve clinical diagnoses and disease management.

Non‐eosinophilic asthma in nonsteroidal anti‐inflammatory drug exacerbated respiratory disease

Background

The cellular inflammatory pattern of nonsteroidal anti‐inflammatory drug–exacerbated respiratory disease (N‐ERD) is heterogeneous. However, data on the heterogeneity of non‐eosinophilic asthma (NEA) with aspirin hypersensitivity are scanty. By examination of N‐ERD patients based on clinical data and eicosanoid biomarkers we aimed to identify NEA endotypes potentially guiding clinical management.

Methods

Induced sputum was collected from patients with N‐ERD. Sixty six patients (49.6% of 133 N‐ERD) with NEA were included in the hierarchical cluster analysis based on clinical and laboratory data. The quality of clustering was evaluated using internal cluster validation with different indices and a practical decision tree was proposed to simplify stratification of patients.

Results

The most frequent NEA pattern was paucigranulocytic (PGA; 75.8%), remaining was neutrophilic asthma (NA; 24.2%). Four clusters were identified. Cluster #3 included the highest number of NEA patients (37.9%) with severe asthma and PGA pattern (96.0%). Cluster #1 (24.2%) included severe only asthma, with a higher prevalence of NA (50%). Cluster #2 (25.8%) comprised well‐controlled mild or severe asthma (PGA; 76.5%). Cluster #4 contained only 12.1% patients with well‐controlled moderate asthma (PGA; 62.5%). Sputum prostaglandin D₂ levels distinguished cluster #1 from the remaining clusters with an area under the curve of 0.94.

Conclusions

Among identified four NEA subtypes, clusters #3 and #1 represented N‐ERD patients with severe asthma but a different inflammatory signatures. All the clusters were discriminated by sputum PGD₂ levels, asthma severity, and age of patients. The heterogeneity of non‐eosinophilic N‐ERD suggests a need for novel targeted interventions.

How does cigarette smoking affect airway remodeling in asthmatics?

Asthma is a prevalent chronic airway inflammatory disease involving multiple cells, and the prolonged course of the disease can cause airway remodeling, resulting in irreversible or partial irreversible airflow limitation and persistent airway hyperresponsiveness (AHR) in asthmatics. Therefore, we must ascertain the factors that affect the occurrence and development of airway remodeling in asthmatics. Smokers are not uncommon in asthmatics. However, there is no systematic description of how smoking promotes airway remodeling in asthmatics. This narrative review summarizes the effects of smoking on airway remodeling in asthmatics, and the progress of the methods for evaluating airway remodeling.

Clinical implications of asthma endotypes and phenotypes

Background: Asthma is a complex disorder with variable clinical expression. Recognizable clinical and laboratory features define phenotypes, and specific biologic pathways define endotypes. Identifying the specific pathway responsible for persistent asthma would enable the clinician to select the optimal inhibitors, which currently are biologic therapies. Objective: To provide an up-to-date review of the current clinical status of endotype and phenotype characterizations of asthma and discuss these categories in relation to the available, or likely available, biologic therapies for asthma. Methods: The medical literature was reviewed based on the search terms: asthma biologics, severe asthma, uncontrolled asthma, corticosteroid-dependent asthma, phenotype, endotype, and type 2. We also used our knowledge of the literature and current research. Results: All of the current biologics, including the recently approved tezepelumab, were most effective with increased type 2 biomarkers, which identify exacerbation-prone asthma. Current biomarkers do not permit consistent identification of specific endotypes to facilitate informed selection of the optimal therapy for an individual patient. Thus, empiricism and the art of care continue to play major roles in treatment selection. Conclusion: Current biologic therapies for asthma and those likely to be U.S. Food and Drug Administration approved within the near future work best in subjects with strong type 2 signatures. Available biomarkers and observable characteristics do not enable clinicians to recognize specific endotypes, but rather subphenotypes or overlapping endotypes. The goal of identifying the optimal patient for a specific therapy remains elusive, but worthy of pursuit. In the interim, the availability of an increasing number of treatment options allows the clinician to help most of his or her patients.