Mucosal airway inflammation in virus-induced COPD exacerbations

Published online: April 10, 2020

Chronic obstructive pulmonary disease (COPD) exacerbations are a major cause of morbidity and mortality and respiratory viral infections (predominantly human rhinoviruses) are the most common trigger of COPD exacerbations. The mucosal cellular inflammatory response induced by viral infection in COPD has not been well characterised and has relied on studies of sputum as bronchial biopsies are difficult to perform in acutely unwell patients.

In an article recently published in The Journal of Allergy & Clinical Immunology (JACI) Zhu and colleagues examined the mucosal inflammatory responses induced by rhinovirus infection in COPD subjects. The authors were able to do this by using an experimental human model of rhinovirus infection that facilitates the use of bronchoscopy and endobronchial biopsy in exacerbated COPD patients. The authors hypothesised that rhinovirus infection recruits inflammatory cells to the bronchial mucosa and that the nature of the inflammatory response is distinct from that seen in non-COPD subjects.  

A significant increase in mucosal eosinophils from baseline was seen in the COPD subjects following RV infection, but not in non-COPD controls. Moreover, higher eosinophil counts were associated with greater virus load, more symptoms, greater falls in lung function and higher sputum inflammatory markers. Submucosal neutrophils were not significantly increased. Previous work from the authors had found that sputum neutrophils are significantly increased in these COPD subjects following rhinovirus infection and they correlate with sputum inflammatory markers such as neutrophil elastase, IL-1β, TNF, CXCL8/IL-8, pentraxin-3 and LL-37. In the current study these sputum markers correlated with submucosal eosinophils rather than with neutrophils.

The authors suggest that virus infection induces an innate inflammatory response and recruitment of both neutrophils and eosinophils. Neutrophils transit rapidly from blood through the mucosa into the airway lumen so sputum neutrophils are the best measure of pulmonary neutrophilic inflammation, whereas eosinophils transit more slowly and are retained in the mucosal compartment so sputum eosinophils may underestimate the contribution of eosinophils in airway inflammation.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.