Severe Neutrophilic Asthma: Pathogenesis and Treatment

Abstract

Asthma is a common chronic airway disease affecting about 358 million people worldwide, and an estimated 7 million children globally. Approximately 10% of patients with asthma have severe refractory disease, which is difficult to control on high doses of inhaled corticosteroids and other modifiers. Among these, are patients with severe neutrophilic asthma. Neutrophilic asthma is a severe phenotype of asthma, characterized by frequent exacerbations, persistent airway obstruction, and poor lung function. Immunopathologically, it is characterized by the presence of high levels of neutrophils in the airways and lungs. Interleukin-17 produced by Th17 cells, plays a key role in the pathogenesis of neutrophilic asthma by expressing the secretion of chemoattractant cytokines and chemokines for the recruitment, and activation of neutrophils. Interleukin-8 is a powerful chemoattractant and activator of neutrophils. Activated neutrophils produce an oxidative burst, releasing multiple reactive oxygen species, proteinases, cytokines, which cause airway epithelial cell injury, inflammation, airway hyperresponsiveness, and remodeling. Furthermore, exasperated neutrophils due to viral, bacterial or fungal infections, and chemical irritants can release extracellular nucleic acids (DNA), designated as NETs (neutrophil extracellular traps), which are more toxic to the airway epithelial cells, and orchestrate airway inflammation, and release alarmin cytokines. Dysregulated NETs formation is associated with severe asthma. Most patients with neutrophilic asthma are unresponsive to the standard of care, including high dose inhaled corticosteroids, and to targeted biologics, such as mepolizumab, and dupilumab, which are very effective in treating eosinophilic asthma. There is unmet need to explore for novel biologics for the treatment of neutrophilic asthma, and in refining therapies, such as bronchial thermoplasty.