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© ERS 2019. Asthma is characterised by typical symptoms in combination with variable airway obstruction and, in many cases, eosinophilic airway inflammation. Most patients with asthma have well-controlled symptoms and a low risk of asthma exacerbations when treated with ICSs. However, ∼5–10% remain symptomatic and/or at risk of asthma exacerbations despite maximum inhaled therapy with ICSs and long-acting β2-agonists. Such patients with severe asthma are responsible for a significant proportion of healthcare costs attributable to asthma and have a large unmet need for better treatment. An important advance in recent years has been the recognition that severe asthma is heterogeneous with respect to clinical presentation, response to treatment and the pattern of lower airway inflammation. Type 2-high airway inflammation is seen in >50% of patients with severe asthma and is driven by innate and adaptive immune mechanism and associated mediators, including IgE, IL-5, IL-13 and IL-4, resulting in the presence of airway eosinophilia. Biological agents blocking IgE, IL-5, and both IL-4 and IL-13 are effective treatments in selected patients with severe asthma with type 2 airway inflammation.

Original publication




Journal article


ERS Monograph

Publication Date





285 - 303