Eosinophils in asthma phenotypes: perpetrators or guilty by association?

25 years after publication of a clinical trial in The Lancet on the anti-IL-5 antibody mepolizumab in individuals with allergic asthma, evidence has accumulated that the pathogenetic role of eosinophils is fundamentally different between asthma phenotypes. In the allergen-driven form of asthma, often starting in childhood or during adolescence (ie, early onset asthma), blood eosinophil counts are variable, mainly dependent on allergen exposure, and play only a minor role (as a so-called sidekick) in allergen-induced asthma symptoms. By contrast, eosinophils are persistently elevated and are crucial drivers of the disease in the intrinsic (eosinophilic) form of asthma, which typically starts in adulthood (ie, adult-onset asthma). These data suggest that eosinophilia should not be considered a treatable trait in people with chronic airway diseases, but only a complement to an accurate clinical diagnosis. This evidence has major implications for the diagnosis of asthma phenotypes and the treatment of asthma (eg, choice of the right biologic).

Eosinophils in asthma phenotypes: perpetrators or guilty by association? Journal Articles