The role of eosinophils in pediatric and adult asthma

Abstract

Background: In adults, asthma is typically classified as Th2-high/Th2-low based on Th2-inflammation markers like eosinophils. In children, it is mostly characterized by atopy.

Aim: We assess whether Th2 asthma phenotypes based on eosinophils and if atopy can be defined in children (as in adults).

Methods: In the ALL-Age-Asthma-Cohort (ALLIANCE), blood eosinophils and specific IgE (sIgE) were assessed in 149 wheezers (7mos–6yrs), 194 asthmatic children (6-18yrs) and 210 asthmatic adults. We defined atopy as any sIgE≥0.7 IU/mL. Eosinophil cutoffs were determined as the 90th percentile of the absolute eosinophil counts in age-matched healthy controls. Phenotypes were defined using low/high eosinophils and atopy.

Results: The prevalence of phenotypes (Th2-low, Eos-only, Atopy-only, Th2-high) was 49.0%, 15.4%, 18.8%, 16.8% in wheezers; 19.1%, 1.5%, 42.3%, 37.1% in asthmatic children and 17.1%, 18.6%, 33.8%, 30.5% in adults. In adults, exacerbations were mostly in the Eos-only phenotype (64.1%) compared to 35.9% and 26.8% in Th2-high and Atopy-only phenotypes (p=0.001). In contrast, in asthmatic children, wheezing episodes were most frequent in the Th2-high phenotype (50.7%) compared to 34.1% in the Atopy-only phenotype (p=0.017). Those with Eos-only were too few for analysis. In wheezers, phenotypes based on eosinophils and atopy had no association with wheezing. However, both atopic groups with/without high eosinophils had the highest risk of asthma at 6yrs (78.9% and 72.7%) compared to the only eosinophilic group (41.7%, p=0.002).

Conclusion: It is unclear if the Th2-phenotype as is described in adults exists in children. Eosinophils possibly play a different role in children.