Air pollution and blood inflammatory phenotypes of asthma

The harmful effects of air pollution on asthma are recognized, but the underlying biological mechanisms are not yet well-known. Studying the associations between air pollution and asthma inflammatory phenotypes may bring new insights. Blood inflammatory phenotypes were identified as previously done among participants with current asthma in the French adult population-based cohort Constances (Tsiavia T, EBioMedicine, 2022). At inclusion, current asthma was defined by self-reporting asthma attacks, symptoms or treatments in the last 12 months. Blood eosinophil (0.25x109/L) and neutrophil (5x109/L) cut-offs defined paucigranulocytic, eosinophilic, neutrophilic and mixed asthma phenotypes. Annual concentrations of PM2.5, black carbon (BC) and NO2 at the participants9 residential addresses at inclusion were estimated using a land-use regression model. Multinomial logistic models adjusted for age, sex, smoking, education and French deprivation index were used. The ORs were expressed for one interquartile range increase of PM2.5 (4.16 µg/m3), BC (0.57 10-5/m) and NO2 (12.8 µg/m3). This study included 14873 participants with current asthma. The paucigranulocytic, neutrophilic, eosinophilic and mixed phenotype accounted for 57%, 6%, 33% and 4% respectively. Using paucigranulocytic phenotype as the reference, the neutrophilic phenotype had significantly higher odd for PM2.5 (OR: 1.11 (1.01-1.21)) and the eosinophilic phenotype had significantly lower odds for BC and NO2 (ORs: 0.95 (0.90-1.00) and 0.91 (0.87-0.96)). No association was evidenced for the mixed phenotype. These results showed that neutrophilic and eosinophilic phenotypes were differently associated with each air pollutant, suggesting different biological mechanisms.