Early-life exposure to ambient air pollution and respiratory outcomes: Mixture and sex-stratified associations with inflammatory cytokine responses

Evidence on the link between air pollution and inflammatory responses is scarce, especially during early life. This study investigates the associations between air pollution exposure, respiratory outcomes, and cytokine responses during the first year of life, and whether these are modified by sex and temperature. The association of residential exposure to ambient PM_2.5, PM₁₀, and NO₂ with the prevalence of bronchitis and wheezing in 1-year-old infants (n = 606) was examined using logistic regression. In the subcohort (n = 508) with cytokine data (TNF-α, MCP-1, IL-8, IL-6, and IL-10, pg/mL) after lipopolysaccharide stimulation, single pollutants were correlated with inflammatory biomarkers by linear regression, and mixture effects were estimated using Bayesian kernel machine regression (BKMR). All models were stratified by sex and adjusted for covariates and residential greenness. Estimates were calculated per IQR increase in PM_2.5, PM₁₀, and NO₂ exposures: 2.0, 2.8, and 9.1 μg/m³, respectively. In boys, an IQR increase in PM_2.5 was associated with higher odds of bronchitis (aOR = 1.50, 95% CI: 1.02 - 2.23) and IL-8 concentrations (23.8%, 95% CI: 11.2 - 37.9%). In girls, an IQR increase in PM_2.5 was associated with elevated concentrations of IL-8 (31.9%, 95% CI: 18.6 - 46.7%) and TNF-α (12.8%, 95% CI: 3.9 - 22.6%). All air pollutants were consistently associated with increased IL-10 concentrations in girls, with PM_2.5 having the strongest effect (35.7%, 95% CI: 14.4 - 61.1%) per IQR increment. BKMR mixture analyses revealed a positive non-linear association between the air pollutant mixture, IL-8, and TNF-α when all air pollutants exceeded their 60th percentile. Infants in the upper temperature tertile showed stronger associations with IL-8 in response to PM_2.5 and NO₂ exposures. Altogether, our findings suggest that PM_2.5 is the primary predictor of respiratory outcomes and inflammatory responses during the first year of life.