Air pollution from traffic during pregnancy impairs newborn's cord blood immune cells: The NELA cohort

Background: Hazards of traffic-related air pollution (TRAP) on the developing immune system are poorly understood. We sought to investigate the effects of prenatal exposure to TRAP on cord blood immune cell distributions; and to identify gestational windows of susceptibility. Methods: In-depth immunophenotyping of cord blood leukocyte and lymphocyte subsets was performed by flow cytometry in 190 newborns embedded in the Nutrition in Early Life and Asthma (NELA) birth cohort (2015-2018). Long-term (whole pregnancy and trimesters) and short-term (15-days before delivery) residential exposures to traffic-related nitrogen dioxide (NO2), particulate matter (PM2.5 and PM10), and ozone (O3) were estimated using dispersion/chemical transport modelling. Associations between TRAP concentrations and cord blood immune cell counts were assessed using multivariate Poisson regression models. Results: Mean number of natural killer (NK) cells decreased 15% in relation to higher NO2 concentrations (>36.4 mu g/m3) during whole pregnancy (incidence relative risk (IRR), 0.85; 95% CI, 0.72, 0.99), with stronger associations in the first trimester. Higher PM2.5 concentrations (>13.3 mu g/m3) during whole pregnancy associated with a reduced mean number of cytotoxic T cells (IRR, 0.88; 95% CI, 0.78, 0.99). Newborns exposed to higher PM10 (>23.6 mu g/m3) and PM2.5 concentrations during the first and third trimester showed greater mean number of helper T type 1 (Th1) cells (P < 0.05). Decreased number of regulatory T (Treg) cells was associated with greater short-term NO2 (IRR, 0.90; 95% CI, 0.80, 1.01) and PM10 (IRR, 0.88; 95% CI, 0.77, 0.99) concentrations. Conclusions: Prenatal exposure to TRAP, particularly in early and late gestation, impairs fetal immune system development through disturbances in cord blood leukocyte and lymphocyte distributions.