Proximity to a Major Road and Plasma Cytokines in School-Aged Children

Traffic-related air pollution (TRAP) may affect immune responses, including those in the T_H2 and T_H17 pathways. To examine whether TRAP is associated with plasma level of T_H17-, T_H1-, and T_H2-related cytokines in children with and without asthma, a cross-sectional study of 577 children (ages 6-14 years) with (n = 294) and without (n = 283) asthma in San Juan (Puerto Rico) was performed. Residential distance to a major road was estimated using geocoded home addresses for study participants. A panel of 14 cytokines, enriched for the T_H17 pathway, was measured in plasma. Asthma was defined as physician-diagnosed asthma and current wheeze. Multivariable linear regression was used to examine the association of residential distance to a major road (a marker of TRAP), asthma, and cytokine levels. Among all participating children, residential proximity to a major road was significantly associated with increased plasma level of IL-31, even after adjustment for relevant covariates and correction for multiple testing. The presence of asthma modified the estimated effect of the residential distance to a major road on plasma TNF-α (P for interaction = 0.00047). Although living farther from a major road was significantly associated with lower TNF-α level in control subjects, no such decrease was seen in children with asthma. In a direct comparison of cases and control subjects, children with asthma had significantly higher levels of IL-1β, IL-22, and IL-33 than control subjects. TRAP is associated with increased levels of proinflammatory cytokines among Puerto Rican children, who belong to an ethnic group with high risk for asthma.