Epidemiological studies indicate that asthmatic children are more susceptible to traffic-related air pollution exposure than non-asthmatic children. Local and systemic inflammation in combination with oxidative stress have been suggested as a possible susceptibility factor.

We investigated effect modification by asthma status for the association between air pollution exposure and systemic effects using whole blood cytokine responsiveness as an inflammatory marker.

The study was nested within the two German birth cohort studies GINIplus and LISAplus and initially designed as a random sub-sample enriched with asthmatic children. Using data from 27 asthmatic and 59 non-asthmatic six-year-old children we measured the production of Interleukin-6 (IL)-6, IL-8, IL-10, monocyte chemotactic protein-1 (MCP-1), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in whole blood after ex-vivo stimulation with urban particulate matter (EHC-93). Air pollution exposure (nitrogen dioxide (NO₂), nitrogen oxides (NOx), particulate matter with an aerodynamic diameter <10 μm (PM₁₀), particulate matter with an aerodynamic diameter <2.5 μm (PM2.5mass), coarse particulate matter (PM_coarse) and PM_{2.5absorbance} (PM_2.5abs)) was modelled for children´s home addresses applying land-use regression. To assess effect modification by asthma status linear regression models with multiplicative interaction terms were used.

In asthmatics exposure to NO₂ was associated with higher production of pro-inflammatory cytokines: adjusted means ratio (MR) 2.22 (95% confidence interval 1.22–4.04) for IL-6 per 2.68 µg/m³ NO₂. The interaction term between asthma status and NO₂ exposure was significant. Results for NO_x, PM₁₀, PM_2.5mass and PM_2.5abs were in the same direction. No association between air pollution and cytokine responsiveness was found in the group of non-asthmatic children and in the overall group.

Traffic-related air pollution exposure is associated with higher pro-inflammatory cytokine responsiveness in whole blood of asthmatic children.