Pro-oxidative diesel exhaust particle chemicals inhibit LPS-induced dendritic cell responses involved in T-helper differentiation

BackgroundEpidemiologic studies show that exposure to ambient particulate matter leads to asthma exacerbation. Diesel exhaust particles (DEPs), a model pollutant, act as an adjuvant for allergic sensitization. Increasing evidence shows that this effect could be mediated by an effect on dendritic cells (DCs).ObjectiveOur aim was to elucidate the mechanism by which pro-oxidative DEP chemicals change DC function so that these antigen-presenting cells strengthen the immune response to an experimental allergen.MethodsWe exposed murine bone marrow–derived DCs and a homogeneous myeloid DC line, BC1, to DEPs and organic extracts made from these particles to determine how the induction of oxidative stress affects cellular maturation, cytokine production, and activation of antigen-specific T cells.ResultsDEP extracts induced oxidative stress in DCs. This change in redox equilibrium interfered in the ability of Toll-like receptor agonists to induce the expression of maturation receptors (eg, CD86, CD54, and I-Ad) and IL-12 production. This perturbation of DC function was accompanied by decreased IFN-γ and increased IL-10 induction in antigen-specific T cells. The molecular basis for the perturbation of DC function is the activation of a nuclear factor-erythroid 2 (NF-E2)–related factor 2–mediated signaling pathway that suppresses IL-12 production. NF-E2–related factor 2 deficiency abrogates the perturbation of DC function by DEPs.ConclusionThese data provide the first report that pro-oxidative DEP chemicals can interfere in TH1-promoting response pathways in a homogeneous DC population and provide a novel explanation for the adjuvant effect of DEPs on allergic inflammation.Clinical implicationsThese data clarify the adjuvant effect of particulate air pollutants in allergic inflammatory disease.