Airborne pollutant ROFA enhances the allergic airway inflammation through direct modulation of dendritic cells in an uptake-dependent mechanism

• ROFA in allergen sensitized-mice is a risk factor for the exacerbation of the symptoms of asthma.
• In vivo ROFA activates myeloid DC, and modulates the mDC/pDC ratio in ROS-dependent manner.
• ROFA is able to induce direct maturation of DC and to maintain the state of activation induced by an allergen.
• The activation of DC by ROFA is the result of endocytosis.
• ROFA does not regulate allergen-specific antibodies.

Studies suggest that airborne pollutants are important cofactors in the exacerbation of lung diseases. The role of DC on the exacerbation of lung inflammation induced by particulate matter pollutants is unclear. We evaluated the effects of residual oil fly ash (ROFA) on the phenotype and function of bone marrow-derived dendritic cells (BMDCs) in vitro and lung dendritic cells (DCs) in vivo, and the subsequent T-cell response. In a model of asthma, exposure to ROFA exacerbated pulmonary inflammation, which was attributed to the increase of eosinophils, IL-5- and IFN-γ-producing T cells, and goblet cells as well as decreased number of Treg and pDC. However, the ROFA showed no ability to modulate the production of anaphylactic IgE. In vitro studies showed that ROFA directly induced the maturation of DCs up-regulating the expression of co-stimulatory molecules and cytokines and MMP production in an uptake-dependent and oxidative stress-dependent manner. Furthermore, ROFA-pulsed BMDC transferred to allergic mice exacerbated eosinophilic inflammation as well as promoted increased epithelial and goblet cells changes. Thus, pollutants may constitute an important and risk factor in the exacerbation of asthma with inhibition of the negative regulatory signals in the lung, with enhanced mDC activation that sustains the recruitment of effector T lymphocytes and eosinophil.