BACKGROUND: Exposure to traffic-related particulate matter promotes asthma and allergic diseases. However, the precise cellular and molecular mechanisms by which particulate matter exposure acts to mediate these effects remain unclear.

OBJECTIVE: We sought to elucidate the cellular targets and signaling pathways critical for augmentation of allergic airway inflammation induced by ambient ultrafine particles (UFP).

METHODS: We used in vitro cell-culture assays with lung-derived antigen-presenting cells and allergen-specific T cells and in vivo mouse models of allergic airway inflammation with myeloid lineage-specific gene deletions, cellular reconstitution approaches, and antibody inhibition studies.

RESULTS: We identified lung alveolar macrophages (AM) as the key cellular target of UFP in promoting airway inflammation. Aryl hydrocarbon receptor-dependent induction of Jagged 1 (Jag1) expression in AM was necessary and sufficient for augmentation of allergic airway inflammation by UFP. UFP promoted TH2 and TH17 cell differentiation of allergen-specific T cells in a Jag1- and Notch 4-dependent manner. Treatment of mice with an anti-Notch 4 antibody abrogated exacerbation of allergic airway inflammation induced by UFP.

CONCLUSION: UFP exacerbate allergic airway inflammation by promoting a Jag1-Notch 4-dependent interaction between AM and allergen-specific T cells, leading to augmented TH cell differentiation.