Diesel exhaust particles stimulate adaptive immunity by acting on pulmonary dendritic cells

Particulate matter, such as diesel exhaust particles (DEPs), modulate adaptive immune responses in the lung; however, their mechanism of action remains largely unclear. Pulmonary dendritic cells (DCs) are crucial mediators in regulating immune responses. We hypothesized that the immunomodulatory effects of DEPs are caused by alteration of DC function. To test this, we instilled mice with DEPs and examined the pulmonary DC recruitment and maturation, their migration to the mediastinal lymph node (MLN), and the subsequent T cell response. We demonstrated that exposure to DEPs increased DC numbers in the bronchoalveolar lavage and the lungs and that DEPs increased the maturation status of these DCs. DEP exposure also enhanced the DC migration to the MLN. Moreover, we showed that DEPs themselves were transported to the MLN in a CCR7- and DC-dependent manner. This resulted in an enhanced T cell recruitment and effector differentiation in the MLN. These data suggest that DEP inhalation modulates immune responses in the lung via stimulation of DC function.