Context: Exposure to ultrafine particles (<100nm in diameter) is postulated to cause chronic obstructive pulmonary disease (COPD). However, the mechanism remains to be elucidated. Objective: We aimed to evaluate whether ultrafine particle exposure causes the infiltration of inflammatory and dendritic cells (DCs) with increased elastase activity, contributing to lung parenchymal destruction. Materials and methods: C57BL/6 male mice were intratracheally instilled with 300 μg ultrafine carbon black (ufCB; 14nm in diameter), and sacrificed at 1, 3, 7 and 14 d post-exposure. Differential cell counts, elastase activities, and desmosine and hydroxyproline in bronchoalveolar (BAL) fluid were determined. Immunofluorescent staining and flow cytometry analysis determined the cell origin of macrophage metalloelastase (MMP-12). Anti-neutrophil antibody was applied to assess the contribution of elastase in ufCB induced lung destruction. Results: ufCB exposure led to significant increases in neutrophils, mononuclear cells and total proteins in BAL fluid. Desmosine and hydroxyproline were significantly increased in the ufCB group. Elastase activities were found to be significantly elevated, with both neutrophil elastase and MMP-12 peaking at 3 d post-exposure. Flow cytometry analysis demonstrated that pulmonary infiltrations of MMP-12 positive DCs, including Langerhans cells-derived DCs, occurred at 3 d and 7 d, while macrophage infiltration was obvious starting at 1 d. Anti-neutrophil antibody significantly reduced neutrophil elastase activity and prevented the increases in BAL desmosine and hydroxyproline following ufCB exposure. Conclusion: For the first time we demonstrate the infiltration of Langerhans and myeloid dendritic cells, and show that elastase production contributes to pulmonary destruction following exposure to ultrafine particles.
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