Inhalation of particulate matter aggravates respiratory symptoms in patients with chronic airway diseases, but the mechanisms underlying this response remain poorly understood. We employed a proteomics approach to examine this phenomenon. Treatment of epithelial cells with BSA-coated titanium dioxide(TiO2) particles altered twenty protein spots on the 2-dimensional gel and these were then analyzed by 2D-nano liquid chromatography tandem mass spectrometry (2D Nano-LC-MS/MS). These proteins included defense-related, cell-activating, and cytoskeletal proteins implicated in the response to oxidative stress. The proteins were classified into four groups according to the time-course of their expression patterns. For validation, RT-PCR was performed on extracts of in vitro TiO2-treated cells, and lung issues from TiO2-treated rats were analyzed by immunohistochemical staining and enzyme immunoassay. TiO2 treatment was found to increase the amount of mRNA for macrophage migration inhibitory factor (MIF). MIF was expressed primarily in epithelium and was elevated in lung tissues and bronchoalveolar lavage fluids of TiO2-treated rats, as compared to sham-treated rats. Carbon black and diesel exhaust particles also induced expression of MIF protein in the epithelial cells.