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Fine particles derived from diesel engines, diesel exhaust particles (DEP), have been shown to augment gene expression of several inflammatory cytokines in human airway epithelial cells in vitro. However, it remains unclear whether or not DEP have any effect on the expression and production of eotaxin, an important chemokine involved in eosinophil recruitment into the airways. We studied the effects of DEP by using a conventional suspended DEP and by a recently established in vitro cell exposure system to diesel exhaust (Abe S, Takizawa H, Sugawara I, and Kudoh S, Am J Respir Cell Mol Biol 22: 296-303, 2000). DEP showed a dose-dependent stimulatory effect on eotaxin production by normal human peripheral airway epithelial cells as well as by bronchial epithelial cell line BET-1A as assessed by specific ELISA. mRNA levels increased by DEP were shown by RT-PCR. DEP showed an additive effect on IL-13-stimulated eotaxin expression. DEP induced NF-κB activation by EMSA as previously reported but did not induce signal transducer and activator of transcription (STAT) 6 activation according to Western blot analysis. Finally, antioxidant agents (N-acetyl cysteine and pyrrolidine dithiocarbamate), which inhibited NF-κB activation but failed to affect STAT6 activation, almost completely attenuated DEP-induced eotaxin production, whereas these agents failed to attenuate IL-13induced eotaxin production. These findings suggested that DEP stimulated eotaxin gene expression via NF-κB-dependent, but STAT6-independent, pathways. [ABSTRACT FROM AUTHOR]

Objective:Epidemiological as well as experimental studies suggest that particulate air pollutants, including diesel exhaust particles (DEP), may play a role in the recent increase of respiratory morbidity and mortality. We studied the effect of DEP on the production of inflammatory cytokines and mediators including IL-8 and granulocyte macrophage colony stimulating factor (GM-CSF) by human airway epithelial cells in vitro. Methodology:Suspended DEP were added to cultured normal human bronchial epithelial cells or transformed BEAS-2B cells. The release of cytokines and mediators was evaluated by enzyme-linked immunosorbent assay. The transcriptional levels of IL-8 mRNA was studied by northern blot analysis and run-on transcription assay. Activation of transcription factors was assessed by electrophoretic mobility shift assay. Results: Non-toxic doses of suspended DEP showed a significant stimulatory effect on IL-8 and GM-CSF production by airway epithelial cells. Diesel exhaust particles increased the steady-state levels of IL-8 mRNA, which was suggested to be largely due to increased transcriptional rates. Electrophoretic mobility shift assay demonstrated that DEP induced increased binding to the specific motif of nuclear factor (NF)-κB, but not of transcription factor AP-1. Both N-acetylcysteine and pyrrolidine dithiocarbamate attenuated the action of DEP on IL-8 mRNA expression, suggesting that oxidant-mediated pathway might be involved in its processes. Transient transfection of airway epithelial cells with wild and NF-κB binding motifs indicated that the activation of NF-κB was essential for IL-8 gene upregulation by reporter gene assay. Conclusions: These results suggested that DEP activate NF-κB, which might be an important pathway for the expression of inflammatory cytokines in vitro. [ABSTRACT FROM AUTHOR]