Constitutive and cytokine-stimulated expression of eotaxin by human airwaysmooth muscle cells

Airway eosinophilia is a prominent feature of asthma that is believed to be mediated in part through the expression of specific chemokines such as eot axin, a potent eosinophil chemoattractant that is highly expressed by epith elial cells and inflammatory cells in asthmatic airways. Airway smooth musc le (ASM) has been identified as a potential source of cytokines and chemoki nes. The aim of the present study was to examine the capacity of human ASM to express eotaxin. We demonstrate that airway myocytes constitutively expr ess eotaxin mRNA as detected by RT-PCR. Treatment of ASM for 24 h with diff erent concentrations of TNF-alpha and IL-1 beta alone or in combination enh anced the accumulation of eotaxin transcripts. Maximal mRNA expression of e otaxin was shown at 12 and 24 h following IL-1 beta and TNF-alpha stimulati on, respectively. The presence of immunoreactive eotaxin was demonstrated b y immunocytochemistry, and constitutive and cytokine-stimulated release of eotaxin was confirmed in ASM culture supernatants by ELISA. Strong signals for eotaxin mRNA and immunoreactivity were observed in vivo in smooth muscl e in asthmatic airways. In addition, chemotaxis assays demonstrated the pre sence of chemoattractant activity for eosinophils and PBMCs in ASM supernat ants. The chemotactic responses of eosinophils were partly inhibited with a ntibodies directed against eotaxin or RANTES, and a combined blockade of bo th chemokines causes >70% inhibition of eosinophil chemotaxis. The results of this study suggest that ASM may contribute to airway inflammation in ast hma through the production and release of eotaxin.