Interleukin-9 receptor expression in asthmatic airways in vivo

Inflammation of the airway wall is a defining feature in asthma and is like ly the cause of the hyperreactivity and variable airflow limitation found i n asthma. Immune response biased toward production of Th2 cytokines has bee n proposed as a mechanism in the pathogenesis of airway inflammation in ast hma. The Th2 cytokine interleukin-9 (IL-9) is one candidate gene for asthma on the basis of position cloning and animal models of airway inflammation. To determine whether IL-9 is involved in the chronic inflammation of the a sthmatic airway, we investigated the expression of IL-9 and the IL-9 specif ic receptor chain in asthmatic airways compared with healthy airways. IL-9 and IL-9 receptor expression in airway epithelial cells and bronchoalveolar lavage cells obtained at bronchoscopy of healthy (n = 9) and mild intermit tent asthmatic individuals (n = 7) were studied by Northern analyses and re verse-transcription polymerase chain reaction technique. Primary and transf ormed human airway epithelial cells were also evaluated for IL-9 specific r eceptor chain expression in vitro. IL-9 was not detected in airways of heal thy or mild asthmatic individuals. In contrast, IL-9 specific receptor chai n expression was found in asthmatic airway samples but not in healthy contr ols. In vitro, airway epithelial cells did not express IL-9 specific recept or chain until stimulation with interferon gamma. Our results support that IL-9 may play a role in the mechanism leading to chronic airway inflammatio n and asthma.