IL-4 and IL-5 mRNA expression in induced sputum of asthmatic subjects: Comparison with bronchial wash

Background: The local production of T-H2-type cytokines is thought to orche strate the ongoing eosinophilic inflammation and contribute to the pathophy siologic features of allergic asthma, Previous studies investigating cytoki ne expression in asthmatic individuals have used invasive fiberoptic bronch oscopy techniques. To date, there have been no reports of cytokine mRNA exp ression in induced sputum as a means of quantifying local inflammatory even ts. Objectives:We examined whether IL-4, IL-5, and IFN-gamma mRNA expression co uld be detected in cells from induced sputum in subjects with mild asthma a nd normal control subjects. In addition, we compared the profile of inflamm atory cells and cytokine mRNA in sputum and bronchial mash fluid. Methods: Cells positive for IL-4, IL-5, and IFN-gamma mRNA mere determined by using in situ hybridization on cytospun aliquots of sputum induced by su ccessive inhalations of hypertonic saline. Inflammatory cells were quantifi ed by using immunologic cell surface markers and immunocytochemistry. Results: IL-4 and IL-5 mRNA were detected in the sputum of all asthmatic su bjects, and the number of cells expressing these cytokines was significantl y higher than that found in control subjects. Colocalization studies showed CD3-positive T cells were the major sources of IL-4 and IL-5 mRNA. Conclusions: This study demonstrates that induced sputum can be used to det ect mRNA for T-H2-type cytokines in bronchial asthma and that the increase in IL-4 and IL-5 mRNA expression is similar to that seen with more invasive techniques. The qualitative differences in inflammatory cell numbers betwe en sputum induction and bronchial mash are consistent with their sampling o f different airway compartments.