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RESEARCH PRODUCT

Increased prostaglandin E2 concentrations and cyclooxygenase-2 expression in asthmatic subjects with sputum eosinophilia.

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Abstract Background Prostaglandin E 2 (PGE 2 ) is known to be produced within human airways, but it is not clear whether in airway diseases it can play a deleterious or a beneficial role. Recently it has been reported that PGE 2 can enhance eosinophil survival in vitro. Objective To evaluate whether the concentrations of PGE 2 in asthmatic airways correlate with the number of eosinophils and can be responsible for eosinophil-enhanced survival and to identify the cyclooxygenase isoform contributing to the synthesis of PGE 2 by cells present in asthmatic airways. Methods Reversed-phase high-performance liquid chromatography and/or specific radioimmunoassay was used to measure PGE 2 concentrations in induced sputum supernatants from 14 control and 30 asthmatic subjects. Correlations between concentrations of PGE 2 and the number of eosinophils in induced sputum were evaluated. Expression of cyclooxygenase-2 (COX-2) in induced sputum cells was determined by immunocytochemistry, and the effect of COX-2 inhibition on PGE 2 production was evaluated with the use of radiolabeled arachidonic acid. The effects on eosinophil apoptosis by PGE 2 or induced sputum supernatants were studied by using peripheral blood eosinophils obtained by negative immunomagnetic selection. Results PGE 2 concentrations resulted in elevated samples from asthmatic subjects and directly correlated with the percentage of eosinophils and the concentrations of eosinophilic cationic protein. Immunostaining for COX-2 showed enhanced expression in macrophages of asthmatic subjects when compared with control subjects, and the use of a specific COX-2 inhibitor provided evidence that PGE 2 synthesis was the result of COX-2 enzymatic activity in asthma-induced sputum cells. Supernatant from induced sputum of asthmatic subjects with high eosinophil counts caused a decreased apoptosis of peripheral blood eosinophils when compared with control subjects, and immunoprecipitation of PGE 2 significantly reverted this phenomenon, suggesting that PGE 2 was present in biologically relevant concentrations in induced sputum. Conclusions The results obtained suggest that COX-2 expression in alveolar macrophages from asthmatic subjects may contribute to enhanced eosinophil survival through an increased PGE 2 production. (J Allergy Clin Immunol 2003;112:709-16.)