Differential expression of IL-10 receptor by epithelial cells and alveolar macrophages

Background:  Interleukin (IL)-10 is a pleiotropic cytokine with a broad spectrum of immunosuppressive and anti-inflammatory effects. IL-10 secretion from alveolar macrophages is defective in patients with asthma and lower concentrations of IL-10 are found in bronchoalveolar lavage (BAL) from asthmatic patients than in normal control subjects. Reduced IL-10 may result in exaggerated and more prolonged inflammatory responses in asthmatic airways. IL-10 acting through the IL-10 receptor (IL-10R) stimulates the transcription factors STAT1 and STAT3. Methods:  We investigated IL-10 and IL-10R expression in normal and asthmatic bronchial epithelium and BAL macrophages using reverse transcription-polymerase chain reaction, immunohistochemistry and Western blotting. The functional effect of IL-10 was examined using granulocyte–macrophage-colony stimulating factor, enzyme-linked immunosorbent assay and Western blotting for phosphorylated STAT1 and STAT3. Results:  IL-10 was not expressed in epithelial cells; furthermore these cells did not express the IL-10R and had no functional response to exogenous IL-10. Bronchial epithelial cells expressed variable levels of phosphorylated STAT1 and STAT3 with no change in expression between normal subjects and asthmatics. IL-10 protein and IL-10R expression was detected in alveolar macrophages from all subjects. Conclusion:  Our study suggests that the bronchial epithelium is not a source of IL-10 and cannot respond to exogenous IL-10 because of a lack of IL-10R expression.