[Detection of IL-5 mRNA in bronchial biopsies from asthmatics by non-radioactive in situ hybridization].

To determine whether IL-5 is locally produced in the bronchial mucosa of asthmatics, and to ascertain the precise cell type producing this cytokine, we examined bronchial biopsies by non-radioactive in situ hybridization and immunohistochemistry. IL-5 cDNA probes were labeled with digoxigenin-dUTP and hybridized to frozen or paraffin tissue sections. Hybridization signals were visualized by an immunohistochemistry technique. An IL-5-producing T cell clone derived from a patient with adult T cell leukemia was used as a positive control. Specific hybridization signals for IL-5 mRNA were observed in the bronchial mucosa of symptomatic asthmatics. No hybridization signal was detected in the control subject in whom no underlying disease was found. Immunohistochemical staining of serial sections using a panel of monoclonal antibodies directed against lymphocyte subsets strongly suggested that cells expressing mRAN for IL-5 were T cells. These results suggest that a cell-cell interaction between T cells and eosinophils through IL-5 may play an important role in the airway inflammation in asthma.