Identification by immunofluorescence of eosinophil granule major basic protein in lung tissues of patients with bronchial asthma.

To clarify the role of the eosinophil in asthma, tests were done to find out whether eosinophil granule major basic protein (MBP) is present at sites of epithelial damage in cases of asthma; this protein is toxic to respiratory epithelium and its levels are raised in the sputa of patients with asthma. The test used was an indirect immunofluorescence test, and the specimens tested were formalin-fixed, paraffin-embedded lung tissue obtained post mortem from patients with asthma and from control patients who had died of other diseases. The antiserum used was specific for MBP because it stained only eosinophils in the peripheral blood and because its activity was removed by absorption with MBP. Both controls and asthmatic patients had MBP in the cells, but patients dying of status asthmaticus also had extracellular MBP in mucus plugs, on damaged epithelial surfaces, and in necrotic areas below the basement membrane. Patients who had died of other diseases associated with severe asthma also had extracellular MBP in mucus plugs and on damaged epithelial surfaces. The results suggest that MBP in the eosinophil granule is released into respiratory tissue of patients with severe asthma and that it is associated with tissue damage.