EOSINOPHILS AS A POTENTIAL SOURCE OF PLATELET-DERIVED GROWTH-FACTOR B-CHAIN (PDGF-B) IN NASAL POLYPOSIS AND BRONCHIAL-ASTHMA

Tissue remodeling in bronchial tissues from asthmatics as well as in nasal polyp (NP) tissues includes sub-basement membrane deposition of collagen, stromal deposition of extracellular matrix protein, and hypertrophy/hyperplasia of airway smooth muscle cells, which are relevant to the cellular and molecular events induced by platelet-derived growth factor (PDGF). Therefore, we investigated the localization of mRNA and protein of PDGF-B chain (PDGF) in NP tissues and bronchial tissues from mild and severe asthmatics by in situ hybridization and immunohistochemistry, respectively. Cells expressing PDGF-B mRNA were found in all nine NP tissues and in bronchial tissues from 2 of 6 normal subjects, 2 of 5 mild asthmatics, and all of 6 severe asthmatics examined. The vast majority of cells expressing PDGF-B mRNA were eosinophils in NP (99.7 +/- 0.2%, mean +/- SD) and asthmatic bronchial tissues (75.0 and 77.8% in mild asthma, and 92.7 +/- 8.1% in severe asthma), but no cells expressing PDGF-B mRNA were eosinophils in normal bronchial tissues. The number of cells expressing the gene in severe asthma tissues (122.3 +/- 32.2/mm(2)) was similar to that in NP tissues (152.8 +/- 73.9/mm(2)) and greater than that in mild asthma tissues (4.7 +/- 7.6/mm(2), P < 0.01), which was not significantly greater than that in normal bronchial tissues (3.4 +/- 5.2/mm(2)). Furthermore, we detected immunolocalization of PDGEF-B in NP tissues and in asthmatic bronchial tissues. The eosinophils purified from peripheral blood were demonstrated to express PDGF-B gene transcript and immunoreactivity after stimulation with A23187. Our results showed for the first time that eosinophils are synthesizing PDGF-B in chronically inflamed airway diseases such as nasal polyposis and bronchial asthma.