Ontogeny of platelet-derived growth factor receptor in fetal rat lung.

There is increasing evidence that platelet-derived growth factor (PDGF) or PDGF-like molecules play a role in fetal lung morphogenesis. Our previous studies demonstrated the presence of PDGF-AA and PDGF-BB homodimers in fetal rat lung. To study further the target cells of PDGF in lung development, immunolocalization studies of PDGF receptors (PDGFR) were conducted on embryonic and fetal rat lung from day 13 to day 21 of gestation (term = 22 days) using two polyclonal PDGFR antibodies, one of which one recognizes both alpha and beta receptors (PDGFR-alpha/beta), while the other is specific for the beta receptor (PDGFR-beta). A similar immunostaining pattern for both antibodies was noted. Immunoreactivity to PDGFR was evident in both epithelial and mesenchymal cells of the embryonic lung bud as early as 13 days gestation. The number of PDGFR immunoreactive cells increased with advancing gestation. Intense immunoreactivity was noted in both epithelial cells and interstitial cells during the saccular stage of lung development. The immunoreactivity to PDGFR was localized to the apical/luminal side of bronchial and distal airway epithelial cells. PDGFR-immunopositive bronchial and vascular smooth muscle cells were detected only during the canalicular and saccular stages of lung development. Immunopositive endothelial cells lining the internal vascular plexuses were observed from days 14-16 of gestation. No PDGFR was detected in endothelial cells of large pulmonary vessels. We conclude that PDGFR are present in airway epithelial cells, interstitial cells, and bronchial and vascular smooth muscle cells and that gestation-dependent up- and down-regulation of PDGFR may play a role in developmental regulation of PDGF bioactivity during lung morphogenesis.