ONTOGENY OF CLARA CELL-SPECIFIC PROTEIN AND ITS MESSENGER-RNA - THEIRASSOCIATION WITH NEUROEPITHELIAL BODIES IN HUMAN FETAL LUNG AND IN BRONCHOPULMONARY DYSPLASIA

Clara cell-specific 10-KD protein (CCSP) is an abundant product of non ciliated bronchiolar epithelial (Clara) ails in the lung, We have dete rmined the temporal-spatial distribution of CCSP and its mRNA in devel oping human lung and in neonatal lung disease, using immunohistochemis try and in situ hybridization. CCSP immunoreactivity was found in nonc iliated bronchiolar epithelial ails from 12 weeks of gestation onward. Tracheal and bronchial epithelia showed positive immunoreactivity at each gestational week after 15 weeks and 14 creeks, respectively. CCSP mRNA was seen in the bronchial and bronchiolar epithelia from 16 week s on; ward and was detected in the trachea from 19 through 23 weeks of gestation. CCSP immunoreactivity and mRNA were present in nonciliated single cells of bronchial and bronchiolar epithelia in fetuses and in infants with and without lung disease. CCSP and CCSP mRNA-containing epithelial cells also formed clusters around neuroepithelial bodies (N EBs), especially at airway branch points, suggesting that NEBs and Cla ra cells might interact during development and during pulmonary regene ration. Femme of evidence of overlapping of some but not all cells exp ressing CCSP, SF-A, and pro-SP-B during lung development, a common cel l lineage is proposed, with subsequent divergence of phenotypes.