TEMPORAL-SPATIAL DISTRIBUTION OF SP-B AND SP-C PROTEINS AND MESSENGER-RNAS IN DEVELOPING RESPIRATORY EPITHELIUM OF HUMAN LUNG

We determined the temporal and spatial distribution of surfactant prot ein B (pro-SP-B) and C (pro-SP-C) mRNAs and proteins by immunohistoche mistry and in situ hybridization in fetal, neonatal, and adult human l ung. Pro-SP-B and SP-B mRNA were detected in bronchi and bronchioles b y 15 weeks' gestation. After 25 weeks, pro-SP-B, active SP-B peptide, and SP-B mRNA were co-localized in bronchiolo-alveolar portal cells an d in Type II epithelial cells. In adult lung, pro-SP-B and SP-B mRNA w ere detected primarily in non-ciliated bronchiolar epithelial cells an d in Type II cells in the alveolus. Pro-SP-C and SP-C mRNA were detect ed in cells lining terminal airways from 15 weeks' gestation and there after. After 25 weeks, SP-C mRNA and precursor protein were detected i n epithelial cells of the bronchiolo-alveolar portals and in Type II c ells, where expression increased with advancing gestational age. Disti nct cellular patterns of staining for pro-SP-B compared with SP-B acti ve peptide support the concept that its proteolytic processing or cell ular routing may be influenced by cell type and/or cell differentiatio n. SP-B and SP-C are expressed primarily in distal conducting and term inal airway epithelium of human fetal lung well in advance of surfacta nt lipid synthesis or physiologic requirements to produce pulmonary su rfactant at the time of birth.