Different expression of surfactant protein B mature peptide and proprotein at 21 weeks' gestation in human fetal pulmonary epithelial cells

Aim: The aim of this study is to evaluate the maturation of pulmonary epithelial cells in human fetal lungs at 21 weeks' gestation. Methods: Eight fetuses at 21 weeks' gestation were evaluated. The maturation of pulmonary epithelial cells was assessed by immunohistochemical examination for surfactant proteins and by electron microscopy. Results: Surfactant protein B mature peptide was detected slightly in the epithelial lining of the bronchioles, but was totally absent in the terminal airways. Surfactant protein B proprotein was clearly detected in the epithelial lining of both bronchioles and terminal airways. Transmission electron microscopy of terminal airway cells showed abundant glycogen granules and few intracellular organelles. Conclusions: The production of mature surfactant protein B in terminal airways is scarce at 21 weeks' gestation, which is associated with the immature mechanism of proprotein processing in the cytoplasm.