We investigated the expression of surfactant protein (SP)-D in pulmonary epithelial cells, compared with the expression of SP-A. A total of 15 fetuses aborted at 8, 15, 19, 20, 21 and 23 weeks gestation and four premature babies who were stillborn or died after birth between May 1997 and October 2001 were included in this study. Fetuses showing any findings associated with preterm premature rupture of membranes or infection were excluded. We performed immunohistochemical examinations for SP-D and SP-A. SP-D was not detected by immunostaining at 8, 15 and 19 weeks gestation. At 21 weeks gestation, SP-D was weakly localized, in some cases (5/9), in the epithelial lining of both bronchioles and terminal airways. In contrast at 21 weeks gestation, SP-A was more markedly detected in the epithelial lining of both bronchioles and terminal airways in all cases but not detected in bronchioles and terminal airways at 8, 15 and 19 weeks gestation.
Conclusion: the findings in this investigation suggests that the production of SP-D in fetal human lungs begins in the bronchiolar and terminal epithelium from about 21 weeks of gestation.