Endoglin (CD105) immuno-expression in human foetal and neonatal lungs

Endoglin is a 180 KDa glycoprotein mainly expressed on endothelial cells of newly formed vessels. Its expression is increased by the hypoxia inducible factor 1 (HIF-1), a potent stimulator of VEGF expression. The relative hypoxic environment in which foetal lung develops favours HIF-1 dependent gene expression, including the endoglin and VEGF ones. Herein, we analysed endoglin immunoexpression in the human neonatal and foetal lung throughout gestation. Lungs from 18 foetuses (9-41 weeks), 7 preterm and 2 term infants were submitted to the immunohistochemical study. A slight immunostaining was found in some mesenchymal aggregates in the lungs of foetuses at the first trimester of pregnancy. At mid gestation, endoglin was evidenced in peri-tubular mesenchymal stem cells or in peri-canalicular vessels and in the endothelia of peri-bronchial vessels; by contrast, no immunoreaction was observed in case of Down syndrome or in a foetus with cardiac malformations. At late gestation and in preterm infants, endoglin antibody labelled endothelia of the alveolar capillaries and of peri-bronchial vessels. In case of alveolar capillary dysplasia (ACD) or macrosomy associated with maternal diabetes, endoglin expression was restricted to peri-bronchial vessels; no immunoreaction was encountered in foetuses with IUGR (intra-uterine growth restriction) or massive pulmonary haemorrhage. Lungs of term infants both displayed atelectasis; there was no evidence of endoglin immunoexpression in one case, whereby only the endothelia of peri-bronchial vessels were stained in the other. Our study suggests that lung vasculogenesis endures throughout gestation. Absence of endoglin staining in some pathologic conditions may reflect lung vasculogenesis disorders; nonetheless, since each pathologic state is represented by a single case in our cohort, further studies are required to clarify this issue.