Apoptosis and proliferation in lungs of human fetuses exposed to chorioamnionitis

To determine whether chorioamnionitis has an impact on the extent of apoptosis and proliferation in fetal lungs. Fetuses exposed to chorioamnionitis have an increased risk of aquiring lung tissue damage in utero.

Lung tissue sections from 35 stillborn fetuses were used in this study. Chorioamnionitis-exposed fetuses were subdivided depending on whether pneumonia was diagnosed (n = 13) or not (n = 10); 12 unaffected fetuses served as controls. Apoptotic and proliferating cells were determined by in-situ terminal deoxytransferase-mediated dUTP nick end labelling (TUNEL) assay and by anti-Ki67 immunohistochemistry, and quantified. The median apoptotic index in lungs of chorioamnionitis-exposed fetuses increased 2.4-fold compared with chorioamnionitis-negative stillborn controls (P = 0.043) and rose 21.6-fold when chorioamnionitis-exposed fetuses additionally developed pneumonia (P < 0.001). Compared with the proliferation index of the control group (PI = 2.3), the median percentage of proliferating cells in the lungs of chorioamnionitis-exposed fetuses decreased (PI = 1.4) (P = 0.036), but increased 1.8-fold (P = 0.036) in fetal lungs of the chorioamnionitis/pneumonia group. By double labellings combining the TUNEL assay or the Ki67 antigen with cell marker proteins, we identified distal airway epithelial cells as the cell type undergoing apoptosis in chorioamnionitis-exposed fetal lungs, while epithelial, endothelial and smooth muscle cells proliferated. Immunolabellings of cleaved caspases -8 and -9 revealed that apoptosis is mediated via initiator caspase-8.

Chorioamnionitis induces apoptosis of distal airway epithelial cells via the caspase-8 pathway and interferes with the normal proliferative activity of epithelial, endothelial, and smooth muscle cells in fetal lungs. Thus, apoptosis and proliferation are an important feature of chorioamnionitis-associated lung injury in utero.