Immunoelectron and cytochemical characterisation of the human placental endothelial paracellular cleft

Abstract

The ontogenesis of endothelial glycoconjugate expression during normal angiogenesis and microvascular development remains unknown. Using intravital fluorescent microscopy, we studied temporal and spatial lectin binding to carbohydrate moieties of luminal microvascular endothelia of the chick embryo chorioallantoic membrane (CAM) during Days 4.5 to 6.0 of the 21-day incubation. We used a battery of eight FITC-lectins (100-200 μg/ml). Fluorescent images from precapillary, capillary, and postcapillary segments of the lectin-perfused microvascular units were analyzed by image analysis software to quantitate differences in lectin binding. Results served to indicate a significant decrease in lectin binding to terminal N-acetyl glucosamine, N -acetyl galactosamine, and the N-acetyl galactosamine disaccharide in the glycocalyx of pre- and postcapillary vessels from Day 4.5 to Day 5.0. Lectin binding to N-acetyl glucosamine and N-acetyl galactosamine subsequently increased at Days 5.0 and 6.0. In the capillaries, lectin binding to endothelial galactose, fucose, and sialic acid increased significantly from Day 5.5 to Day 6.0. That these temporal changes in lectin binding to endothelial luminal glycoconjugates coincide with concomitant changes in CAM microvascular permeability (Rizzo et al., in press) serves to suggest a possible association between expression of endothelial glycoconjugates and the ontogeny of microvascular perm-selectivity during normal angiogenesis.