Ultrastructural localization of lectin receptors on the luminal and abluminal aspects of brain micro-blood vessels

Abstract

Lectin- or glycoprotein-colloidal gold complexes were used for detection of specific monosaccharide residues in mouse brain micro-blood vessels (MBVs). The lectins tested recognize the following residues: β-D-galactosyl (Ricinus communis agglutinin-120, RCA-1), α-N-acetylgalactosaminyl (Helix pomatia agglutinin, HPA), α-D-mannosyl and α-D-glucosyl (Concanavalin A, Con A), sialoglycoconjugates (Limax flavus agglutinin, LEA), N-acetylglucosaminyl and sialyl (wheat germ agglutinin, WGA), and α-L-fucosyl (Ulex europeus agglutinin, UEA-1). Use of these lectin-gold complexes and ultrathin sections of Lowicryl K4M-embedded tissue makes it possible to gain insights into localization of lectin receptors in the entire cross-section of MBV walls. Receptors for all lectins, except UEA-1, were found on both luminal and abluminal fronts of the endothelial cells (ECs). Differential labeling of luminal and abluminal fronts of ECs with some lectins (Con A, HPL) is considered to reflect the polarity of the endothelium. Some differences noted in the distribution of lectin receptors in the wall of representatives of three types of MBVs (capillaries, arterioles, and venules) are thought to be associated with different functions performed by the above-mentioned segments of the microvasculature in maintenance of the blood-brain barrier.