Ultrastructural localization of lectin receptors on cerebral endothelium.

Oligosaccharide residues on the endothelial luminal plasma membrane of rat cerebral cortical vessels were localized using biotinylated lectins. In addition, the effect of pretreatment of brain slices with neuraminidase prior to the binding of cationized ferritin (CF) and certain lectins was studied. Conjugates of biotinylated lectins and avidin-D horseradish peroxidase reaction product were evenly distributed on the endothelium of arterioles, capillaries, and venules. Lectin binding sites were observed on the plasma membrane of pinocytotic vesicles open onto the vascular lumen and at the luminal end of the interendothelial space only. The following sugar residues were localized: alpha-D-mannosyl, alpha-D-glucosyl, beta-N-acetylglucosaminyl, sialyl, D-galactosyl, alpha-L-fucosyl, and alpha-N-acetyl-D-galactosaminyl. Following pretreatment of brain slices with neuraminidase beta-D-gal-(1-3)-D-galN-acetyl groups were demonstrated on endothelium. In this respect, cerebral endothelium differs from noncerebral endothelium which is reported to have peanut agglutinin binding sites without neuraminidase pretreatment. Anionic groups on cerebral endothelium were demonstrated at the same locations as the lectin binding sites. Following neuraminidase pretreatment there was reduction, but not absence, of CF binding supporting the observation that surface charge is not wholly due to sialyl groups. The role of monosaccharide residues in states of altered cerebrovascular permeability remains to be determined.