DIFFERENCES IN THE LECTIN-BINDING PATTERNS OF THE PERIPORTAL AND PERIVENOUS ENDOTHELIAL DOMAINS IN THE LIVER SINUSOIDS

We have studied the distribution patterns of carbohydrate terminals on the endothelial surface of the mouse liver microvasculature. For this purpose, a wide battery of FITC lectins specific to glucose, mannose, galactose, fucose, N-acetyl-neuraminic acid, N-acetyl-galactosamine and N-acetyl-glucosamine residues were incubated on liver cryostat sections or intraportally perfused under physiological conditions. All the resulting hepatic sections were examined under fluorescent microscopy and confocal laser scanning microscopy. With the exception of N-acetyl-galactosamine- and fucose-binding lectins, all the perfused lectins specifically bound to the microvascular wall as confirmed by blocking methods using their corresponding sugars. A wide range of binding was, however, observed among the lectins, and the latter were classified into four groups according to their affinities for the different segments of the hepatic microvasculature: (a) equal affinity for all segments (concanavalin A); (b) different affinities depending on acinar zone (wheat germ agglutinin, Ricinus communis toxin, phytohemagglutinin E, Erythrina cristagalli agglutinin and Pisum sativum agglutinin); (c) preferential binding to the sinusoidal network (Lathyrus odoratus, phytohemagglutinin); and (d) lectins that fail to bind to the hepatic microvasculature (N-acetyl-galactosamine- and fucose-binding lectins). Sinusoidal segment walls in acinar zone 1 expressed a higher concentration of certain lectin-binding carbohydrate residues (N-acetyl-neuraminic acid, N-acetyl-galactosamine, galactose, mannose and glucose) than in acinar zone 3. The labeling patterns obtained through the incubation of liver sections or through in vivo perfusion with the different lectins did not always coincide. Only concanavalin A, wheat germ agglutinin and phytohemagglutinin E lectins proved to be concordant (i.e., they produced identical labeling patterns in both procedures). Wheat germ agglutinin was thus selected for further experiments because of its concordance and acinar zone - related binding variations that remained even in perfusion experiments at wheat germ agglutinin - saturating concentrations. Furthermore, as determined by an in situ saturation wheat germ agglutinin - binding assay and Scatchard analysis, the binding capacity of the sinusoidal segments in zone 1 was greater than that in zone 3 (6: 1). To correlate this significant zonal binding difference to specific endothelial cells, we performed a flow cytometric analysis of sinusoidal cells isolated from the intraportally FITC-wheat germ agglutinin - perfused livers and from non-wheat germ agglutinin - perfused livers, which were incubated in vitro with wheat germ agglutinin. Results show identical three-modal distributions of sinusoidal cells according to green fluorescence. In addition, separate analysis of forward angle light scatter and integrated side light scatter of each of these cell populations revealed two subsets of the endothelial cell - compatible phenotype: type I (low forward angle light scatter, high integrated side scatter, with 43% high wheat germ agglutinin - binding cells and 57% low or non-wheat germ agglutinin - binding cells) and type 11 (high forward angle light scatter, low integrated side scatter, with 53% low wheat germ agglutinin - binding and 47% non-wheat germ agglutinin - binding). Thus two functional subsets of endothelial cell populations from liver sinusoids can be distinguished on the basis of their different affinities for wheat germ agglutinin.