Characterization of galactose-containing glycoconjugates in the human retina: A lectin histochemical study

Abstract

Seven specimens of morphologically normal formalin-fixed and paraffin-embedded human retina were studied using a panel of fourteen biotinylated lectins, all of which react with glycoconjugates containing galactose and N-acetylgalactosamine residues. Agaricus bi-sporus (ABA), Bauhiniapurpurea (B?A),Phaseolus vulgaris (PHA-E), peanut (PNA) and Ricinus communis (RCA-1) agglutinins labeled photoreceptor cells prior to enzymatic predigestion. BPA and PNA bound specifically to cones. The plexiform layers reacted with ABA, BPA and PHA-E, while only ABA and PHA-E labeled the nuclear layers. After pretreatment with neuraminidase to remove terminal sialii acid, all five lectins, as well as Erythrina cristagalli (ECA), Helixpomatia (HP A) and Madura pomifera (MPA) agglutinins labeled both rods and cones. Furthermore, the plexiform layers additionally reacted with ECA PNA and RCA-1, and the nuclear layers with BPA and RCA-1 after neuraminidase pretreatment. Retinal vascular endothelial cells consistently bound ABA, ECA, PHA-E and RCA-1, but they could also bine BPA, HP A, Bandeiraea simplicifolia (BSA-I), Dolichos biflorus (DBA) and Euonymus europaeus (EEA) agglutinins in unpretreated sections, a well as MP A, PNA, soybean (SBA) and Sophora japonica (SJA) agglutinins subsequent to predigestion with neuraminidase. The nonpig-mented ciliary epithelium reacted with the same lectins as photorecepfc cells, but it was also labeled by DBA. Sambucus nigra agglutinin (SNA) did not specifically bind to any intraocular structure. These findings favor the theory that, in unpretreated specimens, Gal(Bl-→3)GalNAc (BPA and PNA) is mainly responsible for labeling of cones, while Gal(Bl-→3/4)GlcNAc units, partly substituted with terminal sialic acid (PHA-E and RCA-1), explain labeling of rods. Following pretreatment with neuraminidase, further Gal(Bl-→3)GalNAc (BPA and PNA) and, especially, Gal(Bl-→3/4)GlcNAc (BPA, ECA, PHA-E, PNA and RCA-1) and aGalNAc units (BPA, HP A and MP A), the latter partly linked to the protein backbone, contribute to labeling of photoreceptoi cells. Gal(Bl-→3/4)GlcNAc units may be mainly responsible for labeling of nuclear and plexiform layers. Finally, other related receptor sites (SBA and SJA), some of which are blood-group specific (BSA-I, DBA, EEA and HP A) are restricted to retinal vascular endothelia.