The use of sugar-coated beads to study phagocytosis in normal and dystrophic retina

In this study, a technique is described for coupling the sugars to carboxylated latex beads for use in phagocytic studies of dystrophic and normal retinal pigment epithelium. The presence and distribution of the sugars, mannose and fucose, on the bead surfaces are visualized by transmission electron microscopy using the lectin-Ferritin conjugates. Concanavalin A-Ferritin (Con A-Fe) and Ulex-europeus-Ferritin (Ulex-Fe), respectively. Both lectin-Ferritin conjugates label the surfaces of the sugar coated beads. Control experiments to determine the extent of nonspecific lectin-Ferritin binding using Con A-Fe with fucose-coated beads, Ulex-Fe with mannose-coated beads, or beads without coupling reagent show little to no labeling. Lectin-Ferritin conjugates are also incubated with the appropriate sugar-coated beads and their competing sugars and little to no labeling is observed. Our data shows that when sugar-coated beads are presented to retinal pigment epithelial explants, differences in phagocytic uptake are observed. Uncoated beads are avidly taken up by normal and dystrophic tissue, but fucose-coated beads are not taken up by either. Twice as many mannose beads are phagocytized by the normal as compared to dystrophic tissue. It remains to be established whether these differences in bead uptake indicate a difference in ligand-receptor interactions between normal and dystrophic retinal pigment epithelium.