Lectin binding by microvillous membranes and coated-pit regions of human syncytial trophoblast.

The distribution of saccharides on the microvillous membrane of the human syncytial trophoblast was investigated using ferritin conjugates of four lectins: concanavalin A (specific for alpha-D-manno- and alpha-D-glucopyranosyl residues), wheatgerm agglutinin (specific for N-acetylglucosamine), Limulus polyphemus lectin (specific for N-acetylneuraminic acid), and Lotus tetragonolobus lectin (specific for alpha-L-fucose). Concanavalin A and wheatgerm agglutinin (WGA) reacted strongly with the surface membrane and ferritin deposits were also observed in coated pit regions of the membrane. Lectins from L. polyphemus and L. tetragonolobus, however, reacted only weakly with the microvillous border and neither reacted with coated pits. Enhanced agglutinability of trophoblast cells in comparison with other foetal cells from the same conceptus was seen with WGA. This agglutination was inhibited by addition of acetylglucosamine or by a solubilized membrane fraction which was bound by a column of WGA-Sepharose. The membrane fraction which did not bind to the column did not inhibit agglutination. Electrophoresis of the WGA-bound membrane proteins revealed six subunits, the major band having an apparent mol. wt. of 55 000. A protein of this mol. wt was also seen in coated vesicles isolated from equivalent human placentae.