Involvement of membrane galactose in the in vivo and in vitro sequestration of desialylated erythrocytes.

The influence of terminal beta-galactose residues for the in vitro and in vivo sequestration of sialidase-treated erythrocytes by macrophages was investigated. Preincubation of rat peritoneal macrophages with galactose, oligosaccharides, glycoproteins and glycolipids with terminal beta-galactose residues inhibits both binding and phagocytosis of sialidase-treated erythrocytes by masking a beta-galactose-specific lectin on the macrophage cell membrane. These inhibition studies show that binding via demasked erythrocyte surface beta-galactosyl residues to this lectin is necessary for the subsequent phagocytosis step. According to these observations, repeated injections of lactose (30mM serum concentration) and asialo-fetuin (10-30 microM serum concentration) into the blood stream of rabbits led to a reduction of the rapid sequestration rate of sialidase-treated erythrocytes. Asialo-fetuin proved to be a much more potent inhibitor than lactose, in accordance with the in vitro experiments. This inhibition is reversible, as after the disappearance of the inhibitory effect, the sialidase-treated erythrocytes were again rapidly removed from the circulation to an extent similar to that of the experiments without inhibitors. No significant influence on binding and phagocytosis was measured in the presence of sialyllactose and native fetuin in vitro, or of native fetuin on sequestration in vivo. The experiments with rabbits show that a beta-galactosyl-specific lectin seems to be involved in the mechanism of sequestration of desialylated erythrocytes in vivo, as has been observed in vitro with rat peritoneal macrophages.