The Role of Membrane Sialyl and Galactosyl Residues in Regulation of the Life-Time of Rabbit Erythrocytes

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Abstract
Rabbit erythrocytes are radioactively labeled by galactose oxidase/borohydride treatment. Incubation of the erythrocytes with neuraminidase before this treatment results in 7% increase of 3H incorporation. No 3H label can be released from the erythrocytes by .beta.-galactosidases from Escherichia coli and Streptococcus pneumoniae. .alpha.-Galactosidase leads to liberation of 68% of the label, with or without prior neuraminidase treatment of the erythrocytes. .alpha.-Galactosidase-treated rabbit erythrocytes almost completely lose agglutinability with human anti-B sera. When incubated in heat-inactivated autologous serum they are intensively agglutinated in the cold. After the addition of rabbit complement they are lysed. Correspondingly, 51Cr-labeled, .alpha.-galactosidase-treated rabbit erythrocytes undergo a rapid intravascular hemolysis after autologous retransfusion. This is in contrast to the behavior of neuraminidase-treated erythrocytes, the survival time of which is also drastically decreased, without significant release of 51Cr into the plasma. About 10% of the sequestered desialylated erythrocytes reappear in the circulation after 2 days. Rabbit erythrocytes incubated with neuraminidase in the presence of inhibitory concentrations of 2-deoxy-2,3-dehydro-N-acetyl-neuraminic acid survive normally. Partial destruction of the polyhydroxy side chains of sialic acids of rabbit erythrocyte membranes by periodate causes moderate (T/2 = 4.5 d) shortening of the lifeftime. Oxidation of the C6 hydroxyl groups of terminal erythrocyte-surface galactose and N-acetylgalactosamine residues by galactose oxidase, with or without prior neuramiridase treatment, leads to intravascular hemolysis. Reduction of either periodate- or galactose oxidase-treated cells with borohydride normalizes their lifetime, and the survival kinetics of both neuraminidase- and galactose oxidase-treated erythrocytes become similar to those of erythrocytes treated with neuraminidase only. N-Acetylneuraminic acid, N-glycoloylneuraminic acid and their C7- and C8-analogues from periodate/borohydride-treated erythrocytes were analyzed by gas chromatography-mass spectrometry. The experiments show that the survival of rabbit erythrocytes in the circulation is protected by sialyl and .alpha.-galactosyl residues of the cell membrane. The mechanism of erythrocyte clearance based on these findings is discussed.