Relation of membrane surface structure and erythrocyte aggregation was investigated by modifying glycoproteins of erythrocytes with trypsin, chymotrypsin and neuraminidase, with a special regard to survival of erythrocytes in circulation. The velocity of erythrocyte aggregation was measured with a rheoscope combined with a video camera, an image analyzer and a computer. (1) Human aged erythrocytes fractionated by a density gradient centrifugation with Percoll were more accelerative in aggregation than young erythrocytes. Young erythrocytes induced in rat by administration of recombinant human erythropoietin were less accelerative in aggregation than normally produced erythrocytes. These phenomena were discussed on the basis of structural change of membrane surface proteins during in vivo aging of erythrocytes. (2) Erythrocyte aggregation was affected by negative charge density of membrane surface (mainly of sialic acid). But structural change of glycoproteins, especially of glycophorin A, was greatly effective on the erythrocyte aggregation. The phenomena were proposed as a model of removal of in vivo aged erythrocytes.
