Chronic lymphatic leukemia (CLL): Cell surface changes detected by lectin binding and their relation to altered glycosyltransferase activity

Binding studies with five purified plant lectins were used to investigate membrane alterations in lymphocytes from patients with CLL. Compared to normal human B lymphocytes, CLL lymphocytes had fewer receptors for E-phytohemagglutinin, wheat germ agglutinin, and concanavalin A, and more receptors for L-phytohemagglutinin. Receptors for Ricinus communis agglutinin were the same on both normal and CLL cells. Since the lectins bind to complex carbohydrates on the cell surface, these data suggested that the carbohydrate composition of CLL membranes differed from that of normal lymphocytes. To investigate this point, exposed membrane sialoglycoproteins on intact cells were radiolabeled by a combination of mild periodate oxidation followed by reduction with NaB³H₄. Analysis by SDS polyacrylamide gel electrophoresis of extracts from the radiolabeled cells indicated that the CLL cell membranes contained the same protein components as normal lymphocyte membranes but that these components were generally less heavily glycosylated in CLL. To investigate mechanisms responsible for the altered glycosylation of CLL cell membrane components, we examined glycosyltransferase activities in cells from CLL patients and normal donors. Compared to normal cells, CLL cells showed, decreased ability to transfer N-acetylglucosamine from UDP-N-acetylglucosamine to appropriate exogenous or endogenous glycoprotein acceptors. We conclude that CLL lymphocytes are characterized by a specific pattern of altered cell surface glycoproteins that can be detected by lectin-binding studies. These alterations may be related to decreased glycosyltransferase activity in the CLL lymphocyte.