Monoclonal antibodies reveal saccharide structures of glycoproteins and glycolipids as differentiation and tumour-associated antigens.

adenocarcinoma and squamous cell carcinoma of the lung (Huang et al., 1983). Recently, many laboratories have described this oligosaccharide antigen as a differentiation marker restricted to the myeloid cells (Andrews etal., 1983; Giradet et al., 1983; Gooi et al., 1983; Huang et al., 1983; J. L. Magnani, E. D. Ball, M. W. Fanger, L. C. Huang, S. Hakomori & V. Ginsburg, unpublished work). In particular, three antibodies (PMN6, PMN29 and PM81) show differences in cell binding, but all recognize an oligosaccharide sequence in lacto-N-fucopentaose 111. PMN6 and PMN29 bind specifically to granulocytes but differ in the ability to bind certain cell lines (Ball et al., 1983), while PM81 binds granulocytes, eosinophils, monocytes and most acute myelocytic leukaemia cells(J. L. Magnani, E. D. Ball, M. W. Fanger, L. C. Huang, S. Hakomori & V. Ginsburg, unpublished work). Despite these differences the binding of all three monoclonal antibodies to cells is inhibited by the oligosaccharide, 1acto-Nfucopentaose 111. Radioimmunoassays using purified glycolipids containing the sugar sequence in lacto-N-fucopentaose 111 demonstrate different binding characteristics for each monoclonal antibody. PM81 binds lower concentrations of glycolipids than PMN29, while PMN6 requires the highest concentration of glycolipids for binding. Autoradiography of thin-layer chromatographs of glycolipid antigens stained with radioactive antibodies supports these results. The data suggest that the binding of these monoclonal antibodies to cells is dependent on the quantity of lacto-N-fucopentaose 111-containing molecules on the cell surface (J. L. Magnini, E. D. Ball, M. W. Fanger, L. C. Huang, S. Hakomori & V. Ginsburg, unpublished work). Each antibody requires a different concentration of antigen for binding. Under this threshold concentration a cell may contain antigen, but will not bind antibodies.