Biochemical characterization of a tumor-associated vertebrate lectin, recognized by activated macrophages

Activated macrophages, that display alpha-linked galactopyranosyl residues on their surface, and affinity adsorbents prepared by the covalent coupling of galactopyranoside to agarose, both adsorb two polypeptides from detergent extracts of all tumor cell lines tested. The larger polypeptide, Mr 100,000 is a cell surface component as judged by its availability to lactoperoxidase catalysed cell surface iodination. This polypeptide was found to be non-covalently associated with a smaller polypeptide, Mr 60,000, present on the inner face of the plasma membrane. Molecules with identical molecular sizes were also found to adsorb to activated macrophages from detergent extracts of chicken embryo cell membranes, suggesting an oncofetal nature for these proteins. Activated macrophages, and affinity adsorbents prepared by the covalent coupling of galactopyranoside to agarose, also bind the plant lectin, isolectin B4, prepared from the seeds of Griffonia simplicifolia. Based on these findings, we put forth the hypothesis that macromolecules of the same specificity, that is affinity to galactopyranosyl residues, must show homologies in their binding sites. We have predicted, therefore, that antisera prepared against the plant lectin, GSI-B4(1), should cross-react with galactopyranosyl-binding vertebrate lectins present on the surface of tumor cells. We were able to generate a number of hybridomas that produce antibodies reactive with both the plant and vertebrate lectins. Inhibition experiments, employing various mono- and disaccharides, suggest that the specificities of these antibodies are for determinants intimately associated with the galactosyl binding site on the lectin molecule. These antibodies were found to have moderate selectivity for tumor cells when tested in an immunohistochemical procedure using fresh-frozen or paraffin embedded sections of human biopsy material.(ABSTRACT TRUNCATED AT 250 WORDS)