Purification and characterization of a lectin-like molecule specific for galactose/N-acetyl-galactosamine from tumoricidal macrophages.

A lectin-like molecule (macrophage lectin) was purified from murine peritoneal exudate macrophages which had been induced with an antitumor streptococcal preparation, OK-432. The purified macrophage lectin from both 3H-labeled and unlabeled macrophages after rechromatography on a beta-D-galactose-Bio-Gel P-100 column gave a broad single band corresponding to 45-60 kDa on SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The broadness of this band was due to high N-glycosylation of the lectin, because the lectin gave a compact band corresponding to 35 kDa on SDS-PAGE after deglycosylation. The lectin required Ca2+ for binding and showed an optimum pH of around 6. The sugar specificity of the lectin was examined by means of an inhibition assay using simple sugars and neoglycoproteins. The lectin was found to be specific for D-galactose/N-acetyl-D-galactosamine, and not inhibited with D-mannose or N-acetyl-D-glucosamine at all. The lectin was detected on the surface of OK-432-elicited and thioglycolate-elicited macrophages, but it was not detected on resident macrophages. Moreover, the binding of tumor cells to macrophages was inhibited by the addition of the purified lectin to the binding mixture. These results suggest that this lectin is expressed on the surface of activated macrophages, and that it participates in the interaction between tumoricidal macrophages and tumor cells.