Leishmania donovani-macrophage binding mediated by surface glycoproteins/antigens: characterization in vitro by a radioisotopic assay.

A radioisotopic assay was developed to quantitate the binding of Leishmania donovani promastigotes to hamster peritoneal macrophages in vitro. The binding was temperature dependent and required no serum factors. Binding was reduced by preloading macrophages with zymosan granules or unlabeled promastigotes, but not with latex leads or opsonized erythrocytes. Binding was reduced by 10 mM EGTA that was reversible by the addition at an equimolar concentration of calcium, but not magnesium ions. Sialic acid, D-glucose, D-mannose and their derivatives reduced the binding, whereas L-fucose, D-galactose and their related sugars did not. Pretreatment of promastigotes with neuraminidase, alpha-mannosidase, alpha-N-acetylglucosaminidase or beta-glucosidase reduced their binding to macrophages. Prior trypsinization of either macrophages or promastigotes also substantially reduced the binding. At 4 degrees C, prior opsonization of promastigotes with subagglutination titers of antiserum doubled the level of binding but in combination with Protein A reduced it to 50% of its normal binding level. Prior opsonization of macrophages decreased their binding to promastigotes significantly at 4 or 37 degrees C. The results indicate that binding of Leishmania donovani promastigotes to hamster peritoneal macrophages is a ligand-receptor interaction involving their antigenic surface membrane proteins. The binding ligands of the parasites appear to have at least sialol, glucosyl, mannosyl and N-acetylglucosaminyl terminal residues as binding determinants. Thus, receptor-mediated endocytosis, defined in a broader sense, appears to be the mechanism by which leishmanias gain entry into macrophages.