Antibody-directed liposomes. Determination of affinity constants for soluble and liposome-bound antifluorescein.
We have used the binding of liposomes conjugated with antifluorescein antibody specific for fluorescein isothiocyanate-modified erythrocytes as a model for multivalent antigen-antibody interactions. We examined a series of liposome preparations which were conjugated to between 0 and 332 active antibodies per liposome. The antigen binding capacity and mean intrinsic affinity of the soluble and conjugated antibody were determined by fluorescence quenching of carboxyfluorescein. Liposome-cell interaction data were fitted with a Scatchard-type equation. Functional affinity of liposomes for cells was up to 1000-fold greater than the intrinsic affinity of the antibody for soluble ligand. Analysis for binding at high cell concentrations revealed that liposome-induced cell agglutination reduces the number of available binding sites per cell.
D000818:Animals; D000906:Antibodies / Q000008:administration & dosage*; D000936:Antigen-Antibody Complex / Q000032:analysis; D002417:Cattle; D004912:Erythrocytes / Q000276:immunology / Q000378:metabolism; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D008081:Liposomes / Q000008:administration & dosage*; D013861:Thiocyanates / Q000378:metabolism
D000906:Antibodies; D000936:Antigen-Antibody Complex; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008081:Liposomes; D013861:Thiocyanates; C024098:6-carboxyfluorescein; D016650:Fluorescein-5-isothiocyanate