Inhibition of P. falciparum IRBC binding to placental CSPG by C4S dodecasaccharides containing one to six 4-sulfate groups. Inhibition was performed with 80, 40, 20 or 10 μg/ml solutions of dodecasaccharides of varying sulfate contents or polysaccharide. The assays were performed two times each in duplicates. The extent of inhibition by oligosaccharides of varying sulfate content is expressed as IRBC binding relative to that of the control. Values are plotted as means + SEM. In the case of placental isolate, complete inhibition was observed at 120 μg/ml of 12 mer-2S and polysaccharide, whereas in laboratory strains, 80 μg/ml of 12 mer-2S and of polysaccharide could fully inhibit binding (not shown). NS, not significant, *, p <0.01.