Polyanion inhibition of the hbs-wt peptide binding to heparin in the BSA-heparin ELISA. An ELISA was used to determine the inhibition of the hbs-wt peptide binding to heparin by various polyanions. The hbs-wt peptide was added to BSA-heparin coated plates and detected by a horse-radish peroxidase conjugated antibody that recognizes the FLAG epitope. Polyanions used to inhibit hbs-wt peptide binding to heparin included those used in the pvRII binding and P. knowlesi invasion assays. Also included were dextran sulfate and sodium spirulan which have also been shown to be potent inhibitors of X4 HIV strains. Percentage inhibition of binding was determined by dividing the absorbance at each polyanion concentration by the absorbance at 0 μg/ml of the polyanion.