Purified recombinant LAV gp120 (1 μg/100 μl 10 mM NaOAc pH 4.0) was immobilized by NHS/EDC coupling on a dextran coated, CH-activated C5 sensorchip (Biacore, Sweden) at densities yielding 3500-5000 response units (RU). Surface plasmon resonance was carried out using a Biacore 1000. Binding to immobilized proteins diluted in HBS-EP buffer (Biacore, Sweden) was tested at various concentrations at a flow rate of 5 μl/min for a period of 6 min.