Since a 1000-fold molar HOCl excess was sufficient to transform HSA into a viral entry inhibitor we generated HOCl-modified samples of three serum albumins from human, mouse and bovine by using a 1000-fold excess of HOCl. Using these three serum albumin preparations, we studied binding of mHSA, mBSA and mMSA to LAV (NL4-3) gp120 by surface plasmon resonance spectroscopy (SPR) (Figure 2a , c, e). The experiment demonstrated that serum albumin modified by a 1000-fold molar excess of HOCl bind to the immobilized gp120. No binding of mHSA, mBSA and mMSA to gp41 immobilized on a biosensor (binding < 5 RU, data not shown) was observed. Thus, binding was specific for gp120 envelope. Bound protein was removed from the gp120-biosensor by treatment with 100 mM HCl and 100 mM NaOH. This regeneration procedure retained the ability of immobilized gp120 to bind rCD4 and V2-and V3-loop specific antibodies. Also no binding to gp120 was measured using normal, non-modified HSA, BSA and MSA (Figure 2b , d, f). In these control experiments response units (RU) in SPR were also below 5 RU. Binding of HOCl-modified proteins was compared to gp120-binding of rCD4 and gp120-specific antibodies (Figure 2g ). At 50 μg/ml the modified proteins showed between 50-70% of the gp120 binding activity observed with rCD4 at 10 μg/ml. Binding of antibodies generated by immunization with CHOderived SF2-gp120 (Serum ADP429) or by a V3 loop peptide (IRIQRGPGRAFTIGC) (mab EVA 3047) showed binding responses at 1:80 dilution (Serum ADP429) or 25 μg/ml (mab EVA 3047) about 30 40 times as high as the HOCl-modifed serum albumins at 50 μg/ml.