Figure 2. Effect of Peptide 3 on gp120:V3 loop peptide binding to cells. (a) The binding of 100 μM N-terminal biotinylated gp120:V3(IIIb) to THP-1 cells was measured in the presence of various concentrations of peptide 3. In each case, the non-specific binding (in the presence of 10 mM unlabelled gp120:V3 loop peptide) has been subtracted. (b) Chemotaxis in response to 100 ng/ml SDF1α was measured in the presence of various concentrations of peptide 3. (c) and (d) As for (a) and (b) except that the CXCR4 receptor antagonist AMD3100 was used in place of Peptide 3. (e) As for (a) except that the effect of Peptide 3 on the binding of gp120:V3(BaL) to THP-1 cells was determined. (f) As for (b) except that the effect of Peptide 3 on chemotaxis induced by 25 ng/ml MIP1α was determined. All binding reactions were performed with 106 cells in 100 μl of binding medium at 4°C. Chemotaxis assays were performed with 5 × 104 cells per well. Values are mean ± SEM of triplicate determinations.