U83A and U83A-N high-affinity binding CCR5 and human chemokine displacement. Competition binding assays on (A) U373-MAGI-CCR5E, (B) PBMCs, and (C) COS-7 CCR5. Data are the percentage of maximum bound iodinated chemokine, determined in absence of cold competitor. (A-B) Total displacement was obtained by 10 nM CCL3 (•); (C) kinetics are shown. Each point represents mean values ± standard deviations of triplicates. IC₅₀ for U373-MAGI-CCR5E cells is as follows: U83A, 1.1 × 10⁻¹⁰ M, U83A-N, 8.3 × 10⁻⁹ M; IC₅₀ for PBMCs is as follows: U83A-N, 9.2 × 10⁻⁸ M; IC₅₀ for COS-7 CCR5 cells is as follows: CCL3 0.2 × 10⁻⁹ M and no displacement by U83A-Ndel.