CCX721 is a potent antagonist of CCR1-mediated functions, as tested with human monocytes, with all known chemokine ligands and in physiologically relevant human serum. (A) Potency values for CCX721 are shown, measured using CCR1-expressing THP-1 cells, and include results with chemotaxis, radioligand binding, and cytoplasmic calcium flux assays. (B) CCR1- or CCR5-specific chemotaxis assays, with increasing concentrations of CCX721 added, were conducted in chemotaxis buffer with n = 8 replicates per point; migration signals were normalized to controls. (C) Chemotaxis of freshly isolated human monocytes to a range of CCL3 concentrations, with n = 8 replicates per point, was conducted in the presence of human serum, with or without the addition of 10nM CCX721. (D) Summary data for all CCR1 ligands in this serum chemotaxis assay.