Fig. 2. The mutant CCR2bY139F receptor impairs the response to RANTES but to SDF-1α. (A) CCR2bY139F/CCR5 double-transfected HEK-293 cells were incubated with biotin-labeled mAbs to CCR2, CCR5 or CXCR4 or their respective isotype-matched control mAbs, followed by isothiocyanate-labeled streptavidin. (B) Ca²⁺ flux was triggered by 10 nM RANTES, 10 nM MCP-1, or a combination of both chemokines (0.1 nM each) as indicated using CCR2bY139F/CCR5-co-transfected HEK-293 cells. Results are expressed as a percentage of the maximum chemokine-induced Ca²⁺ response. The figure depicts one representative experiment of four performed. (C) Ca²⁺ mobilization was determined as in Figure 1B, following stimulation of CCR2b Y139F/CCR5-co-transfected HEK-293 cells with different concen trations of MCP-1 or SDF-1α, separately or simultaneously as indicated. Results are expressed as a percentage of the maximum chemokine-induced response. The mean ± SD of three independent experiments is shown. (D) HEK-293 cells co-transfected with the CCR2bY139F and CCR5 receptors were processed as in Figure 1D. Arrows indicate the monomer and the dimer.