i[VREY]₄, a CCL5-mimicking peptide, binds to CXCL12. (A) Binding kinetics of CXCL12 to i[VREY]₄ by surface plasmon resonance. i[VREY]₄-biot was immobilized onto a neutravidin-conjugated C1 sensor chip (914 RU), and CXCL12 was injected at 62.5 ng/mL, 125 ng/mL, 250 ng/mL, 500 ng/mL, and 1000 ng/mL. Red traces represent the single-site fit to the raw data (blue). Kinetic parameters of 3 independent experiments are indicated as mean ± standard deviation. (B) Expansions of ¹⁵N HSQC spectra are shown for ¹⁵N-labeled CXCL12 in the absence (red peaks) and presence of i[VREY]₄ at concentrations of 20 µM (green peaks), 40 µM (purple peaks), and 200 µM (blue peaks). (C) The interaction of endogenous CXCL12 with i[VREY]₄-biot (1 µM) in human blood was quantified on platelets by proximity ligation with DuoLink by flow cytometry (C) and visualized by confocal microscopy on platelets (scale bar, 2 µm) (n = 3) (D). Data represent mean ± standard deviation from the indicated numbers of independent experiments. **P ≤ .01, ***P ≤ .001 as analyzed by one-way analysis of variance with Dunnett’s multiple comparison test (panel C). MFI, mean fluorescence intensity.