Nuclear magnetic resonance (NMR) spectroscopy of PF4 and IL-8 interaction.¹H-¹⁵N HSQC spectra of ¹⁵N-labeled PF4 in the absence (blue) and presence (red, 1:1 ratio) of unlabeled IL-8 are shown. The spectra were collected at 40°C (pH = 5.0). Insets show an expansion of 3 regions (A43, I42, and H23) to exemplify the chemical-shift changes occurring upon addition of IL-8 to PF4 solution. Also, the proton chemical-shift dependence versus PF4/IL-8 ratio is presented for I42 as an example. Dashed line is plotted to visualize the trend of the chemical-shift dependence.