Figure. Concentration-dependent activation of CX3CR1 by CX3CL1. Reporter cells were transfected with either the expression plasmid for C-X3-C motif chemo­kine receptor 1 (CX3CR1) or the mock plasmid and treated with various concentrations of C-X3-C motif chemo­kine ligand 1 (CX3CL1). Data points shown are the mean ± SEM of an experiment performed in triplicate, and the curve is a fit to Hill equation with an EC50 of 1.8 nM.