Figure. Concentration-dependent activation of CXCR4 by cXCL12a. Reporter cells were transfected with either the expression plasmid for C-X-C motif chemo­kine receptor 4 (CXCR4) or the mock plasmid and treated with various concentrations of C-X-C motif chemo­kine ligand 12a (CXCL12a). 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 5.4 nM.