Cell-derived CXCL12 gradients are isoform-specific with regards to the time to steady state, gradient magnitude, and amount of CXCL12 in the proximate environment.

A, Higher ECM binding affinity and higher secretion rate correspond to a higher gradient magnitude, but a longer time to form it. Error bars represent SEM of 5 simulations. Both clusters contain 100 cells. Cell clusters are placed 100 μm apart. B, CXCL12 gradients and total concentrations in the tissue vary with each isoform. Cell numbers were the same as in A. C, CXCL12-β (center) and -γ (right) create microenvironments with higher CXCL12 concentrations than CXCL12-α (left). On each plot, the x- and y-axes correspond to the number of cells in each cluster: 25, 50, 75, 100, 125, 150, 175, 200. D, the number of CXCL12-secreting cells in a cluster influences gradients, while the effect of the number of CXCR7+ cells is less pronounced. The x- and y-axes are the same as in C. For C and D, free and ECM-bound CXCL12 was summed. For all simulations in this figure, an average over 5 simulations is reported.