Endothelial CXCR7 influences CXCL12 gradient direction by controlling CXCL12 concentrations near but not far from the vasculature.

200 endothelial CXCR7 cells (83% coverage of the blood vessel), 200 CXCL12-secreting cells, and 200 CXCR7+ cells in tissue were placed in the simulation. A, Locally, endothelial CXCR7+ cells scavenge CXCL12 and influence the endothelial-tissue gradient direction. We arbitrarily define positive gradients as those that point from the vasculature to the tissue, and negative gradients point from the tissue to the vasculature. Maximum gradients over a 24-hour simulation are shown. B, CXCL12 concentration profiles (corresponding to the maximum gradients shown in A) indicate endothelial CXCR7 significantly decreases concentrations near the blood vessel and has a much lower effect far away. Curves begin at 10μm because this designates the first grid compartment next to the vasculature (Setup 2, Fig 1B and 1C).