VEGF-A secreted from transplanted islets recruits Gr-1+ leukocytes. (A) VEGF-A protein measurements in islet grafts in abdominal muscle 1 (n = 5), 2 (n = 6), and 14 (n = 5) days after transplantation (tx). Values are expressed as relative to the VEGF-A content in abdominal muscle on the contralateral side of the linea alba. *P < .05. (B) Confocal z-projection image of a transplanted wild-type pancreatic islet (blue, Celltracker) in the cremaster muscle of a wild-type mouse 4 days after transplantation. Blood vessels (red, CD31-mAb) surround and penetrate the islet, and Gr-1+ leukocytes (green, Gr-1-mAb) are gathered around the graft. Bar represents 50 μm. (C) Confocal z-projection image of a VEGF-A−/− islet 4 days after transplantation to a wild-type mouse cremaster muscle with few surrounding leukocytes and no ingrowing blood vessels. The blood vessels that are visible lie beneath the graft. Bar represents 50 μm. (D) Confocal z-projection image showing a site in a wild-type cremaster muscle distant from a transplanted islet illustrating the background level of leukocyte extravasation in these tissues. Bar represents 50 μm. (E) Quantification of the Gr-1+ area per confocal image of islet grafts 3-5 days after transplantation. VEGF-A−/− islets (n = 8 mice, 14 islets) had less than half of the amount of recruited leukocytes compared with wild-type islets (n = 8 mice, 15 islets). *P < .05. (F) Vessel densities in the transplanted islets from wild-type and VEGF-A−/− mice. (G) Numbers of leukocytes that adhere to a 100-μm part of postcapillary venules in the cremaster muscle after stimulation with MIP-2 (n = 5), VEGF-A (n = 5), or bicarbonate buffer (control, n = 3). *P < .05, compared with time 0 minutes for MIP-2. #P < .05, compared with time 0 minutes for VEGF-A. (H) Numbers of leukocytes that emigrate from postcapillary venules into the cremaster muscle after stimulation with MIP-2 (n = 5), VEGF-A (n = 5), or bicarbonate buffer (control, n = 3). *P < .05, compared with time 0 minutes for MIP-2. #P < .05, compared with time 0 minutes for VEGF-A.