Apoptotic cells trigger enhanced binding of leukocytes to endothelial cells. (A) Exposure of HMEC-1 cells and HUVECs to apoptotic HMEC-1 cells for 4 hours increased adhesion of PMNs and MΦ, whereas exposure to necrotic cells failed to induce enhanced binding of leukocytes to HMEC-1 cells. HUVECs coincubated with necrotic HMEC-1 cells showed enhanced binding of MΦ but not of PMNs. (B) The supernatant of HMEC-1 cells that were exposed to apoptotic ECs is sufficient to promote increased binding of neutrophils to HMEC-1 cells, whereas the pretreated cells alone do not show enhanced binding of neutrophils. (C) Incubation of HMEC-1 cells with CECs isolated from patients with PR3-ANCA–associated vasculitis leads to a significant increase in adhesion of neutrophils. MΦ indicates primary blood mononuclear cells (monocytes/macrophages); PMN, polymorphonuclear cells (neutrophils). Data represent mean ± SEM of 5 (A,C) or 3 (B) independent experiments. Mann-Whitney U test was performed to compare differences in leukocyte adhesion (*P < .01; *P < .001).