Objective: Recruitment of neutrophils to sites of inflammation requires coordinated regulation of their capture, activation, and migration on vascular endothelium. This study examines whether exposure of neutrophils to antineutrophil cytoplasmic antibodies (ANCAs) can disrupt this sequence of events.
Methods: Isolated human neutrophils were perfused in the presence or absence of ANCA-positive IgG over endothelial cells that had been activated with either 2 units/ml or 100 units/ml of tumor necrosis factor alpha (TNFalpha) for 4 hours.
Results: When endothelial cells were activated with 100 units/ml of TNFalpha, neutrophils were captured from flow, a small proportion of adherent cells rolled, and the majority transmigrated through the endothelial cell monolayer. When neutrophils were treated with ANCA IgG immediately before, 5 minutes before, or 15 minutes before perfusion, none rolled on contact with the endothelium, but the majority still transmigrated. When endothelial cells were activated with 2 units/ml of TNFalpha, the majority of untreated adherent neutrophils rolled, a few transmigrated, and the number that attached decreased with time during washout. In contrast, when neutrophils were pretreated with ANCA IgG just before perfusion, adhesion was stabilized, and the number of neutrophils that transmigrated was increased 10-fold. Priming of the neutrophils with TNFalpha before the addition of ANCA further increased the stability of neutrophil binding, but did not significantly increase transmigration.
Conclusion: Rather than frustrating the transmigration process, ANCAs promoted the migration of neutrophils through the endothelium. That the effect was evident at a relatively low level of endothelial activation suggests that ANCAs may potentiate the early vasculitic lesion and promote tissue damage and recruitment of other proinflammatory cells.