Treatment of rolling neutrophils with antineutrophil cytoplasmic antibodies causes conversion to firm integrin-mediated adhesion

Objective. The vascular lesions associated with autoimmune small-vessel vas culitis may arise from activation of circulating neutrophils by antineutrop hil cytoplasmic antibodies (ANCA), resulting in increased adhesion of these neutrophils to the vessel wall, The present study examined the effects of ANCA-positive IgG (ANCA IgG), derived from patients with small-vessel vascu litis, on neutrophil adhesion. Methods. An in vitro, flow-based adhesion assay was used to determine the e ffects of ANCA IgG on neutrophils rolling on P-selectin presented by a mono layer of activated platelets. The platelets act as a surrogate vessel wall and can also support beta 2 integrin-mediated immobilization of neutrophils if they are purposefully activated (e.g., by FMLP). Results. In the absence of any added agents, neutrophils rolled continuousl y over the platelet monolayer. Superfusion of ANCA IgG over rolling cells r esulted in conversion to stationary adhesion accompanied by shape change, T he ANCA-mediated response was transient, peaking at 5-6 minutes and returni ng to baseline by 15 minutes, even in the continued presence of ANCA, In co ntrast, normal (ANCA-negative) IgG and ANCA F(ab')(2) fragments caused mini mal conversion to stationary adhesion. Pretreatment of neutrophils with blo cking antibodies directed toward Fc gamma receptor type IIA or the integrin chain CD11b completely inhibited the ANCA-mediated conversion, confirming that ANCA- mediated activation occurred through Fc gamma receptors and that neutrophil immobilization was mediated by the activated beta 2 integrin (C D11b/CD18). Conclusion. These findings support the concept that ANCA can directly activ ate neutrophils to become firmly adherent to vessel walls, where they may o bstruct flow, initiate tissue damage, and contribute to pathogenesis of vas culitis.