Functional classification of antineutrophil cytoplasmic antibody (ANCA) and its relation with clinical parameters of ANCA-associated vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is characterized by serum ANCA and systemic small-vessel vasculitis. Neutrophils are primed to express ANCA antigens on the plasma membrane. ANCA binding to the antigens can transduce signals into neutrophils, releasing reactive oxygen species (ROS) and contributing to AAV development. ANCA-mediated signals are transduced via two pathways: ANCA antigens crosslinked by ANCA, and Fcγ receptor (FcγR), to which the Fc portion of ANCA binds. This study aimed to demonstrate the association of ANCA-mediated neutrophil activation pathways with clinical manifestations of AAV, including renal dysfunction and kidney survival at 6 months after treatment. For this purpose, IgG was extracted from the serum of AAV patients before treatment (n = 112), and ROS production from neutrophils exposed to IgG and its suppression by FcγR inhibitors (FcX) were assessed. IgG exhibiting higher ROS production than control IgG was classified as ROS-inducing ANCA and the others as ROS-noninducing ANCA. The former was subclassified into antigen-driven ANCA and FcγR-driven ANCA according to whether the ROS production suppression rate by FcX was <50 % or ≧50 %, respectively. As a result, ANCA was classified into ROS-inducing antigen-driven ANCA (n = 74), ROS-inducing FcγR-driven ANCA (n = 22), and ROS-noninducing ANCA (n = 16). Serum levels of blood urea nitrogen and creatinine were significantly higher in patients with ROS-inducing FcγR-driven ANCA than in those with ROS-noninducing ANCA. Patients with ROS-inducing FcγR-driven ANCA had a significantly lower kidney survival rate 6 months after treatment than other patients. The collective findings suggest that ROS-inducing FcγR-driven ANCA may predict poor kidney prognosis in AAV.