Fig. 1.

The mechanism of ANCA production and small-vessel vasculitis [76].

Microorganisms are either captured by dendritic cells or activate the alternative complement pathway. Dendritic cells lead macrophages to release inflammatory cytokines through antigen presentation to T cells. The alternative pathway produces C5a, which stabilizes the C3(H₂O)Bb complex. Inflammatory cytokines or C5a stimulate neutrophils to express MPO and PR3 on their membrane [[77], [78], [79]]. Fab of ANCA binds them, while Fc of ANCA binds with the Fc receptor on neutrophils, which results in the release of ROS, lytic enzymes, and NETs that eventually cause vascular endothelial damage [70].