TLR9 and vasculitis: Serum HMGB1 levels were higher in AAV than healthy controls. HMGB1 enhanced the ability of neutrophils to burst, degranulate, and form NETs. HMGB1 increased the level of meosin in the GEnC and promoted the injury of GEnC. HMGB1 enhanced the proliferation of B cells and TLR9 levels in plasma cells in PBMC from patients with AAV, and the latter was positively correlated with Birmingham vasculitis activity score.