Citrullinated histone H3 identifies neutrophil extracellular trap formation and correlates with renal disease activity in ANCA-associated vasculitis

Abstract Background Anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) often manifests with necrotizing glomerulonephritis. Neutrophil extracellular traps (NETs) are implicated in its pathogenesis; citrullinated histone H3 (H3Cit) is a specific marker of NET formation. To date, no studies have assessed the relationship between H3Cit-positive cells and disease activity in patients with AAV. In this study, we assessed whether H3Cit-positive cells in renal tissue were associated with disease activity. Methods We retrospectively evaluated 50 patients newly diagnosed with AAV by renal biopsy between January 2011 and August 2024. Paraffin-embedded specimens underwent immunohistochemical staining for H3Cit. Patients were classified as H3Cit-positive or H3Cit-negative groups based on the presence of H3Cit-positive cells in glomeruli and/or interstitium. Clinical parameters and histopathological features were compared. Additionally, correlations between H3Cit-positive cell counts and urinary biomarkers were evaluated. Results H3Cit-positive cells were detected in 42 cases (84%) within the interstitium; of these 42 cases, they were also detected in 23 within the glomeruli. Compared with H3Cit-negative cases, the positive group had significantly higher urinary β₂-microglobulin (β₂-MG) and N-acetyl-β-D-glucosaminidase index values. Interstitial H3Cit-positive cell counts positively correlated with urinary β₂-MG levels. The positive group showed more frequent crescent formation and peritubular capillaritis, and H3Cit-positive cells were present in all arteritic lesions. Conclusions H3Cit-positive cells in renal tissue were associated with active glomerular and tubulointerstitial lesions in AAV cases and correlated with urinary markers of interstitial injury. H3Cit immunostaining may serve as a pathological marker of renal disease activity in AAV cases and support clinical assessment at the time of biopsy.