Bowman's capsule rupture links glomerular damage to tubulointerstitial inflammation in ANCA-associated glomerulonephritis.

OBJECTIVES: We have recently described the frequency of Bowman's capsule (BC) rupture in a considerable subset of patients with antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN). Interestingly, recent reports established a better performance of glomerulocentric ANCA scoring systems after adding BC rupture to these classification systems, suggesting that characteristics of this lesion are independent from glomerular lesions. Since BC rupture may link glomerular damage to tubulointerstitial lesions via direct interaction with the surrounding interstitium, we here aimed to expand our current knowledge of this distinct lesion by a systematic description of tubulointerstitial lesions analogous to the Banff classification in association with the presence of BC rupture in ANCA GN. METHODS: A total number of 44 kidney biopsies with confirmed renal involvement of ANCA GN were retrospectively included between 2015 till 2020 in a single-centre observational study. RESULTS: We here show that presence of BC rupture was associated with severe deterioration of kidney function at disease onset, similar to previous findings regarding long-term renal survival. Furthermore, BC rupture in ANCA GN was associated with tubulointerstitial inflammation and ultrastructural analysis revealed direct cellular exchange between Bowman's space and the interstitium, potentially contributing to the observed deterioration of kidney function and worse renal outcome in ANCA GN. CONCLUSIONS: BC rupture is associated with renal outcome in ANCA GN, therefore underscoring the need for further studies with regard to the glomerular-tubulointerstitial interaction in this disease.