Histologic analysis of renal leukocyte infiltration in antineutrophil cytoplasmic antibody–associated vasculitis: Importance of monocyte and neutrophil infiltration in tissue damage

Objective The histopathologic lesions in antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV) have been studied extensively, but the exact composition of the cellular infiltrate is unclear. We undertook this study to analyze renal leukocyte infiltration and the cellular distribution within glomeruli and interstitium in 65 renal biopsy samples obtained from patients newly diagnosed as having AAV. Methods Renal cellular tissue infiltration was assessed with an immunoperoxidase method. Furthermore, the infiltrating cell types were correlated with clinical and histopathologic data. Results The predominant interstitial infiltrating cells were T lymphocytes, while monocytes and, to a lesser extent, granulocytes constituted the dominant infiltrating cell types in glomeruli. Interestingly, lymphocyte infiltration was predominantly periglomerular, especially around glomeruli with sclerosis or heavy crescent formation, while interstitial monocyte and neutrophil infiltration was diffusely distributed over the interstitial tissue. A significant correlation was found for the glomerular infiltration of CD68‐positive macrophages with the presence of glomerular necrosis as well as with the number of glomeruli with crescents (P < 0.0001 and P = 0.005, respectively). No correlation was found for interstitial fibrosis with the infiltration of any leukocyte subset. Furthermore, a significant correlation was found for the interstitial as well as for the glomerular infiltration of CD68‐positive macrophages with serum creatinine concentration at the time of biopsy (P = 0.001 and P = 0.006, respectively). Conclusion These data underscore a major role of monocytes in addition to neutrophils in the tissue damage of AAV.