Monocytes Promote Crescent Formation in Anti-Myeloperoxidase Antibody-Induced Glomerulonephritis

Neutrophils and monocytes express anti-neutrophil cytoplasmic antibody (ANCA) antigens, and activation of these cells by ANCA is central to ANCA-associated vasculitis and necrotizing crescentic glomerulonephritis (NCGN). The importance of neutrophils is established; however, any role of monocytes is less clear. We tested the hypothesis that depletion of CCR2⁺ inflammatory monocytes and their derivatives would abrogate anti-myeloperoxidase (MPO) antibody-induced NCGN in a mouse model. We used passive anti-MPO antibody transfer for NCGN induction in wild-type mice or mice expressing the CCR2 promoter-controlled diphtheria toxin receptor. Both mouse strains showed similar circulating Ly6C^hi and Ly6C^lo monocytes and neutrophils at baseline. Diphtheria toxin robustly depleted circulating monocytes only in CCR2 promoter-controlled diphtheria toxin receptor mice, whereas neutrophil numbers were similar. Anti-MPO antibody transfer resulted in nephritic urine by dipstick and albuminuria by enzyme-linked immunosorbent assay, and monocyte depletion had no effect. However, monocyte depletion significantly reduced glomerular necrosis and crescent formation and abrogated monocyte, macrophage, and dendritic cell increase in the affected kidneys, whereas renal neutrophil numbers were not affected. Soluble CD163 increased in serum, but not in urine, with anti-MPO antibody treatment and was completely abolished with monocyte depletion. Our findings establish an important role of monocytes/macrophages for glomerular necrosis and crescent formation in a renal ANCA-associated vasculitis model.