Kidney biopsy findings of monoclonal gammopathy–associated C3 glomerulopathy. (A-B) Light microscopy. (A) Section of renal cortex showing mesangial proliferative glomerulonephritis (periodic acid–Schiff staining, ×400). (B) Diffuse membranoproliferative glomerulonephritis with nodular appearance of the mesangium and glomerular capillary wall deposits (light green trichrome, ×400). (C-D) Immunofluorescence microscopy. Diffuse granular capillary wall and mesangial bright deposits (anti-C3 fluorescein isothiocyanate-conjugate, ×400). (E-F) Electron microscopy. (E) Nodular (pseudohumps) electron-dense mesangial deposits (asterisk) and intramembranous dense deposits (arrow). Scale bar, 1 µm (original magnification ×8000). (F) Nodular electron-dense mesangial deposits (asterisk) and interrupted intramembranous dense deposits displaying a sausage-shaped (arrow). Scale bar, 1 µm (original magnification ×15 000).