Light, immunofluorescence, and electron microscopy of kidney and other pathology in FH W1206R mutant mice. (A) PAS staining of kidney sections. (i) A normal-looking FH^W/W mouse glomerulus. (ii-v) Representative FH^R/R mouse kidney sections (from 30 mice analyzed) showed features of aHUS, including arteriolar thrombosis (ii, black square), capillary wall thickening and double contours in glomeruli (iii, white arrows), afferent arteriolar thrombosis in arteriole (iv, yellow asterisk), and expanded matrix and microthrombi in capillary lumen (v, blue arrows). Scale bars represent 25 μm (i-ii, left; iii-v) and 50 μm (ii, right). (B) Immunofluorescence staining of C3 and fibrin or fibrinogen. C3 staining was restricted to the Bowman’s capsule only in FH^W/W mice, whereas weak C3 staining of a granular pattern was observed in the glomerulus of FH^R/R mice. Strong fibrin and fibrinogen staining of a diffuse pattern was detected both in capillaries and in mesangial lesions of FH^R/R mouse glomeruli, but not in FH^W/W mouse glomeruli. Scale bar, 25 μm. (C) Electron microscopy of kidneys. A FH^W/W mouse (15-week-old female, 1 of 2 WT mice analyzed by electron microscopy) kidney showed normal basement membrane and foot processes. In a representative FH^R/R mouse (15-week-old female, 1 of 4 mutant mice analyzed by electron microscopy) kidney, the glomerular capillary wall showed subendothelial expansion with fluffy granular material (yellow arrow) and mesangiolysis with rarefaction of mesangial matrix (red asterisk), with no electron-dense deposits. Scale bars represent 2 μm (FH^W/W, left, and FH^R/R) and 500 nm (FH^W/W, right). (D) hematoxylin and eosin staining of brain sections from a representative FH^R/R mouse with neurological abnormalities. Ischemic changes (arrow, left panel), thrombus formation (arrow, right panel) or intracerebral hemorrhage (area circled by dotted line) were observed. Scale bar, 25 μm. (E) Hematoxylin and eosin staining of liver, lung, spleen, and kidney sections from representative FH^R/R mice showed thrombi (arrows) in large blood vessels. Scale bars represent 25 μm (left panel of each organ) and 50 μm (right panel of each organ).