Fig. 3. Immunohistochemical demonstration of ATTR amyloid in the transgenic model.

To determine the amyloid type, heart (a) and tongue (b) were stained with anti-human TTR, anti-mouse apoAII or anti-mouse SAA antisera, as indicated, followed by alcoholic alkaline Congo red. Bright field images show the immunohistochemical signal (brown), and faint red Congo red stained amyloid in a representative amyloidotic line N4 mouse (n = 15). The amyloid deposits exhibited the characteristic red-green birefringence when viewed by polarising microscopy. The coincidence of TTR signal and amyloid, together with the absence of apoAII and SAA signal, demonstrates that the amyloid is of ATTR type. In places, the intense anti-TTR staining obscured the Congo red staining, the extent of which is clearly visible in the closely adjacent sections stained for apoAII and SAA. Scale bar, 100 µm (a) and 200 µm (b). hTTR human TTR, mApoAII mouse apolipoprotein A2, mSAA mouse serum amyloid A protein.