Amyloid angiopathy of the human brain: immunohistochemical studies using markers for components of extracellular matrix, smooth muscle actin and endothelial cells.

Cerebral amyloid angiopathies comprise a heterogeneous group of conditions characterised by amyloid deposition in leptomeningeal and cortical vessels. We have studied the deposition of extracellular matrix components in such vessels from controls and ten cases with marked amyloid angiopathy. Arterial vessels which were heavily loaded with amyloid often showed lack of immunostaining to collagen type I, III, V and VI in the amyloid-containing parts of the vessel wall but some immunoreactivity remained in the adventitia. The subintimal region of some arterioles presented a faint staining with collagen V and collagen VI antisera. Immunostaining to collagen IV and laminin revealed normal reactivity in the vascular basal lamina and frequently remaining activity in the media. Immunostaining for actin showed a complete or partial loss of reactivity in the amyloid-containing parts of the media but often there was a thin line of staining at the position of pericytes. The endothelial markers did not reveal any changes compared with controls. In other cerebral microangiopathies, for instance Binswanger's leukoencephalopathy, CADASIL and cases presenting hyalinosis there is a deposition of fibrillary collagens in the wall of afflicted microvessels. Degeneration of smooth muscle cells and absence of marked fibrosis in some of the arterial vessels in cases of amyloid angiopathy may explain why such vessels are susceptible to ruptures and haemorrhages.