Local neovascularization and cellular composition within vulnerable regions of atherosclerotic plaques of human carotid arteries.

An improved immunohistochemical method has been used to assess neovascularization within the vulnerable 'shoulder' regions of atherosclerotic plaques from carotid arteries. A combination of monoclonal antibodies (CD31, CD34, +/- von Willebrand factor) was shown to be far more effective than conventional techniques in demonstrating extensive vascularizations within the 'shoulder' and cap regions of late-stage plaques. Such sites were shown to be microfocal, often appearing as a plexus of both large and small vessels which occupied a significant proportion of the 'shoulder' area. These regions of marked neovascularization were commonly associated with accumulations of macrophages, mast cells, and T-cells, indicative of local inflammatory reactions. The matrix components elastin and collagen type VI showed variable distributions which suggested extensive tissue remodelling, whereas collagen type IV was recognized as a basement membrane protein of most blood vessels, as well as being associated with 'stellate' smooth muscle cells. Evidence of local microvascular damage within the shoulder regions of some specimens was demonstrated by extravascular red blood cells, macrophages containing haemosiderin, and perivascular fibrin deposition. These local haemorrhages derived from microvessels beneath the lining of the arterial lumen are a further indication of how the microfocal vascularization of the plaque 'shoulder' might contribute to further complications of inflammation and plaque destabilization in late-stage disease.