The human atherosclerotic plaque.

The fibrous plaque is regarded as the vascular lesion most characteristic of atherosclerosis. The notion that these lesions develop from mural thrombi has received considerable support, and there is also much support for the idea that plaques form as a reaction to mechanical or chemical damage to the endothelium. As an alternative to these two hypotheses, Benditt and Benditt have suggested that plaques represent monoclonal proliferation of altered smooth muscle cells similar to leiomyomas. Evidence in favor of this suggestion has been obtained using tissues from human black females who are heterozygous for the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD). In such individuals, as a result of random inactivation of the X-chromosome during embryogenesis, all normal tissues contain both the A and B isoenzymes of G6PD, when assayed electrophoretically, whereas plaques and other lesions suspected of being of monoclonal origin contain predominantly one isoenzyme. A certain proportion of fatty streaks also show a single G6PD isoenzyme pattern, suggesting that some fatty streaks act as the foreunners of the fibrous plaque.