- 15 tumors by investigating the pair of x-linked isoenzymes. Benditt and Benditt (1973) (author's reference 40) investigated by this means individual atherosclerotic plaques from various regions of the aorta and common iliac arteries of 4 human females. The data were reported to show that the fibrous caps of the atheromatous plaques were composed of cells that produce solely or predominantly one of the two isoenzymes, whereas samples of artery wall media and intima were regularly composed of a mixture of the two isoenzyme cell types. These investigators considered an alternative to the injury-repair hypothesis of spontaneous atherosclerosis on the basis of the following considerations: cells of spontaneous atherosclerotic lesions differ from cells of normal artery wall and cells populating a repair site in size, composition of associated extracellular material (e.g. preponderance of collagen rather than elastin), and in the absence of intercellular junctions. These investigators stated that these differences and the results of their enzyme analysis of plaques and normal vessel comoonents imply that atherosclerotic plaques in human beings arise by another mechanism. suggest two possibilities: They stated that these features either the cells of athercsclerotic plaques “derive from a population of cells different from those of the normal arterial media or they are transformed cells, and if the latter is so, cells of atherosclerotic plaques, like those of the benign smooth muscle tnmors of the uterine, could be expected to be monoclonal. It is at this point that Benditt and Benditt seem to have used the term, monoclonal, to suggest origin not only from one of the two