Identification of Macrophages in Intimal Thickening of Rat Carotid Arteries by Cytochemical Localization

Complete desquamation of the endothelium of the rat carotid artery by balloon catheter stripping resulted within 2 weeks in the formation of a large intimal thickening. After an enzyme cytochemical technique was applied to localize cytosolic purine nucleoside phosphorylase (PNP), light microscopical evaluation indicated that this intimal thickening in normochoiesteroiemic rats was composed of 5.8 % to 11.8 % (mean 8.8%) PNP-positive cells. At the electron microscopic level, all these PNP-positive cells were identified as macrophages by the absence of a basement membrane and plasmalemmal vesicles and by the occurrence of specific intracyto-plasmic granules. The nearly nonreactive intimal cells were classified as modified smooth muscle cells. Additional evidence of the macrophage nature of the PNP-stained intimal cells was obtained by differential immunogold labeling of these cells with a monoclonal antibody against rat macrophages. Moreover, in hypercholester-olemic rats, only the cells stained for PNP transformed into foam cells (between 8.5% and 11.4 % of all nucleated intimal cells; mean 9.6%). This study shows that PNP cytochemistry discriminates macrophages from modified smooth muscle cells in th