Assessment of lesions in BAC⁺ApoE^–/– mice. (a) Lesions in aortic roots of BAC⁺ApoE^–/– mice (left) and ApoE^–/– (right) mice (×5) were stained with ORO to detect the accumulation of lipids. BAC⁺ApoE^–/– mice showed 2.7 times decrease in lesion size compared with the ApoE^–/– mice (b). ORO-stained sections were used for the assessment of lesions (c and d) (×24; inset ×4, transversely sectioned aortic root). Lesions were markedly smaller and less well-developed in BAC⁺ApoE^–/– mice as compared with ApoE^–/– mice. Markedly less ORO positivity was seen in foam cells from BAC⁺ApoE^–/– mice as compared with ApoE^–/– mice. A color overlay based on hue, saturation, and intensity further shows a dramatic decrease in ORO positivity (green color) in lesions from BAC⁺ApoE^–/– mice (e), compared with ApoE^–/– mice (f) (×24). For the assessment of lesion complexity in BAC⁺ApoE^–/– mice, lesions in aortic roots of BAC⁺ApoE^–/– mice (g) and ApoE^–/– mice (h) were stained with Movat’s pentachrome to visualize extracellular matrix deposition within the lesions (×24; inset ×4, transversely sectioned aortic root). Small amounts of matrix rich in proteoglycans, especially versican (reflected here as sea-green color corresponding to glycosaminoglycan content), is observed in lesions from BAC⁺ApoE^–/– mice, particularly near the noduli Arantii. Furthermore, these early lesions have only a very faint intimal positivity. However, in lesions of the ApoE^–/– mice, glycosaminoglycan is observed in deep intimal areas of the lesions underlying the foam cell–rich regions. Also, extracellular matrix deposition is observed interwoven with extracellular cholesterol clefts and near the noduli Arantii. A color overlay reflecting extracellular matrix based on hue, saturation, and intensity shows differential localization of these components (green color) in BAC⁺ApoE^–/– (i) and ApoE^–/– mice (j) (×24). An aortic valve cusp is denoted in g (arrow).