Assessment of plaque composition and structure. Representative brachiocephalic plaque sections showing (a) lipid cavities: plaque regions showing absence of all components of UST stain, (b) inflammatory cells: MAC2 immunohistochemistry (brown), (c) collagen: picrosirius red (red stain), (d) smooth muscle: SMA immunohistochemistry (brown). Scale bar = 100 μm. (e) Example of a large atherosclerotic plaque from a saline-treated ApoE−/− mouse, showing only a single plaque per section and no buried fibrous layers. (f) Example of three buried fibrous layers in a plaque (black, green and red arrows mark each fibrous layer) taken from a DEP-treated ApoE−/− mouse. UST staining, scale bar = 100 μm. (g) DEP instillation increased the average number of distinct plaques within each cross-section of lesion and the number of buried fibrous layers per section. Mean ± S.E.M. Values obtained from analysis of serial sections at 100 μm intervals for each animal; Mean number of sections per group = 4.4 ± 0.7 for ApoE-saline (n = 8), 4.4 ± 0.8 for ApoE-DEP (n = 7), *P < 0.05, Mann–Whitney test comparing saline with DEP. All images shown are from arteries from DEP-instilled ApoE−/− mice, except panel 3e, taken from saline-treated ApoE−/− mouse.