Histology of the aortic sinuses from mice at various ages. Sections were cut from 24-week (A,C,E) and 48-week (G,I,K) L^–/–/A^–/–, and from 24-week (B,D,F) and 48-week (H,J,L) L^–/–/A^–/–/FG^–/– mice. H&E (A,B) and Masson's trichrome stains (C,D), and anti-SMC (E,F,G,H), antifibrin(ogen) (I,J), and antimacrophage immunostains (K,L). Original magnification, × 200. (A) A well-formed fibrous cap (red arrowhead) encapsulating a foam cell-laden core (green arrowhead). (B) An intermediate size lesion with a thinning cap (red arrowheads). Focal acellular patches (green arrowhead), cellular debris, extracellular lipids, foam-like cells, and cholesterol clefts (blue arrowhead) within the core. (C) The collagen-rich fibrous cap (red arrowheads) encapsulates a collagen-negative foam cell core (green arrowheads). (D) Collagen is associated within the subcapsular region (red arrowheads). (E) A cellular multilayered region of SMCs associated with the fibrous cap (red arrowheads), as well as the normally positive medial compartment (green arrowheads). (F) Numerous single-layered positive SMCs (red arrowheads) at the endothelium. (G) Positive (dark red) SMC cells in the subluminal region, which are intensely positive (red arrowheads) and diffusely scattered among negative bordering cells. A few positive SMCs within the core (green arrowheads). (H) A thin, faint SMC layer (red arrowheads) in the subluminal region diffusely scattered among negative bordering foci. (I) Fibrin deposits (red staining) in the underlying subcapsular region. Patchy areas of fibrin are associated with the endothelium (red arrowheads). Diffuse areas of fibrin deposition in the lipid core (green arrowheads). (J) Negative anti-Fg immunostaining. (K) Macrophages (brown stain) in the thinned cap, in the subendothelium (red arrowheads), and within the lipid core (green arrowheads). (L) Several macrophages (brown stain) diffusely scattered within the core and at the base (red arrowheads).