Ingestion of lipids by mural cells and inflammatory cells. Adipophilin was expressed in the mural cells of intimal hyperplasia or myointima -like sIA walls (A). In degenerated sIA walls, adipophilin staining does not only stain cells but mostly extracellular debris (B). CD45 and Oil-Red-O double stainings showed presence of inflammatory cells in wall areas abundant in extracellular lipid (C-D, CD45 in brown with DAB, Oil-Red-O and hematoxylin background stain). CD45 positive cells were also found in areas without lipid accumulation (marked with * in C). Most foam cells observed were CD45 negative (marked with arrows in D) and therefore not leukocytes. Expression of 15-lipoxygenase, a known intracellular oxidant of lipids (18), was found in aneurysm wall cells (E, 15-lipoxygenase in brown with DAB and hematoxylin background stain, x40 magnification). Double stainings with CD68 (F, 15-lipoxygenase in brown with DAB and CD68 in blue with AFOS, nuclear fast red background stain) demonstrated that most cells expressing 15-lipoxygenase were not CD68+ macrophages (F), although some double positive cells were also found (data not shown).