Atherosclerotic plaque caps are locally weakened when macrophages density is increased.

The density of macrophages, identified by the antibody EBMII, in human aortic plaque caps was counted. A contiguous strip of cap tissue was tested mechanically. Aortic plaque caps which had undergone rupture (ulceration) at one end (n = 18) were compared with caps of intact plaques (n = 22). The caps of ruptured plaques showed a significant increase in macrophage density, an increased extensibility and decreased maximum stress (force per unit area) at fracture when compared with caps from intact plaques.