C3 and atherosclerosis: In contrast, prior studies in mice models of atherosclerosis (Ldlr-/- or ApoE-/- Ldlr-/- background) and knock-out C3 expression (C3-/-) evidenced that atherosclerotic lesions developed in the absence of C3 have a lower content of vascular smooth muscle cells (VSMCs) and collagen, hallmark of vulnerable plaques, and are of a larger size than those plaques developed in animals with a sufficient content of C3 [20,21].