[17], [31], [32] The degradation is usually ascribed to matrix proteinases (especially MMP-2 and -9) produced by infiltrating leukocytes, which are commonly observed in mature human IAs and in animal models of IA. [6]–[8], [17] However, it is important to recognize that such observations of inflammatory infiltration have been made only after a fully developed aneurysm is evident (in the case of human specimens) or weeks after an aneurysm-inducing manipulation is made (in animal studies). Here, MMP2 is linked to aneurysm.