Representative histological images demonstrating the grading system used to categorize medial elastin and SMC destruction and macrophage accumulation. Aneurysmal aortas from porcine pancreatic elastase-infused mice were stained with Elastic Van Gieson (EVG) stain for medial elastin, SMC α-actin antibody for SMCs and CD68 antibody for macrophages, respectively. Medial elastolysis and SMCs as well as macrophage densities were graded as I (mild) to IV (severe). Grade I: elastin degradation, SMC loss, or aggregate macrophage accumulation involves <25% of aortic circumference (AC) or diffuse macrophage infiltration. Grade II: elastin degradation, SMC loss, or aggregate macrophage accumulation involves ≥25% but <50% of AC. Grade III: elastin degradation, SMC loss, or aggregate macrophage accumulation involves ≥50% but <75% of AC. Grade IV: elastin degradation, SMC loss, or aggregate macrophage accumulation involves ≥75% of AC.