MMP9 and triple-A syndrome: However, Ccl3−/− and Ccr5−/− (Chemokine receptors) mice exhibit exaggerated abdominal aortic aneurysm (AAA) with augmented macrophage infiltration and (matrix metalloproteinase) MMP‐9 expression, whilst CCL3 treatment reverses this phenomenon in both wild‐type and Ccl3−/− mice by the CCL3–CCR5 axis [33].