(a) Aortic diameter changes after CaCl₂ treatment with WT macrophage infusion in MMP-2KO and MMP-9KO mice. Aortic diameters were measured before (white bars) and 8 weeks after (gray bars) CaCl₂ incubation. Bars shown in each group represent the mean ± SE of six to eight mice. The diameter in MMP-9KO mice increased significantly with macrophage infusion (*P < 0.01). (b) Gelatin zymography analysis of MMP activities expressed in WT peritoneal macrophages (lane 1) and aorta of MMP-9KO mouse infused with WT macrophages (lane 2). (c–e) Histologic analysis. Paraffin sections were stained for elastin fibers (Trichrome), and sections were photographed and shown with the lumen at the top. (c) The MMP-9KO mouse infused with MMP-9KO macrophages; (d) the MMP-9KO mouse infused with WT macrophages; (e) the MMP-2KO mouse infused with WT macrophages.