Decreased fibrinolytic capacity has been sug-

Expansion of atherosclerotic abdominal aortic aneurysm (AAA) has been attributed to remodeling of the extracellular matrix by active proteolysis. We used in situ hybridization to analyze the expression of fibrinolytic genes in aneurysm wall from eight AAA patients. All specimens exhibited specific areas of inflammatory infiltrates with macrophagelike cells expressing urokinase-type plasminogen activator (u-PA) and tissue-type PA (t-PA) mRNA. Type 1 PA inhibitor (PAM-) mRNA was expressed at the base of the necrotic atheroma of all specimens and also within some of the inflammatory infiltrates where it frequently colocalized in regions contining u-PA and t-PA mRNA expressing cells.However, in these areas, the cellular distribution of the transcripts for t-PA and u-PA extended far beyond the areas of PAT-i expression. These observations suggest a local ongoing proteolytic process, one which is only partially counteracted by the more restricted expression of PAT-i mRNA. An abundance of capillaries was also obvious in all inflammatory infiltrates and may reflect local angiogenesis in response to active pericellular fibrinolysis. The increased fibrinolytic capacity in AAA wall may promote angiogenesis and contribute to local proteolytic degradation of the aortic wall leading to physical weakening and active expansion of the aneurysm. (J. Clin. Invest. 1995. 96:639-645.)

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