Enhanced Tumor Necrosis Factor‐α Expression in Small Sized Abdominal Aortic Aneurysms

Circulating levels of tumor necrosis factor alpha (TNF- alpha) are elevated in the patients with abdominal aortic aneurysm (AAA). We investigated TNF- alpha expression and cellular infiltration in the walls of AAAs of different sizes. Twenty-seven surgical specimens of AAAs were categorized according to the maximum aneurysm diameter into a small size group (less than 50 mm in diameter, n = 8; S group), a medium-sized group (50 to 59 mm in diameter, n = 11; M group), and a large size group (larger than 59 mm in diameter, n = 8; L group). The level of TNF- alpha and interleukin-1 beta(IL-1 beta) in the aneurysm wall was measured by ELISA. Immunohistochemical staining was performed to observe the TNF- alpha expression and the infiltration of macrophages and lymphocytes in aneurysm walls. Enzyme-linked immunosorbent assay showed that the level of TNF- alpha in the S group (5.47 +/- 3.48 pg/mg protein) was significantly higher ( p < 0.05) than that in the M group (2.70 +/- 1.33 pg/mg protein) or the L group (1.82 +/- 1.21 pg/mg protein). No significant difference in IL-1 beta was observed between the S, M, and L groups. Immunohistochemical analysis also showed that TNF- alpha was expressed strongly in the S group but was negative or weakly positive in the M and L groups. Furthermore, the expression of TNF- alpha was seen mainly where the aneurysm wall showed atheromatous change and macrophage infiltration. These results indicated that the expression of TNF- alpha in the aneurysm wall was enhanced in small AAAs, and this enhancement might be related to the infiltration of macrophages.