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-1beta (IL-1beta) 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-1beta was observed between the S, M, and L groups. Immunlohistochemical 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.