TNF-alpha is present in atherosclerotic lesions, activates endothelial adhesion molecule expression, stimulates the release of proinflammatory cytokines and matrix metalloproteinases and promotes smooth muscle cell proliferation and migration. Taken together these observations suggest that TNF-alpha may be functionally involved in early atherosclerosis development. To further evaluate this hypothesis we compared vascular TNF-alpha and TNF receptor expression in atherosclerosis-susceptible apoE-/-/LDL receptor-/- mice and control C57BL/6 mice. The aortas of 8 week old apoE-/-/LDLreceptor-/- mice displayed immunoreactivity for TNF-alpha as well as TNF p55 and p75 receptors (2.1 +/-1.6%, 5.6 +/- 1.5% and 3.6 +/- 1.3% of total media area, respectively), but did not have any detectable lesions. A marginal increase in TNF-alpha and TNF receptor immunoreactivity was observed at 12 weeks and atherosclerotic plaques were detected in 1 out of 5 animals. At 16 weeks TNF-alpha expression in the media was increased more than four-fold as compared with 8 week old mice, and atherosclerosis was widespread. TNF-alpha immunoreactivity was also observed in all plaques. In addition, at the same age a tendency towards increased TNF-alpha mRNA levels was detected in the double knockout mice compared to age-matched controls. A further increase in TNF-alpha and TNF receptor immunoreactivity as well as plaque size was observed at 20 weeks. With only a few exceptions, no TNF-alpha or TNF receptor immunoreactivity was detected in C57BL/6 control mice. These findings demonstrate that medial TNF-alpha and TNF receptor expression precedes lesion formation in apoE-/-/LDL receptor-/- mice.