Quantitative evaluation of the terminal C5b-9 complement complex by ELISA in human atherosclerotic arteries

A quantitative ELISA using monoclonal and polyclonal antibodies against neoantigens of the terminal C5b-9 complement complex was used to evaluate the presence of terminal complexes in 68 human arterial samples with or without atherosclerotic involvement. Plasma levels of SC5b-9 were directly compared with the corresponding levels eluted from the femoral arteries in six patients undergoing surgical procedures. The plasma concentration of SC5b-9 in these donors was in the range of 30-90 arbitrary units (AU)/ml, equivalent to 100-300 ng/ml SC5b-9 or 45-130 AU/100 mg plasma protein. All the arterial samples contained detectable amounts of C5b-9. The aortic normal and fatty streaks intimae presented a minimum mean value of 65 +/- 12 AU/100 mg total protein, in the range of normal plasma SC5b-9 levels. The corresponding media contained significantly higher amounts of terminal complexes (115 +/- 30 AU/100 mg protein). Markedly increased levels of C5b-9 were eluted from aortic intimal thickenings (350 +/- 100 AU/100 mg protein) and the corresponding media (300 +/- 53 AU/100 mg protein). Similar concentrations were found in aortic fibrous plaques (340 +/- 80 AU/100 mg protein). The observed correlation between C5b-9 levels and atherosclerotic alterations in arterial walls is suggestive of chronic complement activation with involvement of the terminal complement sequence at these sites. These processes may contribute to progression of the arteriosclerotic lesions.