Activation of the human terminal complement pathway in atherosclerosis

The presence of the terminal C5b-9 complement complex in tissues indicates that complement activation has occurred in situ with subsequent membrane damage, tissue injury, and inflammatory response mediation. The terminal C5b-9 neoantigens of the complement system, S protein, C3d, C3d, and apolipoprotein B deposits were localized in 20 aortic fibrous plaques, 12 aortic intimal thickenings, 8 aortic fatty streak intimae, 14 coronary fibrous plaques, 5 coronary intimal thickenings, and 8 femoral fibrous plaques, using an indirect and double-staining immunoperoxidase technique. The specific granular deposits were present from the early to the advanced stages of atherosclerosis in relation to the degree of fibrosis and necrosis. The different double-staining localization of C5b-9 and S protein may suggest local assembly of the complex as a consequence of complement activation and may sustain its role in the chronic progression of atherosclerosis.