PURPOSE: Accumulation of oxidized LDL in the arterial wall is believed to play a key role in the development of atherosclerosis. Experimental studies have identified the presence of immune responses against epitopes in oxidized LDL that protects against atherosclerosis. We have produced human recombinant IgG against one of these epitopes (aldehyde-modified apoB-100 amino acids 661-680) and demonstrated that treatment with this human IgG1 2D03 antibody markedly reduces atherosclerosis in hypercholesterolemic mice. METHODS: In the present study, we screened a panel of 25 carotid plaques associated with clinical symptoms and 26 clinically silent plaques obtained at surgery for presence of the aldehyde-modified apoB-100 peptide defined by the 2D03 antibody and compared the expression of this epitope with other plaque constituents, plasma lipoproteins levels, plasma oxidized LDL and autoantibodies against apoB-100 peptides. RESULTS: We demonstrated that the epitope is commonly expressed in human atherosclerotic plaques and that plaques associated with clinical symptoms have an almost three-fold higher content of this epitope (8.6+/-4.9% versus 22.1+/-12.2% immunostaining of total plaque area, p