In situ characterization of the foam cells in early human atherosclerotic lesions.

Erythrocytes (E) sensitized with IgG antibodies bound to the fatty streaks in cryostat sections of early human atherosclerotic lesions. E sensitized with IgA or IgM antibodies of F(ab') 2 fragments of IgG did not bind. The binding was inhibited by intact IgG and by Fc fragments but not by F (ab')2 fragments or by albumin, indicating the presence of receptors for the Fc part of IgG (FcR). E sensitized with IgM antibodies and human complement did not bind. The FcR were also studied using soluble immune complexes of horseradish peroxidase (HRP) and rabbit IgG antibodies to HRP. The peroxidase activity was detected histochemically. The bound complexes were localized to most of the lipid cells (foam cells) in the lesions. The cytoplasm of the FcR positive foam cells stained diffusely for acid alpha- naphthyl acetate esterase. Most of the foam cells were stained with monoclonal antibodies against HLA-DR antigens. The data indicate that most foam cells in early atherosclerotic lesions are derived from monocytes.