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Figure 1 Double immunostaining of coronary plaque tissue from a 65-year-old man with subacute unstable angina. (A) Immunohistochemical staining (red reaction product) using anti–angiotensin I-converting enzyme antibodies and an immuno-alkaline phosphatase reaction that identifies as angiotension I-converting enzyme-positive cells the endothelium and numerous stromal cells, arranged in clusters or isolated in the stroma. (B) After removal of the red reaction product, the same area is stained in brown with an immunoperoxidase reaction revealing CD68-positive macrophages. Comparison of the two figures reveals also that some strongly angiotensin I-converting enzyme-positive cells do not correspond to macrophages.