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Figure 4 Double immunostaining of coronary plaque tissue from a 71-year-old woman with subacute unstable angina stained in sequence as in Figure 1. Immunohistochemical procedure for angiotensin I-converting enzyme (A: red color) and alpha-actin (B: brown color). Comparison of the two figures demonstrates that some actin-positive cells of the smooth muscle cell type are also angiotensin I-converting enzyme-positive.