The study investigates the presence and function of myeloperoxidase, a heme protein secreted by activated macrophages, in human atherosclerotic lesions. Myeloperoxidase is known to generate reactive intermediates that oxidize lipoproteins in vitro. The researchers used a rabbit polyclonal antibody to detect myeloperoxidase in surgically excised human vascular tissue. Western blotting and immunocytochemistry revealed the presence of a 56-kD protein in detergent extracts of atherosclerotic arteries, which comigrated with authentic myeloperoxidase. This protein bound to a lectin-affinity column and eluted with methyl mannoside, indicating its identity as myeloperoxidase. Enzymatic activity in detergent extracts of atherosclerotic lesions was confirmed by peroxidase activity and the generation of hypochlorous acid (HOCl), a cytotoxic oxidant. Immunostaining of atherosclerotic tissue sections showed intense staining in macrophage-rich regions, particularly adjacent to cholesterol clefts in lipid-rich lesions. These findings suggest that myeloperoxidase is a component of human vascular lesions and may contribute to atherogenesis by catalyzing oxidative reactions in the vascular wall.The study investigates the presence and function of myeloperoxidase, a heme protein secreted by activated macrophages, in human atherosclerotic lesions. Myeloperoxidase is known to generate reactive intermediates that oxidize lipoproteins in vitro. The researchers used a rabbit polyclonal antibody to detect myeloperoxidase in surgically excised human vascular tissue. Western blotting and immunocytochemistry revealed the presence of a 56-kD protein in detergent extracts of atherosclerotic arteries, which comigrated with authentic myeloperoxidase. This protein bound to a lectin-affinity column and eluted with methyl mannoside, indicating its identity as myeloperoxidase. Enzymatic activity in detergent extracts of atherosclerotic lesions was confirmed by peroxidase activity and the generation of hypochlorous acid (HOCl), a cytotoxic oxidant. Immunostaining of atherosclerotic tissue sections showed intense staining in macrophage-rich regions, particularly adjacent to cholesterol clefts in lipid-rich lesions. These findings suggest that myeloperoxidase is a component of human vascular lesions and may contribute to atherogenesis by catalyzing oxidative reactions in the vascular wall.