Protein S and SR-A immunoreactivity of human atherosclerotic and nonatherosclerotic arteries. Human aorta, and carotid and coronary arteries were fixed in formalin and embedded in paraffin. Immunostaining was performed using the antihuman protein S antibody (1:200), antihuman SR-A antibody (1:100), biotinylated secondary antibody, and avidin-biotin reaction using peroxidase enzyme. Brown color represents positive staining of protein S or SR-A. (A) Protein S immunoreactivity in human aorta, and carotid and coronary arteries. Nonimmune rabbit IgG was used as negative controls. (B) Soluble protein S blocked immunostaining with anti–protein S antibody in human aorta. Anti–protein S antibody was preincubated with soluble protein S before adding to the slides. (C) Localization of protein S and SR-A immunoreactivity in serial sections of human aorta and carotid artery (magnification ×400). (i) Protein S immunostaining (positive area) for an atherosclerotic region of human aorta. (ii) SR-A immunostaining (negative area) for an atherosclerotic region of human aorta. (iii) Protein S immunostaining (negative area) for an atherosclerotic region of human carotid artery. (iv) SR-A immunostaining (positive area) for an atherosclerotic region of human carotid artery. Red arrows indicate positive staining.