Demonstration of contractile protein in endothelium and cells of the heart valves, endocardium, intima, arteriosclerotic plaques, and Aschoff bodies of rheumatic heart disease.

were obtained at autopsy of a 7-year- old boy who died of leukemia and a 60-year-old woman who died with diabetes mellitus and coronary atherosclerosis; blocks of aorta were obtained from the latter patient. The fluoresceinated antiserums to human uterine, cardiac, or skeletal muscle were also tested with samples obtained either at necropsy or biopsy, of normal-appearing liver, heart, skeletal muscle, kidney, salivary gland, mammary tissue, and skin, with a pilonidal sinus abscess, and with aspirated samples of bone marrow. with blocked by prior exposure of the tissue to nonfluoresceinated antiserum to cardiac actomyosin or myosin, respectively. It could not be inhibited by prior absorption of F-ACAM or F-ACM with uterine actomyosin or myosin, or blocked by prior exposure of the tissue to nonfluoresceinated antiserums to uterine actomyosin or myosin. These observations demonstrate that cells and cell fragments in atrial myocardial Aschoff bodies contain actomyosin antigenically similar to that of striated cardiac muscle. The intensity of immunofluorescent staining of cells and cell fragments in myocardial Aschoff bodies by F-ACAM or F-ACM varied considerably, indicating that some cells in myocardial Aschoff bodies contained more cardiac actomyosin than others.