ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL STUDIES ON MYOCARDIAL BIOPSIES FROM A PATIENT WITH EOSINOPHILIC ENDOMYOCARDITIS

Right ventricular endomyocardial biopsy specimens from a 13-year-old b oy with hypereosinophilia were studied by light and electron microscop y using the EG2 monoclonal antibody, which recognizes a common epitope of eosinophil cationic protein and eosinophil protein-X. Although the endocardial layer was of normal thickness, many eosinophils, mononucl ear cells, and free eosinophil granules were observed in the endocardi um and in the vicinity of degenerated myocardial cells. Under electron microscopy, many of the specific granules in and out of eosinophils h ad lost their crystalloid internae and displayed reversed density, and there were many degranulated eosinophils with reduced number of granu les. Immunohistochemically, large amounts of eosinophil cationic prote in and protein-X were observed within cardiocytes when many of them we re degenerated. Deposits of the proteins were also found in some small vessels. On electron microscopy, accumulations of gold particles, whi ch bind to eosinophil cationic protein and protein-X, were seen in ass ociation with specific granules and on the myofilaments in both degene rated and normal-appearing cardiocytes. The presence of eosinophil cat ionic proteins within cardiocytes may play an important role in the pa thogenesis of eosinophilic endomyocardial disease.