IDENTIFICATION OF PROGRAMMED CELL-DEATH (APOPTOSIS) IN-SITU BY MEANS OF SPECIFIC LABELING OF NUCLEAR-DNA FRAGMENTS IN HEART BIOPSY SAMPLES DURING ACUTE REJECTION EPISODES

Background and Methods: In sixty-three endomyocardial biopsy samples c ollected from six heart transplant recipients for the diagnosis of acu te rejection episodes, the presence of apoptosis in individual cells w as investigated in tissue sections by in situ labeling of nuclear DNA breaks by nick end labeling with biotinylated poly deoxyuridin triphos phate introduced by terminal deoxynucleotidyl transferase and alkaline phosphatase-conjugated streptavidin. In the samples collected at the moment of transplantation, no apoptotic cells were observed. Apoptotic nuclei were found in the myocytes and capillary endothelial and conne ctive tissue cells of endomyocardial biopsy samples obtained from day 7 to day 146 after transplantation with a different prevalence accordi ng to the rejection grade (International Society for Heart and Lune Tr ansplantation classification). Results: In all the rejection grade 3A (eight of eight). in half of the rejection grade 2 (four of eight), an d in some rejection grade 1B (three of eight) cases, apoptotic myocyte s were found within or in the neighborhood of the inflammatory areas. In the rejection grades 0 and 1A and in the ''Quilty'' effect zones, n o apoptotic myocytes could be observed. Apoptotic endothelial and inte rstitial cells were observed in all the rejection grades but with a hi gher prevalence in rejection grades 2 and 3A. Conclusions: During reje ction episodes, apoptosis of myocytes is one of the mechanisms of immu ne-mediated death, and its investigation in tissue sections may repres ent a valuable tool for the diagnosis of myocyte damage.