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 collected from six heart transplant recipients for the diagnosis of acute rejection episodes, the presence of apoptosis in individual cells was investigated in tissue sections by in situ labeling of nuclear DNA breaks by nick end labeling with biotinylated poly deoxyuridin triphosphate 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 connective tissue cells of endomyocardial biopsy samples obtained from day 7 to day 146 after transplantation with a different prevalence according to the rejection grade (International Society for Heart and Lung Transplantation classification).

RESULTS

In all the rejection grade 3A (eight of eight), in half of the rejection grade 2 (four of eight), and in some rejection grade 1B (three of eight) cases, apoptotic myocytes were found within or in the neighborhood of the inflammatory areas. In the rejection grades 0 and 1A and in the "Quilty" effect zones, no apoptotic myocytes could be observed. Apoptotic endothelial and interstitial cells were observed in all the rejection grades but with a higher prevalence in rejection grades 2 and 3A.

CONCLUSIONS

During rejection episodes, apoptosis of myocytes is one of the mechanisms of immune-mediated death, and its investigation in tissue sections may represent a valuable tool for the diagnosis of myocyte damage.