Apoptosis in acute pulmonary allograft rejection and cytomegalovirus infection

Apoptosis is a form of programmed cell death, characterized by activation o f endonucleases that cleave DNA into oligonucleosomal fragments, which can be identified by in situ terminal deoxyribonucleotide transferase-mediated dUTP nick-end labeling (TUNEL). This process has recently been implicated i n cardiac and hepatic allograft rejection, and we investigated its contribu tion to acute pulmonary allograft rejection and cytomegalovirus (CMV) pneum onitis by in situ TUNEL of transbronchial biopsy specimens. In situ TUNEL w as performed on 70 transbronchial biopsy samples collected from 25 pulmonar y allograft recipients for diagnosis of acute rejection or CMV pneumonitis, and the number of apoptotic nuclei/mm(2) was correlated with the rejection grade (International Society of Heart and Lung Transplantation classificat ion). During acute pulmonary allograft rejection, apoptotic nuclei were dem onstrated in pulmonary parenchymal cells and mononuclear infiltrating cells , and the number of apoptotic cells was positively correlated with the reje ction grade. In addition, a marked increase in the density of apoptotic cel ls was found in pulmonary allografts with CMV pneumonitis. We conclude that apoptosis contributes to cell death during acute pulmonary allograft rejec tion and CMV infection.