Background: Obliterative bronchiolitis (OB) is the principal long-term complication of lung and heart-lung transplantation. OB is characterized histologically by inflammation, epithelial cell loss, fibrosis, and obliteration of the terminal airways. The contribution of apoptosis and peroxynitrite formation in OB was examined and assessed whether immunohistochemical markers of these reactions in transbronchial biopsy specimens were predictive of OB development.
Methods: Pulmonary tissue samples from lung transplant recipients with OB (n = 5) or without OB (control group; n = 7) were investigated by in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) and nitrotyrosine immunohistochemistry. Furthermore, TUNEL and nitrotyrosine expression was compared between matched transbronchial biopsy specimens from the two patient groups.
Results: Sections with active OB displayed a significantly increased number of TUNEL-positive epithelial cells and macrophages compared with very little TUNEL in control specimens. TUNEL was almost absent in inactive OB. Nitrotyrosine was detected in all samples of pulmonary tissue, but nitrotyrosine expression was more intense in patients with active OB. There was no apparent temporospatial correlation of TUNEL and nitrotyrosine expression, and in matched transbronchial specimens, these immunohistochemical markers failed to identify patients with imminent risk of developing OB.
Conclusions: Apoptosis contributes to the pathophysiology of active OB but is apparently not directly paralleled by tissue peroxynitrite formation. In transbronchial biopsy specimens, markers of apoptosis and peroxynitrite formation are not valid predictors of OB and more studies are required to deliniate the role of these mechanisms in pulmonary allograft rejection.