Enhancement of obliterative airway disease in rat tracheal allografts infected with recombinant rat cytomegalovirus.

Background: Cytomegalovirus infection has been identified as a significant risk factor for the development of obliterative bronchiolitis in human lung transplant recipients. This study was designed to assess the influence of rat cytomegalovirus (RCMV) on the pathogenesis and development of obliterative bronchiolitis in an experimental model of obliterative airway disease, which occurs after allogenic heterotopic tracheal transplantation in rodents.
Methods: Sixty Lewis rats were infected intraperitoneally with 10(7) plaque-forming units of recombinant lac-Z-tagged RCMV expressing the gene for beta-galactosidase. Rats were either infected at the time of surgery (acute infection, n = 30) or 56 days before surgery (chronic infection, n = 30). Tracheae from Brown Norway (allograft) or Lewis (isograft) rats were implanted and wrapped in the greater omentum of infected Lewis rats. RCMV infection was verified in different recipient tissues by in vitro plaque-assays and by direct in situ staining for beta-galactosidase activity. The tracheal grafts were harvested on days 7, 14, and 21 after transplantation and stained with hematoxylin-eosin and Masson's trichrome. The peritracheal cellular inflammation was scored visually. The cellular density of the infiltrating cells and the extent of airway obliteration were analyzed by use of computer-digitized morphometry and compared with uninfected allografts as control.
Results: Both acute and chronic cytomegalovirus infection produced significantly higher mononuclear cell density values on days 7 and 14 compared with noninfected controls, indicating a more intense immune response in the infected allografts. Tracheal allograft obliteration was also more extensive after acute and, in particular, after chronic cytomegalovirus infection (64% narrowing after 21 days compared with 36% in grafts from noninfected control animals).
Conclusions: Our experimental results provide direct evidence that the tracheal grafts were infected with RCMV and that the development of obliterative airway disease was enhanced in the acutely and chronically infected allografts compared with grafts from noninfected control animals.