J Prop

AIRWAY PATHOLOGY IN THE TRANSPLANTED RAT LUNG

Bronchiolitis obliterans has emerged as the most significant long-term complication of human heart-lung transplantation. Possible causes include rejection, infection, altered bronchial circulation, and denervation. We attempted to assess the role of some of these possibilities by reviewing the airway histology in nonimmunosup-pressed orthotopic rat left lung allografts in three strain combinations: BN-to-LEW (major histocompatibility complex [MHC]-incompatible) n=27; (LEW × BN)Fi-to-LEW, n=11; and F344-to-LEW (minor loci-incompatible) n=18. Fifteen syngeneic transplants (LEW-to-LEW) served as controls. After assigning the lungs to a rejection phase (latent, vascular, alveolar, or destructive), the airway pathology was specifically examined. In the latent phase, only changes attributable to transplantation per se were identified. In the vascular phase in the BN-to-LEW rats and (LEW × BN)F1-to-LEW rats, the bronchioles were surrounded by dense cuffs of activated lymphocytes. The lymphocytic infiltrate then progressively involved the lamina propria and epithelium, where it became associated with focal epithelial cell necrosis. Eventually the epithelium became ulcerated (alveolar phase), and the submucosa and luminal surface became replaced by granulation tissue, which frequently protruded into the lumen in a bronchiolitis obliterans pattern. In the destructive phase the changes were similar to those in the alveolar phase, but were more severe. In the F344-to-LEW rats the airway changes were less prominent, although the remainder of the lungs was at comparable phases of rejection. These changes were not observed in the right (nontransplanted) lungs or the control (LEW-to-LEW) lungs. The findings in these animals suggest that the process of rejection affects the airways and may result in posttransplantation bronchiolitis obliterans.

Lung transplantation in the rat. III. Functional studies in iso- and allografts☆

Recently a microsurgical technique for orthotopic left lung transplantation in the rat was developed. The aim of this study was to investigate the influence of the operation itself and of an unmodified rejection reaction on the function of the transplanted rat lung. Orthotopic left lung transplantation was performed in 59 rats (34 isografts and 25 allografts). Isografts demonstrated a mean left lung perfusion of 23.1% in the first two postoperative weeks. Seven out of the 10 animals, subjected to a repeated scintigraphy 5-10 weeks later, had an increased graft perfusion, resulting in an almost normal mean left lung perfusion of 34.8%. At that time chest roentgenography revealed a good aeration of the grafts, that at autopsy had a normal aspect. Allografts showed an initial mean left lung perfusion (24.6%) similar to the isografts, which, however, declined sharply a few days later (4.3%). At that time chest roentgenography revealed totally opalescent grafts that at autopsy had the hepatized aspect characteristic of lung allograft rejection. These results of isogeneic and allogeneic lung transplantation in the rat were comparable with those of canine auto- and allotransplantation. For immunogenetic and economical reasons lung transplantation in the rat is a good alternative animal model in lung transplantation research.

Inadequate antibody response against respiratory viral infection in long-surviving rat lung allografts

Lung transplant recipients suffer from a high number of viral infections. It has been suggested that the defense against viral infections is impaired in lung transplants. Therefore, we investigated in rat lung transplants whether antibody responses against an intrapulmonary viral infection were impaired in 3 groups of rats with: (1) BN-to-LEW allogeneic lung transplants, (2) LEW-to-LEW syngeneic lung transplants, and (3) nontransplanted LEW lungs. All rats (including those with nontransplanted, normal lungs) were treated with cyclosporine on days 2 and 3 after operation; this treatment is adequate to induce permanent graft acceptance of the allografts. Six months after transplantation, viral infections with Sendai virus (parainfluenza type I) were induced intratracheally. At day 0, immediately before infection, and at days 4, 7, 21, and 56 after infection, 4 rats in each group were killed for histological evaluation of the lungs. The number of antibody-positive cells in the bronchus-associated lymphoid tissue (BALT) in the lungs and in the spleen, and presence of the virus in the lungs were determined by immunohistology. Serum antibody titers were followed for 56 days after infection. The allogeneically transplanted lungs failed to respond adequately against the virus: the number of antibody-positive cells in the BALT did not increase after infection, serum antibody titers were hardly detectable, and virus was present in the airways of the lungs up to day 21 after infection. In contrast, in the syngeneically and nontransplanted lungs, the number of antibody-forming cells in the BALT increased steeply until day 7, serum antibody titers rose until day 14, and virus could be detected only on day 4 after infection. This study shows that in rat lung allografts, both the local antibody production in the BALT and the systemic antibody response against a respiratory viral infection are inadequate. As a consequence, the virus is present longer in these allografted lungs and can exert its damaging effect over a longer period of time. These results may explain why lung transplants are so susceptible to viral infections.

Combined heart-lung transplantation in the rat: comparison of thoracic and abdominal operation techniques

Recently, we developed two techniques for the combined transplantation of heart and the left lung into the left hemithorax of rats. One technique, with two vessel anastomoses, comprised the microsurgical repair of aorta, anterior vena cava, and left main bronchus. With the other, single vessel technique, only the aorta and bronchus were anastomosed. In this study, we determined the function and histology of syngeneic and cy-closporine (CsA)-treated allogeneic grafts transplanted with both techniques, and compared the results with those of heterotopic heart-lung grafts transplanted with a. previously described technique for transplantation into the rats abdomen. The survival rate of rats operated with either of the thoracic transplantation techniques was high (83%). Lungs and hearts of the grafts functioned well for over two months and had normal morphology when the double vessel technique was used. With the single vessel technique, the function of the lungs started to deteriorate from the third postoperative week onward, probably secondary to congestion. The results of thoracic grafts were superior to those of abdominal transplants, where the nonventilated lungs–especially during immunosuppression–wesre frequently infected. We conclude that these new techniques for thoracic transplantation are most suitable for research of combined heart-lung transplantation.