Pre-transplant donor-specific transfusions induce allograft rejection and IL-2 gene expression in the WKY-->F344 functional tolerance model of rat lung transplantation.

Our previous studies have shown that a spontaneous functional tolerance develops in a rat model of lung transplantation (WKY-->F344). The tolerance observed in this model may be due to the minor histocompatible differences in this combination, however, the possibility of a tolerogenic effect related specifically to the lung allograft must be considered. To further examine this model, the effect of pre-transplant donor-specific spleen cell transfusions (DSTs) was examined on the functional tolerance state seen in this model. F344 rats received WKY spleen cells on days -45 and -30 before lung transplantations. Control F344 rats received lung transplants without DSTs. Recipients in both groups were killed on day 7, 14, 21 and 49 post-transplant, and allograft rejection (AR) was graded histologically (stage 0-IV). Intragraft cytokine gene transcripts were examined on day 7 and 14 post-transplant using reverse transcriptase-polymerase chain reaction (RT-PCR) techniques to investigate the underlying immunological events occurring in each group. In addition, allogeneic (WKY) and third party (BN) skin grafts were placed on lung recipients at day 35 post-transplant to evaluate the development of systemic tolerance. It was seen that control animals showed moderate to severe lymphocytic infiltrations (stage II-III AR) in the first 3 weeks followed by spontaneous recovery with stage I-II AR on day 49. In marked contrast, DST-treated animals showed more aggressive AR with severe lymphocytic infiltration and haemorrhagic infarction (stage III-IV AR) by day 14-21, without any evidence of recovery on day 49. WKY skin grafts showed prolonged survival in control animals, but were promptly rejected in DST-treated animals. Intragraft cytokine gene expression in control animals was characterized by no or weak expression of IL-2 and high IL-10, while DST-treated animals showed high levels of IL-2 transcripts. IL-2:IL-10 and IL-2:IL-4 ratios were significantly increased in DST-treated animals compared with controls on day 7 post-transplant. It was concluded that pre-transplant DSTs did not enhance allograft survival, but actually induced AR and ablated any immunological benefit of the lung allograft on induction of tolerance in the WKY-->F344 lung transplant model. It was found that the DST-induced AR was associated with a deviation of cytokine immune responses from a predominant Th2 to Th1 profile characterized by increased IL-2 gene expression in the allografts. We also conclude that factors other than the degree of histocompatibility matching, such as the route and timing of alloantigen exposure, and the amount or nature of alloantigens associated specifically with lung allografts, are involved in deviating native immune responses toward acceptance or rejection of lung allografts in this model of lung transplantation.

Perivascular delivery of a nitric oxide donor inhibits neointimal hyperplasia in vein grafts implanted in the arterial circulation.

OBJECTIVE: Nitric oxide has been reported to reduce intimal hyperplasia as a response to arterial injury. This study was designed to assess the possible effect of perivascular application of a nitric oxide donor on neointimal proliferation occurring in veins exposed to the dynamics of the arterial circulation in a hypercholesterolemic rabbit model. METHODS: Autologous jugular vein grafts were implanted in the carotid circulation of 20 hypercholesterolemic rabbits. A mixture of a biodegradable polymer and the nitric oxide donor, spermine/nitric oxide, which releases nitric oxide with a half-life of 39 minutes, was applied periadventitially at the time of implantation. Controls were veins bathed in saline solution, polymer alone, and polymer plus the carrier vehicle spermine without nitric oxide. Animals (n = 5 in each group) were put to death on day 28 for morphometric analysis, cell count, and immunohistochemical staining. RESULTS: Treatment with perivascular nitric oxide donor significantly decreased wall thickness (126 +/- 24 microm vs 208 +/- 45 microm, p = 0.0017) and area (124 +/- 22 microm2/microm vs 211 +/- 37 microm2/microm, p = 0.005). With the carrier vehicle spermine alone, there was a trend toward reduced intimal thickness, but the change was not statistically significant. In the grafts treated with nitric oxide donor, expression of insulin-like growth factor, fibroblast growth factor, thrombospondins, fibronectin, and tenascin was reduced. CONCLUSION: The periadventitial delivery of nitric oxide donor produces a reduction of neointimal hyperplasia in veins implanted in the arterial circulation. The mechanism of action is not entirely clear, but the reduction cannot be explained on the basis of decreased cell proliferation alone. Other possibilities are modulation of protein synthesis of vascular smooth muscle cells and production of extracellular matrix components.

Accumulation of platelets in rat syngeneic lung transplants: a potential factor responsible for preservation-reperfusion injury.

BACKGROUND: Platelets are known to play an important role in the pathogenesis of adult respiratory distress syndrome as well as preservation-reperfusion injury of liver allografts. However, the role of platelets in pulmonary preservation-reperfusion injury is unknown. In this study, we examined whether the extent of platelet accumulation in the preserved and subsequently reperfused lungs correlated with the degree of preservation-reperfusion injury in a rat lung isotransplant model. METHODS: Heart-lung blocks from donor rats were flushed with and preserved in modified Euro-Collins solution at 4 degrees C for 0 hr (n=5), 6 hr (n=6), and 24 hr (n=6). The left lung was divided from the heart-lung block, transplanted into the recipient rat, and reperfused for 1 hr. Lung injury was evaluated by the left-to-right pulmonary blood flow ratio, the weight gain of the isograft, and the scores for histological categories of lung injury (intra-alveolar edema, intra-alveolar hemorrhage, and capillary congestion). Small portions of the lung isograft were excised and stained with an antibody specific for rat platelets. A scoring system was developed to semiquantitate the intensity of antibody staining in isografts. RESULTS: Lung isografts were injured and platelets accumulated in the capillaries in proportion to the length of preservation endured before transplantation. The extent of platelet accumulation evaluated by our morphological scoring system correlated significantly with the degree of lung injury assessed by the blood flow ratio (P<0.001), the weight gain (P<0.001), and the histological scores for intra-alveolar hemorrhage (P<0.05) and for capillary congestion (P<0.001). CONCLUSIONS: The results of this study suggest that platelet accumulation is a potential factor responsible for preservation-reperfusion injury of lung isografts in the rat.