Clopidogrel reduces the development of transplant arteriosclerosis.

BACKGROUND: Transplant arteriosclerosis, the hallmark feature of chronic rejection, is still the major limiting factor for the long-term success of heart transplantation. Platelets have been implicated to play a role in the pathogenesis of this disease. Therefore the aim of this study was to investigate whether platelet inhibition alone has a positive effect on the development of transplant arteriosclerosis. METHODS: Fully major histocompatibility complex-mismatched C57BL/6 (H2(b)) donor aortas were transplanted into CBA (H2(k)) recipients, and mice received different doses (1, 10, and 20 mg/kg) of clopidogrel or control saline as a daily intraperitoneal injection for 30 days. Blood was analyzed on days 2, 7, 14, and 30 by using a platelet aggregation test (adenosine diphosphate) for effectiveness of the treatment. Grafts were analyzed by means of histology and morphometry on day 30 after transplantation. RESULTS: When mice were treated daily with 1 mg/kg clopidogrel in the absence of any other immunosuppression, transplant arteriosclerosis was significantly reduced compared with that seen in saline-treated control animals (intimal proliferation of 66% +/- 9% [1 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 7, P < or = .03). Daily application of 10 mg/kg and 20 mg/kg clopidogrel also significantly reduced the development of transplant arteriosclerosis compared with that seen in control animals (intimal proliferation of 61% +/- 11% [10 mg/kg clopidogrel] vs 54% +/- 10% [20 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 8, P < or = .003). There was, however, no additional beneficial effect when compared with mice treated with 1 mg/kg clopidogrel (P = .06). Isografts did not show any signs of vascular lesions on day 30 after transplantation. CONCLUSION: These results demonstrate that monotherapy with clopidogrel can effectively reduce the formation of transplant arteriosclerosis in a murine aortic allograft model.

Mouse endothelial CD40 expression does not play a role during the development of transplant arteriosclerosis.

Endothelial cells (ECs) are of major interest in allograft rejection. The authors and others have recently shown in different mouse allograft models that, during the development of transplant arteriosclerosis, donor ECs are replaced by recipient ECs. It was the aim of this study to characterize the phenotype of ECs during the development of transplant arteriosclerosis further, with particular interest in their capability to express CD40. Abdominal aortic allografts were transplanted across a full major histocompatibility complex (MHC) barrier using BALB/c (H-2d) mice as donors and C57BL/6 (H-2b) mice as transplant recipients. Aortic allografts were harvested on days 7 and 30 after transplantation and analyzed by double-immunohistochemistry for expression of CD40 and CD31. As the authors have previously shown that ECs in the aortic allograft model are of donor origin on day 7 after transplantation, whereas by day 30 donor ECs have been replaced by ECs of recipient origin, these two time points were chosen for analysis of CD40 expression. Double-immunohistochemistry for CD40 and CD31 revealed no endothelial expression of CD40 at either time point. These initial results obtained with the anti-CD40 monoclonal antibody (mAb) (clone 3/23) were confirmed by two further experiments using two different anti-CD40 mAbs (clone HM40-3 and clone 1/10) that bind to epitopes of the CD40 receptor distinct to that of 3/23. Neither mAb revealed endothelial expression of CD40. Further analysis of the composition of the cellular infiltrate demonstrated that the majority of macrophages were CD40 positive. The data indicate that in this mouse model of aortic transplantation, neither recipient- nor donor-derived ECs express CD40 during the development of transplant arteriosclerosis. Therefore, in contrast to rat or human ECs, CD40 expression by mouse ECs does not seem to play a major role in this form of allograft rejection.