Suppression of acute rejection prevents graft arteriosclerosis after allogeneic aorta transplantation in the rat.

Rat aortic allografts develop arteriosclerotic alterations in the vascular wall that are histologically similar to those observed in chronic rejecting vascular allografts. We used cyclosporine and rapamycin (RAPA) in two different rat strain aorta transplantation models to investigate the effect of immunosuppression on posttransplant graft arteriosclerosis. High dose CsA (25 mg/kg, 3 times/week) treatment significantly inhibited intimal proliferation in the "strong" WAG-BN model (P < 0.01) as well as in the "weak" BN-WAG combination (P < 0.001), compared with untreated allogeneic controls. In the latter combination, even fewer intimal lesions were present than in WAG autotransplants, suggesting that CsA may also inhibit the arteriosclerotic response to mechanical injury. RAPA (3 mg/kg, 3 times/week) was as effective as CsA in reducing intimal lesions (P < 0.01 and P < 0.001 in the BN-WAG and WAG-BN models, respectively). Low dose CsA (5 mg/kg, 3 times/week) was only partially effective in preventing intimal lesions. Histology of the nontreated allografts showed ongoing acute rejection in the adventitial layer. The degree of cellular infiltration correlated with the severity of arteriosclerotic lesions. High dose CsA and RAPA treatment prevented adventitial infiltration in both models, while low dose CsA was only moderately effective. In conclusion, in the present study, the degree of arteriosclerotic involvement after allogeneic aorta transplantation was related to the severity of cellular adventitial infiltration. The myointimal thickening was inhibited by effective immunosuppressive treatment. These observations may imply that chronic rejection develops after ineffective immunosuppression.