Coronary arteriosclerosis after T-cell-mediated injury in transplanted mouse hearts: role of interferon-gamma.

This study evaluated the contribution of acute parenchymal rejection and interferon (IFN)-gamma to the development of graft arterial disease (GAD) in totally allogeneic murine cardiac transplants. BALB/c (H-2d) hearts were transplanted into wild-type C57BL/6 (B6, H-2b) or B6 IFN-gamma-deficient (GKO) recipient mice. Assessing the role of acute parenchymal rejection in the GAD process involved two different immunosuppression protocols using anti-CD4 and -CD8 monoclonal antibodies (MAbs): virtually complete long-term immunosuppression (denoted as complete immunosuppression) was achieved by administering both MAbs 6, 3, and 1 day before transplantation and weekly thereafter; in contradistinction, a single, early, transient episode of rejection (transient rejection) was attained by administering MAbs beginning 4 days after transplant and then at weekly intervals. The extent and duration of T cell depletion under these two regimens were evaluated using flow cytometric analysis of peripheral blood lymphocytes. After a single injection of MAbs, peripheral blood CD4+ and CD8+ T cell depletion was approximately 98% at 1 week and approximately 88% at 2 weeks. After three injections (analogous to days 6, 3, and 1 before transplant), peripheral blood CD4+ and CD8+ T cell depletion was >98% at 2 weeks and approximately 87% at 4 weeks. Functioning cardiac allografts were removed at 8 and 12 weeks after transplant and analyzed by hematoxylin and eosin, elastic tissue, and immunohistochemical stains, and the severity of parenchymal rejection versus GAD was scored. With complete immunosuppression (antibody before and after transplant), BALB/c allografts showed little parenchymal rejection or GAD, suggesting that persistent depletion of T cells blocked subsequent development of GAD. However, even a single transient acute rejection episode allowed the subsequent development of GAD accompanied by augmented major histocompatibility complex (MHC) class II, VCAM-1, and ICAM-1 expression at 12 weeks; these allografts showed no residual CD4+ or CD8+ T cells. In comparison, allografts undergoing transient rejection in GKO recipients did not develop GAD, despite persistent macrophage and natural killer cell (NK) infiltrates comparable to those seen in wild-type recipients. Moreover, the arterioles of hearts transplanted into GKO recipients showed no or minimal increases in MHC class II, ICAM-1, and VCAM-1 relative to baseline expression. In conclusion, a single episode of allogeneic injury mediated by T cells suffices to evoke subsequent graft arteriosclerosis, even in the absence of additional T-cell-mediated injury, and the process appears to depend on IFN-gamma.