Triple drug immunosuppression significantly reduces aortic allograft arteriosclerosis in the rat

We evaluated the effect of triple drug immunosuppression (cyclosporine A 10 mg . kg(-1). d(-1), methylprednisolone 0.5 mg . k(-1). d(-1), and azathioprine 2 mg . kg(-1). d(-1)) on the development of allograft arteriosclerosis (chronic rejection). The recipients of rat aortic allografts from the DA (AG-B4, RT1(a)) to the WF (AG-BZ, RT1(u)) strain were either treated with triple drug immunosuppression (n=23) or left untreated (n=23) and used as controls. The grafts were removed 7, 14, 30, 90, and 180 days after transplantation, and vascular wall changes were evaluated by quantitative histology, [H-3]thymidine autoradiography, and immunohistochemistry. Nonimmunosuppressed aortic allografts developed progressive arteriosclerotic alterations 1 to 6 months after transplantation that were virtually identical to those observed during chronic rejection in human cardiac allografts. Linear regression analysis revealed that triple drug immunosuppression with clinically relevant dosages of drugs significantly reduced intimal thickening (r=.69 versus r=.88, P<.05). Concomitantly, there was a marked reduction in the number of inflammatory cells (P<.01) and their rate of proliferation (P<.025) in the allograft adventitia during the period of acute inflammation (30 days after transplantation). Immunohistochemistry revealed that the number of helper T cells (W3/25) and monocyte/macrophages (OX42) but not cytotoxic T cells (OX8) or natural killer cells (3.2.3) was significantly (P<.05) reduced. The number of adventitial cells expressing interleukin-2 receptor (CD25) (P<.05), MHC class II (OX6) (P<.05), and leukocyte function-associated antigen-1 alpha-chain (CD11a) (P<.025) was also significantly reduced at 30 days. Triple drug immunosuppression downregulated the induction of MHC class II and intercellular adhesion molecule-1 on the graft endothelium but had no significant effect on the number of subendothelial inflammatory cells. In addition, [H-3]thymidine autoradiography demonstrated that triple drug immunosuppression significantly reduced the rate of cell proliferation in the media, composed of smooth muscle cells, 30 and 90 days after transplantation. Thus, triple drug immunosuppression efficiently reduced the development of allograft arteriosclerosis by downregulating the inflammatory response and the level of immune activation in the allograft adventitia during the acute rejection period, resulting in diminished intimal thickening of the graft in the long run. These results support the concept that allograft arteriosclerosis is due to or al least initialed by immune injury of the graft.