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Background-Allograft coronary atherosclerosis (TxCAD) is the leading cause of death after the first year after transplantation. TxCAD is believed to be a form of chronic rejection of the cardiac allografts. This study was undertaken to determine whether TxCAD could develop in the absence of a cellular alloimmune response. Methods and Results-Inbred lean Zucker rats (Ͼ26 generations) served as donors and recipients of the cardiac grafts.Donor hearts were explanted at 60 or 90 days. Explanted hearts were processed for coronary artery histological analysis. Cytokine expression was determined by reverse transcription-polymerase chain reaction, and the presence of T cells within the explanted hearts was evaluated by immunohistochemistry. Forty-six transplantations were made, and TxCAD developed in all but one of the transplanted hearts. Overall, one third of the vessels examined were affected by TxCAD, and in roughly half of these vessels, the disease was severe. Native hearts were free of atherosclerosis. Interleukin-2 was absent from the transplanted hearts, and T cells were present in minimal amounts (Ͻ1 per low-power field). Conclusions-TxCAD developed in the absence of a cellular alloimmune response in these genetically similar donors and recipients. The observed TxCAD was significant and comparable to what is found in rat allografting models.

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