Prognostic Importance of Viability and A Study of A Second Set Allograft Valve: An Experimental Study

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Abstract
An experimental study of transplantation of first and second set aortic valve allografts in heterotopic infrarenal aortic position in inbred rats with varying histocompatibility is described. On the 20th and 50th postoperative days, there was deposition of donor-specific antibodies on the allograft endothelia of the weakly allogeneic, non-MHC group, as evidenced by immunofluorescence studies, whereas the nonviable grafts showed no identifiable antibodies on their endothelia. The endothelia were mostly lost at day 100; previous focal mononuclear cellular infiltrates disappeared. The ground substances, however, were maintained until the 250th day. In the nonviable allografts, the media was completely acellular on the 50th day with collagen disintegration and changes in ground substance on the 100th day. Loss of endothelia and replacement by fibrin deposits with transient focal cellular infiltrations were the most significant early microscopic findings. Acellularity, fibrous neointima, and leaflet thickening due to varying degrees of fibrosis with changes in ground substance and focal infiltrations of macrophages around degenerated collagenous matrix of aortic valve allografts are the significant late changes. The second set allograft valves showed no difference in the rate or type of healing, but early degeneration while the second set skin grafts underwent accelerated rejection, thus confirming prior sensitization. This finding confirms the weak antigenicity of cardiac valve allografts. Therefore, the use of cardiac valve allografts for secondary valve replacement might be favorable if properly used. Limitation of antigen incompatibility by considering at least the ABO matching and reduction of a recipient's immunological reactivity might be a proper step to achieve a longer survival of viable allografts.