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Fresh heart valve allografts were preserved at 4°C for 14 days, cryopreserved and stored for 63 days, and studied for endothelial viability and antigenicity, in order to obtain some information on the immunobiological status of allografts before transplantation. The surgical technique described by Ross for subcoronary position is preferred and briefly outlined. Four explanted incompatible allografts were studied by light and scanning electron microscopy and immunohistochemistry to assess the immunological reactions and tissue changes that occurred between 9 days and 16 weeks post‐operatively. Valve leaflet motion and opening velocities were studied by echocardiography post‐operatively to establish a baseline with which to distinguish early leaflet degeneration. Distensibility of the aortic annulus was studied postoperatively by supraaortic angiography to justify one of the goals of reconstruction of the aortic root with allografts. Antibiotic preserved allografts at 4°C showed no viable endothelial cells after 8 days while the cryopreserved allografts demonstrated a high rate of viable endothelial cells capable of expressing surface antigens (HLA class I and II). Although the valve explants showed focal mono‐nuclear cell infiltrations with T‐lymphocytes, the allografts healed in place. The “classic” findings of rejection could not therefore be demonstrated. In summary, cryopreserved valve allografts, like the fresh, are antigenic. It is therefore recommended to use compatible valve grafts, when possible, which might be a positive step to improve the functional longevity of valve allografts. Immune response after valve allograft transplantation does not cause acute valvular dysfunction but rather chronic tissue changes which might lead to early degeneration of the allograft. The opening velocities ol preserved aortic and pulmonary allografts were normal at 3–4 years postoperatively irrespective of histocompatibility. Echo‐cardiography might be a useful tool to detect early degenerative changes ofincompatible valve leaflets. The aortic root is distensible after allograft transplantation.

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Nowadays the acute and especially chronic lung rejection are the major problems after lung transplantation (L-Tx) with relevant influence on longterm survival. We performed lung transplantation in rats to study a possible role of ultrastructural lesions in the graft during the acute rejection process, concerning their reversibility/irreversibility and influence of the chronic rejection. Based on histologic and immunohistologic studies after L-Tx in MHC-different and strong reactive rat strain combination AVN-LEW and filial generation (AVN-LEW)F1-LEW (n = 57 and n = 32) electronmicroscopic studies (TEM, SEM) were performed in the combination AVN-LW (n = 20) on postoperative day 0, 1, 2 and 5, all without immunsuppressive therapy. Syngenic grafts (LEW-LEW; n = 12) served as controls. Histologically the allografts were classed according to the proven acute rejection phases latent, vascular, alveolar and destructive. The immunhistological and electronmicroscopic results correlated with these rejection phases. There was no difference between the rat strain combinations. All allografts developed acute rejection on postoperative day 2 and were destroyed on postoperative day 5/6. Initially T-helper-cells, later cytotoxic-T-cells and macrophages played the predominent role in the acute rejection process. In the ultrastructural specimens alterations of the blood vessels, pneumocytes type-II, and surfactant gave more information. Initially flattening of endothelial cells and circumscribed lesions of graft vessels occur, increasing in the allografts up to extensive vascular wall destructions, accompanied by total thrombotic occlusion. Disturbances of surfactant production observed in the grafts of all strain combinations are not homogenous.(ABSTRACT TRUNCATED AT 250 WORDS)

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