The effect of allogeneic or xenogeneic immune responses and preservation techniques on transplanted aortic valve grafts.

We examined the effect of allogeneic and xenogeneic immune responses on the histopathological changes in aortic valve grafts and the influence of preservation techniques on these changes. Brown Norway rats and Syrian hamsters were used as allogeneic and concordant xenogeneic donors of aortic valve grafts, respectively. The allografts and xenografts were implanted heterotopically in the abdominal aorta of Lewis rat recipients immediately after harvest (homovital), after cryopreservation, or after preservation with antibiotics at 4 degrees C (fresh preservation). Allografts and xenografts were explanted at days 7, 28 or 56 and at days 3, 7 or 14, respectively, for the histopathological examination. The allografts underwent histological changes characteristic of graft arteriosclerosis. No significant effect of cryopreservation on these changes was observed. The fresh-preserved graft was, however, predisposed to focal destruction of the elastic fibers and to early disappearance of the leaflet. The lesions in xenografts were characterized by severe destruction of the elastic fibers. Compared to homovital xenografts, both cryopreserved and fresh-preserved xenografts showed more prominent disruption of the elastic fibers, well-developed valvular and vascular thrombi and earlier disappearance of the leaflet. In conclusion, it could be assumed that failure in retention of cellular and extracellular components during fresh preservation accelerates structural deterioration of allografts. As for xenografts, even the extracellular matrix may have potential xenogeneic immunogenicity. There is a possibility of these preservation techniques reducing xenogeneic immunogenicity of the endothelial cells, probably because of loss of these cells. However, it appears that, even in this setting, other cellular and extracellular components could trigger immune responses causing structural deterioration of xenografts.