Immunological aspects of fresh and cryopreserved aortic valve transplantation in rats

Background. The influence of immune activation on valve allograft degenerat ion remains unclear. We studied the combined effect of major histocompatibi lity complex (MHC)-incompatibility and cryopreservation on valve performanc e, histomorphology, and tissue antigenicity in rats. Methods. Fresh or cryopreserved allogeneic aortic valves from WAG (RT1(u)) rats were transplanted to DA (RT1(a)) recipients and syngenic transplants s erved as controls. After 7 or 21 days, valves were examined for competence and morphology. Immune reactivity of the recipient was measured by concanav alin A (conA) stimulation and analysis of donor-reactive Helper T-lymphocyt e frequencies (HTLf) in peripheral blood and spleen. Results. Syngenic grafts demonstrated normal competence and structure. Allo grafts lost their competence over time caused by destruction of the leaflet s combined with cellular infiltration in the vascular wall. Cryopreservatio n induces early loss of competence and retrovalvular thrombosis. Cryopreser ved allografts were also heavily infiltrated. ConA stimulation indices and HTLf were higher in allogeneic recipients compared to syngenic recipients ( p < 0.03). Cryopreserved allografts elicited a lower immune response compar ed with fresh allografts (p < 0.03). Conclusions. Aortic valve allografts are able to induce a donor-reactive im mune response that is related to early graft destruction and incompetence. Cryopreservation appears to diminish but not eliminate the antigenicity of the allograft. (C) 2001 by The Society of Thoracic Surgeons.