Mechanism of calcification of porcine bioprosthetic aortic valve cusps: role of T-lymphocytes.

Calcification of glutaraldehyde-preserved porcine aortic valve bioprosthetic cusps limits their success as cardiac valve substitutes. Subcutaneous implants of porcine bioprostheses in rats and rabbits have provided a convenient experimental tool to study this calcification process. Previous clinical research has suggested that the host's immune response to the porcine xenograft tissue may contribute to the calcific degeneration. To investigate the possible contribution of the immune response, porcine bioprosthetic cusps implanted subcutaneously in congenitally athymic (nude) BALBc mice and normal controls were analyzed biochemically and histologically after retrieval at 21 days. Calcification was comparable in implants retrieved from athymic (calcium 95.5 +/- 24.5 micrograms/mg) and normal mice (calcium 102.3 +/- 4.66 micrograms/mg). Explants from nude mice demonstrated fewer adherent cells than those from normal animals, but the morphologic characteristics of the calcification were the same in both groups, with dystrophic mineralization of the spongiosa predominating. Thus, normal T-lymphocyte function is not necessary for porcine bioprosthetic calcification, and immunologic processes do not contribute to this process.