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Immunoglobulins and complement deposits in mitroflow pericardial bioprosthetic heart valves--a contributing factor to structural deterioration.

BACKGROUND AND AIMS OF THE STUDY
Twenty-two bovine pericardial Mitroflow prostheses were explanted after 73-114 months from either the aortic or mitral position because of clinical failure. All the samples exhibited cuspal tears and foldings. Eleven prostheses were calcified. The aim was to study biological factors involved in the structural deterioration.


METHODS
Histologic and biochemical assays were carried out on the deteriorated, non-calcified and on the calcified leaflets. Labelled antibodies and avidinbiotinyilated peroxydase complex were used to detect plasma proteins and cells in the cusps.


RESULTS
Fibrin covered the cuspal surface and accumulated in the deep disrupted layers (19/22). Scattered fibronectin filaments were seen across the transversal sections (20/22). IgG, complement fractions C1q, C3, C4 (20/22), macrophages (sixteen) and cells containing granulocyte elastase were revealed in the altered matrix. These plasma proteins and cells were detected in the disintegrated matrix of non-calcified and of calcified leaflets. IgA was present in amorphous cuspal thickenings with lipid infiltration (12/22). Western blot analysis of the PBS-2% SDS extracts from the leaflets indicated the breakdown of fibrinogen/fibrin, fibronectin and of complement proteins C3, C4 and C5.


CONCLUSIONS
The results suggest the activation of the complement by the non-hemocompatible, chemically processed bovine pericardium. The bioactive peptides generated in this process can stimulate monocyte migration, phagocytosis and exocytosis of proteases able to degrade the glutaraldehyde cross-linked macromolecular matrix. These biological factors can contribute, together with the mechanical stress, to the structural deterioration of the bioprosthesis.