Histopathological parallels in infective endocarditis and degenerative defects of native heart valves and their bioprostheses

Abstract

Background. Detailed study of the histopathological events and mechanisms accompanying the infectious process in native heart valves and their biological prostheses is very important due to the variability of clinical manifestation of infective endocarditis (IE).Aim: To study cellular infiltration of aortic heart valves (AVs) and bioprosthetic heart valves (BPs) affected by infection, as well as to search for common patterns or differences of native and BPs characterized by degenerative changes in the leaflet apparatus.Material and Methods. We studied the leaflets of AVs affected IE (n = 10) or calcific aortic stenosis (CAS) (n = 11), as well as the leaflets of BPs affected by IE (n = 5) or structural valve degeneration (SVD) (n = 10) and removed from the mitral position during re-prosthetics surgery. Histological sections were prepared using a cryostat microtome. Cell typing was performed by staining with antibodies to the CD45, CD68 CD3, CD19, myeloperoxidase (MPO) and CD31 markers using immunohistochemical analysis. Bacteria were visualized by Gram staining of histological sections. The expression of MPO in the studied samples was determined by Western blotting.Results. Colonies of gram-positive cocci and gram-negative rod-shaped bacteria were registered into native AKs affected by IE. BPs affected by SVD are characterized by the presence of mixed colonies of gram-positive cocci and gram-negative rod-shaped bacteria. Immunophenotyping demonstrated leukocyte infiltration (CD45+) in all studied heart valves. AVs and BPs with infectious lesions and BPs affected by SVD were characterized by inflammatory infiltrates included macrophages (CD68+), neutrophils (MPO+) and single T-lymphocytes (CD3+). In calcified AVs, we found no neutrophils; the clusters of immune cells were represented by macrophages and single T-lymphocytes. In both groups of AVs, single cells positive for the vascular endothelial marker CD31 were noted in the fibrous layer. The highest expression of MPO was observed in AVs affected by IE in comparison to other studied valves.Conclusion. AVs affected by infection compared to native heart valves affected by CAS are characterized by aggressive infiltration by neutrophils. Neutrophils and bacterial agents were also detected in BPs regardless of the diagnosed IE. These results indicate the involvement of bacterial invasion in the development of SVD of the biological element of BPs and indicate the necessarily for a detailed study of this phenomenon.