Features of IgG subclass deposition in the biological component of epoxy-treated xenogenic bioprosthetic heart valves

Objective: to evaluate changes in the immunogenicity of epoxy-treated xenogeneic bioprosthetic heart valves (BHVs) during in vivo function by detecting human IgG antibodies in the biomaterial of explanted samples. Materials and methods. Fourteen BHVs explanted during repeat valve replacement were examined. Of these, three valves were removed at 1, 20, and 42 days after implantation, while 11 valves had functioned for periods ranging from 3 to 25 years. Histological sections were prepared from the valve leaflets and analyzed by immunohistochemistry using antibodies against human immunoglobulin G (IgG), as well as Russell–Movat pentachrome staining. Selected leaflet fragments were additionally examined by scanning electron microscopy. Results. BHVs removed due to early dysfunction after 1, 20, and 42 days of implantation showed no signs of biomaterial degeneration; however, small thrombi were detected on their leaflet surfaces. In contrast, valves that had functioned for 3 to 25 years exhibited clear features of structural degeneration of the biological tissue, including leaflet tears and extensive calcification. These BHVs were also characterized by moderate macrophage infiltration and a slight increase in pannus on the valve surface. Immunohistochemical staining of histological sections for human IgG revealed intense antibody deposition within the biomaterial of all examined BHVs, irrespective of implantation duration. Positive IgG staining was localized along the fibers of the xenogeneic tissue and was absent in recipient tissues, including thrombi and pannus. Conclusion. The biological component of BHVs retains its immunogenic properties even after long-term (up to 25 years) function in the recipient’s body.