Differences in xenoreactive immune response and patterns of calcification of porcine and bovine tissues in α-Gal knock-out and wild-type mouse implantation models.

Abstract

Although bioprostheses are widely used in cardiovascular surgery, their durability is limited due to degeneration. Degeneration of bioprostheses limiting its clinical use results from multiple factors, and immune reaction has been considered to be one of the most important factors. The study objectives were to compare the mechanical characteristic differences of porcine and bovine prostheses, assess the differences in immune reaction among different species and tissues as well as elucidate bioprosthetic failure patterns in α-Gal knock-out (KO) and wild-type mouse implantation models. Six groups of different xenogeneic tissues (porcine pericardium, aortic valve, aortic wall; bovine pericardium, aortic valve and aortic wall) were implanted into the subcutaneous tissue of the wild-type mouse (n = 4) and the KO mouse (n = 4) (four xenogeneic tissue segments per each mouse). Mechanical and chemical tests, including tensile strength measurement and thermal stability test for pericardial tissues and pronase test for different xenogeneic tissues, were performed before implantation. Anti-α-Gal antibody titres (IgM and IgG antibodies) were measured using serum enzyme-linked immunosorbent assay analyses before implantation and 30, 60 and 90 days after implantation. Implanted tissues were harvested after 90 days and studied for histopathology and quantification of calcification. There were no significant differences in tensile strength and shrinkage temperature between the porcine and bovine pericardia, although the bovine pericardia showed a greater elasticity than the porcine pericardia (elongation at tensile strength, 74.8 ± 4.5% vs 50.0 ± 8.7%, P < 0.001). Resistance towards pronase degradation was not different among the groups of tissues (Groups 1-6, 89.1 ± 7.6, 95.1 ± 1.8, 90.3 ± 5.3, 93.7 ± 3.3, 89.1 ± 2.4 and 89.1 ± 3.0%, respectively; P = 0.061). The IgM titres of the α-Gal KO mice were significantly higher at 30 days after implantation (0.71 ± 0.27 vs 1.07 ± 0.48, P = 0.004), whereas the IgG titres of the α-Gal KO mice remained higher until 60 days after implantation (at 30 days, 0.81 ± 0.07 vs 1.28 ± 0.79, P = 0.017; at 60 days, 0.54 ± 0.16 vs 1.43 ± 1.10, P = 0.045) than those of the wild-type mice. Calcium levels of tissues implanted into the α-Gal KO mice were significantly higher than those implanted into the wild-type mice regardless of tissue type (from Groups 1-6, 4.72 ± 1.75 vs 27.76 ± 22.73 μg/mg; 3.05 ± 1.04 vs 15.90 ± 6.98 μg/mg; 2.13 ± 1.48 vs 29.76 ± 30.71 μg/mg; 1.02 ± 0.53 vs 5.97 ± 1.40 μg/mg; 3.18 ± 3.41 vs 30.55 ± 66.69 μg/mg; 6.21 ± 5.56 vs 21.65 ± 17.77 μg/mg, all P ≤ 0.002). Chronic immune response to the α-Gal antigen may cause more severe tissue calcification in α-Gal KO mice. Removal of α-Gal antigenicity is strongly advised in xenogeneic bioprosthetic tissue implantation.