Immune response to bovine pericardium implanted into α1,3-galactosyltransferase knockout mice: feasibility as an animal model for testing efficacy of anticalcification treatments of xenografts.

Objectives: Glutaraldehyde (GA)-fixed xenografts are prone to calcification after implantation in humans and there is evidence that immune reaction to the Galα1,3-Galβ1,4GlcNAc-R (α-Gal) antigen may play a part in this process. The objectives of this study were to evaluate the immune response of α1,3-galactosyltransferase knockout (α-Gal KO) mice to bovine pericardium and to evaluate the effect of various anticalcification treatments on bovine pericardium using mouse subcutaneous implantation model.
Methods: Bovine pericardial tissues were divided into eight groups according to the method of anticalcification treatments. Prepared tissues were subcutaneously implanted into the α-Gal KO and wild-type mice for 2 months, and anti-α-Gal antibodies were measured at 2 weeks and 2 months after implantation. Explanted tissues were examined by immunohistochemistry and calcium contents of the explanted tissues were measured.
Results: Titres of IgM and IgG antibodies in the α-Gal KO mice increased significantly according to the duration of implantation, whereas titres of IgM and IgG antibodies in the wild-type mice increased until 2 weeks after implantation without further increase thereafter. Titres of IgG antibodies measured at 2 months after implantation were significantly higher in the α-Gal KO mice than in the wild-type mice. Immunohistochemistry revealed macrophages surrounding the pericardial tissues irrespective of the mouse type into which the tissues implanted, whereas T-cells could only be observed in the tissues implanted into the α-Gal KO mice. Except the high-concentration GA-treated group, calcium contents of anticalcification-treated groups were all significantly lower or tended to be lower than that of the control group, irrespective of the mouse type. Calcium contents of the control group were significantly higher in the α-Gal KO mice than in the wild-type mice.
Conclusions: Bovine pericardium implanted into the α-Gal KO mice caused significant increase in anti-α-Gal antibodies, showed some histologic evidences of chronic rejection and revealed a potential toward more calcification. These findings suggest a possible role of immune response in calcification of xenografts. High-concentration GA fixation alone did not prove to be an effective anticalcification treatment in mouse subcutaneous implantation model. α-Gal KO mouse subcutaneous implantation model might be a feasible animal model for testing efficacy of anticalcification treatments incorporating immunologic approach.