Contribution of IFN-γ to acute allograft failure in murine cardiac transplants: Role in vascular thrombosis

Abstract

390 We investigated the role of IFN-γ in acute cardiac allograft failure using IFN-γ deficient (GKO) mice. Without immunosuppression, BALB/c[H-2d] into wild type C57BL/6 [B6, H-2b] total allogeneic mismatched cardiac grafts ceased beating at 7.2 ± 0.2 days (n=9); BALB/c hearts transplanted into B6GKO ceased beating at 6.6 ± 0.1 days(n=6). Although grafts in both wild type and GKO recipients showed comparably severe mononuclear cell infiltration (rejection), allografts in GKO recipients also showed profound acute coagulation necrosis with vascular thrombosis demonstrable by fibrin staining. By immunohistochemical staining, plasminogen activator inhibitor-1 (PAI-1) was strikingly increased in allografts transplanted into B6GKO hosts relative to B6 wild types; no difference was seen in tissue plasminogen activator staining for allografts in wild type vs GKO hosts. Without immunosuppression, MHC I-mismatched allografts, characterized by a predominant CD8 T cell response (bml into B6), functioned for at least 12 weeks (n=10) and showed only moderate acute rejection. In contrast, bml into B6GKO allografts ceased beating at 7.7 ± 0.7 days(n=7), and showed rejection with coagulative necrosis and vascular thrombosis. Without immunosuppresiosion, MHC II-mismatched allografts, characterized by a predominant CD4 T cell response (bml2 into B6), ceased beating at 31.5± 6.2 days (n=6), and showed severe rejection. In contrast, bml 2 into B6GKO allografts functioned for at least 12 weeks and showed only moderate rejection without coagulative necrosis or vascular thrombosis. To specifically evaluate the role of T cell subpopulations, CD4 and/or CD8 T cells were selectively depleted in recipients by appropriate mAb administration pre-transplant, as shown below. Graft survival times were: BALB/c into B6(anti-CD4): 38.3 ± 6.7 days (n=3), BALB/c into B6GKO (anti-CD4): 10.7± 5.0 days (n=3), BALB/c into B6 (anti-CD8): 12.0 ± 2.3 days(n=5), BALB/c into B6GKO (anti-CD8): 14.3 ± 1.5 days (n=3), BALB/c into B6 (anti-CD4 and CD8): 31.7 ± 3.2 days (n=9), BALB/c into B6GKO(anti-CD4 and CD8): 38.2 ± 7.3 days (n=5). All grafts in the above demonstrated comparably severe rejection; notably, coagulative necrosis and thrombosis were not seen. The results suggest that acute cardiac allograft failure, particularly in GKO, may include a component of vascular thrombosis due to increased PAI-1 activity. Increased thrombosis is particularly evident in the setting of MHC I mismatches, but cannot be wholly attributed to an effect of CD8T cells.