Graft protective effect and induction of CD4⁺Foxp3⁺ cell by Thrombomodulin on allograft arteriosclerosis in mice

Thrombomodulin (TM) is a promising therapeutic natural anti-coagulant, which exerts the effects to control disseminated intravascular coagulation. However, little is known whether TM on micro-vessels could play an important role in the regulation of intimal hyperplasia. We investigated the vessel-protective effect of TM in the survival of fully major histocompatibility complex (MHC)-mismatched murine cardiac allograft transplantation.

CBA recipients transplanted with a C57BL/6 heart received intraperitoneal administration of normal saline or 0.2, 2.0, and 20.0 μg/day of TM for 7 days (n = 5, 7, 11, and 11, respectively). Immunohistochemical and fluorescent staining studies were performed to determine whether CD4⁺Foxp3⁺ regulatory T cell were generated at 2 and 4 weeks after grafting. Morphometric analysis for neointimal formation in the coronary arteries of the transplanted allograft was conducted at 2 and 4 weeks after grafting.

Untreated CBA recipients rejected C57BL/6 cardiac grafts acutely (median survival time [MST], 7 days). CBA recipients exposed with the above doses had significantly prolonged allograft survival (MSTs, 17, 24 and 50 days, respectively). Morphometric assessment showed that intimal hyperplasia was clearly suppressed in the left and right coronary arteries or allografts from TM-exposed recipients 2 and 4 weeks. Immunohistochemical studies at 2 weeks showed more CD4⁺Foxp3⁺ cells and lower myocardial damage in the allografts from TM-exposed recipients. Notably, fluorescent staining studies demonstrated that TM-exposed recipients 4 weeks post-engraftment had strong aggregation of CD4⁺Foxp3⁺ cells in the intima of the coronary arteries of the cardiac allografts.

TM may prolong the survival of fully MHC-mismatched cardiac allografts through suppressing intimal hyperplasia and inducing the accumulation of regulatory CD4⁺Foxp3⁺ cells within coronary arteries.