The protective role of Toll-like receptor 3 and type-I interferons in the pathophysiology of vein graft disease

Background: Venous grafts are commonly used as conduits to bypass occluded arteries. Unfortunately, patency rates are limited by vein graft disease (VGD). Toll like receptors (TLRs) can be activated in vein grafts by endogenous ligands. This study aims to investigate the role of TLR3 in VGD. Methods: Vein graft surgery was performed by donor caval vein interpositioning in the carotid artery of recipient Tlr2(-/-), Tlr3(-/-), Tlr4(-/-) and control mice. Vein grafts were harvested 7, 14 and 28d after surgery to perform immunohistochemical analysis. Expression of TLR-responsive genes in vein grafts was analysed using a RT2-profiler PCR Array. mRNA expression of type-I IFN inducible genes was measured with qPCR in bone marrow derived macrophages (BMM). Results: TLR2, TLR3 and TLR4 were observed on vein graft endothelial cells, smooth muscle cells and macrophages. Tlr3(-/-) vein grafts demonstrated no differences in vessel wall thickening after 7d, but after 14d a 2.0-fold increase (p = 0.02) and 28d a 1.8-fold increase (p = 0.009) compared to control vein grafts was observed, with an increased number of macrophages (p = 0.002) in the vein graft. Vessel wall thickening in Tlr4(-/-) decreased 0.6-fold (p = 0.04) and showed no differences in Tlr2(-/-) compared to control vein grafts. RT2-profiler array revealed a down-regulation of type-I IFN inducible genes in Tlr3(-/-) vein grafts. PolyI:C stimulated BMM of Tlr3(-/-) mice showed a reduction of Ifit1 (p = 0.003) and Mx1 (p < 0.0001) mRNA compared to control. Conclusions: We here demonstrate that TLR3 can play a protective role in VGD development, possibly regulated via type-I IFNs and a reduced inflammatory response.