Targeted Deletion of Fgl-2/Fibroleukin in the Donor Modulates Immunologic Response and Acute Vascular Rejection in Cardiac Xenografts

Abstract

Background— Xenografts ultimately fail as a result of acute vascular rejection (AVR), a process characterized by intravascular thrombosis, fibrin deposition, and endothelial cell activation. Methods and Results— We studied whether targeted deletion of Fgl-2, an inducible endothelial cell procoagulant, (Fgl-2 −/− ) in the donor prevents AVR in a mouse-to-rat cardiac xenotransplantation model. By 3 days after transplant, Fgl-2 +/+ grafts developed typical features of AVR associated with increased levels of donor Fgl-2 mRNA. Grafts from Fgl-2 −/− mice had reduced fibrin deposition but developed cellular rejection. Treatment with a short course of cobra venom factor and maintenance cyclosporine resulted in long-term acceptance of both Fgl-2 +/+ and Fgl-2 −/− grafts. On withdrawal of cyclosporine, Fgl-2 +/+ grafts developed features of AVR; in contrast, Fgl-2 −/− grafts again developed acute cellular rejection. Rejecting Fgl-2 +/+ hearts stained positively for IgG, IgM, C3, and C5b-9, whereas rejecting Fgl-2 −/− hearts had minimal Ig and complement deposition despite xenoantibodies in the serum. Furthermore, serum containing xenoantibodies failed to stain Fgl-2 −/− long-term treated hearts but did stain wild-type heart tissues. Treatment of Fgl-2 −/− xenografts with mycophenolate mofetil and tacrolimus, a clinically relevant immune suppression protocol, led to long-term graft acceptance. Conclusions— Deletion of Fgl-2 ameliorates AVR by downregulation of xenoantigens and may facilitate successful clinical heart xenotransplantation.

Targeted Deletion of fgl2 Leads to Impaired Regulatory T Cell Activity and Development of Autoimmune Glomerulonephritis

“…These proteins have been shown to exhibit coagulant and angiogenic activity, as well as immunoregulatory activity (1,2,30). Similar to other members of the fibrinogen superfamily, our laboratory has recently discovered (19) that FGL2 inhibits murine DC maturation and adaptive T cell immune responses, in addition to its role in innate immunity through its ability to activate the coagulation system (7)(8)(9)(10)(11)(12)(13)(14)(15).…”

“…FGL2 was first cloned from human CTLs, and its protein structure deduced from the nucleotide sequence showed a high degree of homology to fibrinogen ␤ and ␥ subunits (3). FGL2 has been shown to play an important role in innate immunity as an immune coagulant expressed by activated reticuloendothelial cells (macrophages and endothelial cells) (4 -6) and has been implicated in the pathogenesis of several inflammatory disorders, including viral hepatitis (7)(8)(9)(10), allo-and xenograft rejection (11)(12)(13), and cytokine induced fetal loss (14,15). In a previous report (13), we showed that Ab to FGL2 ameliorated allograft rejection.…”

Fibrinogen-like protein 2/fibroleukin prothrombinase contributes to tumor hypercoagulability via IL-2 and IFN-γ

“…Fgl2 functions as a strong prothrombinase which directly cleaves prothrombin to thrombin leading to fibrin deposition in the absence of factor Ⅶ or factor Ⅹ [10] . The direct prothrombinase activity of fgl2 is implicated in the pathogenesis of several inflammatory disorders including fulminant hepatitis and severe hepatitis, alloand xeno-graft rejection [4,11,12] . Furthermore, its role is also evidenced in murine and human cytokine induced fetal loss [5,[13][14][15] and neonatal death from contractile dysfunction and rhythm abnormalities during embryonic and postnatal development [16] .…”

Xenotransplantation as a model of integrated, multidisciplinary research

“…In this context, several target gene candidates for transgenic expression (e.g., CD39, TFPI, thrombomodulin, hirudin, CD73), or knock-out (e.g., Tissue Factor, PAR3, PAR4, Fgl-2) in pig tissues have been identified. Encouraging results, although only obtained in vitro 66 and in small animal models, [67][68][69][70][71] have provided a basis for the future genetic manipulation of porcine organs possibly able to overcome thrombotic events that compromise xenograft survival.…”