The relationship between acute rejection and chronic rejection is highly dependent on specific MHC matching: a multi-strain rat heterotopic heart transplant study

The complex role of iNOS in acutely rejecting cardiac transplants

This review summarizes the evidence for a detrimental role of nitric oxide (NO) derived from inducible NO synthase (iNOS) and/or reactive nitrogen species such as peroxynitrite in acutely rejecting cardiac transplants. In chronic cardiac transplant rejection, iNOS may have an opposing beneficial component. The purpose of this review is primarily to address issues related to acute rejection, which is a recognized risk factor for chronic rejection. The evidence for a detrimental role is based upon strategies involving nonselective NOS inhibitors, NO neutralizers, selective iNOS inhibitors, and iNOS gene deletion in rodent models of cardiac rejection. The review is presented in the context of the impact on various components, including graft survival, histological rejection, and cardiac function, which may contribute to the process of graft rejection in toto. Possible limitations of each strategy are discussed in order to understand better the variance in published findings, including issues related to the potential importance of cell localization of iNOS expression. Finally, the concept of a dual role for NO and its downstream product, peroxynitrite, in rejection vs immune regulation is discussed.

Reciprocal role of cyclins and cyclin kinase inhibitor p21WAF1/CIP1 on lymphocyte proliferation, allo-immune activation and inflammation

Background

Immune activation that results due to the aberrant proliferation of lymphocytes leads to inflammation and graft rejection in organ transplant recipients. We hypothesize that the cell cycle control and inflammation are parallel events, inhibition of cellular proliferation by cyclin kinase inhibitor specifically p21 will limit inflammation and prevent allograft rejection.

Methods

We performed in vitro and in vivo studies using lymphocytes, and rat heart transplant model to understand the role of cyclins and p21 on mitogen and allo-induced lymphocyte activation and inflammation. Lymphocyte proliferation was studied by ³H-thymidine uptake assay and mRNA expression was studied RT-PCR.

Results

Activation of allo- and mitogen stimulated lymphocytes resulted in increased expression of cyclins, IL-2 and pro-inflammatory cytokines, which was inhibited by cyclosporine. The over-expression of p21 prolonged graft survival in a completely mismatched rat heart transplant model resulted by inhibiting circulating and intra-graft expression of proinflammatory cytokines.

Conclusion

Cyclins play a significant role in transplant-induced immune activation and p21 over-expression has potential to inhibit T cell activation and inflammation. The results from this study will permit the design of alternate strategies by controlling cell cycle progression to achieve immunosuppression in transplantation.

Anti-transforming growth factor antibody at low but not high doses limits cyclosporine-mediated nephrotoxicity without altering rat cardiac allograft survival: potential of therapeutic applications

BACKGROUND

Long-term treatment of cardiac transplant recipients with cyclosporine results in a progressive decline in kidney function in a large number of patients. This complication is one of the most important prognostic parameters that determine the outcome of cardiac transplantation. Transforming growth factor-beta (TGF-beta) is one of the most potent mediators of the fibrogenic effects of cyclosporine.

METHODS AND RESULTS

With the use of an experimental rodent model, heterotopic heart transplantation was performed, creating histocompatibility-disparate allografts. Because TGF-beta in part mediates both the immunosuppressive and nephrotoxic effects of cyclosporine, recipients were treated with cyclosporine with and without anti-TGF-beta antibody to determine whether anti-TGF-beta antibody could reduce the nephrotoxic effects of cyclosporine. Intrarenal expression of TGF-beta, collagen, fibronectin, matrix metalloproteinase-2, and tissue inhibitor of metalloproteinase-2 was studied with the use of reverse transcription-polymerase chain reaction. Intrarenal expression of TGF-beta protein was studied by immunohistochemistry and with the use of ELISA to quantify circulating levels of TGF-beta protein in plasma. Cyclosporine-induced graft survival (immunosuppressive effect) was abrogated with a higher concentration (2.5 mg/kg) of anti-TGF-beta antibody, whereas a lower concentration (1 mg/kg) inhibited both cyclosporine-induced expression of fibrogenic molecules and renal toxicity.

CONCLUSIONS

These results provide credence to the pivotal role of TGF-beta in immunosuppression-associated renal toxicity in recipients of cardiac transplantation. Furthermore, these findings support a potentially significant therapeutic use of optimal concentration of anti-TGF-beta antibody to ameliorate cyclosporine-associated nephrotoxicity in cardiac transplant recipients.

Egr-1 in vascular smooth muscle cell proliferation in response to allo-antigen

BACKGROUND

Early growth response factor-1 (Egr-1) plays an important role in regulating multiple factors involved in the progression of vascular lesions. This study examined our hypothesis that Egr-1 plays a critical role in the early stage of chronic cardiac allograft rejection and in the proliferation of the smooth muscle cell response to alloantigen.

MATERIALS AND METHODS

Antisense Egr-1 oligodeoxynucleotide (ODN) was ex vivo gene transfected into the donor hearts from DBA/2 mice, followed by heterotopic allografting into B10.D2 recipients. The allografts were harvested on day 30. Egr-1 and its target molecules, such as platelet-derived growth factor (PDGF)-A, basic fibroblastic growth factor (bFGF), vascular cell adhesion molecule (VCAM)-1, transforming growth factor (TGF)-beta and nonmuscle myosin heavy chain B (SMemb), were identified immunohistochemically, and the percentage of the lumen occluded by the intima was calculated. For the cell proliferation assay, sensitized T cells were harvested from B10.D2 recipients as stimulator and then added to the SMCs, which were harvested from DBA/2 mouse aorta. Cellular proliferation was measured and Egr-1 and its target gene expression were examined by real-time RT-PCR.

RESULTS

Egr-1 and its target genes were expressed in the thickened intima from untreated recipients. Egr-1 antisense ODN inhibited not only Egr-1 expression but also its target genes and significantly suppressed intimal thickening of coronary arteries. Egr-1 antisense ODN also significantly inhibited cell proliferation and expressions of Egr-1 and Egr-1 target genes in a mixed cell culture model.

CONCLUSION

We conclude that Egr-1 plays an important role in the formation of the cardiac allograft vasculopathy responding to alloantigens.

Analysis of transforming growth factor-beta and profibrogenic molecules in a rat cardiac allograft model treated with cyclosporine

BACKGROUND

Long-term treatment of heart transplantation recipients with cyclosporine (CsA) results in chronic nephrotoxic effects, which frequently lead to progressive renal failure. Transforming growth factor (TGF)-beta and other fibrogenic molecules are leading candidates for these effects, because CsA is known to induce TGF-beta. In this study we compared the expression of TGF-beta, collagen, fibronectin, metalloproteinases, and tissue inhibitors of metalloproteinases in kidneys from recipients of heterotopic heart transplants treated with CsA for 30 and 180 days.

METHODS

Using a clinically relevant experimental rodent model (strain combination Wistar Furth [RT1u] into Lewis [RT1l]), heterotopic heart transplantation was performed, creating disparate cardiac allografts. The transplant study population was divided into three groups: controls and those receiving CsA immunosuppression therapy to maintain graft survival for 30-day and 180-day periods. Comparisons were made of intrarenal expression of TGF-beta, collagen, fibronectin, metalloproteinase-2 (MMP-2), MMP-9, and tissue inhibitor of MMP-2, using reverse transcriptase-polymerase chain reaction. Intrarenal expression of TGF-beta protein was also compared using immunochemical staining technique, and circulating levels of TGF-beta protein were quantified by ELISA.

RESULTS

Intrarenal expression of TGF-beta, collagen, fibronectin, MMP-2, MMP-9, and tissue inhibitor of MMP-2 was significantly increased in rats treated with CsA for 180 days compared with untreated rats and those treated for 30 days. Circulating levels and intrarenal expression of TGF-beta were also significantly increased in rats treated for 180 days.

CONCLUSION

Posttransplantation nephrotoxicity in cardiac transplant recipients treated with CsA for a long term is related to increased expression of TGF-beta and other fibrogenic genes. Therapies designed to inhibit expression of TGF-beta could ameliorate CsA-associated nephrotoxicity in cardiac transplant recipients.

Tolerance and chronic rejection

The most common cause of chronic allograft loss is an incompletely understood clinicopathological entity called chronic rejection (CR). Recent reports suggest an improvement in long-term renal allograft survival, although it is not clear from these data whether a true reduction of biopsy-proven CR has occurred. Although newer immunosuppressive medications have greatly reduced the incidence of acute rejection (AR) in the early post-transplantation period, the ideal therapy for both AR and CR would be to achieve a state of tolerance. By definition, such a state should allow for indefinite allograft survival, with no histopathological evidence of CR, despite immunocompetence in the host (i.e. without the need for chronic immunosuppression). Although several experimental studies are able to achieve tolerance, with clear improvement in allograft survival, detailed studies on graft function and morphology are often not included. This review will discuss possible ways that tolerance induction could lead to a CR-free state. General mechanisms of CR and transplantation tolerance induction are discussed as well as the difficulties in translating small animals studies into large animals and humans.