Rat Cardiac Allograft Rejection Research Articles

PDGF-A, -C, and -D but not PDGF-B Increase TGF-β1 and Chronic Rejection in Rat Cardiac Allografts

Chronic rejection is the main reason for the poor long-term survival of heart transplant recipients and is characterized by cardiac allograft inflammation, fibrosis, and arteriosclerosis. We examined the specific roles of different platelet-derived growth factor (PDGF) ligands (A-D)--potent mesenchymal cell mitogens--in rat cardiac allografts. PDGFR-alpha mRNA was upregulated in acutely-rejecting, and PDGF-A and PDGF-C mRNA in chronically-rejecting cardiac centhatn allografts. In acute rejection, PDGFR-alpha immunoreactivity increased in the media of arteries. In chronically-rejecting allografts, immunoreactivity of all PDGF ligands and receptors--except that of PDGF-B ligand--was found in the intima of arteries, and the expression of PDGF-A and PDGF-C was seen in cardiomyocytes. Intracoronary adeno-associated virus-2 (AAV2)-mediated PDGF-A and -D gene transfer enhanced cardiac allograft inflammation. AAV2-PDGF-A, AAV2-PDGF-C, and AAV2-PDGF-D significantly upregulated profibrotic TGF-beta1 mRNA and accelerated cardiac fibrosis and arteriosclerosis. In contrast, AAV2-PDGF-B did not aggravate chronic rejection. We found that alloimmune response induces PDGF-A, PDGF-C, and PDGF-D expression in the graft vasculature. PDGF-A, PDGF-C, and PDGF-D mediated profibrotic and proarteriosclerotic effects in transplanted hearts involving the TGF-beta1 pathway. Inhibition of signaling of all PDGF-ligands except that of PDGF-B may thus be needed to inhibit chronic rejection in cardiac allografts.

Prevention of Rat Cardiac Allograft Rejection by Host Th2 Cell Adoptive Transfer

We have recently shown that ex vivo manufactured, rapamycin-resistant donor Th2 cells (Th2.R cells) prevent the rejection of allogeneic bone marrow grafts through a process that involves IL-4-mediated polarization of host T cells towards a Th2 phenotype. Because donor T cell therapy lacks feasibility in the setting of cardiac allograft transplantation using cadaveric donors, we developed an approach to prevent rejection that incorporates host Th2 cell therapy prior to organ transplantation. The aims of the study were to: (1) develop a method for the ex vivo manufacture of rat Th2.R cells and inject such syngeneic Th2.R cells just prior to class I and class II disparate cardiac allografting; (2) determine whether such adoptive host Th2.R cell transfer polarizes post-transplant immunity towards a Th2 phenotype; and (3) evaluate in a preliminary manner whether Th2.R cell transfer reduces graft rejection in a model that uses sub-optimal cyclosporine therapy. Recipient-type (Black Norway, BN) CD4+ T cells were co-stimulated with anti-rat anti-CD3 and –CD28 antibodies in the presence of rapamycin, rrIL4, rhuIL-2, and rhIL7 (3-day culture interval). The Th2.R cell cytokine phenotype was determined by intra-cellular flow cytometry and multi-analyte testing of supernatants obtained after repeat co-stimulation. Th2.R cells were injected (i.v.; 1 × 107 cells) 2–3 hours prior to cardiac allografting (donor strain, Dark Agouti; DA). Cardiac function was evaluated clinically by cardiac palpation through day 28 post-grafting. At day 28, histology studies and immune function studies were performed, including assessment of host-anti-donor alloreactivity. Engraftment controls (cohort #1) and rejection controls (cohort #2) received cyclosporine (CSA) through the full 28 days or only through day 18, respectively; the experimental cohort (#3) received host Th2.R cells followed by the short-course of CSA. Supernatants from the Th2.R cell product contained 1500 pg/ml IL-4 and only 50 pg/ml of IFN-γ; the frequency of IL-4+ cells and IFN-γ+ cells was 10% and 1%, respectively. Clinical rejection was observed in cohort #2 (3/3 subjects) whereas all subjects in cohorts #1 and #3 had full cardiac function through day 28 (cohort #1- 2/3 subjects; cohort #3- 3/3 subjects). Relative to rejection controls, Th2.R cell recipients had a reduced frequency of intra-cardiac CD8+ T cells (%CD8+ T cells, 9.2 ± 6.2 vs. 1.1 ± 0.3; p<0.001) and spleen CD8+ T cells (1.9 ± 0.2 vs. 0.5 ± 0.2; p=0.014). Furthermore, after ex vivo re-stimulation with donor-type dendritic cells, intra-cardiac CD8+ T cells from Th2.R cell recipients tended to produce less IFN-γ relative to rejection controls (pg/ml in supernatant; 15.7 ± 1.4 vs. 44.2 ± 1.4; p=0.07) and tended to produce increased IL-4 relative to rejection controls (1974 ± 140 vs. 260 ± 291; p=0.07). This study demonstrates a feasible and successful methodology for inducing recipient based immunotolerance by generating rapamycin-resistant Th2 cells in the rat species.. Adoptive transfer of host-type Th2.R cells just prior to fully genetically-disparate cardiac allograft transplantation results in a shift towards Th2 cytokines post-transplant, a reduction in the frequency of intra-cardiac T cell infiltration, and shows promise as a novel method to prevent cardiac allograft rejection.

Further study of anti-ICOS immunotherapy for rat cardiac allograft rejection

To study the effect of B7-CD28 costimulatory signal blockade by adenovirus-mediated cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (AdCTLA-4Ig) on cardiac allograft survival in DA (RT1(a)) to LEW (Lewis RT1(l)) rat combinations. We evaluated the effect of combined AdCTLA-4Ig and anti-inducible costimulator (ICOS) antibody immunotherapy on rat cardiac allograft acceptance. Unlike AdCTLA-4Ig alone, anti-ICOS immunotherapy combined with AdCTLA-4Ig induced stable tolerance without causing chronic rejection. The combined immunotherapy also prevented the accelerated cardiac rejection caused by donor-type test skin grafting. Immunohistochemical analyses revealed remarkable inflammatory mononuclear cell infiltration with typical vasculopathy, especially ICOS-positive cells in the grafts, in recipients treated with AdCTLA-4Ig alone. In contrast, anti-ICOS therapy combined with AdCTLA-4Ig reduced the ICOS-positive inflammatory cell infiltration of the graft significantly. The most important finding is that possible cardiac arrest caused by secondary donor-type skin graft was prevented by combined immunotherapy of AdCTLA-4Ig and anti-ICOS antibody, despite skin graft rejection. Our results identified a major role played by the ICOS-ICOSL pathway in chronic and accelerated cardiac allograft rejection, providing a novel approach to preventing the chronic rejection of vascularized organ allografts.

Foxp3-expressing Regulatory T Cells Expanded With CD28 Superagonist Antibody Can Prevent Rat Cardiac Allograft Rejection

It is well known that CD4(+)CD25(+) regulatory T (Treg) cells play a central role in the suppression of autoimmunity, inflammation and allograft rejection. Therefore, therapeutic agents that capable of enhancing the number and activity of this T-cell subset are highly desirable. The present study was designed to investigate the effects of superagonistic CD28-specific monoclonal antibody (supCD28 MAb) on preferentially expanded rat naturally occurring CD4(+)CD25(+) Treg (nTreg) cells and its applicability in cardiac transplantation. A single administration of supCD28 MAb preferentially proliferated nTreg cells. The increase of Foxp3 expression and polarization toward a Th2 cytokine profile correlated with decreased production of interferon-gamma and increased production of interleukin-4 and -10 in the expanded CD4(+)CD25(+) Treg subset, which was capable of suppressing CD4(+)CD25(-) T-cell proliferation after purification. Furthermore, supCD28 MAb administration revealed that nTreg cells were preferentially proliferating in vivo and recruited into the grafts, resulting in significant prolongation of full MHC-mismatch cardiac graft survival. Our data demonstrate that supCD28 MAb targets expansion of nTreg cells in vivo and maintains and enhances their regulatory functions, which represents a major advance toward the therapeutic use of polyclonally activated Treg cells as cellular therapy for treatment of allograft rejection.

360: Constantly Stable HIF-1α in Myeloid Cells Prevents Acute Rejection in Rat Cardiac Allografts

Hypoxia inducible factor-1 (HIF-1) is a transcription factor promoting transcription of various downstream genes involved in cytoprotection, anti-inflammation and proliferation. HIF-1 is stabilized in hypoxia, whereas in normoxia HIF-1 is rapidly degraded via anti-oncogene Von hippel lindau (VHL) protein. The aim of this study was to investigate acute rejection in recipient with HIF-1α-deletions (no HIF-1 activity) or VHL-deletions (constitutively stable HIF-1 activity) in granulocytes and monocytes/macrophage lineage in normoxic conditions.

Total glucosides of peony as adjuvant therapy for prevention of cardiac allograft rejection in rats

To evaluate the role of total glucosides of peony (TGP) as adjuvant therapy for prevention of cardiac allograft rejection in rats. Rats with cardiac allograft were randomly divided into control group, tacrolimus-treated group, TGP-treated group and tacrolimus plus TGP-treated group. Graft survival time was observed. Allografts in some cases were examined by histological study seven days after transplantation. At the same time, the levels of CD4(+) and CD8(+) T cell subsets in peripheral blood were examined by using flow cytometry; the hepatic function and renal function of recipients were also tested. The graft survival time of the tacrolimus-treated group and tacrolimus plus TGP-treated group was (11.14+/-1.57) d and (13.57+/-1.99) d, respectively. The graft survival time of the tacrolimus plus TGP-treated group was longer than that of the tacrolimus-treated group (P<0.05). The histological study showed that the rejection of the tacrolimus plus TGP-treated group was slighter than that of the tacrolimus-treated group. The levels of CD4(+) T cell subset in the peripheral blood of the tacrolimus-treated and tacrolimus plus TGP-treated groups were (38.71+/-5.15)% and (32.43+/-4.39)% respectively 7 days after transplantation. The level of CD4(+) T cell subset in the tacrolimus plus TGP-treated group was lower than that in the tacrolimus-treated group (P<0.05). The level of CD8(+) T cell subset and the hepatic and renal function had no significant differences between the tacrolimus-treated group and the tacrolimus plus TGP-treated group. Effects of tacrolimus plus TGP in prevention of rejection are better than tacrolimus monotherapy in rats with cardiac allograft and without increasing side effects.

A Critical Role for Allograft Inflammatory Factor-1 in the Pathogenesis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is characterized by massive synovial proliferation, angiogenesis, subintimal infiltration of inflammatory cells and the production of cytokines such as TNF-alpha and IL-6. Allograft inflammatory factor-1 (AIF-1) has been identified in chronic rejection of rat cardiac allografts as well as tissue inflammation in various autoimmune diseases. AIF-1 is thought to play an important role in chronic immune inflammatory processes, especially those involving macrophages. In the current work, we examined the expression of AIF-1 in synovial tissues and measured AIF-1 in synovial fluid (SF) derived from patients with either RA or osteoarthritis (OA). We also examined the proliferation of synovial cells and induction of IL-6 following AIF-1 stimulation. Immunohistochemical staining showed that AIF-1 was strongly expressed in infiltrating mononuclear cells and synovial fibroblasts in RA compared with OA. Western blot analysis and semiquantitative RT-PCR analysis demonstrated that synovial expression of AIF-1 in RA was significantly greater than the expression in OA. AIF-1 induced the proliferation of cultured synovial cells in a dose-dependent manner and increased the IL-6 production of synovial fibroblasts and PBMC. The levels of AIF-1 protein were higher in synovial fluid from patients with RA compared with patients with OA (p < 0.05). Furthermore, the concentration of AIF-1 significantly correlated with the IL-6 concentration (r = 0.618, p < 0.01). These findings suggest that AIF-1 is closely associated with the pathogenesis of RA and is a novel member of the cytokine network involved in the immunological processes underlying RA.

Electroporation‐mediated interleukin‐10 overexpression in skeletal muscle reduces acute rejection in rat cardiac allografts

Human interleukin 10 (hIL-10) may reduce acute rejection after organ transplantation. Our previous data shows that electroporation-mediated transfer of plasmid DNA to peripheral muscle enhances gene transduction dramatically. This study was designed to investigate the effect of electroporation-mediated overexpression of hIL-10 on acute rejection of cardiac allografts in the rat. The study was designed to evaluate the effect of hIL-10 gene transfer on (a) early rejection pattern and (b) graft survival. Gene transfer was achieved by intramuscular (i.m.) injection into the tibialis anterior muscle of Fischer (F344) male recipients followed by electroporation 24 h prior to transplantation. Heterotopic cardiac transplantation was performed from male Brown Norway rat to F344. Four groups were studied (n = 6). Treated animals in groups B1 and B2 received 2.5 microg of pCIK hIL-10 and control animals in groups A1 and A2 distilled water. Graft function was assessed by daily palpation. Animals from group A1 were sacrificed at the cessation of the heart beat of the graft and those in group B1 were sacrificed at day 7; blood was taken for ELISA measurement of hIL-10 and tissue for myeloperoxidase (MPO) measurement and histological assessment. To evaluate graft survival, groups A2 and B2 were sacrificed at cessation of the heart beat of the graft. Histological examination revealed severe rejection (IIIB-IV) in group A1 in contrast to low to moderate rejection (IA-IIIA) in group B1 (p = 0.02). MPO activity was significantly lower in group B1 compared to group A1 (18 +/- 7 vs. 32 +/- 14 mU/mg protein, p = 0.05). Serum hIL-10 levels were 46 +/- 13 pg/ml in group B1 vs. 0 pg/ml in group A1. At day 7 all heart allografts in the treated groups B1 and B2 were beating, whereas they stopped beating at 5 +/- 2 days in groups A1 and A2 vs. 14 +/- 2 days in group B2 (p = 0.0012). Electroporation-mediated intramuscular overexpression of hIL-10 reduces acute rejection and improves survival of heterotopic heart allografts in rats. This study demonstrates that peripheral overexpression of specific genes in skeletal muscle may reduce acute rejection after whole organ transplantation.

Dimeric but not Monomeric Soluble CD40 Prolongs Allograft Survival and Generates Regulatory T Cells that Inhibit CTL Function

We previously reported that adenovirus mediated CD40Ig gene therapy (AdCD40Ig) induced long-term acceptance of fully allogeneic rat cardiac allografts, however, the underlying mechanism has not been fully clarified. To address this we have compared the ability of dimeric and monomeric soluble CD40 to prolong allograft survival in vivo and generate regulatory T cells in vitro. The ability of CD40Ig (soluble dimmer, containing an Fc region) or CD40/Myc/His (soluble monomer, lacking an Fc region) therapy to generate CD4CD25 regulatory T cells in vitro and to prevent rejection of rat cardiac allografts (ACI to LEWIS) was compared. Immunoregulatory capacity of regulatory T cells generated was determined by suppression of alloantigen specific proliferation and cytotoxicity. Dimeric soluble CD40Ig did not inhibit CD4 T cell proliferation but rather promoted IL-2 production and the generation of CD4CD25 T cells, which regulated alloantigen-specific cytotoxic T lymphocyte activity. Treatment with either AdCD40Ig or purified soluble CD40Ig prolonged the survival of rat cardiac allografts. In contrast, although monomeric soluble CD40/Myc/His suppressed IL-12 production in a similar manner to that achieved by CD40Ig, it did not augment IL-2 production. Moreover, while CD40/Myc/His also generated CD4CD25 T cells, they did not exhibit regulatory activity and administration of soluble CD40/Myc/His failed to prolong cardiac allograft survival. These results suggest signaling through CD154 in addition to blocking of CD154-CD40 interaction is important for the immunomodulatory effects of soluble CD40Ig. Taken together, our results provide new insight into the mechanism of immunomodulation by soluble CD40 constructs.

The role of CC and CXC chemokines in cardiac allograft rejection in rats

Acute cellular rejection is due in part to an upregulation of chemokine genes, resulting in eventual cell-mediated cytotoxicity. The role of chemokines in acute cardiac allograft rejection is not fully characterized presently. These studies compared the patterns of expression for multiple chemokines in rodent cardiac allograft rejection. Allogeneic transplants were performed from Brown–Norway donors to Lewis recipients. Survival studies utilized daily administration of neutralizing antisera to MCP-1, CINC, and MIP-1α. Patterns of mRNA and protein expression were determined by Northern blots and immunohistochemistry. Allogeneic controls rejected at mean of 6.5 days. Neutralization of MCP-1 (10.8 days, P < 0.001) and MIP-1α (7.5 days, P = 0.004) function, but not CINC (6.2 days, P > 0.05), significantly prolonged allograft survival. Message expression for the beta chemokines studied were increased by day 2 and continued to increase until day 6 just before rejection, while CINC levels did not change as dramatically after day 2. Chemokine protein levels mirrored mRNA patterns by IHC analysis. MCP-1 and MIP-1α appear to play regulatory roles in cardiac allograft rejection, while CINC is expressed, but not functional, in injury development. Beta chemokine activity should be studied further in hope of developing more targeted immunosuppression, or identifying specific chemokines that may be useful for immunosurveillance purposes.

925. Electroporation Mediated Gene Transfer of Human Interleukin-10 to Skeletal Muscle Reduces Acute Rejection in Rat Cardiac Allografts

Background Electroporation-mediated transfer of plasmid DNA has been demonstrated to enhance gene transduction dramatically. The aim of this study was to investigate the impact of overexpression of human IL-10 (hIL-10) on acute rejection of cardiac allografts in the rat.

The interaction between FK778 and tacrolimus in the prevention of rat cardiac allograft rejection is dose dependent.

The synthetic malononitrilamide FK778 inhibits T- and B-cell responsiveness, phagocyte effector function, exerts inhibitory activity against cytomegalovirus, and is thus one of the most promising new immunosuppressive drugs. The aim of this study was to evaluate the combination of FK778 and tacrolimus in a high-responder rat cardiac transplantation model. The Brown Norway-Lewis rat strain combination was used to investigate graft survival after 10 days of posttransplant oral therapy with FK778 (5 or 20 mg/kg), tacrolimus (2 or 8 mg/kg), or combination regimens at varying doses (5+2 mg/kg, 10+1 mg/kg, or 20+8 mg/kg). Grafts were harvested after cessation of cardiac contractions. Combination indices (CI) were calculated for drug combinations. In untreated recipients, allograft survival was 6.2+/-0.4 days. FK778 at 20 mg/kg and tacrolimus at 2 or 8 mg/kg significantly prolonged graft survival to a mean survival time (MST) of 17.0+/-2.8, 18.5+/-2.7, and 25.0+/-2.5 days, respectively. The two low-dose drug combinations achieved a graft survival of 23.2+/-2.9 and 25.2+/-3.1 days, which was significantly longer compared with FK778 at 5 mg/kg, FK778 at 20 mg/kg, and tacrolimus at 2 mg/kg (P </=0.003) and was similar to that of high-dose tacrolimus therapy (8 mg/kg). The drugs showed synergistic interactions (CI values of 0.62 and 0.52, respectively). With the high-dose drug combination, MST was 30.0+/-4.1 days, which was significantly longer compared with all other groups (P </=0.012). However, drugs showed only additive interaction (CI=0.95), and recipients suffered enhanced toxic side effects. This study provides evidence that FK778 and tacrolimus show supportive interaction in their immunosuppressive potency that is synergistic in low-dose combinations and additive in higher doses.

Cyclosporine treatment preserves coronary resistance artery function in rat cardiac allografts

Background A marked decline in vascular myogenic response occurs during the course of rat cardiac allograft rejection. Two important contributory features are an inducible nitrous oxide synthase (iNOS)-catalyzed, NO-mediated vasodilation and a loss of smooth muscle function. In this study, we examine the effect of cyclosporine immunosuppressive therapy on the alleviation of arterial dysfunction of coronary resistance arteries in allografts using pressure myography. Methods Rats receiving heterotopic abdominal cardiac transplantation were treated with cyclosporine (5 mg/kg), Cremophore or distilled water. Coronary septal arteries (internal diameter 200 μm) were dissected from isograft (Lewis to Lewis) and allograft (Fisher to Lewis) rat hearts at Day 21 post-transplantation and mounted on a pressure myograph. Pressure-induced vasoconstriction was measured before and after iNOS inhibition with aminoguanidine (AG; 100 μmol/liter). Both endothelium-based (ACh-induced) and endothelium-independent (sodium nitroprusside–induced) vasorelaxation were also recorded in each group. Results Pressure-induced myogenic contraction was reduced in allograft coronary arteries at Day 21 post-transplantation compared with matched isografts ( p < 0.05). AG potentiated myogenic tone in allograft arteries, but had no effect on untreated Day 21 isograft vessels, indicating the presence of iNOS-based relaxation only in allograft vessels. Depolarization-induced vasoconstriction was lower in allograft compared with isograft arteries ( p < 0.05). Cyclosporine therapy also improved depolarization-induced constriction in allograft vessels compared with untreated groups ( p < 0.05). Furthermore, cyclosporine therapy preserved endothelium-based and endothelium-independent vasorelaxation in allograft arteries at Day 21 post-transplantation. Conclusions Cyclosporine immunosuppressive therapy has a significant effect on the alleviation of early endothelial and smooth muscle dysfunction in coronary allograft arteries.

Inhibition of poly-ADP ribose synthase (PARS) increases cardiac myocyte survival during acute cardiac allograft rejection in rats

Death of cardiomyocytes by apoptosis and by necrosis is a hallmark of acute cardiac allograft rejection. Studies of cardiac myoblasts and cardiac myocytes in culture indicated that activation of poly ADP ribose synthase (PARS) by agonists such as NO, peroxynitrite and TNFalpha contribute to both forms of cardiac muscle cell death. To investigate the role of PARS activation in acute allograft rejection Lewis-Wistar-Furth heterotopic abdominal heart transplantation was performed in rats. In animals treated with the PARS inhibitor 5-aminoisoquinolinone (5AIQ) (3 mg/kg i.p. bid) cardiac allograft survival was prolonged from 6 ± 2 to 10 ± 1.7 days (n=6, n=8 diff p<0.02). At day 5 following transplantation PARS mRNA, protein and poly ADP ribose protein were increased in the allografts of both groups. Myocyte damage determined by the TUNEL technique and immunoperoxidase staining for soluble fibronectin was reduced by 66% from 16.7 to 5.7 damaged myocytes per mm2 myocardium in vehicle vs. 5AIQ treated allografts. Myocardial inflammation was also reduced by 49% for ED1+ macrophages, 34% for CD3+ lymphocytes and 51% for NOS-2+ inflammatory cells.

Activation of proinflammatory mediators in heart transplants from brain-dead donors: evidence from a model of chronic rat cardiac allograft rejection

Activation of proinflammatory mediators in heart transplants from brain-dead donors: evidence from a model of chronic rat cardiac allograft rejection

A High Isoflavone Soy Protein Diet and Intravenous Genistein Delay Rejection of Rat Cardiac Allografts

Genistein, a soy isoflavone, has in vitro immunosuppressive properties. We investigated whether genistein or dietary soy protein containing isoflavones could influence the outcome of rat cardiac allografts. Lewis rats were fed a diet with protein from high isoflavone soy protein fraction (HIS), casein (CAS) or casein with isoflavones added (CI) starting 1 wk before heart transplants from Wistar Furth donors, and continuing throughout the study. HIS-fed rats had significantly prolonged time to rejection compared with CAS- and CI-fed recipients (10.8 +/- 2.62 vs. 7.18 +/- 0.75 and 7.22 +/- 0.44 d, P < 0.001). Intravenous genistein [20mg/(kg. d) for 14 d] significantly prolonged heart survival compared with controls and dissolvent-treated recipients (23.2 +/- 7.4 vs. 8.4 +/- 1.3 and 11.4+/3.6 d, P < 0.0005), and had an additive effect when given to heart recipients also receiving low dose cyclosporine for 7 d (30.8 +/- 2.3 vs. 23.4 +/- 2.4 d, P < 0.005). Concanavalin A-stimulated lymphocytes, isolated from Lewis rats given intraperitoneal genistein for 7 d, had decreased production of interferon gamma compared with controls or dimethyl sulfoxide-treated groups (22.6 +/- 9.9 vs 149 +/- 105 and 154 +/- 103 micro g/L, P < 0.05). In conclusion, a high isoflavone soy diet and intravenous genistein, but not isoflavone extract alone, delay rejection of rat cardiac allografts, with an additive effect in cyclosporine-treated rats. In addition, intraperitoneal genistein has immunosuppressive properties in vivo.

Donor brain death intensifies the recipient inflammatory response in chronic rat cardiac allograft rejection

Donor brain death intensifies the recipient inflammatory response in chronic rat cardiac allograft rejection

Macrophage accumulation associated with rat cardiac allograft rejection detected by magnetic resonance imaging with ultrasmall superparamagnetic iron oxide particles.

Acute cardiac allograft rejection continues to be the cause of graft loss and contributes to the morbidity and mortality after cardiac transplantation. In this study, we report a new method for detecting organ rejection in transplantation with an MR-based technique using dextran-coated ultrasmall superparamagnetic iron oxide (USPIO) particles. These particles ( approximately 27 nm in diameter) are known to shorten relaxation times in MRI experiments. A new rat model of heterotopic heart and lung transplantation has been developed for MRI experiments. Allotransplantations (DA-->BN) were performed (n=8), with syngeneic transplantations (BN-->BN) serving as controls (n=8). MR images were obtained with a gradient echo method. At postoperative day 7, allotransplants developed moderate rejection as determined histopathologically. A significant reduction in MR signal intensity was observed after USPIO injection into rats with allotransplanted hearts. Syngeneic transplants showed no differences in MR signal intensity before and after USPIO injections. After injection of USPIO particles at postoperative day 6, a group of allotransplanted rats was treated with cyclosporin A (3 mg/kg). Animals treated with cyclosporin A for 7 days showed no reduction in MR signal intensity after USPIO reinjection at day 14, whereas animals treated for 4 days showed a significant decrease in MR signal intensity in the transplanted hearts indicative of acute graft rejection. Pathological analysis of these animals revealed that dextran-coated USPIO particles were taken up by the infiltrating macrophages that accumulated within the rejecting cardiac graft. This MRI method offers promise as a noninvasive method for detecting transplant allograft rejection.

TC99M MCP-1 imaging of chronic rejection in rat cardiac allografts

Monocyte Chemoattractant Protein 1 (MCP-1) is a chemokine important to the recruitment of perivascular monocytes in transplanted organs. Its expression is associated with the development of chronic rejection as manifested by graft coronary artery disease (GCAD) following cardiac transplantation. This study assesses whether radiolabelled MCP-1 binds to its receptors in chronic cardiac allografts and thereby provides a potential imaging modality to assess GCAD. Methods: Allogeneic (PVG-.ACI, n59) and syngeneic (ACI.ACI, n59) rat heterotopic heart transplants were performed. Allograft recipients were treated with 7.5mg/kg/day of oral Cyclosporin A for ten days until tolerance was achieved. After 90 days, animals were infused intravenously with Tc99m MCP-1 and sacrificed after one hour. Radioactivity of heart tissues was measured in scintillation well counters and expressed as a ratio to that of uptake in the overall blood pool. Autoradiographs were imaged by exposing 50-micron desiccated sections on a phosphoimager overnight. Additional sections were fixed in 10% formalin prior to paraffin embedding and cutting into 5-micron sections for elastin von Gieson staining. Hearts were scored for luminal narrowing and intima to media ratio (I/M) with computerized image analysis. Results: Allografts exhibited significantly more luminal narrowing (22.5610.7% vs. 2.664.6%, p5.0005) and higher I/M (0.17360.151 vs. 0.01560.029, p5.0088) than isografts. The ratio of heart tissue well counts to that of the blood pool demonstrated 1.44 times greater Tc99m MCP-1 uptake in allografts (1.04) compared to isograft controls (0.72) (p50.03). The figure shows representative autoradiograph images of native, isograft, and allograft cross sections. Conclusion: Tc99m bound MCP-1 is higher in allografts vs. isografts which is consistent with a greater degree of vasculopathy. These data provide a foundation for the development of a potentially noninvasive imaging assay of chronic rejection after heart transplantation.

Altered alloimmune response toward grafts from brain-dead donors in chronic rat cardiac allograft rejection

Altered alloimmune response toward grafts from brain-dead donors in chronic rat cardiac allograft rejection