Macrophage-derived interleukin-18 in experimental renal allograft rejection.

BACKGROUND: Interleukin 18 (IL-18) is primarily a macrophage-derived, pro-inflammatory cytokine. As macrophages can act as effector cells in acute rejection, we examined the role of IL-18 in a rat model of acute renal allograft rejection. METHODS: Life-sustaining orthotopic DA to Lewis allograft and Lewis-Lewis isograft kidney transplants were performed. In the same model, macrophage-depleted animals, achieved with liposomal-clodronate therapy, were also studied. Macrophage (ED1+) accumulation and IL-18 expression was assessed by immunohistochemistry. CD11b+ cells (macrophages) were isolated from kidney and spleen by micro beads. Real-time PCR was used to assess IL-18 and INF-gamma mRNA expression in tissue and cell isolates. RESULTS: Allografts, but not isografts, developed severe tubulo-interstitial damage and increased serum creatinine by day 5 (P<0.001). Immunohistochemistry revealed a greater ED1+ cell accumulation in day 5 allografts compared with isografts (P<0.001). IL-18 mRNA expression was increased 3-fold in allografts compared to isografts (P<0.001). Accordingly, IL-18 protein was increased in allografts (P<0.001), and was predominantly expressed by ED1+ macrophages. CD11b+ macrophages isolated from allografts had a 6-fold upregulation of IL-18 mRNA expression compared to isograft macrophages (P<0.001). Macrophage depletion resulted in a marked attenuation of allograft rejection, ED1+ and IL-18+ cells were significantly reduced (P<0.05) as was IL-18 mRNA expression (29.28+/-2.85 vs 62.48+/-3.05, P<0.001). INF-gamma mRNA expression (P<0.01) and iNOS (P<0.001) production were also significantly reduced in the macrophage-depleted animals. CONCLUSION: This study demonstrates that IL-18 is significantly increased during acute rejection and is principally produced by intra-graft macrophages. We hypothesize that IL-18 upregulation may be an important macrophage effector mechanism during the acute rejection process.     

Beyond operational tolerance: effect of ischemic injury on development of chronic damage in renal grafts

BACKGROUND: The induction of operational tolerance is the holy grail of clinical transplantation. However, in animal models with operational tolerance, long- term grafts still develop chronic damage. The elucidation of the impact of allogenic versus nonallogeneic factors in such a model is important. This study examined the effect of a clinically relevant combination of warm ischemia and cold preservation in the absence of allogeneic response (isografts) and in the context of operational tolerance. METHODS: Dark Agouti (DA) rat kidneys were transplanted into DA recipients (isografts) or Albino Surgery recipients (allografts) tolerized by two transfusions of DA blood, under cover of cyclosporin A. Grafts were subjected to minimal cold preservation or to 30 mins warm ischemia followed by 24 hrs cold preservation. RESULTS: After an initial peak of renal dysfunction, serum creatinine concentration returned to normal in isografts and nonischemic allografts, but remained significantly elevated in ischemic allografts (P<0.0002) throughout 6 months follow-up. Both allograft groups developed proteinuria. At 6 months, ischemic isografts and nonischemic allografts demonstrated very mild tubular atrophy and interstitial fibrosis. Tubulointerstitial injury was significantly more severe in ischemic allografts (P<0.01 vs. nonischemic allografts) and was associated with increased infiltrating monocyte/macrophages and NK cells (P<0.05). Moderate glomerulosclerosis was a feature of both allograft groups (P<0.05). CONCLUSIONS: The modified allogeneic response in operationally tolerant recipients acts in synergy with ischemia/reperfusion injury in the development of chronic damage. Strategies to limit or modify the initial ischemia/reperfusion injury may ameliorate chronic tubulointerstitial damage. Progressive glomerular damage and proteinuria in allografts may require other pharmacological intervention.     

Cold ischemia augments allogeneic-mediated injury in rat kidney allografts

BACKGROUND: Some clinical studies demonstrate that kidney grafts with prolonged cold ischemia experience early acute rejection more often than those with minimal ischemia. The mechanism, however, is putative. Therefore, the aim of this study was to unravel the impact of ischemia on the immune response in rat kidney allografts compared with that in isografts. METHODS: To induce ischemic injury, donor kidneys were preserved for 24 hours in 4 degrees C University of Wisconsin solution before transplantation. No immunosuppression was administered. The histomorphology according to the BANFF criteria for acute rejection and infiltrating cells were assessed at days 1, 2, 3, 4, 6, and 8 post-transplantation. RESULTS: In allografts, exposure of the kidney to ischemia led to a significantly earlier onset of interstitial cell infiltration and tubulitis compared with nonischemic allografts. The BANFF score of interstitial cell infiltration was 1 +/- 0 vs. 0.25 +/- 0.29 at day 3 and 2 +/- 0 vs. 1.25 +/- 0.25 at day 4. In contrast, in isografts, the effect of ischemia on the histology was not significant. From day 6, the histologic differences between ischemic and nonischemic grafts disappeared. Ischemia led to a more intense expression of P-selectin (day 1), intercellular adhesion molecule-1 (ICAM-1; day 2), and major histocompatibility complex (MHC) class II on endothelium and proximal tubular cells (day 2) in both allografts and isografts. Concurrently with the up-regulated ICAM-1 and MHC expression, significantly more CD4(+) cells and macrophages infiltrated the ischemic allografts at days 2 and 3 and the ischemic isografts at day 4. Importantly, the influx of these cells after ischemia was significantly greater in allografts than in isografts. CONCLUSIONS: Cold ischemia augments allogeneic-mediated cell infiltration in rat kidney allografts. The earlier onset of acute rejection in 24-hour cold preserved allografts may be prevented by better preservation or treatment using tailored immunosuppression.     

Altered intragraft immune responses and improved renal function in MHC class II-deficient mouse kidney allografts

BACKGROUND: During renal allograft rejection, expression of MHC class II antigens is up-regulated on the parenchymal cells of the kidney. This up-regulation of MHC class II proteins may stimulate the intragraft alloimmune response by promoting their recognition by recipient CD4+ T cells. In previous studies, absence of donor MHC class II antigens did not affect skin graft survival, but resulted in prolonged survival of cardiac allografts. METHODS: To further explore the role of MHC class II antigens in kidney graft rejection, we performed vascularized kidney transplants using donor kidneys from A(beta)b-deficient mice that lack MHC class II expression. RESULTS: At 4 weeks after transplant, GFR was substantially depressed in control allografts (2.18+/-0.46 ml/min/kg) compared to nonrejecting isografts (7.98+/-1.62 ml/min/kg; P<0.01), but significantly higher in class II- allografts (4.38+/-0.60 ml/min/kg; P<0.05). Despite the improvement in renal function, class II- allograft demonstrated histologic features of acute rejection, not unlike control allografts. However, morphometric analysis at 1 week after transplantation demonstrated significantly fewer CD4+ T cells infiltrating class II- allografts (12.8+/-1.2 cells/mm2) compared to controls (25.5+/-2.6 cells/mm2; P=0.0007). Finally, the intragraft profile of cytokines was altered in class II- allografts, with significantly reduced expression of Th2 cytokine mRNA compared to controls. CONCLUSIONS: These results support a role of MHC class II antigens in the kidney regulating immune cells within the graft. Further, effector pathways triggered by class II antigens promote renal injury during rejection.     

Real-time polymerase chain reaction analysis reveals an evolution of cytokine mRNA production in allograft acceptor mice

BACKGROUND: The relative contribution of pro-inflammatory and anti-inflammatory cytokines in promoting the rejection or acceptance of experimental cardiac allografts remains controversial. We hypothesized that the posttransplantation induction of a new immune response to graft alloantigens at a distant delayed-type hypersensitivity (DTH) site would force the immune system to reveal its current disposition toward graft alloantigen as it initiates the new immune response. Thus, we should be able to monitor the evolution of the immunologic relationship between allograft recipients and their grafts at any time posttransplantation by challenging the recipient for DTH responses to donor alloantigen and evaluating the cytokine profiles displayed at the DTH site. METHODS: We have used the sensitive and quantitative technique of real-time polymerase chain reaction to evaluate the patterns of donor alloantigen-induced cytokine mRNA production for interleukin (IL)-2, interferon (IFN)-gamma, IL-4, IL-10, and transforming growth factor (TGF)-beta. We evaluated cytokine mRNA expression in cardiac allografts and in donor alloantigen-challenged DTH sites in mice that have either accepted or rejected cardiac allografts. RESULTS: We observed the following. (1) Normal hearts and pinnae exhibited detectable baseline production of cytokine mRNAs: TGF-beta>IFN-gamma=IL-10>IL2->IL-4. (2) Both the accepted and rejecting cardiac allografts produced increased amounts of all cytokine mRNAs tested and displayed few quantitative differences in cytokine mRNA production. Notably, accepted allografts displayed enhanced IL-10 mRNA production on day 7 posttransplantation, but not on day 60 posttransplantation and reduced IFN-gamma mRNA production on day 60, but not day 7. (3) There was a high degree of variability in production levels among the various cytokine mRNAs, both for background levels and for allograft-stimulated levels. (4) Donor-reactive DTH sites of allograft rejector mice displayed a broad array of cytokine mRNAs, whereas the DTH sites of allograft acceptor mice displayed only IL-4 mRNA production. (5) Provision of exogenous TGF-beta or IL-10 at a DTH challenge site of allograft rejector mice caused a shift in the cytokine mRNA profile that minimized IFN-gamma and IL-2 mRNA production but spared IL-4, IL-10, and TGF-beta mRNA production. CONCLUSIONS: A broad array of cytokine mRNAs may be stockpiled for future use in cardiac allografts, regardless of whether the grafts will be accepted or rejected. This stockpile is continuously replenished for as long as the graft survives, thereby obscuring any changes in immune disposition of the graft recipient toward graft alloantigens. However, such changes can be revealed by challenge with donor alloantigens at a distant site (DTH challenge). In allograft acceptor mice, this disposition evolves from pro-inflammatory to anti-inflammatory.     

Intragraft cytokine profile during human liver allograft rejection.

Forty-three human liver allograft biopsies and normal liver were directly analyzed for inflammatory and immunoregulatory cytokine gene expression by polymerase chain reaction (PCR). IL-5 gene expression was predominantly present in biopsies from liver allografts with histopathological evidence of acute rejection. IL-2 gene expression was rarely observed in rejecting allografts or allografts without evidence of rejection. In contrast, IL-4 message was readily detectable in the majority of liver allografts regardless of clinical status. The inflammatory mediators IL-1 beta, TNF-alpha, and IL-6 were detected with similar frequency in rejecting allografts and allografts without evidence of rejection. These findings suggest that inflammatory and immunoregulatory cytokines are produced within the allograft. Moreover, IL-5 may play a role in the local mechanisms of liver allograft rejection.     

Antiproliferative effects of NKH477, a forskolin derivative, on cytokine profile in rat lung allografts.

OBJECTIVE: NKH477 was recently identified as a water-soluble forskolin derivative and was reported to prolong survival of murine cardiac allografts. However, the mechanism of the efficacy is not clear in vivo. The aim of this study was to investigate the immunosuppressive effects of NKH477 on acute lung allograft rejection in the rat model and its mechanism of action in vivo. METHODS: Left lungs were transplanted orthotopically from Brown-Norway donors to Lewis recipients. Recipient rats were untreated or treated daily with different doses of NKH477. Grafts were excised on Day 3 or Day 5 to determine histopathological rejection and expressions of interleukin (IL)-2, IL-4, IL-10, and interferon (IFN)-gamma by enzyme-linked immunosorbent assay. The cytokine expression at Day 3 or Day 5 was also evaluated in recipient spleens by immunohistochemistry. Furthermore, mesenteric lymph node cells from recipients at Day 5 were cultured alone or stimulated with donor antigens for 72 hours to determine cell proliferation by means of thymidine incorporation. RESULTS: NKH477 significantly extended allograft survival time in a dose-dependent manner and reduced histopathological rejection. Treatment with NKH477 inhibited IFN-gamma and IL-10 expression, whereas expression of these cytokines were markedly upregulated in the untreated allografts. Expression of IL-2 and IL-10 also increased in the spleen of untreated allorecipients. NKH477 suppressed expression of both cytokines in the spleen. In addition, lymphocyte proliferation was inhibited in NKH477-treated recipients as compared with untreated recipients. CONCLUSION: These results suggest that NKH477 exerts an antiproliferative effect on lymphocytes in vivo with an altered cytokine profile in rat recipients of lung allografts.     

Interleukin-18 Affects Local Cytokine Expression But Does Not Impact on the Development of Kidney Allograft Rejection

Interleukin-18 is predominantly a macrophage-derived cytokine with a key role in inflammation and cell-mediated immunity. Having previously demonstrated IL-18 upregulation in a rat model of kidney rejection, here we examined IL-18 in a fully MHC-mismatched murine model of acute kidney rejection using IL-18-deficient recipients (IL-18-/-) and animals administered neutralizing IL-18 binding protein (IL-18BP). Gene expression of IL-18 and its receptor were significantly upregulated in allografts compared to isografts, as was the cellular infiltrate (T cells and macrophages) (p < 0.001). Allografts developed kidney dysfunction (p < 0.05) and tubulitis (p < 0.01) not observed in controls. There was a significant reduction in gene expression of IL-18 downstream pro-inflammatory molecules (iNOS, TNFalpha and IFNgamma) in IL-18-/- recipients (p < 0.01), and IL-18BP-treated animals. The CD4+ infiltrate and IL-4 mRNA expression was greater in the IL-18-/- recipients than wild-type (WT) allografts and IL-18BP-treated animals (p < 0.05), suggesting a Th2-bias which was supported by IFNgamma and IL-4 ELISPOT data and an increased eosinophil accumulation (p < 0.001). Neither IL-18 deficiency nor neutralization prevented renal dysfunction or tubulitis. This study demonstrates increased production of IL-18 in murine kidney allograft rejection and provides evidence that IL-18-induced pathways of inflammation are active. However, neither IL-18 deficiency nor neutralization was protective against the development of allograft rejection.     

Mixed hematopoietic chimerism prevents allograft vasculopathy.

BACKGROUND: Mixed hematopoietic chimerism has been shown to induce long-term acceptance of transplant organs. We determined whether mixed chimerism prevented allograft vasculopathy, using the rat aortic allograft model. METHODS: Mixed chimeras were prepared by reconstituting lethally irradiated (1100 cGy) WF rats with a mixture of T-cell depleted (TCD) syngeneic (WF) plus TCD allogeneic (ACI) bone marrow. Donor-specific (ACI) or third-party (F344) aortic grafts were transplanted into mixed chimeric animals 1 to 2 months after bone marrow reconstitution. No immunosuppressive drugs were administered. At 30 days postoperatively, aortic allografts were harvested for histology and measurement of cytokine mRNA by semiquantitative RT-PCR. Some aortic grafts were harvested at 90 and 180 days after transplantation for histological analysis. The degree of intimal hyperplasia and cytokine gene expression were compared among 4 groups: I (syngeneic; ACI donors to ACI recipients), II (allografts; ACI to WF), III (donor specific; ACI donor to chimeras) and IV (third-party; F344 to chimeras). RESULTS: There was no difference in the degree of intimal hyperplasia (IH) between groups I and III. Groups II and IV had significantly more IH than group I. Compared to group I, levels of mRNA for IFN-y, IL-2, IL-10 and iNOS in groups II and IV were higher, while there was no difference in mRNA levels between group I and III. CONCLUSIONS: These data suggest that mixed chimerism prevents allograft vasculopathy. Mixed chimerism holds great promise in clinical transplantation as a means to prevent allograft vasculopathy.     

1alpha,25-dihydroxyvitamin D3 shows strong and additive immunomodulatory effects with cyclosporine A in rat renal allotransplants.

BACKGROUND: Vitamin D3 and its metabolites have long been found to exert immunosuppressive effects both in vivo and in vitro. The present study investigated the effect of 1alpha,25-dihydroxycholecalciferol (1,25DHC) on vascularized renal allografts in rats. METHODS: Three days prior to transplantation, two groups of animals were subjected to 1,25DHC (1 microg/kg/day IP) and a low calcium diet, which was continued until the end of the experiments. Recipient organs were removed and single allografts were transplanted in a high responder strain combination (ACI --> Lewis). Following transplantation, low-dose cyclosporine A (3.2 mg/kg/day CsA) administration was started in two experimental groups of recipients (one group receiving 1,25 DHC additionally) whereas the control allograft recipients received no immunosuppression (control III). Graft survival and renal function was monitored until death or the end of experiments and allograft rejection was assessed histologically using the Banff classification. RESULTS: 1,25DHC significantly prolonged allograft survival in comparison to control III (9.6 +/- 1 vs. 5.7 +/- 0.2 days; P=0.009). In addition, a combination of 1,25DHC and low-dose CsA increased allograft survival compared to CsA administration alone (24 +/- 0.9 vs. 13 +/- 0.3 days; P=0.008). 1,25DHC preserved renal creatinine clearance and decreased proteinuria in comparison to control III, and the combination of 1,25DHC and low-dose CsA again showed an additive effect on preservation of renal function. 1,25DHC and low-dose CsA both decreased interleukin (IL)-2 and IL-12 expression levels in serum and allografts, and a combination treatment produced the strongest attenuation of IL-2 and IL-12 expression. In addition, 1,25DHC increased IL-4 and IL-10 expression levels in allografts, whereas CsA alone did not alter IL-4 and IL-10 expression. In contrast, combination of 1,25DHC and low-dose CsA showed a significant increase in IL-10 expression levels whereas IL-4 expression was not elevated. CONCLUSION: Monotherapy with 1,25DHC significantly prolongs survival of renal allografts and preserves graft function in rats. A combination of 1,25DHC and CsA caused an additive effect on graft survival with differential regulation of pro- and anti-inflammatory cytokines, as compared to 1,25DHC administration alone.     

The effect of A2A adenosine receptor agonist on composite tissue allotransplant survival: an in vivo preliminary study

BACKGROUND: In vitro experimental studies showed that A2a receptor agonists reduce allostimulatory functions of the dendritic cells through modulation of surface expression of the costimulatory molecules and down-regulation of cytokines. Similar suppressive effects on dendritic cells have also been observed with Cyclosporine A (CsA). In this study we sought to explore if combined use of these two drugs in vivo could prolong the survival of composite tissue allografts across MHC barriers. MATERIALS AND METHODS: A total of 24 hindlimb transplantations were performed across a major MHC barrier from Brown Norway rats (BN; RT1n) to Lewis rats (Lew; RT1l) In the control group, either isografts (group 1, n = 2) or allografts (group 2, n = 3) were performed and no treatment was given. In the experimental group three kinds of treatment protocols were used: (1) A2a adenosine receptor agonist alone (group 3, n = 6); (2) CsA alone (group 4, n = 7); and (3) A2a adenosine receptor agonist + CsA combined treatment (group 5, n = 6). Mean survival times of each group as well as cytokine levels including IL-2, IL-4, IL-10, INF-gamma, and TNF-alpha were analyzed by ELISA. RESULTS: Isografts survived indefinitely. The mean survival times for allograft groups (group 2 to 5) were 9.8 +/- 1.3, 10.5 +/- 1.0, 29.8 +/- 1.7, and 22 +/- 1.4 days, respectively. Statistically, there was no difference between the allograft control group and the A2a adenosine receptor agonist treated group (P = 0.35). However, survival of the allografts in the CsA-treated group was significantly higher than the A2a adenosine receptor agonist treated (P < 00001) and combined CsA + A2a adenosine receptor agonist treated group (P < 0.0001). In vivo A2a adenosine receptor agonist treatment alone increased the levels of IL-2, INF-gamma, and TNF-alpha, which are important cytokines for induction of allotransplant rejection. However A2a adenosine receptor agonist in combination with CsA significantly reduced the levels of suppressor cytokines IL-4 and IL-10. CONCLUSION: As opposed to the previous in vitro studies, the results from this in vivo study showed that A2a adenosine receptor agonist treatment does not prolong composite tissue allograft survival. Compared to CsA treatment alone, the allotransplant survival was even shorter with the combined treatment. Treatment with A2a adenosine receptor agonist possibly promotes the differentiation of alloreactive CD4 cells predominantly into T-helper 1 phenotype. As a result, the levels of stimulatory cytokines contributing to allograft rejection are increased and suppressor cytokines are reduced, leading to accelerated allograft rejection.     

Late graft dysfunction after prolonged cold ischemia of the donor kidney: inhibition by cyclosporine.

BACKGROUND: The present study was devised to elucidate the influence of prolonged cold ischemia on the development of chronic transplant dysfunction (CTD) in kidney isografts (Brown Norway-->Brown Norway; BN-->BN) and in kidney allografts (BN-->Wistar Agouti/ Rij [WAG]) under temporary cyclosporine (CsA) therapy. METHODS: To induce ischemic injury, BN donor kidneys were preserved for 24 hr in 4 degrees C University of Wisconsin solution before transplantation. Renal function (proteinuria), histomorphology according to the BANFF criteria for CTD, and infiltrating cells were assessed. Grafts were examined both early at days 2, 3, 6, and 10, and late at week 26 (allografts) or at week 52 (isografts). RESULTS: Nonischemic isografts preserved a normal function and morphology. Ischemic isografts developed a progressive proteinuria over time and demonstrated significantly more glomerulopathy with macrophage (Me) infiltration and intimal hyperplasia than nonischemic controls at week 52. During the initial 10 days, there was an increased infiltration of MHC class II+ cells, predominantly CD4+ cells and Mphi, coinciding with up-regulated intercellular adhesion molecule-1 expression. CsA treatment in ischemic isografts inhibited infiltration of MHC II+ cells in the early stage, which was accompanied by significantly less renal damage at week 52 compared with untreated controls (proteinuria: 59+/-8 vs. 134+/-19 mg/24 hr; BANFF score: 2.8+/-0.4 vs. 4.3+/-1.0). Under CsA therapy, 24-hr cold ischemia of the allograft affected neither the onset or progress of proteinuria, nor the histomorphology (BANFF score: 7.8+/-2.4 vs. 7.3+/-1.9). In both ischemic and nonischemic allografts, intercellular adhesion molecule-1 expression and mononuclear cell infiltration (CD4, CD8, Mphi was abundantly present during the first 10 days and function deteriorated rapidly. CONCLUSIONS: Prolonged cold ischemia plays a role in the induction of CTD, but its deleterious effect can be successfully inhibited by CsA. Therefore, the alloantigeneic stimulus is the overriding component in the multifactorial pathogenesis of CTD.     

排斥反应中移植心脏局部白细胞介素1βmRNA的表达状态

目的 探讨白细胞介素（IL）-1βmRNA在移植心脏局部表达状态与移植心脏自然生存时间的关系。方法 建立大鼠异位心脏移植模型,不同品系大鼠之间的移植供、受体分别为SD大鼠和Wistar大鼠（共66只）;同品系大鼠之间的移植供受体均为Wistar大鼠（共66只）。于术后第1、3、5、7、9、11天,分别切取移植心脏各6只,提取总RNA,将目的引物和对照引物在同一管中扩增,以两者象素值比值均数做曲线图,观察排斥反应时IL－1βmRNA的动态表达情况。结果 不同品系移植心脏的停跳高峰在术后第6－10天。排斥反应时移植心脏局部IL－1βmRNA的表达水平明显增高,峰值在术后第1天。结论 IL－1β在心脏移植排斥反应中可能起着重要作用,IL－1β mRNA的动态检测可望成为早期诊断排斥反应的指标。     

Function of the vascular endothelial growth factor receptors Flt-1 and Flk-1/KDR in the alloimmune response in vivo

BACKGROUND: We have recently reported that vascular endothelial growth factor (VEGF) functions as a proinflammatory cytokine to regulate the trafficking of leukocytes into allografts in the early posttransplant period. VEGF binds two major VEGF receptors: VEGFR-1 (flt-1) and VEGFR-2 (flk-1/KDR). Here, we wished to investigate the expression and function of VEGF receptors in the process of acute allograft rejection in vivo. METHODS: We performed fully MHC-mismatched C57BL/6 (H-2b) into BALB/c (H-2d) vascularized heterotopic murine cardiac transplants and we examined the expression of VEGF and VEGF receptors by immunohistochemistry during acute allograft rejection. Next, we treated mice with specific neutralizing monoclonal antibodies against murine VEGFR-1 and VEGFR-2 and examined their effect on the development of acute allograft rejection by histology and by analysis of graft survival. The intragraft expression of cytokines and chemokines were also evaluated by quantitative real-time PCR analysis. RESULTS: The expression of VEGF, VEGFR-1 and VEGFR-2 were significantly up-regulated during allograft rejection as compared to isografts. Administration of either anti-VEGFR-1 or anti-VEGFR-2 alone failed to inhibit allograft rejection. However, coadministration of both antibodies together inhibited leukocyte infiltration of allografts and prolonged allograft survival. Furthermore, the effect of VEGFR blockade was associated with the downregulation of intragraft cytokine and chemokine expression. CONCLUSIONS: Our data suggest that VEGF-VEGFR interactions function in the alloimmune response in vivo. Targeting VEGFRs may represent a novel therapy to protect allografts following clinical transplantation.