Arterial intimal thickening produced by alloantibody and xenoantibody

Approach and Management of Hypertension After Kidney Transplantation

Hypertension is one of the most common cardiovascular co-morbidities after successful kidney transplantation. It commonly occurs in patients with other metabolic diseases, such as diabetes mellitus, hyperlipidemia, and obesity. The pathogenesis of post-transplant hypertension is complex and is a result of the interplay between immunological and non-immunological factors. Post-transplant hypertension can be divided into immediate, early, and late post-transplant periods. This classification can help clinicians determine the etiology and provide the appropriate management for these complex patients. Volume overload from intravenous fluid administration is common during the immediate post-transplant period and commonly contributes to hypertension seen early after transplantation. Immunosuppressive medications and donor kidneys are associated with post-transplant hypertension occurring at any time point after transplantation. Transplant renal artery stenosis (TRAS) and obstructive sleep apnea (OSA) are recognized but common and treatable causes of resistant hypertension post-transplantation. During late post-transplant period, chronic renal allograft dysfunction becomes an additional cause of hypertension. As these patients develop more substantial chronic kidney disease affecting their allografts, fibroblast growth factor 23 (FGF23) increases and is associated with increased cardiovascular and all-cause mortality in kidney transplant recipients. The exact relationship between increased FGF23 and post-transplant hypertension remains poorly understood. Blood pressure (BP) targets and management involve both non-pharmacologic and pharmacologic treatment and should be individualized. Until strong evidence in the kidney transplant population exists, a BP of <130/80 mmHg is a reasonable target. Similar to complete renal denervation in non-transplant patients, bilateral native nephrectomy is another treatment option for resistant post-transplant hypertension. Native renal denervation offers promising outcomes for controlling resistant hypertension with no significant procedure-related complications. This review addresses the epidemiology, pathogenesis, and specific etiologies of post-transplant hypertension including TRAS, calcineurin inhibitor effects, OSA, and failed native kidney. The cardiovascular and survival outcomes related to post-transplant hypertension and the utility of 24-h blood pressure monitoring will be briefly discussed. Antihypertensive medications and their mechanism of actions relevant to kidney transplantation will be highlighted. A summary of guidelines from different professional societies for BP targets and antihypertensive medications as well as non-pharmacological interventions, including bilateral native nephrectomy and native renal denervation, will be reviewed.

Antibody ligation of human leukocyte antigen class I molecules stimulates migration and proliferation of smooth muscle cells in a focal adhesion kinase-dependent manner

Chronic rejection manifests as transplant vasculopathy, which is characterized by intimal thickening of the vessels of the allograft. Intimal thickening is thought to result from the migration and proliferation of vascular smooth muscle cells (SMC) in the vessel media, followed by deposition of extracellular matrix proteins. The development of post-transplantation anti-human leukocyte antigen (HLA) antibodies (Ab) is strongly correlated with the development of transplant vasculopathy and graft loss. Here we demonstrate that cross-linking of HLA class I molecules on the surface of human SMC with anti-HLA class I Ab induced cell proliferation and migration. Class I ligation also increased phosphorylation of focal adhesion kinase (FAK), Akt, and ERK1/2 in SMC. Knockdown of FAK by siRNA attenuated class I-induced phosphorylation of Akt and ERK1/2, as well as cell proliferation and migration. These results indicate that ligation of HLA class I molecules induces SMC migration and proliferation in a FAK-dependent manner, which may be important in promoting transplant vasculopathy.

Conversion from cyclosporin A to sirolimus retards the progression of chronic allograft nephropathy in the long term in a rat kidney transplantation model

In a rat renal allograft model, the long-term effect of conversion from cyclosporin A (CsA) to sirolimus on recipient kidneys and growth factor expression were compared with continuous use or withdrawal of CsA. Kidneys from Fisher 344 rats were orthotopically transplanted into Lewis rats. Four Fisher 344 to Lewis allograft groups were treated post-transplant as follows: (i) CsA (transplant to week 8) then sirolimus (weeks 8 - 24); (ii) CsA (transplant to week 24); (iii) CsA (transplant to week 8) then vehicle (weeks 8 - 24); (iv) control vehicle (transplant to week 24). A fifth group underwent syngeneic isograft (Lewis to Lewis) with no drug treatment. Proteinuria was measured every 4 weeks and grafts harvested at 24 weeks for morphological and immunohistochemical analysis. Conversion from CsA to sirolimus resulted in a significant decrease in proteinuria at 24 weeks, a lower Banff sum score and lower expression of transforming growth factor mRNA compared with continuous use or withdrawal of CsA. In conclusion, conversion from CsA to sirolimus retarded progression of chronic allograft nephropathy in the rat model.

Vascular complications in renal transplantation: a single-center experience in 1367 renal transplantations and review of the literature

Renal transplantation is the treatment of choice for end-stage renal disease. Vascular complications in renal transplantation are not uncommon and may often lead to allograft loss. The most common vascular complications are transplant renal artery stenosis, transplant renal artery thrombosis, transplant renal vein thrombosis, biopsy-induced vascular injuries, pseudoaneurysm formation, and hematomas. Transplant renal artery and vein thrombosis have an early onset and a dramatic clinical manifestation and usually lead to allograft loss. In contrast, transplant renal artery stenosis has better treatment possibilities, whereas the rest do not occur so often. In our institution, 1367 renal transplantations were performed from September 1980 to April 2005. During this period, we encountered 38 major vascular complications leading to graft loss and 19 transplant renal artery stenoses with successful treatment in the majority of cases. According to these data, we can conclude that renal transplantation is a safe therapeutic procedure for renal failure.

Role of alloantibodies in the pathogenesis of graft arteriosclerosis in cardiac transplantation

Graft arteriosclerosis (GA) remains the leading obstacle to long-term survival of cardiac allografts. The pathogenesis of this chronic disease, though perceived to be multifactorial, is most likely immune-driven. Based on clinical and experimental observations, the humoral arm of the immune system has long been suspected to play a pivotal role in the disease process. In this article, we shall review the evidence generated from key clinical and experimental studies on the role of alloantibodies in GA. We will argue that although the strong correlation between the presence of anti-donor antibodies in clinical and experimental GA is highly suggestive of a pathogenic role for alloantibodies, a direct causal link between GA and the humoral arm of the alloresponse cannot yet be established based on the currently available evidence, and may in fact be one of a number of pathogenic processes that potentiate this vasculopathy. Finally, in this article, we shall discuss some of the potential mechanisms by which alloantibodies may exert their pathogenic effect in GA.

Percutaneous treatment of transplant renal artery stenosis in children

Percutaneous treatment of renal artery stenosis (RAS) is an accepted procedure and numerous reports have been published. However, experience with its use in RAS in the transplanted kidney in children is scarce. Since 1994 we have diagnosed RAS in seven children with the use of Doppler ultrasonography (US), confirming it with percutaneous angiography (PAG). In six of the seven patients percutaneous transluminal angioplasty (PTA) was performed. In one patient a metallic stent was placed due to the extension of the arterial lesion, and a second stent was placed in another child when a re-stenosis was diagnosed 1 month after the PTA. All patients presented with hypertension (de novo or 30% increase over previous values). After ruling out acute rejection, calcineurin inhibitor toxicity, and urinary obstruction, US was performed and, when an increase in arterial flux velocity was registered, PAG was also performed. Six children showed an increase in serum creatinine (Cr) and proteinuria. Blood pressure decreased after the procedure and Cr returned to previous levels in all children. One of the grafts was lost due to chronic transplant rejection 7 years later. The other children have a functioning kidney. Although this is a small group of patients, the consistently good results and the lack of reported experience prompted us to communicate our preliminary observation.

Prevention of chronic rejection by pravastatin in a rat kidney transplant model

BACKGROUND

Pravastatin when administered with cyclosporine (CsA) has been shown to ameliorate transplant vasculopathy in the clinical setting. Previously we showed that pravastatin prevents chronic rejection in rat cardiac and liver transplant models. Here we determine whether pravastatin prevents chronic rejection in a rat renal allograft model.

METHODS

Orthotopic renal transplantations were performed using Fisher 344 rats as donors and Lewis rats as recipients. Recipients were treated with low-dose CsA for 10 days to prevent acute rejection. Recipients were divided into three groups: CsA, CsA + pravastatin, and syngeneic. Renal function was assessed by serum creatinine level at day 130. Allografts were evaluated by histology and immunohistochemistry. Serum levels of alloantibodies were measured by flow cytometry. Intragraft cytokine mRNA expression was determined by semiquantitative reverse transcriptase-polymerase chain reaction. Intragraft levels of the antiapoptotic Bag-1 gene were measured by Western blot.

RESULTS

Unlike allografts from the pravastatin group, control allografts demonstrated glomerulosclerosis, vascular obliteration, tubular atrophy, and interstitial fibrosis. Serum creatinine levels and graft infiltration of T cells and macrophages in the pravastatin-treated animals were significantly lower. Intragraft cytokines showed a T helper 2 polarization and decreased transforming growth factor-beta in the pravastatin group. Intragraft expression of Bag-1 was increased in the pravastatin group.

CONCLUSION

This study demonstrates the ability of pravastatin to inhibit chronic rejection in rat renal allografts. Pravastatin's pleiotropic effects of reducing intragraft inflammatory cytokines, inhibiting immune cell infiltration, and causing up-regulation of the antiapoptotic gene Bag-1 suggest that its ability to prevent transplant chronic rejection may be multifactorial.

Renal Arterial Stenosis in Renal Allografts: Retrospective Study of Predisposing Factors and Outcome after Percutaneous Transluminal Angioplasty

PURPOSE

To determine the predisposing factors to transplant renal arterial stenosis (TRAS) and assess the outcome of percutaneous transluminal angioplasty (PTA) as the primary treatment.

MATERIALS AND METHODS

Of 831 renal allograft recipients (584 cadaveric, 247 living related) between January 1991 and December 1998, 72 had hypertension and/or renal dysfunction. All 72 underwent arteriography, and their medical charts were retrospectively reviewed.

RESULTS

Prevalence of TRAS was 3.1% (26 of 831). Technical success rate of PTA was 94% (16 of 17), and clinical success rate was 82% (14 of 17). Those with renal dysfunction had a mean pre-PTA creatinine value of 2.6 mg/dL (230 micromol/L) +/- 0.5 (SD) versus a 1-week post-PTA value of 1.7 mg/dL (150 micromol/L) +/- 0.3 (P <.001). Of those with hypertension, all but one had substantial improvement in mean diastolic blood pressure. At 26.9 months mean follow-up in 16 patients with successful PTA, two stenoses reoccurred, and two grafts were lost to chronic rejection. TRAS was present in 14 of 45 end-to-side anastomoses and 12 of 27 end-to-end anastomoses (P =.31), and TRAS was more prevalent in cadaveric grafts (24 of 584) than in living related grafts (two of 247). In cadaveric grafts, the mean cold ischemia time was 29.0 hours +/- 6.9 in those with TRAS (n = 24), as compared with 25.5 hours +/- 8.1 in those with no TRAS (n = 39; P = .35). Seven of 17 patients with acute rejection and six of 35 with chronic rejection had TRAS.

CONCLUSION

Primary treatment of TRAS with PTA has good intermediate-term results. TRAS is more prevalent in cadaveric allografts with long cold ischemia time.

Angiographic evaluation and treatment of transplant renal artery stenosis

Transplant renal artery stenosis is an uncommon but important complication of renal transplantation. It is a potentially reversible cause of patient morbidity and allograft dysfunction, which can present both early and late in the post-transplant period. Although transplant renal artery stenosis can be detected using noninvasive imaging, definitive diagnosis and percutaneous treatment typically require the use of invasive angiographic techniques. In experienced hands, these studies can be performed safely, effectively and with a low risk of contrast induced nephrotoxicity when alternative contrast agents are used.

Peripheral vascular disease and renal transplant artery stenosis: a reappraisal of transplant renovascular disease

BACKGROUND

Renal transplant artery stenosis (RTAS) continues to be a problematic, but potentially correctable, cause of post-transplant hypertension and graft dysfunction. Older transplant recipients, prone to peripheral vascular disease (PVD), may have pseudoRTAS with PVD involving their iliac system.

METHODS

We retrospectively analyzed 819 patients who underwent kidney transplantation between 1993 and 1997 to determine the contribution of pseudoRTAS to renal transplant renovascular disease. Univariate analyses were performed for donor and recipient variables, including age, weight, gender, race, renal disease, cholesterol and creatinine values, human leukocyte antigen (HLA) matching, cytomegalovirus (CMV) infection, and immunosuppressive medications. Significant variables were then analyzed by a Cox proportional hazards model.

RESULTS

Ninety-two patients (11.2%) underwent renal transplant arteriogram (Agram) or magnetic resonance angiography (MRA) for suspected RTAS. RTAS or pseudoRTAS, defined as one or more hemodynamically significant lesions in the transplant artery or iliac system, was evident in 44 patients (5.4%). Variables significantly associated with RTAS by univariate analysis were weight at the time of transplant (p = 0.0258), male gender (p = 0.034), discharge serum creatinine > 2 mg/dL (p = 0.0041), and donor age (p = 0.0062). Variables significantly associated with pseudoRTAS by univariate analysis were weight at the time of transplant (p = 0.0285), recipient age (p = 0.0049), insulin-dependent diabetes mellitus (IDDM; p = 0.0042), panel reactive antibody (PRA) at transplant (p = 0.018), and body mass index (p = 0.04). Weight at transplant and donor age remained significantly associated with an increased risk for RTAS in a multivariate stepwise Cox proportional hazards model. IDDM, transplant PRA, weight at transplant, and donor age were significantly associated with an increased risk for pseudoRTAS in a multivariate stepwise Cox proportional hazards model. Importantly, both RTAS and pseudoRTAS were associated with poorer graft survival (p < 0.007 for each).

CONCLUSIONS

Renal transplant renovascular disease encompasses pre-existing PVD acting as pseudoRTAS, as well as classical RTAS. Efforts to identify and correct renal transplant renovascular disease of either nature are important, given its negative impact on graft survival.

Alloantibody-Mediated Class I Signal Transduction in Endothelial Cells and Smooth Muscle Cells: Enhancement by IFN-γ and TNF-α

Chronic rejection is the major limiting factor to long term survival of solid organ allografts. The hallmark of chronic rejection is transplant atherosclerosis, which is characterized by the intimal proliferation of smooth muscle cells, endothelial cells, and fibroblasts, leading to vessel obstruction, fibrosis, and eventual graft loss. The mechanism of chronic rejection is poorly understood, but it is suspected that the associated vascular changes are a result of anti-HLA Ab-mediated injury to the endothelium and smooth muscle of the graft. In this study we have investigated whether anti-HLA Abs, developed by transplant recipients following transplantation, are capable of transducing signals via HLA class I molecules, which stimulate cell proliferation. In this report we show that ligation of class I molecules with Abs to distinct HLA-A locus and HLA-B locus molecules results in increased tyrosine phosphorylation of intracellular proteins and induction of fibroblast growth factor receptor expression on endothelial and smooth muscle cells. Treatment of cells with IFN-γ and TNF-α up-regulated MHC class I expression and potentiated anti-HLA Ab-induced fibroblast growth factor receptor expression. Engagement of class I molecules also stimulated enhanced proliferative responses to basic fibroblast growth factor, which augmented endothelial cell proliferation. These findings support a role for anti-HLA Abs and cytokines in the transduction of proliferative signals, which stimulate the development of myointimal hyperplasia associated with chronic rejection of human allografts.

Marked mitigation of transplant vascular sclerosis in FasLgld (CD95L) mutant recipients. The role of alloantibodies in the development of chronic rejection

BACKGROUND

In the acute rejection of allografts, the interaction between Fas (CD95) and its ligand (FasL; CD95L) has been shown to be involved in mediating apoptotic cell death. The role, however, of these molecules in the pathogenesis of transplant vascular sclerosis is as yet undetermined. The present study was therefore designed to address this issue.

MATERIAL

C3H/HEJ FasLgld (FasL-; H2k) spontaneously mutant mice were used either as donors or recipients of aortic allografts; wild-type C57B1/6 (B6; H2b) were used as corresponding recipients or donors (n=6/group), respectively. Controls included aortas transplanted across appropriate allogeneic and syngeneic strain combinations. For histopathological evaluations, the grafts were harvested at day 40 after transplantation, at which time, splenocytes and sera were also obtained for mixed leukocyte reaction and complement-mediated microcytotoxicity assays, respectively.

RESULTS

Similar to aortas obtained from allogeneic controls, allografts harvested from FasL- -->B6 recipients had morphological evidence of chronic rejection characterized by circumferential intimal thickening with partial disruption of the elastic membranes. Correspondingly, heightened antidonor cellular reactivity was also witnessed in these recipients. On the contrary, B6 allografts harvested from the majority of C3H-->FasL- recipients exhibited marked preservation of aortic morphology. Although these recipients had diminished antidonor cellular proliferation, the titers of alloantibodies were markedly elevated.

CONCLUSION

The presence of FasL-expressing functional cytotoxic T cells is required for the pathogenesis of transplant vascular sclerosis. The significant reduction and/or absence of chronic rejection with the concomitant retention of antidonor humoral response in C3H FasL- recipients of B6 aortas prompt us to suggest that perhaps posttransplantation vasculopathy is initiated by cell-mediated cytotoxicity with its perpetuation facilitated by alloantibodies.

Postoperative production of anti-donor antibody and chronic rejection in renal transplantation

To study the relevance of anti-donor antibody (ADA) to chronic rejection in kidney transplantation, we retrospectively examined the long-term kinetics of ADA by flow cytometric analysis. Among 537 recipients who underwent living-donor kidney transplantation between 1986 and 1994, 29 patients with chronic rejection (CR group) and 33 patients with stable graft function (ST group) were randomly selected for analysis. Patient serum taken 1 or 2 days before transplantation, serum taken 1 month after transplantation, and the most current serum were analyzed for the presence of ADA to donor T and B cells. In the CR group, IgG antibody to donor B cells of the most current serum was positive in 25 of 29 patients, whereas it was positive in only 5 patients in the ST group P<0.001. The mean fluorescent intensity of the antibody was also significantly higher in the CR group than that in ST group P<0.01. In contrast, IgG antibody to donor T cells of the most current serum was positive in only five patients in the CR group. No significant difference was observed in the pretransplant and 1-month posttransplant sera between the CR and ST groups. We conclude that the posttransplant production of IgG antibody to donor B cells seemed to be highly relevant to chronic rejection.

Anti-HLA antibody ligation to HLA class I molecules expressed by endothelial cells stimulates tyrosine phosphorylation, inositol phosphate generation, and proliferation

The major threat to long-term survival of solid organ allografts is chronic rejection. Progressive narrowing and ultimate luminal occlusion of the arteries and arterioles of the transplanted organ are the hallmarks of the disease. The mechanism of chronic rejection is poorly understood, but it is suspected that the associated vascular changes are a result of anti-HLA antibody-mediated injury to the endothelium. We have postulated that anti-HLA antibodies initiate chronic rejection by binding to class I molecules on the endothelium and transducing signals that result in endothelial cell activation and proliferation. Our data demonstrate that anti-HLA class I antibodies transduce signals in endothelial cells stimulating increased tyrosine phosphorylation of intracellular proteins. Antibody binding to class I antigens also leads to the generation of inositol phosphate and endothelial cell proliferation. These results indicate that anti-HLA antibodies can deliver functionally important signals to endothelial cells, a finding that may be fundamental to an understanding of the mechanisms of chronic rejection.

Monitoring of soluble HLA alloantigens and anti-HLA antibodies identifies heart allograft recipients at risk of transplant-associated coronary artery disease

The development of accelerated transplant-related coronary artery disease (T-CAD) is the major obstacle to long-term survival of cardiac allografts. We have investigated the role of various demographic and immunologic parameters as prognostic indicators of T-CAD in a population of 274 heart allograft recipients. Our data demonstrate that patients who experience more than 1 episode of acute rejection per year and/or develop antidonor HLA antibodies are at increased risk of developing T-CAD. Using HLA-A2 as a marker for the release of soluble HLA antigens from the donor, we established that recipients displaying circulating donor alloantigens for more than 26 weeks following transplantation are at increased risk of developing T-CAD (P=0.008). This association suggests that the release of alloantigens from the allograft is indicative of chronic injury and/or that it stimulates chronic rejection via the indirect allorecognition pathway. Our findings indicate that patients at risk of developing T-CAD can be identified by monitoring the release of donor alloantigens and production of antidonor HLA antibodies following transplantation.

Renal artery stenosis after renal transplantation

Stenosis of the transplant renal artery was discovered in 113 of 971 (11.6%) renal transplantation patients between three months and five years after transplantation. Diagnosis was reached by angiography performed because of hypertension, with or without impaired renal function. The stenosis was repaired in 63 patients with cure or improvement of hypertension in 35, and improvement of renal function in 12 of 23 patients with impaired renal function. The different types of stenosis were: recipient renal artery stenosis, suture line stenosis, donor artery stenosis (the most common), and multiple stenoses. The causes implicated were: recipient atheroma, faulty suture technique, hemodynamic disorders, trauma, and immunologic mechanisms. As the incidence of this complication is underestimated, routine angiography in all transplant recipients is suggested.

Ten years of experience with vascular complications in renal transplantation

From 1970 to 1980, 341 consecutive renal transplants were performed in 307 patients at our hospital. Operative technique was uniform and performed by a single surgeon. Acute arterial thrombosis occurred in 12 kidneys (3.5 per cent) and venous thrombosis occurred in 3 (0.9 per cent). All of these kidneys were lost. Renal artery stenosis, diagnosed in 17 kidneys (4.9 per cent), resulted from surgical technique or rejection and was associated with hypertension in all cases. Of these kidneys 5 responded to drug therapy alone, 4 to transluminal angioplasty and 5 to surgical reconstruction. Three grafts were lost. Vascular complications occurred in 9 per cent of our patients. The results suggest that factors other than surgical technique alone can contribute to the incidence of vascular complications.

Balloon catheter dilatation of stenotic renal artery anastomoses. Experiments in the pig

Stenotic renal artery anastomoses were produced in pigs in order to investigate the effects of transluminal angioplasty. Six weeks after surgery unilateral dilatation with a modern balloon catheter was performed in 8 pigs. These animals were reexamined with angiography and pressure gradient recording 8 to 10 weeks after dilatation and with post-mortem angiography 8 to 10 weeks later. Only 2 arteries had minimal residual stenoses, while in 6 arteries the stenoses were completely eliminated. Microscopic examination showed thinning of the fibrotic vessel wall, with defects in the internal elastic lamina.

Immunologic aspects of heart disease

All forms of heart disease, whether caused by streptococcus group A, aseptic heart injury, virus, hypersensitivity, autoimmune conditions, or graft-versus-host reactions, have in common allogenic transformation of the myocardial cell membrane and production of multifunctional autoantibodies, in addition to cause-specific antibodies, some of which cross-react with heart tissue. The outcome of this immunologic insult depends on the ability of the host's immunoregulatory mechanisms to dispose swiftly of the offending antigen and antibody or their complexes. Heart disease often results when these mechanisms, exemplified here, are not intact or when they function inappropriately in genetic or acquired settings and in varying haplotype frames.

Immunological aspects of atheroma: a review

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Immunologic considerations in renovascular hypertension

For decades certain diseases, such as glomerulonephritis, polyarteritis nodosa, scleroderma and serum sickness, have been linked with autoimmune pathogenesis. During recent years a host of additional diseases traditionally thought to have some genetic predisposition but with obscure etiology have been suspected of being autoimmune in nature. Rheumatoid arthritis, diabetes, myasthenia gravis and thyroiditis are diseases of widely divergent organ systems, yet may well have common pathways of pathology via immune complexing mechanisms. Herein we present evidence supporting the concept that renal artery stenosis (occurring primarily in association with the middle aortic syndrome or after renal transplantation) is of immune etiology. Although the specific antigenic agent is still to be defined there is growing acceptance of the theory that medium and large vessels are subject to autoimmune vasculitis in many aspects similar to the autoimmune affections of small vessels. Several cases are presented. Some of these suggest an immune reaction by the natural history but without evidence of immunochemical reactants in the involved vessels, presumably because active disease was arrested at the time of study. In other cases immunofluorescent preparations demonstrate reactants in the walls of the vessels to document the hypothesis more convincingly.

Arterial stenosis complicating renal allotransplantation in man: a study of 38 cases

Of 306 renal transplantations, stenosis of the artery supplying the grafted kidney was found in 38 patients three months to two years after they had undergone renal transplantation. The diagnosis was made by arteriography done because of refractory hypertension with or without impaired renal function in 36 patients and as a routine investigation in two normotensive patients. The stenosis was corrected surgically in 14 patients, with resultant lasting relief of hypertension in ten patients and improvement of renal function in five out of six patients with impaired renal function. Different types of stenosis were recognized: stenosis of the recipient artery, stenosis of the suture line, stenosis of the donor renal artery (segmental or diffuse) and multiple forms. The most frequent site of stenosis was the donor artery. There seems to be no single cause of stenosis: atheroma of the recipient vessels, faulty suture technique, hemodynamic disturbances, trauma to donor or recipient arteries account for some cases, whereas in other cases the evidence points to an immune mechanism. This complication of renal transplantation may be more frequent than is thought at present; therefore, routine renal arteriography should be performed at repeated intervals in all transplanted patients.