Macrophage index predicts short-term renal allograft function and graft survival

Renal PKC-ε deficiency attenuates acute kidney injury and ischemic allograft injury via TNF-α-dependent inhibition of apoptosis and inflammation

Acute kidney injury (AKI) increases the risk of morbidity and mortality after major surgery and transplantation. We investigated the effect of PKC-ε deficiency on AKI and ischemic allograft damage after kidney transplantation. PKC-ε-deficient and wild type (WT) control mice were subjected to 35 min of renal pedicle clamping to induce AKI. PKC-ε deficiency was associated with a marked improvement in survival and an attenuated loss of kidney function. Furthermore, functional MRI experiments revealed better renal perfusion in PKC-ε-deficient mice than in WT mice one day after IRI. Acute tubular necrosis and neutrophil infiltration were markedly reduced in PKC-ε-deficient mice. To determine whether this resistance to ischemia-reperfusion injury resulted from changes in local renal cells or infiltrating leukocytes, we studied a life-supporting renal transplant model of ischemic graft injury. We transplanted kidneys from H2b PKC-ε-deficient mice (129/SV) and their corresponding WT littermates into major histocompatibility complex-incompatible H2d recipients (BALB/c) and induced ischemic graft injury by prolonged cold ischemia time. Recipients of WT allografts developed severe renal failure and died within 10 days of transplantation. Recipients of PKC-ε-deficient allografts had better renal function and survival; they had less generation of ROS and upregulation of proinflammatory proteins (i.e., ICAM-1, inducible nitric oxide synthase, and TNF-α) and showed less tubular epithelial cell apoptosis and inflammation in their allografts. These data suggest that local renal PKC-ε expression mediates proapoptotic and proinflammatory signaling and that an inhibitor of PKC-ε signaling could be used to prevent hypoxia-induced AKI.

The biomechanical alterations in the CD14+ monocytes of patients with living donor renal transplantation

Living-donor renal transplantation is an ideal treatment for patients with end stage renal disease because it affords earlier transplantation and better graft for long term survival. CD14+ monocytes are the predominant inflammatory cells in renal allograft intimal arteritis. The biomechanical alterations in CD14+ monocytes would affect the function of graft. The aim of the present study was to explore the changes in the biorheological properties of CD14+ monocytes before and after the living donor renal transplantation. We found that the viscoelastic properties of CD14+ monocytes were greatly decreased after renal transplantation. Confocal microscopy showed that the F-actin content was increased when the oral immunosuppressive agents started. We also found that two cytoskeletal regulatory proteins, cofilin1 and profilin1, changed. Our results suggest that the immunosuppressive agents could significantly change the biorheological characteristics of the CD14+ mononuclear cells and the biomechanical changes may greatly affects their function, which would play a critical role to gain longer immune-tolerance stage.

Expression of hypoxia-inducible factor-1α (HIF-1α) in infiltrating inflammatory cells is associated with chronic allograft dysfunction and predicts long-term graft survival

BACKGROUND

In chronic kidney failure, a hypoxic state, infiltrating inflammatory cells play a crucial role in the progression to end-stage renal disease. No studies have evaluated the influence of hypoxia and infiltrating inflammatory cells on chronic allograft dysfunction.

METHODS

Renal transplant recipients who underwent renal allograft biopsy with interstitial fibrosis/tubular atrophy (IF/TA) were enrolled and renal allograft tissue sections were processed for immunohistochemical staining including hypoxia-inducible factor-1α (HIF-1α), nitrotyrosine, α-smooth muscle actin and e-cadherin. Patients with total renal tissue HIF score ≥1 were defined as positive for HIF-1α. To assess the phenotype of the infiltrating cells, dual staining of HIF-1α with CD45, CD68 and CD3 was performed. The correlation between HIF-1α score and Banff's score was analysed. Clinical parameters including renal survival among patients with or without an expression of HIF-1α were compared.

RESULTS

Out of 55 patients enrolled, 23 patients (41.8%) had an HIF-1α score ≥1 (Group B). Compared with Group A (total renal HIF score <1), Group B had a significantly higher Banff score of interstitial infiltrates (i) (P = 0.029), vascular fibrous intimal thickening (cv) (P = 0.007) and arteriolar hyaline thickening (ah) (P = 0.026). Clinically, patients with an HIF-1α score were associated with a poor graft survival. Significantly inferior allograft survival was noted in Group B. HIF scores had an adjusted hazard ratio of 3.25 (95% confidence inteval: 1.71-6.16, P = 0.0003) in allograft failure.

CONCLUSIONS

We first demonstrated the expression of HIF-1α protein among infiltrating inflammatory cells in areas with IF/TA in patients with chronic allograft dysfunction.

Macrophage activation is associated with poorer long-term outcomes in renal transplant patients

Long-term graft and patient survival after renal transplantation are largely determined by progression of chronic allograft dysfunction and cardiovascular disease. Inflammation plays a crucial role in both disease processes. We prospectively analyzed the association of early peri-transplant inflammatory burden on long-term outcomes in 144 consecutive deceased donor renal allograft recipients. Single time point and cumulative levels of markers of acute phase response (serum amyloid A [SAA] and C-reactive protein [SCRP]) and macrophage activation (serum and urine neopterin) were measured daily during the immediate post-operative period. Mean patient follow-up was 16 yr. Graft and patient survival rates at one-, five-, and 10-yr were 90%, 70%, and 51%, and 97%, 77%, and 59%, respectively. Graft loss occurred in 90 patients, of whom 71 died with a functioning graft and 19 returned to dialysis. CRP, SAA and neopterin (NEOP) levels were all elevated post-operatively. High levels of NEOP, in contrast to SAA or SCRP, were associated with poorer graft and patient survival (p < 0.05), specifically with death from cardiovascular events and cytomegalovirus IgG positivity. These findings strongly suggest that early post-transplant macrophage activation, as reflected by NEOP levels, is associated with poorer long-term graft and patient survival.

Monocytes/macrophages in kidney allograft intimal arteritis: no association with markers of humoral rejection or with inferior outcome

BACKGROUND

Several studies indicate that interstitial and intracapillary monocytes/macrophages (MO) represent a significant proportion of graft-infiltrating cells in renal allografts and that their presence may unfavourably affect clinical outcome. Much less is known about the role of MO in vascular rejection of transplanted kidneys. The aim of our study was to determine the cellular composition of immune cell infiltrates in intimal arteritis and to analyse whether it is associated with features of humoral immunity and impaired graft survival.

METHODS

In 34 recipients with vascular rejection, we determined the proportion of intimal and interstitial MO and T-cells (expressed as ratio of CD68- and CD3-positive cells) in immunohistochemically double-labelled slides.

RESULTS

Intimal arteritis is always composed of T-cells and MO with a median CD68/CD3 ratio of 1.03. In 47% of cases, however, T-cells predominate (CD68/CD3 ratio <1). The median interstitial CD68/CD3 ratio is 0.61, with T-cells dominating in 64% of cases. There is no correlation between the cellular composition of arterial and interstitial infiltrates. The proportion of interstitial and arterial MO has no impact on graft survival, and is, in contrast to previous reports on MO in allograft glomerulitis and capillaritis, not associated with C4d staining.

CONCLUSIONS

Intimal arteritis in kidney allograft rejection is composed of a mixed infiltrate of MO and T-lymphocytes. In contrast to MO in PTCitis and glomerulitis, the MO in intimal arteritis are not associated with markers of humoral immune response and there are no different allograft outcomes between MO and T-lymphocyte-dominated groups.

Selective CCR2-targeted macrophage depletion ameliorates experimental mesangioproliferative glomerulonephritis

The CCL2/CCR2 chemokine/receptor axis directs the chemotaxis of infiltrating monocytes/macrophages and T cells and plays a pivotal role in tissue damage and fibrosis in kidney diseases. The eradication of the activated leucocytes should diminish the production of inflammatory mediators, limit tissue damage and ameliorate disease. A recombinant fusion protein (OPL-CCL2-LPM) comprised of the human CCL2 (monocyte chemoattractant protein-1) chemokine fused to a truncated form of the enzymatically active A1 domain of Shigella dysenteriae holotoxin (SA1) has been developed. The CCL2 portion binds specifically to CCR2-bearing leucocytes and the fusion protein enters the cells, where the SA1 moiety inhibits protein synthesis resulting in cell death. The compound was tested in a model of anti-thymocyte serum (ATS)-induced mesangioproliferative glomerulonephritis (ATS-GN). Male rats were injected with ATS on day 0 and treated intravenously with vehicle, 50 or 100 microg/kg of OPL-CCL2-LPM Q2D from days 2, 4, 6 and 8. Urine and blood were collected on days 0, 5 and 9. Animals were sacrificed on day 9. No treatment-related effects on body weight or signs of clinical toxicity were observed. Urine protein levels were decreased in treated animals. At the highest dose, histopathological analyses of kidney sections revealed maximum reductions of 36, 31, 30 and 24% for macrophage count, glomerular lesions, alpha-smooth muscle actin and fibronectin respectively. These results indicate a significant protective effect of OPL-CCL2-LPM in this model of nephritis.

Differential effects of donor-specific alloantibody

Alloantigen exposure typically provokes an adaptive immune response that can foster rejection of transplanted organs, and these responses present the most formidable biological barrier to kidney transplantation. Although most cellular alloimmune responses can be therapeutically controlled with T-cell-specific immunosuppressants, humoral alloimmune responses remain relatively untamed. Importantly, humoral immunity, typically manifesting as allospecific antibody production, is increasingly recognized for its variable appearance after kidney transplantation. Indeed, the appearance of alloantibody can herald the onset of rapid and destructive antibody-mediated rejection or have no demonstrable acute effects. The factors determining the end result of alloantibody formation remain poorly understood. This review will discuss the breadth of alloantibody responses seen in clinical kidney transplantation and provide an overview of potential factors explaining the phenotypic variability associated with humoral alloimmunity. We propose several avenues ripe for future investigation including the influence of innate immune components and the potential influence of heterologous immune responses in determining the ultimate clinical import of an alloantibody response.

Complement 5a receptor inhibition improves renal allograft survival

Complement activation plays a key role in mediating apoptosis, inflammation, and transplant rejection. In this study, the role of the complement 5a receptor (C5aR) was examined in human renal allografts and in an allogenic mouse model of renal transplant rejection. In human kidney transplants with acute rejection, C5aR expression was increased in renal tissue and in cells infiltrating the tubulointerstitium. Similar findings were observed in mice. When recipient mice were treated once daily with a C5aR antagonist before transplantation, long-term renal allograft survival was markedly improved compared with vehicle-treatment (75 versus 0%), and apoptosis was reduced. Furthermore, treatment with a C5aR antagonist significantly attenuated monocyte/macrophage infiltration, perhaps a result of reduced levels of monocyte chemoattractant protein 1 and the intercellular adhesion molecule 1. In vitro, C5aR antagonism inhibited intercellular adhesion molecule 1 upregulation in primary mouse aortic endothelial cells and reduced adhesion of peripheral blood mononuclear cells. Furthermore, C5aR blockade markedly reduced alloreactive T cell priming. These results demonstrate that C5aR plays an important role in mediating acute kidney allograft rejection, suggesting that pharmaceutical targeting of C5aR may have potential in transplantation medicine.

Monocyte infiltration and kidney allograft dysfunction during acute rejection

Multiple cell types infiltrate acutely rejecting renal allografts. Typically, monocytes and T cells predominate. Although T cells are known to be required for acute rejection, the degree to which monocytes influence this process remains incompletely defined. Specifically, it has not been established to what degree monocytes impact the clinical phenotype of rejection or how their influence compares to that of T cells. We therefore investigated the relative impact of T cells and monocytes by correlating their presence as measured by immunohistochemical staining with the magnitude of the acute change in renal function at the time of biopsy in 78 consecutive patients with histological acute rejection. We found that functional impairment was strongly associated with the degree of overall cellular infiltration as scored using Banff criteria. However, when cell types were considered, monocyte infiltration was quantitatively associated with renal dysfunction while T-cell infiltration was not. Similarly, renal tubular stress, as indicated by HLA-DR expression, increased with monocyte but not T-cell infiltration. These data suggest that acute allograft dysfunction is most closely related to monocyte infiltration and that isolated T-cell infiltration has less acute functional impact. This relationship may be useful in assigning acute clinical relevance to biopsy findings.

Evaluating the accuracy of functional biomarkers for detecting histological changes in chronic allograft nephropathy

The most common cause of late kidney transplant failure is chronic allograft nephropathy (CAN). Much research has focused on identifying biomarkers (or correlates) that would predict subsequent CAN and allow timely intervention. Functional biomarkers such as serum creatinine and estimated glomerular filtration rate (eGFR) have been widely adopted, even though they have not been rigorously evaluated as surrogate markers. This study evaluated serum creatinine and eGFR for predicting the early histopathological changes seen in transplant protocol biopsies (TPB). We prospectively followed 289 kidney transplant patients in the Southern Alberta Transplant Program who had TPB at 6-12 months post-transplant. Tissue samples (n = 280) were independently examined by renal pathologists. The ability of serum creatinine or eGFR to predict the threshold level for abnormal histopathology was evaluated by calculating the area under the receiver operator characteristic curve. Serum creatinine and eGFR had poor predictive value (most confidence intervals included 0.5, indicating no predictive ability) for ten individual histological measurements (Banff 97 scores), and the Chronic Allograft Damage Index. We conclude that serum creatinine and eGFR have a limited clinical role in predicting the early histopathological changes that precede CAN and should not be used for this purpose.

Urinary cytotoxic molecular markers for a noninvasive diagnosis in acute renal transplant rejection

Perforin (P), Granzyme B (GB) and Fas-Ligand (FAS-L) are cytotoxic molecules involved in acute rejection (AR) after renal transplantation. A noninvasive diagnostic test to monitor AR and other complications could improve clinical management. We investigated the predictive and diagnostic interest of target mRNA measurements, with a quantitative PCR assay, in AR, as well as in other clinical complications recurrent in kidney transplantation. One hundred and sixty-two urine specimens from 37 allograft recipients were investigated. Clinical settings were AR, urinary tract infection (UTI), cytomegalovirus infection (CMVi) or disease (CMVd), chronic allograft nephropathy (CAN), delayed graft function (DGF) and stable graft course (controls). In the case of AR, mRNA levels of all three molecules were significantly higher than in recipients not showing any clinically evident signs of complication. Indeed, it was observed that expression levels of P, GB and Fas-L mRNA also increase in other clinical situations such as UTI, CMV and DGF. Finally, kinetic studies in three patients with AR revealed that increased P, GB and Fas-L mRNA levels could precede or were concomitant with increased serum creatinin levels. P, GB and Fas-L gene expression in urine specimens were upregulated in AR episodes but also in UTI, CMV infection and DGF. Therefore, this technique would appear to be of limited clinical value as a noninvasive method of diagnosing AR.

Post-transplant sCD30 and neopterin as predictors of chronic allograft nephropathy: impact of different immunosuppressive regimens

Immunological monitoring for chronic allograft nephropathy (CAN) is of great potential interest. We assessed serum soluble CD30 (sCD30) together with in vitro Th2-type responses (IL-4, IL-10, CD4 helper activity) and neopterin in a prospective study of 84 renal transplant recipients with 2-year follow-up. Patients were randomized to CsA/Aza, CsA/MMF and Tacr/Aza, respectively, to analyze the effect of immunosuppression on posttransplant sCD30 and neopterin. ATG induction and acute rejections did not alter sCD30 levels whereas CMV disease was associated with transient upregulation of sCD30 (p = 0.003 at 4 months) and sustained upregulation of neopterin (corrected for graft function (Neo/CR) p = 0.005 at 2 years). Tacr versus CsA treatment proved to be an independent variable associated with downregulation of 1-year sCD30, which was positively related to Neo/CR (p = 0.007 and 0.01, respectively; logistic regression). Importantly, increased 1-year sCD30 and Neo/CR were associated with decreased glomerular filtration rate at 2 years (p = 0.02 and p < 0.0005, respectively) and evidence of CAN (p < 0.0005). High 1-year sCD30 could not be attributed to enhanced Th2-type responses and was not associated with HLA antibody formation. Our data suggest that elevated sCD30 and neopterin predict graft deterioration by CAN. Tacr effectively downregulates these responses and might be of advantage in patients with elevated sCD30 or neopterin.

Mechanisms of chronic allograft dysfunction

This review was designed to highlight new findings that have contributed to our knowledge of the pathogenesis of late graft dysfunction. Both immune and nonimmune causes contribute to its development. Specific contributors to late graft dysfunction have been recently recognized and are potential targets for new treatment options. The variables associated with late graft failure include donor age and tissue quality, brain death and other issues specific to the deceased donor, tissue injury secondary to organ preservation, alloimmune-mediated injury, and posttransplantation factors in the recipient, such as viral infections, hypertension, drug toxicity, and hyperlipidemia. One of the critical variables that is controllable is the total ischemic time; the longer the ischemic episode, the worse the long-term results of the transplant are. Another significant obstacle to long-term allograft survival is the MHC barrier. The roles of B cells and alloantibody as effectors of alloimmunity have been underestimated; emerging studies strongly suggest that previous sensitization and/or de novo donor-anti-human lymphocyte antigen (HLA) antibodies secondary to poor HLA matching portend a poor prognosis for allograft survival, even in the presence of chronic T-cell-specific immunosuppression.