Acute Renal Allograft Rejection Research Articles

Repeated Injections of IL-2 Break Renal Allograft Tolerance Induced via Mixed Hematopoietic Chimerism in Monkeys.

Tolerance of allografts achieved in mice via stable mixed hematopoietic chimerism relies essentially on continuous elimination of developing alloreactive T cells in the thymus (central deletion). Conversely, while only transient mixed chimerism is observed in nonhuman primates and patients, it is sufficient to ensure tolerance of kidney allografts. In this setting, it is likely that tolerance depends on peripheral regulatory mechanisms rather than thymic deletion. This implies that, in primates, upsetting the balance between inflammatory and regulatory alloimmunity could abolish tolerance and trigger the rejection of previously accepted renal allografts. In this study, six monkeys that were treated with a mixed chimerism protocol and had accepted a kidney allograft for periods of 1-10 years after withdrawal of immunosuppression received subcutaneous injections of IL-2 cytokine (0.6-3 × 10(6) IU/m(2) ). This resulted in rapid rejection of previously tolerated renal transplants and was associated with an expansion and reactivation of alloreactive pro-inflammatory memory T cells in the host's lymphoid organs and in the graft. This phenomenon was prevented by anti-CD8 antibody treatment. Finally, this process was reversible in that cessation of IL-2 administration aborted the rejection process and restored normal kidney graft function.

Study of the association between the donors and recipients angiotensin-converting enzyme insertion/deletion gene polymorphism and the acute renal allograft rejection.

Background: Angiotensin converting enzyme (ACE) is involved in various pathophysiological conditions including renal function. ACE levels are under genetic control. Objectives: This study was designed to investigate the association between the donors and recipients ACE-I/D gene polymorphism and risk of acute rejection outcome in renal allograft recipients. Patients and Methods: ACE-I/D polymorphism was determined in 200 donor-recipient pairs who had been referred to Afzalipour hospital in Kerman. ACE-I/D polymorphism was detected using polymerase chain reaction (PCR). Acute rejection (AR) during at least six months post-transplantation was defined as a 20% increase in creatinine level from the postoperative baseline in the absence of other causes of graft dysfunction which responded to antirejection therapy. Results: The observed allele frequencies were II 9.8%, ID 35.6% and DD 44.4% in donors and II 9.8%, ID 35.1% and DD 52.7% in recipients. There were no significant association between ACE genotypes and AR episodes (ORID=0.96 [0.18-5.00] and ORDD: 1.24 [0.25-6.07] for the donors) and (ORID: 0.29 [0.06-1.45] and ORDD: 0.75 [0.19-2.90] for the recipients). Conclusions: It seems that donor and recipient ACE-I/D genotype might not be a risk factor for acute renal allograft rejection. However, due to conflicting results from this and other studies, multicenter collaborative studies with more participants and concomitant evaluation of ACE polymorphism with other polymorphisms in renin–angiotensin system (RAS) are suggested to determine whether ACE genotypes are significant predictors of renal allograft rejection.

Attenuation of acute rat renal allograft rejection by apolipoprotein E-mimetic Peptide.

In addition to its well-described role in lipid metabolism, apolipoprotein E (ApoE) exerts immunomodulatory functions. A protective role of ApoE and ApoE-mimetic peptide (ApoE(133-149)) application was documented in several inflammatory disorders. In this study, we test the hypothesis that ApoE(133-149) promotes renal allograft survival. Dark Agouti, Brown Norway, and Fischer 344 kidneys were transplanted to Lewis rats to investigate fatal and reversible acute rejection. Apolipoprotein E expression was assessed in intravascular leukocytes of renal grafts, in graft tissue and in recipient blood plasma. Recipients of Brown Norway kidneys were treated with ApoE(133-149), and graft survival was monitored until day 100. Graft infiltration, cytokine, and chemokine production were analyzed. Intravascular graft leukocytes and renal tissue obtained from animals undergoing reversible acute rejection expressed increased levels of ApoE mRNA, whereas during fatal rejection, ApoE expression was reduced or remained unchanged. Animals treated with ApoE(133-149) showed prolonged allograft survival, which was associated with a reduced infiltration of CD8 and α/β T-cell receptor-expressing cells, diminished Granzyme B mRNA expression, and decreased caspase-3 activation. Endogenous ApoE overexpression and exogenous application of ApoE(133-149) seem to protect renal allografts from fatal acute rejection. This effect was associated with a reduced influx of cytotoxic T cells.

Noninvasive Imaging of Acute Renal Allograft Rejection by Ultrasound Detection of Microbubbles Targeted to T-lymphocytes in Rats.

We propose CD3-antibody-mediated contrast-enhanced ultrasonography using human T-lymphocytes for image-based diagnosis of acute allograft rejection (AR) established in a rat renal transplantation model. 15 minutes after tail vein injection of 30 × 10(6) human T-lymphocytes, contrast media/microbubbles conjugated with an anti-human CD3 antibody was applied to uni-nephrectomized 10-week-old allogeneically transplanted male rats (Lewis-Brown Norway (LBN) to Lewis, aTX) and ultrasound was performed to investigate the transplanted kidney as well as the native kidney. In vivo results were confirmed via immunohistochemical stainings of CD3 after post mortem dissection. Syngeneically transplanted rats (LBN to LBN, sTX), rats with ischemia/reperfusion injury (IRI, 45 min. warm ischemia), and rats subjected to acute cyclosporin A toxicity (CSA) (cyclosporine 50 mg/kg BW for 2 days i. p.) served as controls. Accumulation of human T-lymphocytes was clearly detected by antibody-mediated sonography und was significantly increased in allografts undergoing AR (5.41 ± 1.32 A. U.) when compared to native control kidneys (0.70 ± 0.08A. U.). CD3 signal intensity was low in native kidneys, sTX (0.99 ± 0.30 A. U.), CSA (0.10 ± 0.02 A. U.) and kidneys with IRI (0.46 ± 0.29 A. U.). Quantification of the ultrasound signal correlated significantly with the T-cell numbers obtained by immunohistochemical analysis (R2 = 0.57). Contrast-enhanced sonography using CD3-antibodies is an option for quick and highly specific assessment of AR in a rat model of renal transplantation.

Strength of Donor-Specific Antibodies With the Use of Luminex Single-Antigen Beads Is a Reliable Predictor of Acute Rejection in Living-Relative Kidney Recipients

BackgroundLuminex single-antigen assay is a promising technique for determination of donor-specific antibodies (DSAs) in renal transplantation. MethodsSerum samples from living-relative renal recipients before and after renal transplantation were examined with the use of Luminex single-antigen assay. The impact of de novo DSAs on the early clinical outcomes of renal allograft was analyzed. ResultsOf the 61 patients included, 15 patients (24.6%) presented de novo DSA (4 class I, 4 class II, and 7 both classes) after transplantation, and the average (median) cumulative strength of DSA was 1,283 (range, 0–10,802) mean fluorescence index (MFI) for class I versus 1,324 (range, 0–14,985) MFI for class II (P > .05). Twelve (19.7%) of the 61 patients experienced a clinical/subclinical acute rejection (AR) episode within the 1st 2 years after transplantation. A clinical/subclinical AR episode was diagnosed in 40% of DSA(+) patients and 13.0% of DSA(−) patients (P < .05). DSA(+) patients who developed an AR episode had a higher mean cumulative MFI value (8,118.3 ± 5,287.4; range, 1,785–14,985) than patients who did not develop an AR episode (3,283.7 ± 2,601.0; range, 786–8,113; P < .05). Serum creatinine levels in the DSA(+) group were significantly higher than in the DSA(−) group at 12 and 24 months after transplantation. The graft survival rates at 2 years in the DSA(+) and DSA(−) groups were not different (86.7% vs 91.3%; P > .05). ConclusionsPatients with de novo DSAs at high strength may suffer a high risk of developing an AR episode. Therefore, careful monitoring of de novo DSAs with the use of Luminex single-antigen beads may help in early intervention for AR in renal allografts and to minimize renal damage caused by the antibodies.

MicroRNA-10b downregulation mediates acute rejection of renal allografts by derepressing BCL2L11

Kidney transplantation is the major therapeutic option for end-stage kidney diseases. However, acute rejection could cause allograft loss in some of these patients. Emerging evidence supports that microRNA (miRNA) dysregulation is implicated in acute allograft rejection. In this study, we used next-generation sequencing to profile miRNA expression in normal and acutely rejected kidney allografts. Among 75 identified dysregulated miRNAs, miR-10b was the most significantly downregulated miRNAs in rejected allografts. Transfecting miR-10b inhibitor into human renal glomerular endothelial cells recapitulated key features of acute allograft rejection, including endothelial cell apoptosis, release of pro-inflammatory cytokines (interleukin-6, tumor necrosis factor α, interferon-γ, and chemokine (C–C motif) ligand 2) and chemotaxis of macrophages whereas transfection of miR-10b mimics had opposite effects. Downregulation of miR-10b directly derepressed the expression of BCL2L11 (an apoptosis inducer) as revealed by luciferase reporter assay. Taken together, miR-10b downregulation mediates many aspects of disease pathogenicity of acute kidney allograft rejection. Restoring miR-10b expression in glomerular endothelial cells could be a novel therapeutic approach to reduce acute renal allograft loss.

Spleen tyrosine kinase contributes to acute renal allograft rejection in the rat

Kidney allografts induce strong T-cell and antibody responses which mediate acute rejection. Spleen tyrosine kinase (Syk) is expressed by most leucocytes, except mature T cells, and is involved in intracellular signalling following activation of the Fcγ-receptor, B-cell receptor and some integrins. A role for Syk signalling has been established in antibody-dependent native kidney disease, but little is known of Syk in acute renal allograft rejection. Sprague-Dawley rats underwent bilateral nephrectomy and received an orthotopic Wistar renal allograft. Recipient rats were treated with a Syk inhibitor (CC0482417, 30 mg/kg/bid), or vehicle, from 1 h before surgery until being killed 5 days later. Vehicle-treated recipients developed severe allograft failure with marked histologic damage in association with dense leucocyte infiltration (T cells, macrophages, neutrophils and NK cells) and deposition of IgM, IgG and C3. Immunostaining identified Syk expression by many infiltrating leucocytes. CC0482417 treatment significantly improved allograft function and reduced histologic damage, although allograft injury was still clearly evident. CC0482417 failed to prevent T-cell infiltration and activation within the allograft. However, CC0482417 significantly attenuated acute tubular necrosis, infiltration of macrophages and neutrophils and thrombosis of peritubular capillaries. In conclusion, this study identifies a role for Syk in acute renal allograft rejection. Syk inhibition may be a useful addition to T-cell-based immunotherapy in renal transplantation.

Donor genotype and intragraft expression of CYP3A5 reflect the response to steroid treatment during acute renal allograft rejection

Donor genotype and intragraft expression of CYP3A5 reflect the response to steroid treatment during acute renal allograft rejection

The Role of Spleen Tyrosine Kinase in Acute Renal Allograft Rejection in the Rat.

The Role of Spleen Tyrosine Kinase in Acute Renal Allograft Rejection in the Rat.

Donor Genotype and Intragraft Expression of CYP3A5 Reflect the Response to Steroid Treatment During Acute Renal Allograft Rejection.

Donor Genotype and Intragraft Expression of CYP3A5 Reflect the Response to Steroid Treatment During Acute Renal Allograft Rejection.

Type of Rejection and Biopsy Findings After Induction Therapy With a Single Dose of Rituximab.

Introduction. A variety of data indicates a role for B cells in acute renal allograft rejection. We report the type of biopsy proven acute rejection (BPAR) and biopsy findingsafter induction therapy with a single dose of the anti-B cell antibody rituximab. Patients and methods. In a single centre, double-blind, placebo-controlled study, 280 adult renal transplant patients were randomised between a single dose of rituximab (375 mg/m2) or placebo during transplant surgery. Maintenance immunosuppression consisted of tacrolimus, mycophenolate mofetil, and steroids. The primary end point was the incidence BPAR within six months after transplantation. Biopsies were scored independently by two blinded pathologists according to the updated Banff 07 criteria. Additionally biopsies were scored for CD20+, CD79a+ (B-cell markers), and CD138+ (plasma cell marker) cells and C4d. Protocol graft biopsies were not performed. Results. The incidence of BPAR was comparable between rituximab-treated (23/138, 16.7%) and placebo-treated patients (30/142, 21.2%, p=0.25 by log-rank test). Most rejections were T cell mediated according to the Banff classification. Rituximab-treated patients tended to have less antibody mediated rejections (ABMR), compared to placebo-treated patients (4/138, 2.9% vs. 11/142, 7.7% p=0.11). An additional analysis of biopsies performed during the first six months showed that biopsies of rituximab-treated patients had significantly less CD20+ cells and significantly less (clusters of) CD79a+ cells in their biopsies (CD20+ cells 18.5% vs 82.9%, p<0.01 and score for CD79a+ 0.15 vs 1.56, p<0.01), and tended to have less C4d deposition (8.2% vs. 15.8%, p=0.13) compared with biopsies from placebo-treated patients. There was no difference in the score for CD138+ cells (0.35 vs 0.48, p=0.43). Conclusion. The results of our study suggest that a single dose of rituximab may reduce the incidence of biopsy proven acute rejection in immunised patients. The incidence of ABMR tended to be lower after rituximab, especially in immunised patients. After rituximab treatment, significantly less B-cells were found in the biopsies. DISCLOSURES:Hilbrands, L.: Grant/Research Support, Hoffmann-La Roche, Astellas Pharma.

Histone Methylation Inhibitor DZNep Amilorates Acute Renal Allograft Rejection in Rat Transplantation.

Histone Methylation Inhibitor DZNep Amilorates Acute Renal Allograft Rejection in Rat Transplantation.

Serum Fractalkine and Interferon-Gamma Inducible Protein-10 Concentrations Are Early Detection Markers for Acute Renal Allograft Rejection

ObjectiveThe aims of this study were to determine if characterization of serum concentrations of interferon-gamma inducible protein-10 (IP-10), fractalkine, and their receptors (CXCR3 and CX3CR1) were predictive of acute allograft rejection in kidney transplant recipients. MethodsKidney transplant recipients (n = 52) were enrolled in this study and divide into either the acute rejection (AR, n = 15) or non–acute rejection (NAR, n = 35) groups. Serum samples from recipients were collected 1 day prior to transplantation and on days 1, 3, 5, 7, and 9 post-transplantation. The accuracy of chemokine concentrations for predicting acute rejection episodes was evaluated using receiver operator characteristic (ROC) curves. ResultsAR was diagnosed in 15 patients based on histologic changes to renal biopsies. AR patients had significantly higher serum fractalkine, CXCR1, IP-10, and CXCR3 levels compared to levels observed in the NAR group and healthy controls. Fractalkine and IP-10 had the largest area under the ROC curve at 0.86 (95% confidence interval: 0.77–0.96). Following steroid therapy, chemokine levels decreased, which may serve to predict the therapeutic response to steroid therapy. ConclusionMeasuring serum levels of fractalkine, IP-10, and their receptors (especially the fractalkine/IP-10 combination) may serve as a noninvasive approach for the early diagnosis of renal allograft rejection.

Participation of Functionally Active Plasma Cells in Acute Rejection and Response to Therapy in Renal Allografts

Acute rejection (AR) includes T-cell-mediated and antibody-mediated rejection. The inflammatory infiltrate comprised not only T cells but also varying amounts of B cells (CD20(+)) and plasma cells (CD138(+)). The latter are associated with poor clinical outcomes, but their functional status is not clear. The phosphorylation of the S6 ribosomal protein (p-S6RP) is present in cells that are metabolically active, thus identifying functionally active antibody-secreting plasma cells. This study was designed to evaluate the clinical significance of functionally active p-S6RP plasma cells in AR in renal allografts. Renal allografts with biopsy evidence of AR during 2006-2009 were included. Immunohistochemistry staining for CD20, CD138, and p-S6RP was performed on paraffin-embedded slides and scaled as 0-6. The response to antirejection treatment was assessed by the serum creatinine ratio (CrR) at rejection episode (time 0) and following treatment (4 and 12 weeks). Patients with lower scores (0-2) were compared with a higher scored group (3-6). The T-test was conducted using statistical significance of p<0.05. A total of 28 patients (40.7 ± 14.3 year; M:F=15:13) were diagnosed with acute T-cell-mediated rejection (I and II). The p-S6RP staining in the high-score group had a significantly higher CrR (p<0.05) than the low-score group at the time of biopsy, 4 and 12 weeks following treatment. There was no significant difference in the CrR between groups for CD20 or CD138 staining. Functional antibody-secreting p-S6RP plasma cells are actively participating in AR and associated with poor response to treatment in renal allografts.

A noninvasive assay for monitoring renal allograft status

Transplant rejection is a serious complication, sometimes threatening life of the patient. Although recent development of the new generation of immunosuppressive drugs reduced the incidence of acute rejection in kidney transplantation, the absence of noninvasive biomarkers of the rejection does not allow often the optimization of a prompt antirejection therapy. Serum creatinine is the most widely used marker for allograft function, however, it is not sensitive and specific enough to detect acute rejection. Other biomarkers are even less valuable for this purpose. Histological examination of renal allograft biopsy still remains the golden standard for diagnosing acute renal allograft rejection. Therefore, there is a high demand for reliable biomarkers for noninvasive monitoring of renal allograft status. Examination of urine in renal transplant recipients provides a logical and readily accessible approach for this monitoring. The high potency biomarkers for kidney allograft monitoring are fragments of DNA in recipient urine that originated from renal allograft cells. Because of the difference in the genetic origin these DNA can be distinguished from recipient DNA. Quantitative analysis of donor’s DNA, derived from cells of renal allograft, in recipient’s urine might be a reliable predictive tool for the kidney transplant rejection. We developed an assay to quantitate donor DNA content in recipient urine. Application of the technique—coamplification at lower denaturation temperature-PCR (COLD-PCR) increased the abundance of donor DNA that usually presents in recipient urine in quantities that are out of the detection range. This assay has a potential for routine application in clinical practice after statistical validation and additional modifications.

The Identification of Novel Potential Injury Mechanisms and Candidate Biomarkers in Renal Allograft Rejection by Quantitative Proteomics

Early transplant dysfunction and failure because of immunological and nonimmunological factors still presents a significant clinical problem for transplant recipients. A critical unmet need is the noninvasive detection and prediction of immune injury such that acute injury can be reversed by proactive immunosuppression titration. In this study, we used iTRAQ -based proteomic discovery and targeted ELISA validation to discover and validate candidate urine protein biomarkers from 262 renal allograft recipients with biopsy-confirmed allograft injury. Urine samples were randomly split into a training set of 108 patients and an independent validation set of 154 patients, which comprised the clinical biopsy-confirmed phenotypes of acute rejection (AR) (n = 74), stable graft (STA) (n = 74), chronic allograft injury (CAI) (n = 58), BK virus nephritis (BKVN) (n = 38), nephrotic syndrome (NS) (n = 8), and healthy, normal control (HC) (n = 10). A total of 389 proteins were measured that displayed differential abundances across urine specimens of the injury types (p < 0.05) with a significant finding that SUMO2 (small ubiquitin-related modifier 2) was identified as a "hub" protein for graft injury irrespective of causation. Sixty-nine urine proteins had differences in abundance (p < 0.01) in AR compared with stable graft, of which 12 proteins were up-regulated in AR with a mean fold increase of 2.8. Nine urine proteins were highly specific for AR because of their significant differences (p < 0.01; fold increase >1.5) from all other transplant categories (HLA class II protein HLA-DRB1, KRT14, HIST1H4B, FGG, ACTB, FGB, FGA, KRT7, DPP4). Increased levels of three of these proteins, fibrinogen beta (FGB; p = 0.04), fibrinogen gamma (FGG; p = 0.03), and HLA DRB1 (p = 0.003) were validated by ELISA in AR using an independent sample set. The fibrinogen proteins further segregated AR from BK virus nephritis (FGB p = 0.03, FGG p = 0.02), a finding that supports the utility of monitoring these urinary proteins for the specific and sensitive noninvasive diagnosis of acute renal allograft rejection.

Longitudinal Analysis of Whole Blood Transcriptomes to Explore Molecular Signatures Associated With Acute Renal Allograft Rejection

In this study, we explored a time course of peripheral whole blood transcriptomes from kidney transplantation patients who either experienced an acute rejection episode or did not in order to better delineate the immunological and biological processes measureable in blood leukocytes that are associated with acute renal allograft rejection. Using microarrays, we generated gene expression data from 24 acute rejectors and 24 nonrejectors. We filtered the data to obtain the most unambiguous and robustly expressing probe sets and selected a subset of patients with the clearest phenotype. We then performed a data-driven exploratory analysis using data reduction and differential gene expression analysis tools in order to reveal gene expression signatures associated with acute allograft rejection. Using a template-matching algorithm, we then expanded our analysis to include time course data, identifying genes whose expression is modulated leading up to acute rejection. We have identified molecular phenotypes associated with acute renal allograft rejection, including a significantly upregulated signature of neutrophil activation and accumulation following transplant surgery that is common to both acute rejectors and nonrejectors. Our analysis shows that this expression signature appears to stabilize over time in nonrejectors but persists in patients who go on to reject the transplanted organ. In addition, we describe an expression signature characteristic of lymphocyte activity and proliferation. This lymphocyte signature is significantly downregulated in both acute rejectors and nonrejectors following surgery; however, patients who go on to reject the organ show a persistent downregulation of this signature relative to the neutrophil signature.

Longitudinal Analysis of Whole Blood Transcriptomes to Explore Molecular Signatures Associated with Acute Renal Allograft Rejection

In this study, we explored a time course of peripheral whole blood transcriptomes from kidney transplantation patients who either experienced an acute rejection episode or did not in order to better delineate the immunological and biological processes measureable in blood leukocytes that are associated with acute renal allograft rejection. Using microarrays, we generated gene expression data from 24 acute rejectors and 24 nonrejectors. We filtered the data to obtain the most unambiguous and robustly expressing probe sets and selected a subset of patients with the clearest phenotype. We then performed a data-driven exploratory analysis using data reduction and differential gene expression analysis tools in order to reveal gene expression signatures associated with acute allograft rejection. Using a template-matching algorithm, we then expanded our analysis to include time course data, identifying genes whose expression is modulated leading up to acute rejection. We have identified molecular phenotypes associated with acute renal allograft rejection, including a significantly upregulated signature of neutrophil activation and accumulation following transplant surgery that is common to both acute rejectors and nonrejectors. Our analysis shows that this expression signature appears to stabilize over time in nonrejectors but persists in patients who go on to reject the transplanted organ. In addition, we describe an expression signature characteristic of lymphocyte activity and proliferation. This lymphocyte signature is significantly downregulated in both acute rejectors and nonrejectors following surgery; however, patients who go on to reject the organ show a persistent downregulation of this signature relative to the neutrophil signature.

SPECT- and PET-based approaches for noninvasive diagnosis of acute renal allograft rejection.

Molecular imaging techniques such as single photon emission computed tomography (SPECT) or positron emission tomography are promising tools for noninvasive diagnosis of acute allograft rejection (AR). Given the importance of renal transplantation and the limitation of available donors, detailed analysis of factors that affect transplant survival is important. Episodes of acute allograft rejection are a negative prognostic factor for long-term graft survival. Invasive core needle biopsies are still the “goldstandard” in rejection diagnostics. Nevertheless, they are cumbersome to the patient and carry the risk of significant graft injury. Notably, they cannot be performed on patients taking anticoagulant drugs. Therefore, a noninvasive tool assessing the whole organ for specific and fast detection of acute allograft rejection is desirable. We herein review SPECT- and PET-based approaches for noninvasive molecular imaging-based diagnostics of acute transplant rejection.

Macrophages Contribute to Cellular But Not Humoral Mechanisms of Acute Rejection in Rat Renal Allografts

Cells of the monocyte/macrophage lineage have been implicated as effectors in acute allograft rejection based on short-term depletion studies. However, the therapeutic potential of targeting monocyte/macrophages in acute rejection is unknown. We investigated the potential of a c-fms kinase inhibitor (fms-I) in acute renal allograft rejection. Lewis rats underwent bilateral nephrectomy and received an orthotopic Dark Agouti renal allograft. Recipients received fms-I or vehicle from the time of transplantation until being killed on day 5. Vehicle-treated rats developed severe allograft rejection with massive macrophage and T-cell infiltration. In contrast, fms-I substantially inhibited renal allograft dysfunction and structural damage with abrogation of macrophage and dendritic cell infiltration but had only a minor effect on the T-cell infiltrate. However, fms-I suppressed T-cell activation within the allograft, whereas systemic T- and B-cell activation was not affected. In a longer-term study to assess therapeutic potential, fms-I-treated rats developed severe antibody-mediated rejection on day 8 after transplantation. These transplants exhibited features of antibody-mediated rejection including capillaritis with thrombosis, acute tubular injury, IgG and C4d deposition, and neutrophil infiltration and activation. Interestingly, T-cell activation within these rejecting allografts remained suppressed, indicating separation of T-cell and antibody-mediated rejection. This study demonstrates the ability of c-fms kinase blockade to selectively deplete monocyte/macrophages in acute allograft rejection, although this did not result in significant prolongation of allograft survival. Furthermore, we identify contrasting roles for macrophages in cellular and humoral mechanisms of acute renal allograft rejection.