The relevance of induced class II HLA antigens and macrophage infiltration in early renal allograft biopsies

Single-cell and bulk RNA sequencing highlights the role of M1-like infiltrating macrophages in antibody-mediated rejection after kidney transplantation

Background

Antibody-mediated rejection (ABMR) significantly affects transplanted kidney survival, yet the macrophage phenotype, ontogeny, and mechanisms in ABMR remain unclear.

Method

We analyzed post-transplant sequencing and clinical data from GEO and ArrayExpress. Using dimensionality reduction and clustering on scRNA-seq data, we identified macrophage subpopulations and compared their infiltration in ABMR and non-rejection cases. Cibersort quantified these subpopulations in bulk samples. Cellchat, SCENIC, monocle2, and monocle3 helped explore intercellular interactions, predict transcription factors, and simulate differentiation of cell subsets. The Scissor method linked macrophage subgroups with transplant prognosis. Furthermore, hdWGCNA, nichnet, and lasso regression identified key genes associated with core transcription factors in selected macrophages, validated by external datasets.

Results

Six macrophage subgroups were identified in five post-transplant kidney biopsies. M1-like infiltrating macrophages, prevalent in ABMR, correlated with pathological injury severity. MIF acted as a primary intercellular signal in these macrophages. STAT1 regulated monocyte-to-M1-like phenotype transformation, impacting transplant prognosis via the IFNγ pathway. The prognostic models built on the upstream and downstream genes of STAT1 effectively predicted transplant survival. The TLR4-STAT1-PARP9 axis may regulate the pro-inflammatory phenotype of M1-like infiltrating macrophages, identifying PARP9 as a potential target for mitigating ABMR inflammation.

Conclusion

Our study delineates the macrophage landscape in ABMR post-kidney transplantation, underscoring the detrimental impact of M1-like infiltrating macrophages on ABMR pathology and prognosis.

A novel phosphocholine-mimetic inhibits a pro-inflammatory conformational change in C-reactive protein

C-reactive protein (CRP) is an early-stage acute phase protein and highly upregulated in response to inflammatory reactions. We recently identified a novel mechanism that leads to a conformational change from the native, functionally relatively inert, pentameric CRP (pCRP) structure to a pentameric CRP intermediate (pCRP*) and ultimately to the monomeric CRP (mCRP) form, both exhibiting highly pro-inflammatory effects. This transition in the inflammatory profile of CRP is mediated by binding of pCRP to activated/damaged cell membranes via exposed phosphocholine lipid head groups. We designed a tool compound as a low molecular weight CRP inhibitor using the structure of phosphocholine as a template. X-ray crystallography revealed specific binding to the phosphocholine binding pockets of pCRP. We provide in vitro and in vivo proof-of-concept data demonstrating that the low molecular weight tool compound inhibits CRP-driven exacerbation of local inflammatory responses, while potentially preserving pathogen-defense functions of CRP. The inhibition of the conformational change generating pro-inflammatory CRP isoforms via phosphocholine-mimicking compounds represents a promising, potentially broadly applicable anti-inflammatory therapy.

Macrophages in Organ Transplantation

Current immunosuppressive therapy has led to excellent short-term survival rates in organ transplantation. However, long-term graft survival rates are suboptimal, and a vast number of allografts are gradually lost in the clinic. An increasing number of animal and clinical studies have demonstrated that monocytes and macrophages play a pivotal role in graft rejection, as these mononuclear phagocytic cells recognize alloantigens and trigger an inflammatory cascade that activate the adaptive immune response. Moreover, recent studies suggest that monocytes acquire a feature of memory recall response that is associated with a potent immune response. This form of memory is called “trained immunity,” and it is retained by mechanisms of epigenetic and metabolic changes in innate immune cells after exposure to particular ligands, which have a direct impact in allograft rejection. In this review article, we highlight the role of monocytes and macrophages in organ transplantation and summarize therapeutic approaches to promote tolerance through manipulation of monocytes and macrophages. These strategies may open new therapeutic opportunities to increase long-term transplant survival rates in the clinic.

Therapeutic applications of the selective high affinity ligand drug SH7139 extend beyond non-Hodgkin's lymphoma to many other types of solid cancers

SH7139, the first of a series of selective high affinity ligand (SHAL) oncology drug candidates designed to target and bind to the HLA-DR proteins overexpressed by B-cell lymphomas, has demonstrated exceptional efficacy in the treatment of Burkitt lymphoma xenografts in mice and a safety profile that may prove to be unprecedented for an oncology drug. The aim of this study was to determine how frequently the HLA-DRs targeted by SH7139 are expressed by different subtypes of non-Hodgkin’s lymphoma and by other solid cancers that have been reported to express HLA-DR. Binding studies conducted with SH7129, a biotinylated analog of SH7139, reveal that more than half of the biopsy sections obtained from patients with different types of non-Hodgkin’s lymphoma express the HLA-DRs targeted by SH7139. Similar analyses of tumor biopsy tissue obtained from patients diagnosed with eighteen other solid cancers show the majority of these tumors also express the HLA-DRs targeted by SH7139. Cervical, ovarian, colorectal and prostate cancers expressed the most HLA-DR. Only a few esophageal and head and neck tumors bound the diagnostic. Within an individual’s tumor, cell to cell differences in HLA-DR target expression varied by only 2 to 3-fold while the expression levels in tumors obtained from different patients varied as much as 10 to 100-fold. The high frequency with which SH7129 was observed to bind to these cancers suggests that many patients diagnosed with B-cell lymphomas, myelomas, and other non-hematological cancers should be considered potential candidates for new therapies such as SH7139 that target HLA-DR-expressing tumors.

Infiltration of Macrophages Correlates with Severity of Allograft Rejection and Outcome in Human Kidney Transplantation

OBJECTIVE

Despite substantial progress in recent years, graft survival beyond the first year still requires improvement. Since modern immunosuppression addresses mainly T-cell activation and proliferation, we studied macrophage infiltration into the allografts of 103 kidney transplant recipients during acute antibody and T-cell mediated rejection. Macrophage infiltration was correlated with both graft function and graft survival until month 36 after transplantation.

RESULTS

Macrophage infiltration was significantly elevated in antibody-mediated and T-cell mediated rejection, but not in kidneys with established IFTA. Treatment of rejection with steroids was less successful in patients with more prominent macrophage infiltration into the allografts. Macrophage infiltration was accompanied by increased cell proliferation as well as antigen presentation. With regard to the compartmental distribution severity of T-cell-mediated rejection was correlated to the amount of CD68+ cells especially in the peritubular and perivascular compartment, whereas biopsies with ABMR showed mainly peritubular CD68 infiltration. Furthermore, severity of macrophage infiltration was a valid predictor of resulting creatinine values two weeks as well as two and three years after renal transplantation as illustrated by multivariate analysis. Additionally performed ROC curve analysis showed that magnitude of macrophage infiltration (below vs. above the median) was a valid predictor for the necessity to restart dialysis. Having additionally stratified biopsies in accordance to the magnitude of macrophage infiltration, differential CD68+ cell infiltration was reflected by striking differences in overall graft survival.

CONCLUSION

The differences in acute allograft rejection have not only been reflected by different magnitudes of macrophage infiltration, but also by compartment-specific infiltration pattern and subsequent impact on resulting allograft function as well as need for dialysis initiation. There is a robust relationship between macrophage infiltration, accompanying antigen-presentation and resulting allograft function.

The Mononuclear Phagocyte System in Organ Transplantation

The mononuclear phagocyte system (MPS) comprises monocytes, macrophages and dendritic cells (DCs). Over the past few decades, classification of the cells of the MPS has generated considerable controversy. Recent studies into the origin, developmental requirements and function of MPS cells are beginning to solve this problem in an objective manner. Using high-resolution genetic analyses and fate-mapping studies, three main mononuclear phagocyte lineages have been defined, namely, macrophage populations established during embryogenesis, monocyte-derived cells that develop during adult life and DCs. These subsets and their diverse subsets have specialized functions that are largely conserved between species, justifying the introduction of a new, universal scheme of nomenclature and providing the framework for therapeutic manipulation of immune responses in the clinic. In this review, we have commented on the implications of this novel MPS classification in solid organ transplantation.

Regulatory macrophages as therapeutic targets and therapeutic agents in solid organ transplantation

PURPOSE OF REVIEW

This review aims to provide a basic introduction to human macrophage biology and an appreciation of the diverse roles played by macrophage subsets in allograft damage and repair. Current and future strategies for therapeutically manipulating macrophage behaviour are discussed.

RECENT FINDINGS

Macrophages are extremely versatile effector cells that exert both immunostimulatory and immunosuppressive effects. This adaptability cannot be explained by differentiation into committed sublineages, but instead reflects the ability of macrophages to rapidly transition between states of functional polarisation. Consequently, categorisation of macrophage subpopulations is not straightforward and this, in turn, creates difficulties in studying their pathophysiology. Nevertheless, particular macrophage subpopulations have been implicated in exacerbating or attenuating ischaemia-reperfusion injury, rejection reactions and allograft fibrosis. Three general strategies for therapeutically targeting macrophages can be envisaged, namely, depletional approaches, in-situ repolarisation towards a regulatory or tissue-reparative phenotype, and ex-vivo generation of regulatory macrophages (M reg) as a cell-based therapy.

SUMMARY

As critical determinants of the local and systemic immune response to solid organ allografts, macrophage subpopulations represent attractive therapeutic targets. Rapid progress is being made in the implementation of novel macrophage-targeted therapies, particularly in the use of ex-vivo-generated M regs as a cell-based medicinal product.

Comprehensive morphometric analysis of mononuclear cell infiltration during experimental renal allograft rejection

The role of specific subtypes of infiltrating cells in acute kidney allograft rejection is still not clear and was so far not examined by different analyzing methods under standardized conditions of an experimental kidney transplantation model. Immunohistochemical staining of CD3, CD20 and CD68 was performed in rat allografts, in syngeneically transplanted rats and in control rats with a test duration of 6 and 28 days. The detailed expression and localization of infiltrating cells were analyzed manually in different kidney compartments under light microscope and by the two different morphometric software programs. Data were correlated with the corresponding kidney function as well as with histopathological classification. The information provided by the morphometric software programs on the infiltration of the specific cell types after renal transplantation was in accordance with the manual analysis. Morphometric methods were solid to analyze reliably the induction of cellular infiltrates after renal transplantation. By manual analysis we could clearly demonstrate the detailed localization of the specific cell infiltrates in the different kidney compartments. Besides infiltration of CD3 and CD68 infiltrating cells, a robust infiltration of CD20 B-cells in allogeneically transplanted rats, even at early time points after transplantation was detected. Additionally an MHC class I expression could reliable be seen in allogeneically transplanted rats. The infiltration of B-cells and the reliable antigen presentation might act as a silent subclinical trigger for subsequent chronic rejection and premature graft loss.

The role of macrophage lineage cells in kidney graft rejection and survival

Large numbers of macrophage lineage cells are present in transplants undergoing ischemia-reperfusion injury and rejection, and their presence correlates with a high probability of rejection. However, the extent to which monocytes and macrophages contribute to kidney graft rejection is poorly understood. The heterogeneity of the monocyte/macrophage lineage cells could be one of the reasons why these cells have been neglected up to now. Circulating monocytes can be divided into various subsets, which are able to give rise to tissue macrophages and dendritic cells. Macrophages are believed to be highly plastic cells that can respond to environmental signals by changing their phenotype and function. Macrophages have established roles in early and late kidney graft inflammation, tissue homeostasis, remodeling, and repair. In kidney transplantation, macrophages are believed to play a role in both damage and repair of the graft, depending on the type of macrophages involved, the environmental drive, and the time after transplantation. The heterogeneity and plasticity of monocytes and macrophages are obstacles to translating the functional relevance of this cell lineage to diagnostic and prognostic clinical parameters and to defining specific, macrophage-related, therapeutic targets. Recent evidence has indicated an immunomodulatory role for the so-called regulatory macrophages in induction of tolerance in kidney transplant recipients. In this article, we summarize current views on monocyte/macrophage immunobiology in kidney transplantation. Key issues for ongoing research are discussed.

Blocking of CCR5 and CXCR3 suppresses the infiltration of macrophages in acute renal allograft rejection

BACKGROUND

The chemokine receptors CCR5 and CXCR3 are expressed by T cells and macrophages. We examined effects of a CCR5/CXCR3 antagonist (TAK), with a particular focus on the role of macrophages, in a rat kidney transplant model.

METHODS

Dark Agouti rat kidneys were transplanted into Lewis rats. The recipients were treated daily with a 10 mg/kg TAK on posttransplant days 0 to 14 and/or 2 mg/kg of cyclosporine A (CsA) on days 0 to 5. Graft survival, histological changes, and the expression of chemokines and chemokine receptors on T cells and macrophages were studied.

RESULTS

Treatment with TAK alone suppressed CD4+T cell infiltration and slightly prolonged graft survival. The expressions of both CCR5 and CXCR3, and activated macrophage-associated cytokines and chemokines, were significantly increased on macrophages that had been separated from rejecting kidneys, compared with those from spleens. However, these upregulations were decreased in macrophages from kidneys that had been treated with TAK. Immunohistochemistry also showed that macrophages infiltrating tubules of rejecting kidney expressed both receptors. In the CsA alone group, macrophages were the dominant infiltrating cells, and all allografts were rejected within 10 days. A combined therapy involving CsA and TAK resulted in decreased macrophage infiltration, and graft survival was substantially prolonged. The levels of activated macrophage-associated cytokines and chemokines were also decreased.

CONCLUSION

The dual blocking of CCR5/CXCR3 can be useful in decreasing rejection, with or without CsA. This mechanism acts, not only to block T-cell recruitment to a kidney graft but to suppress the infiltration of macrophages as well.

Relationship of HLA‐DR Expression to Rejection and Mononuclear Cell Infiltration in Renal Allograft Biopsies

Research on renal biopsies has shown that HLA class I antigens are distributed throughout the renal parenchyma, but that the distribution of HLA-DR varies greatly. We investigated HLA-DR expression in biopsies of 90 renal transplants, and also semiquantitatively assessed the proportions of CD68-, CD3-, and HLA-DR-positive infiltrating cells by immunohistochemistry. The relationships between tubular DR expression and interstitial lymphocyte and macrophage infiltration were examined. Forty of the biopsies showed acute rejection (AR), 33 showed chronic rejection (CR), 10 showed suspected rejection (SR), and 7 showed no evidence of rejection (NR). HLA-DR expression was noted in 35/40 (87.5%) of the AR cases, 22/33 (66.6%) of the CR cases, and 6/10 (60%) of the SR cases. Only 1 (14.3%) of the NR cases exhibited HLA-DR antigen expression in the renal tubules. The proportions of lymphocyte and macrophage infiltration observed in the interstitium were significantly correlated with tubular DR expression in all cases (p<0.01). At 6 months after biopsy was done, 24/35 (68.6%) of the AR patients with tubular DR expression had showed second episode of rejection or showed deteriorated renal function. The remaining 11 AR cases with tubular DR expression had stable renal function at this stage. The cases that had no significant tubular DR expression had no problems with rejection or functional deterioration. These findings are consistent with the theory that expression of HLA-DR antigens on renal tubular cells may be a marker of rejection and poor graft outcome.

Analysis of parathyroid graft rejection suggests alloantigen-specific production of nitric oxide by iNOS-positive intragraft macrophages

BACKGROUND

During acute rejection of organ or tissue allografts T cells and macrophages are dominant infiltrating cells. CD4-positive T cells are important for the induction of allograft rejection and macrophages are important effector cells mediating cytotoxicity via production of nitric oxide (NO) by the inducible NO-synthase (iNOS). In the present study we analysed whether the destruction of primarily nonvascularised parathyroid allografts is also mediated by iNOS-positive macrophages.

METHODS

Hypocalcaemic Lewis rats received parathyroid isografts (from Lewis donors) and allografts (from Wistar Furth donors), respectively, under the kidney capsule. Levels of serum calcium above 2 mmol/L correlated with normal parathyroid function and below 2 mmol/L with parathyroid rejection. Accelerated parathyroid allograft rejection was induced by immunisation of Lewis recipients with the allogeneic peptide P1.

RESULTS

Determination of serum calcium levels is a useful parameter to control parathyroid graft function, and therefore to determine allograft rejection. Macrophages positive for both major histocompatibility complex (MHC) class II molecules and costimulatory molecules accumulated in iso- and allografts, but iNOS-positive macrophages were only detectable in allografts in the presence of activated CD4-positive T cells. These results confirm a cooperation between activated T cells and intragraft macrophages to induce macrophage iNOS expression. Recipients immunised with the allogeneic peptide P1 demonstrated accelerated rejection of allografts (mean+/-SD: 9.2+/-0.9 days) in contrast to nonimmunised animals (mean+/-SD: 15.8+/-1.8 days). Allografts of P1-immunised animals were infiltrated faster by activated CD4-positve T cells and, in addition, the infiltrates of iNOS-positive macrophages were stronger than those in allografts of nonimmunised animals.

CONCLUSIONS

Intragraft iNOS-positive macrophages seem to be able to produce cytotoxic NO involved in the killing of allogeneic cells during the alloimmune response against primarily nonvascularised parathyroid organ grafts. Infiltrates of iNOS-negative macrophages found in parathyroid isografts were caused by antigen-independent inflammation triggered by surgically induced injury. The absence of activated T cells in isografts and their presence in allografts underlines their importance in inducing macrophage iNOS expression.

Heme oxygenase 1: does it have a role in renal cytoprotection?

Heme oxygenase (HO) was first identified as the rate-limiting enzyme in the degradative pathway of heme, but is now recognized to be involved in diverse biological processes. Different isoforms of HO exist; HO-1 (HMOX1) is ubiquitously present in mammalian tissue with low constitutive expression under physiological conditions, but is upregulated in response to a variety of potentially noxious stimuli. HO-1, an integral component of an important cytoprotective mechanism, mediates its action through removal of heme, the generation of heme breakdown reaction products (biliverdin, free iron, and carbon monoxide), and modulation of key cellular molecules. Data from experimental models in which HO-1 was induced or inhibited, together with observations in genetically modified animals, showed a beneficial effect of HO-1 in several pathways leading to kidney injury. The discovery of a functional guanosine thymine tandem repeat polymorphism in the promoter region of the human HO-1 gene has stimulated clinical investigations in a variety of diseases. However, despite theoretical and experimental support for an important pathophysiological role for HO-1, the relevance of this polymorphism in native kidney or renal transplant function is equivocal. This article reviews the molecular genetics of HO-1, its myriad cytoprotective effects allied to how these are mediated, and relates these findings to experimental and clinical evidence of HO-1 involvement in renal disease.

Immunephenotype of glomerular and interstitial infiltrating cells in protocol renal allograft biopsies and histological diagnosis

Patients with a protocol renal allograft biopsy simultaneously displaying interstitial fibrosis/tubular atrophy (IF/TA) and subclinical rejection (SCR) have a shortened graft survival than patients with a normal biopsy, or with a biopsy only displaying IF/TA or SCR. The poor outcome of these patients could be related with a more severe inflammation. We evaluate the immunophenotype of infiltrating cells in these diagnostic categories. Nonexhausted paraffin blocks from protocol biopsies done during the first year were stained with anti-CD45, CD3, CD20, CD68 and CD15 monoclonal antibodies. Glomerular and interstitial positive cells were counted. C4d deposition in peritubular capillaries was evaluated. Histological diagnoses were: normal (n = 80), SCR (n = 17), IF/TA (n = 42) and IF/TA + SCR (n = 17). Only interstitial CD20 positive cells were significantly increased in patients displaying IF/TA + SCR; normal (137 +/- 117), SCR (202 +/- 145), IF/TA (208 +/- 151) and IF/TA + SCR (307 +/- 180 cells/mm(2)), p < 0.01. The proportion of biopsies displaying C4d deposition was not different among groups. The upper tertile of CD20 positive interstitial cells was associated with a decreased death-censored graft survival (relative risk: 3.01, 95% confidence interval: 1.23-7.35; p = 0.015). These data suggest that B-cell interstitial infiltrates are associated with histological damage and outcome, but do not distinguish whether these infiltrates were the cause or the consequence of chronic tubulo-interstitial damage.

Immunophenotype of infiltrating cells in protocol renal allograft biopsies from tacrolimus-versus cyclosporine-treated patients

The prevalence of subclinical rejection is lower in patients receiving tacrolimus than in patients treated with cyclosporine. However, it is not known whether this difference is related to the modulation of a specific cell immunophenotype. We perform a two case-one control study in patients treated with tacrolimus (n=44) or cyclosporine (n=22) with a protocol biopsy performed at 4 to 6 months. Immunophenotype of infiltrating cells was evaluated with monoclonal antibodies directed against CD45 (all leukocytes), CD3 (T lymphocytes), CD68 (monocytes/macrophages), and CD20 (B lymphocytes) and expressed as interstitial positive cells/mm(2). The number of interstitial CD45 (290+/-209 vs. 696+/-560; P<0.01), CD3 (121+/-84 vs. 208+/-104; P<0.01), and CD68 (155+/-232 vs. 242+/-280; P<0.05) but not CD20 (137+/-119 vs. 197+/-154) positive cells was lower in tacrolimus-treated patients. T lymphocytes and macrophages interstitial infiltration was reduced in tacrolimus treated patients evaluated with protocol biopsies in comparison to cyclosporine-treated patients.

Glomerular C3c deposition and intravascular macrophage accumulation in early humoral renal allograft rejection signifies a poor short-term outcome

C4d deposition in the walls of peritubular capillaries is considered the key phenomenon in the histopathological diagnosis of humoral, i.e. antibody-mediated, allograft rejection. We have earlier proposed that deposition of C3c in glomerular capillaries and simultaneous intravascular accumulation of macrophages in allografts with immediate or early humoral rejection indicates a potentially serious condition with very poor prognosis. The clinical outcome of 45 cadaveric grafts with this phenomenon among 1960 renal allografts transplanted at our centre during 1984-1999, and the recipients of the contralateral kidneys, was retrospectively evaluated. Graft failure occurred in 44/45 grafts within 3 weeks, with graft loss in 33/45 (77%) within 4 months and 37/45 (82%) within 1 year. From the contralateral kidneys, 5/33 (15%) were lost within 1 year. In a recent series of early biopsies, we recognised that of 13 cases showing C4d positivity in peritubular capillaries but lacking C3c in glomeruli, 10/13 (77%) were still functioning after 4 months. The mean number of CD68(+) macrophages per glomerular profile, i.e. the glomerular macrophage index, shows a significant difference between C4d(+)C3c(-) and C4d(+)C3c(+) cases (p<0.001). Our results indicate the existence of a clinically important subgroup of early humoral rejection with particular morphological features.

Modifying graft immunogenicity and immune response prior to transplantation: potential clinical applications of donor and graft treatment

Many studies have shown a strong association between initial graft injury and poor long-term graft outcome. Events initiated by unspecific immune-activating processes including brain death and ischemia/reperfusion injury occurring prior to transplantation reduce graft functionality and amplify the host immune response. These events may be particularly relevant for less than optimal grafts with reduced resistance to unspecific injuries. Several approaches to ameliorate immune activation of the graft by treating the donor or the graft have been studied. While various substances have been shown to have protective effects in experimental transplantation, only a few drugs have been tested clinically and have demonstrated beneficial effects. We review the results of experimental and clinical studies on donor or graft immunomodulation prior to transplantation and analyze the evidence to support clinical application of these strategies.

Prevalence and immunohistochemical findings of subclinical kidney allograft rejection and its association with graft outcome

Subclinical acute rejection (SAR) occurs in about 30% of stable renal transplant patients and may be a risk factor for a poor allograft outcome. In the present study, the prevalence and clinical features of subclinical rejection, and the expression of immune activation markers in surveillance graft biopsies were assessed and correlated with late graft outcomes. Protocol biopsies were obtained at 2 and 12 months post-transplant in 32 and 26 patients, respectively, with stable renal function. The Banff 1997 criteria were used for histological diagnosis. Graft function and survival and proteinuria were assessed during the 36 months of follow-up. Immunohistochemical evaluation of cell subpopulations and immunoactivation markers were performed on protocol biopsies. The prevalence of SAR at 2 months and of chronic allograft nephropathy (CAN) at 12 months in representative biopsies was 55 and 50%, respectively. Patients with SAR presented mononuclear cell infiltration with an increased expression of CD3, CD4, CD68, IL-2R and granzyme B. Kidney graft function was significantly worse in patients with SAR at 2 months who had chronic rejection on biopsy at 12 months, but SAR was not associated with a worse graft function, greater proteinuria or a lower graft survival in 3 yr of follow-up. In conclusion, we found an elevated prevalence of SAR at 2 months after transplantation with an increased expression of activation markers. Although an association of SAR with poor graft outcome was not observed, our results suggest that SAR is an immunologically active process and underscore the importance of protocol biopsies in the surveillance of transplanted kidneys.

Clinical graft evolution of lymphocytes, polymorphonuclear cells, and antigen expression in tubular renal cells in the urine sediment of 20 renal allograft recipients

Urinary samples from 20 kidney transplant recipients were studied to determine the cellular composition of the sediments using an immunocytological (IC) technique. The expression of HLA class I (A, B, C) and class II (DR, DQ, DP), CD2, CD3, CD4, CD8, and interleukin (IL)-2 receptor (IL-2R) on lymphocytes was assessed using a panel of monoclonal antibodies. The results were correlated with graft function and with the number of episodes of acute renal graft rejection (AR) during a period of 6 months posttransplantation. The cellular infiltration of lymphocytes (LC) and polymorphonuclear cells (PMNC) also was studied using a standard cytology (SC) technique. During this period, 17 of 30 episodes of graft dysfunction due to AR occurred in 12 patients: 8 to acute tubular necrosis (ATN) (n = 8); 4 to cyclosporine (CsA) toxicity (n = 4) and 1 to amphotericin toxicity (n = 1). The diagnosis of AR was made clinically by 3 independent observers, using biopsy in some cases. The immunocytology showed a significantly increased expression of HLA-DR, DO, and DP namely, greater than 20% positivity in 10% of samples on the tubular epithelial cells (TEC) of patients presenting with versus without AR (P < or =.001). In addition, a high correlation was observed between the expression of IL-2R and the presence of AR (p < or =.002). The standard cytology results showed a significantly increased percentage of LC and decreased percentage of PMNCs in samples obtained 2 days prior to the clinical manifestations of patients who developed AR (P =.001). A greater level of expression of antigen determinants was observed prior to AR. These results suggest that immunocytology of urinary sediments, which is a noninvasive technique, has enormous clinical potential for the differential diagnosis of AR, ATN, and CsA toxicity. In our study, the use of HLA class IL-specific monoclonal antibodies (Abs) gave a 100% specificity, 95% sensitivity, and 95% predictability. Although our results also indicate a potential value in the increased IL-2R expression, these findings must be confirmed by further studies. Furthermore, the combination of both immunologic and SC techniques in urinary sediments allows early detection of AR and is cost effective and simple features that could be used routinely for follow-up of renal transplant recipients.

Macrophages act as effectors of tissue damage in acute renal allograft rejection

BACKGROUND

Macrophages constitute 38% to 60% of infiltrating cells during acute renal allograft rejection. Their contribution to tissue damage during acute rejection was examined by depleting macrophages in a rat model.

METHODS

Lewis rats underwent bilateral nephrectomy and then received a Dark Agouti renal allograft and liposomal-clodronate, control phosphate-buffered saline liposomes, or saline intravenously (n=7 per group) on days 1 and 3 postsurgery. Grafts were harvested on day 5.

RESULTS

Liposomal-clodronate treatment resulted in a 70% reduction in blood ED1+ monocytes and 60% reduction in intragraft ED1+ macrophages (both P<0.01). Half of all remaining interstitial ED1+ cells were undergoing apoptosis (terminal deoxynucleotide transferase-mediated dUTP nick-end labeling+/ED1+), and thus functional depletion of more than 75% of macrophages was achieved. Histologic and functional parameters of acute rejection were attenuated: interstitial infiltrate, tubulitis, and glomerulitis (P<0.01); tubular cell apoptosis (P<0.001); tubular cell proliferation (P<0.001); and serum creatinine (P<0.01). Production of inducible nitric oxide synthase by infiltrating cells and urinary nitric oxide excretion was reduced by 90% (P<0.001). In contrast, no reduction in the number of other leukocytes was seen (CD3+, CD4+, CD8+, and natural killer cells). Activation of lymphocytes (CD25+) and production of lymphocyte effector molecules (granzyme B) were unaltered.

CONCLUSION

This study demonstrates that macrophages contribute to tissue damage during acute rejection.

Macrophage colony-stimulating factor expression and macrophage accumulation in renal allograft rejection

BACKGROUND

Studies of infiltrating cells from acutely rejecting renal allografts show that a high proportion of these cells are macrophages, and early macrophage infiltration is a poor prognostic sign for transplant survival. Macrophage colony-stimulating factor (M-CSF), produced by tubular and mesangial cells, has been associated with macrophage infiltration and proliferation in experimental and human kidney diseases. We investigated the expression of M-CSF in a model of acute rejection.

METHODS

Lewis rats underwent bilateral nephrectomies and received an orthotopic Dark Agouti allograft or Lewis isograft. Animals received cyclosporine (10 mg/kg/day) from day 0 to day 3 and were killed at days 4, 8, or 14 after transplantation. Macrophages (ED1+) and T cells (W3-13+) were identified by immunohistochemistry, and M-CSF expression was identified by Northern blotting and in situ hybridization.

RESULTS

Isografts had normal renal function without histological evidence of rejection. Allografts exhibited a moderate infiltrate at day 4 but progressed to severe rejection at day 14, with elevated serum creatinine level and severe tubulointerstitial damage. Macrophages and T cells were present in equal proportion in the infiltrate at day 4. At day 14, the number of macrophages increased fivefold (2580/mm2), although T cells were unchanged (380/mm2). Proliferating macrophages (ED1+, BrdU+) increased from day 4 (4%) to day 14 (10%). M-CSF mRNA expression was strongly up-regulated in allografts compared with isografts and normal rat. In situ hybridization demonstrated M-CSF expression by resident and infiltrating cells. Renal tubular expression was minimally increased at day 4 but strongly up-regulated at day 14 (more than 50% of tubules positive), particularly in areas of tubular damage. Tubular M-CSF expression colocalized with areas of intense macrophage infiltration and proliferation. Serial sections with double labeling demonstrated that T cells were the dominant source of M-CSF at day 4, yet later in the rejection (day 14) the predominant sites of production were both renal tubular cells and interstitial macrophages.

CONCLUSIONS

Renal production of M-CSF by graft-infiltrating (macrophages and T lymphocytes) and resident (tubular) cells was up-regulated during acute rejection. M-CSF promotes macrophage recruitment and proliferation and may thereby play a pathogenic role in acute rejection. The kinetics of M-CSF production during acute rejection suggest that local macrophage proliferation may be initiated by T cells and perpetuated by both renal tubular and autocrine release.

Cadaver versus living donor kidneys: impact of donor factors on antigen induction before transplantation

BACKGROUND

It is widely recognized that living-related donor (LRD) renal allografts have a higher overall graft survival than cadaver donor transplants. We tested the hypothesis that part of this is attributable to LRD kidneys being obtained under optimal conditions from healthy donors, whereas cadaveric kidneys may have experienced injury as a result of inflammatory events around the time of brain death.

METHODS

We have performed a comparative immunohistochemical analysis of pretransplant donor biopsies from cadaveric (N = 65) and LRD (N = 29) kidneys to determine any differences that may predispose them to subsequent damage. Cryostat sections were stained with antibodies to leukocytes, adhesion molecules, and human leukocyte antigen (HLA)-DR antigens, and the expression was assessed semiquantitatively.

RESULTS

High levels of endothelial E-selectin and proximal tubular expression of HLA-DR antigens, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 were detected in biopsies from cadaveric kidneys, whereas expression of these markers was markedly reduced in LRD kidneys. High levels of tubular antigen expression were significantly associated with traumatic death, prolonged ventilation, and episodes of infection in cadaver donors. Furthermore, the expression of pretransplant tubular antigens in cadaver donor kidneys was significantly associated with early acute rejection following transplantation, suggesting that such kidneys are predisposed to subsequent immune-mediated attack following transplantation.

CONCLUSIONS

These results may explain, in part, the superior outcome of LRD allografts compared with cadaver renal allografts.

Hypothesis: is renal allograft rejection initiated by the response to injury sustained during the transplant process?

Allograft rejection can be caused by numerous factors such as damage to the donor kidney during surgical removal or implantation, injury sustained during the transport process between the donor and recipient, and suboptimal allograft perfusion during the intra- and post-operative period. In cadaveric allografts, damage can occur during cold storage, during the transit stage between donor and recipient, and hemodynamic instability due to the initial damage that caused its removal from the donor (such as brain death or trauma). We hypothesize that rejection requires recognition of this injury in addition to recognition of alloantigens. If indeed injury proves to be one factor in acute rejection episodes, then therapeutic efforts can be made to reduce injury during the transplantation process.

Macrophage migration inhibitory factor expression in human renal allograft rejection

BACKGROUND

Macrophage migration inhibitory factor (MIF) plays a pivotal role in immune-mediated diseases. Despite the long-standing association of MIF with the delayed-type hypersensitivity response, the potential role of MIF in allograft rejection is unknown.

METHODS

MIF expression was assessed by in situ hybridization and immunohistochemistry staining in 62 biopsies of human renal allograft rejection and in normal human kidney.

RESULTS

MIF mRNA and protein is constitutively expressed in normal kidney, being largely restricted to tubular epithelial cells, some glomerular epithelial cells, and vascular smooth muscle cells. In both acute and chronic renal allograft rejection, there was marked up-regulation of MIF mRNA and protein expression by intrinsic kidney cells such as tubular epithelial cells and vascular endothelial and smooth muscle cells. There was also MIF expression by infiltrating macrophages and T cells. Of note, macrophage and T cell infiltrates were largely restricted to areas with marked up-regulation of MIF expression, potentially contributing to the development of severe tubulitis and intimal or transmural arteritis. Quantitative analysis found that increased MIF expression in allograft rejection gave a highly significant correlation with macrophage and T cell accumulation in both the glomerulus and interstitium (P<0.001). In addition, the number of MIF+ tubules and interstitial MIF+ cells correlated significantly with the severity of allograft rejection (P<0.01), and the loss of renal function (P<0.01). In contrast, no up-regulation of renal MIF expression and no leukocyte accumulation was seen in allograft biopsies without evidence of rejection.

CONCLUSIONS

This is the first study to demonstrate that local MIF expression is up-regulated during allograft rejection. The association between up-regulation of MIF expression, macrophage and T cell infiltration and the severity of renal allograft rejection suggests that MIF may be an important mediator in the process of allograft rejection.

Monocytes-macrophages and cytokines/chemokines in fine-needle aspiration biopsy cultures: enhanced interleukin-1 receptor antagonist synthesis in rejection-free kidney transplant patients

BACKGROUND

Monocytes-macrophages are found within kidney allografts during the first days after surgery, where they perform "housekeeping" tasks, participate in postreperfusion injury, and act as antigen-presenting cells, as well as become involved in the effector phase of acute rejection. They also seem to play a prominent role in chronic rejection. We quantified their presence in fine-needle aspiration biopsies and studied the growth factors that, we hypothesized, would mark the different implications of the presence of monocytes-macrophages.

METHODS

Fine-needle aspiration biopsies were obtained from 56 adult renal transplants and analyzed for CD14+ using the alkaline phosphatase-anti-alkaline phosphatase procedure. Thirty-three patients were studied on the production of interleukin (IL)-1 receptor antagonist (IL-1ra), IL-6, IL-8, macrophage colony-stimulating factor, monocyte chemotactic protein 1, and macrophage inflammatory protein 1alpha by aspiration biopsies cultures using enzyme-linked immunosorbent assay techniques.

RESULTS

CD14+ cells were present at significantly higher numbers in steroid-resistant acute rejections but also during the first days after surgery, especially if acute tubular necrosis was present. We found a significantly higher production of IL-1ra by rejection-free patients compared with acutely rejecting patients, and this difference was already established on day 7 after surgery (10+/-10.5 days before rejection).

CONCLUSIONS

Monocytes-macrophages are present at higher numbers in aspiration biopsies of kidney transplant patients suffering either acute tubular necrosis or steroid-resistant rejections, but they are present during the first days after transplant in stable patients, too. The production of IL-1ra is significantly up-regulated in stable patients, which suggests that monocytes-macrophages may constitute an early key factor in the down-regulation of the anti-allograft immune response.

Interaction between proximal tubular cells and allogenic leukocytes mediated by interleukin-1 and prostaglandin

The present study investigates the interaction between proximal tubular cells (TC) and peripheral blood mononuclear cells (PBMC) with respect to interleukin-1 (Il-1) and prostaglandin E2 (PGE2) in co-culture experiments. Stimulator cells were proliferating human TC propagated in culture and characterized by expression of ICAM-1 and MHC-class II in response to cytokines. The presence of TC reduced spontaneous growth of PBMC by 42%, with a concomittant 50% reduction of Il-1 release and a 6-fold increase of PGE2 release in the growth medium. The growth reduction was partly counteracted by addition of II-1 and indomethacin. Addition of II-1 stimulated the PGE2 release from PBMC and TC by about 75% and 500%, respectively. Growth of TC cultured alone was inhibited by II-1 in a dose-dependent manner, with maximum effect at 10 U/ml, whereas PGE2 showed no effect. These results suggest that TC have the capacity to interact with PBMC, and this potentially tissue-protective mechanism induced by TC may have clinical implications.

Detection of interstitial increase in macrophages, characteristic of acute interstitial rejection, in routinely processed renal allograft biopsies using the monoclonal antibody KP1

Acute interstitial rejection (AIR) of renal allografts is accompanied by a characteristic peritubular increase in macrophages, which can be identified with the CD14 monoclonal antibody (mAb) WT14 in cryostat sections. Since frozen tissue is not always available, we tested whether this increase can also be demonstrated in Bouin-fixed, paraffin-embedded biopsies, using the CD68 antimacrophage mAb KP1, which can also be applied to paraffin sections. Sections of 16 biopsies with AIR and 11 controls were stained with KP1. In 25 of the 27 biopsies, macrophages were strongly positive for KP1. Two AIR biopsies were completely negative, probably due to prolonged fixation. In the remaining 14 AIR biopsies, the number of KP1-positive cells was significantly higher than in the controls [1184 +/- 410 per mm2 (mean +/- SD) vs 112 +/- 126 per mm2]. We conclude that, especially in cases in which frozen tissue is not available, the demonstration of increased numbers of monocytes/macrophages with mAb KP1 can be a helpful adjunct in the histological diagnosis of AIR in routinely processed renal biopsies.

Human proximal tubular cells modulate allogen responses of leukocytesin vitro

The interaction between proximal tubular cells and leukocytes was examined. In co-cultures of tubular cells and allogenic leukocytes, tubular cells expressed MHC antigens and ICAM-1. A small number of leukocytes adhered to tubular cells and induced cytotoxic damage. Thus, 65% of the tubular cells were viable after co-culturing with allogenic leukocytes. These cells had low alloreactive capacity, which was not due to lack of interleukin-1 or interferon-gamma. The presence of tubular cells modulated the immune response of leukocytes by reducing the effect of mitogen by 80%, allogens by 65% and interleukin-2 by 40%. A soluble factor released in the co-cultures was a likely mediator, since addition of supernatants from co-cultures suppressed mitogen responses by 27% compared to leukocytes cultured alone. This mediator might be prostaglandin, because addition of indomethacin to co-cultures increased the growth response of leukocytes.