Increased influx of myeloid dendritic cells during acute rejection is associated with interstitial fibrosis and tubular atrophy and predicts poor outcome

Immunoregulation mechanism of VEGF signaling pathway inhibitors and its efficacy on the kidney

Angiogenesis and immunosuppression are closely related pathophysiologic processes. Widely prescribed in malignant tumor and proliferative retinal lesions, VEGF signaling pathway inhibitors may cause hypertension and renal injury in some patients, presenting with proteinuria, nephrotic syndrome, renal failure and thrombotic microangiopathy. VEGF signaling pathway inhibitors block the action of both VEGF-A and VEGF-C. However, VEGF-A and VEGF-C produced by podocytes are vital to maintain the physiological function of glomerular endothelial cells and podocytes. There is still no effective treatment for kidney disease associated with VEGF signaling pathway inhibitors and some patients have progressive renal failure even after withdrawal of the drug. Recent studies reveal that blocking of VEGF-A and VEGF-C can activate CD4 +and CD8+ T cells, augment antigen-presenting function of dendritic cells, enhance cytotoxicity of macrophages and initiate complement cascade activation. VEGF and VEGFR are expressed in immune cells, which are involved in the immunosuppression and cross-talk among immune cells. This review summarizes the expression and function of VEGF-A and VEGF-C in the kidney. The current immunoregulation mechanisms of VEGF signaling pathway inhibitors are reviewed. Finally, combinate strategies are summarized to highlight the proposal for VEGF signaling pathway inhibitors.

Dendritic cells in liver transplantation immune response

Dendritic cells (DCs) are the most powerful antigen presenting cells (APCs), they are considered one of the key regulatory factors in the liver immune system. There is currently much interest in modulating DC function to improve transplant immune response. In liver transplantation, DCs participate in both the promotion and inhibition of the alloreponse by adopting different phenotypes and function. Thus, in this review, we discussed the origin, maturation, migration and pathological effects of several DC subsets, including the conventional DC (cDC), plasmacytoid DC (pDC) and monocyte-derived DC (Mo-DC) in liver transplantation, and we summarized the roles of these DC subsets in liver transplant rejection and tolerance. In addition, we also outlined the latest progress in DC-based related treatment regimens. Overall, our discussion provides a beneficial resource for better understanding the biology of DCs and their manipulation to improve the immune adaptability of patients in transplant status.

Contemporary Biomarkers for Renal Transplantation: A Narrative Overview

Renal transplantation (RT) is the preferred treatment for end-stage renal disease. However, clinical challenges persist, i.e., early detection of graft dysfunction, timely identification of rejection episodes, personalization of immunosuppressive therapy, and prediction of long-term graft survival. Biomarkers have emerged as valuable tools to address these challenges and revolutionize RT patient care. Our review synthesizes the existing scientific literature to highlight promising biomarkers, their biological characteristics, and their potential roles in enhancing clinical decision-making and patient outcomes. Emerging non-invasive biomarkers seemingly provide valuable insights into the immunopathology of nephron injury and allograft rejection. Moreover, we analyzed biomarkers with intra-nephron specificities, i.e., glomerular vs. tubular (proximal vs. distal), which can localize an injury in different nephron areas. Additionally, this paper provides a comprehensive analysis of the potential clinical applications of biomarkers in the prediction, detection, differential diagnosis and assessment of post-RT non-surgical allograft complications. Lastly, we focus on the pursuit of immune tolerance biomarkers, which aims to reclassify transplant recipients based on immune risk thresholds, guide personalized immunosuppression strategies, and ultimately identify patients for whom immunosuppression may safely be reduced. Further research, validation, standardization, and prospective studies are necessary to fully harness the clinical utility of RT biomarkers and guide the development of targeted therapies.

High soluble HLA-DQB2 levels in posttransplant serum are associated with kidney graft dysfunction

HLA-DQB2 is a gene of limited polymorphism, with unknown function that presents at least two transcript variants: v1, which encodes the full-length beta-chain, and v2, which lacks exon 4 and could give rise to a soluble protein. We previously showed a strong correlation between high v2 expression in preimplantation biopsies (PIB) of kidneys from young (18- to 49-year olds) but not from old, deceased donors and 1-year posttransplant low (estimated glomerular filtration rate < 45 ml/min/1.73 m² ) graft function (GF). In this study, we aimed to investigate the impact of posttransplant soluble HLA-DQB2 (sDQB2) serum levels, v1 expression in PIB, and recipient HLA-DQB2 rs7453920 A/G polymorphism on GF. sDQB2 was evaluated by enzyme-linked immunosorbent assay in sera from 114 recipients, collected at least 1 year (median 2.1 years) after transplantation. Higher sDQB2 levels were observed in recipients of kidneys from young, but not from old, donors that had a ≥30% decline in GF within 1 year after blood collection for sDQB2 determination. Among the 15 recipients of kidneys from young donors with sDQB2 ≥ 1.52 ng/ml, 40% presented a ≥30% decline in GF, whereas this occurred in none of the 43 recipients with lower sDQB2 levels (p = 0.007; OR: 36.5). Expression of HLA-DQB2 variant 1, measured by reverse transcription-polymerase chain reaction (RT-PCR) in 92 PIB from young or old donors, did not significantly differ between transplants with high or low 4-year GF. HLA-DQB2 rs7453920 single nucleotide polymorphism (SNP) frequencies did not significantly differ between recipients with low or high 4-year GF. We conclude that HLA-DQB2 variant 1 expression in PIB and recipient rs7453920 SNP polymorphism are not associated with graft outcome. On the other hand, the association, in transplants of kidneys from young donors, between high posttransplant serum sDQB2 levels and decline in GF is a very interesting finding that deserves a validation study in a larger cohort.

Protective Role of Kynurenine 3-Monooxygenase in Allograft Rejection and Tubular Injury in Kidney Transplantation

Renal tubular epithelial cells (TECs) are the primary targets of ischemia-reperfusion injury (IRI) and rejection by the recipient's immune response in kidney transplantation (KTx). However, the molecular mechanism of rejection and IRI remains to be identified. Our previous study demonstrated that kynurenine 3-monooxygenase (KMO) and kynureninase were reduced in ischemia-reperfusion procedure and further decreased in rejection allografts among mismatched pig KTx. Herein, we reveal that TEC injury in acutely rejection allografts is associated with alterations of Bcl2 family proteins, reduction of tight junction protein 1 (TJP1), and TEC-specific KMO. Three cytokines, IFN γ , TNFα, and IL1β, reported in our previous investigation were identified as triggers of TEC injury by altering the expression of Bcl2, BID, and TJP1. Allograft rejection and TEC injury were always associated with a dramatic reduction of KMO. 3HK and 3HAA, as direct and downstream products of KMO, effectively protected TEC from injury via increasing expression of Bcl-xL and TJP1. Both 3HK and 3HAA further prevented allograft rejection by inhibiting T cell proliferation and up-regulating aryl hydrocarbon receptor expression. Pig KTx with the administration of DNA nanoparticles (DNP) that induce expression of indoleamine 2,3-dioxygenase (IDO) and KMO to increase 3HK/3HAA showed an improvement of allograft rejection as well as murine skin transplant in IDO knockout mice with the injection of 3HK indicated a dramatic reduction of allograft rejection. Taken together, our data provide strong evidence that reduction of KMO in the graft is a key mediator of allograft rejection and loss. KMO can effectively improve allograft outcome by attenuating allograft rejection and maintaining graft barrier function.

Non-permissive human conventional CD1c+ dendritic cells enable trans-infection of human primary renal tubular epithelial cells and protect BK polyomavirus from neutralization

The BK polyomavirus (BKPyV) is a ubiquitous human virus that persists in the renourinary epithelium. Immunosuppression can lead to BKPyV reactivation in the first year post-transplantation in kidney transplant recipients (KTRs) and hematopoietic stem cell transplant recipients. In KTRs, persistent DNAemia has been correlated to the occurrence of polyomavirus-associated nephropathy (PVAN) that can lead to graft loss if not properly controlled. Based on recent observations that conventional dendritic cells (cDCs) specifically infiltrate PVAN lesions, we hypothesized that those cells could play a role in BKPyV infection. We first demonstrated that monocyte-derived dendritic cells (MDDCs), an in vitro model for mDCs, captured BKPyV particles through an unconventional GRAF-1 endocytic pathway. Neither BKPyV particles nor BKPyV-infected cells were shown to activate MDDCs. Endocytosed virions were efficiently transmitted to permissive cells and protected from the antibody-mediated neutralization. Finally, we demonstrated that freshly isolated CD1c⁺ mDCs from the blood and kidney parenchyma behaved similarly to MDDCs thus extending our results to cells of clinical relevance. This study sheds light on a potential unprecedented CD1c⁺ mDC involvement in the BKPyV infection as a promoter of viral spreading.

Dr Sylvia Gardner first discovered the BK polyomavirus (BKPyV) in the urine of a kidney-transplant recipient in 1970. In the 1990’s, the widespread use of potent immunosuppressive drugs such as tacrolimus, sirolimus or mycophenolate mofetil led to the emergence of BKPyV nephropathy. Recently, various studies reported a specific influx of myeloid dendritic cells (mDCs) in the renal tissue of kidney-transplant patients who were diagnosed with a BKPyV nephropathy. MDCs are immune cells both residing in tissues and migrating to other organs or compartments like the blood when changes in their environment occur. Their main functions are the detection of danger signals such as pathogens or tumors and the processing of antigens to prime naïve specific effectors of the adaptive immune response. Although anti-BKPyV cellular immune responses have been investigated in post-transplant recipients as well as healthy individuals, supporting an active role of mDCs little is known about how mDCs and BKPyV interact with each other. Our study provides the basis to understand the role played by mDCs in virus capture through an unprecedented endocytic mechanism and possibly in viral protection from neutralization by specific antibodies. Moreover, we showed that mDCs are unable to sense BKPyV particles or BKPyV-infected dying cells as a danger signal, supporting the view that other DC subsets might act as the true antigen presenting cells that promote the adaptive immune response against BKPyV infection.

Circulating Long Noncoding RNA LNC-EPHA6 Associates with Acute Rejection after Kidney Transplantation

Acute rejection (AR) of a kidney graft in renal transplant recipients is associated with microvascular injury in graft dysfunction and, ultimately, graft failure. Circulating long noncoding RNAs (lncRNAs) may be suitable markers for vascular injury in the context of AR. Here, we first investigated the effect of AR after kidney transplantation on local vascular integrity and demonstrated that the capillary density markedly decreased in AR kidney biopsies compared to pre-transplant biopsies. Subsequently, we assessed the circulating levels of four lncRNAs (LNC-RPS24, LNC-EPHA6, MALAT1, and LIPCAR), that were previously demonstrated to associate with vascular injury in a cohort of kidney recipients with a stable kidney transplant function (n = 32) and recipients with AR (n = 15). The latter were followed longitudinally six and 12 months after rejection. We found higher levels of circulating LNC-EPHA6 during rejection, compared with renal recipients with a stable kidney function (p = 0.017), that normalized one year after AR. In addition, LNC-RPS24, LNC-EPHA6, and LIPCAR levels correlated significantly with the vascular injury marker soluble thrombomodulin. We conclude that AR and microvascular injury are associated with higher levels of circulating LNC-EPHA6, which emphasizes the potential role of lncRNAs as biomarker in the context of AR.

Kidney dendritic cells: fundamental biology and functional roles in health and disease

Dendritic cells (DCs) are chief inducers of adaptive immunity and regulate local inflammatory responses across the body. Together with macrophages, the other main type of mononuclear phagocyte, DCs constitute the most abundant component of the intrarenal immune system. This network of functionally specialized immune cells constantly surveys its microenvironment for signs of injury or infection, which trigger the initiation of an immune response. In the healthy kidney, DCs coordinate effective immune responses, for example, by recruiting neutrophils for bacterial clearance in pyelonephritis. The pro-inflammatory actions of DCs can, however, also contribute to tissue damage in various types of acute kidney injury and chronic glomerulonephritis, as DCs recruit and activate effector T cells, which release toxic mediators and maintain tubulointerstitial immune infiltrates. These actions are counterbalanced by DC subsets that promote the activation and maintenance of regulatory T cells to support resolution of the immune response and allow kidney repair. Several studies have investigated the multiple roles for DCs in kidney homeostasis and disease, but it has become clear that current tools and subset markers are not sufficient to accurately distinguish DCs from macrophages. Multidimensional transcriptomic analysis studies promise to improve mononuclear phagocyte classification and provide a clearer view of DC ontogeny and subsets.

Monoclonal immunoglobulin G deposits on tubular basement membrane in renal allograft: is this significant for chronic allograft injury?

Background

Tubular basement membrane immune deposits (TBMID) has rarely been observed in renal allografts. It is usually found in BK virus nephropathy and immune complex glomerulonephritis; however, its significance is not well understood. We conducted a retrospective clinicopathological study on monoclonal immunoglobulin G (IgG) TBMID.

Methods

We studied 7177 renal allograft biopsy specimens obtained from Tokyo Women’s Medical University from 2007 to 2015 and performed light microscopic, electron microscopic and immunofluorescence studies.

Results

Tubular basement membrane (TBM) deposits of IgG were found in 73 biopsies from 61 patients and the IgG subclass was obtained in 31 biopsies. There were no cases of monoclonal IgA or IgM TBMID. In total, 13 biopsies from 10 patients showed monoclonal IgG TBMID. Of these, seven showed monoclonal IgG1κ TBMID and one each showed monoclonal IgG2κ, IgG2λ and IgG3κ TBMID. Conversely, eight patients showed polyclonal IgG TBMID. In electron microscopy, large granular electron-dense deposits (EDDs) in the TBM were detected in all patients with monoclonal IgG1κ TBMID. EDDs were absent in TBM in patients with monoclonal IgG2κ, IgG2λ or IgG3κ TBMID. Progression of interstitial fibrosis and tubular atrophy (IFTA) was significantly higher in patients with monoclonal IgG1κ TBMID than in those with polyclonal IgG TBMID (P < 0.05). There were no significant differences in the other clinical parameters between monoclonal IgG1κ and polyclonal IgG TBMID.

Conclusions

This is the first study of patients with monoclonal IgG TBMID in renal allografts. We found that monoclonal IgG1κ TBMID was associated with EDD formation in TBM and IFTA progression.

Plasmacytoid dendritic cells promote acute kidney injury by producing interferon-α

Acute kidney injury (AKI) is a common clinical complication associated with high mortality in patients. Immune cells and cytokines have recently been described to play essential roles in AKI pathogenesis. Plasmacytoid dendritic cells (pDCs) are a unique DC subset that specializes in type I interferon (IFN) production. Here, we showed that pDCs rapidly infiltrated the kidney in response to AKI and contributed to kidney damage by producing IFN-α. Deletion of pDCs using DTR^BDCA2 transgenic (Tg) mice suppressed cisplatin-induced AKI, accompanied by marked reductions in proinflammatory cytokine production, immune cell infiltration and apoptosis in the kidney. In contrast, adoptive transfer of pDCs during AKI exacerbated kidney damage. We further identified IFN-α as the key factor that mediated the functions of pDCs during AKI, as IFN-α neutralization significantly attenuated kidney injury. Furthermore, IFN-α produced by pDCs directly induced the apoptosis of renal tubular epithelial cells (TECs) in vitro. In addition, our data demonstrated that apoptotic TECs induced the activation of pDCs, which was inhibited in the presence of an apoptosis inhibitor. Furthermore, similar deleterious effects of pDCs were observed in an ischemia reperfusion (IR)-induced AKI model. Clinically, increased expression of IFN-α in kidney biopsies was observed in kidney transplants with AKI. Taken together, the results of our study reveal that pDCs play a detrimental role in AKI via IFN-α.

Impact of infection on transplantation tolerance

Allograft tolerance is the ultimate goal of organ transplantation. Current strategies for tolerance induction mainly focus on inhibiting alloreactive T cells while promoting regulatory immune cells. Pathogenic infections may have direct impact on both effector and regulatory cell populations, therefore can alter host susceptibility to transplantation tolerance induction as well as impair the quality and stability of tolerance once induced. In this review, we will discuss existing data demonstrating the effect of infections on transplantation tolerance, with particular emphasis on the role of the stage of infection (acute, chronic, or latent) and the stage of tolerance (induction or maintenance) in this infection-tolerance interaction. While the deleterious effect of acute infection on tolerance is mainly driven by proinflammatory cytokines induced shortly after the infection, chronic infection may generate exhausted T cells that could in fact facilitate transplantation tolerance. In addition to pathogenic infections, commensal intestinal microbiota also has numerous significant immunomodulatory effects that can shape the host alloimmunity following transplantation. A comprehensive understanding of these mechanisms is crucial for the development of therapeutic strategies for robustly inducing and stably maintaining transplantation tolerance while preserving host anti-pathogen immunity in clinically relevant scenarios.

Mesenchymal Stromal Cells for Transplant Tolerance

In solid organ transplantation lifelong immunosuppression exposes transplant recipients to life-threatening complications, such as infections and malignancies, and to severe side effects. Cellular therapy with mesenchymal stromal cells (MSC) has recently emerged as a promising strategy to regulate anti-donor immune responses, allowing immunosuppressive drug minimization and tolerance induction. In this review we summarize preclinical data on MSC in solid organ transplant models, focusing on potential mechanisms of action of MSC, including down-regulation of effector T-cell response and activation of regulatory pathways. We will also provide an overview of available data on safety and feasibility of MSC therapy in solid organ transplant patients, highlighting the issues that still need to be addressed before establishing MSC as a safe and effective tolerogenic cell therapy in transplantation.

Non-invasive Biomarkers of Acute Rejection in Kidney Transplantation: Novel Targets and Strategies

Kidney transplantation is considered the favored treatment for patients suffering from end-stage renal disease, since successful transplantation is associated with longer survival and improved quality of life compared to dialysis. Alloreactive immune responses against the donor kidney may lead to acute rejection of the transplant. The current diagnosis of renal allograft rejection mainly relies on clinical monitoring, including serum creatinine, proteinuria, and confirmation by histopathologic assessment in the kidney transplant biopsy. These parameters have their limitations. Identification and validation of biomarkers, which correlate with or predict the presence of acute rejection, and which could improve therapeutic decision making, are priorities for the transplantation community. There is a need for alternative, less invasive but sensitive markers to diagnose acute graft rejection. Here, we provide an overview of the current status on research of biomarkers of acute kidney transplant rejection in blood and urine. We specifically discuss relatively novel research strategies in biomarker research, including transcriptomics and proteomics, and elaborate on donor-derived cell-free DNA as a potential biomarker.

Calcium-Binding Proteins S100A8 and S100A9: Investigation of Their Immune Regulatory Effect in Myeloid Cells

High expression levels of the calcium-binding proteins S100A8 and S100A9 in myeloid cells in kidney transplant rejections are associated with a favorable outcome. Here we investigated the myeloid cell subset expressing these molecules, and their function in inflammatory reactions. Different monocyte subsets were sorted from buffy coats of healthy donors and investigated for S100A8 and S100A9 expression. To characterize S100A9high and S100A9low subsets within the CD14+ classical monocyte subset, intracellular S100A9 staining was combined with flow cytometry (FACS) and qPCR profiling. Furthermore, S100A8 and S100A9 were overexpressed by transfection in primary monocyte-derived macrophages and the THP-1 macrophage cell line to investigate the functional relevance. Expression of S100A8 and S100A9 was primarily found in classical monocytes and to a much lower extent in intermediate and non-classical monocytes. All S100A9+ cells expressed human leukocyte antigen—antigen D related (HLA-DR) on their surface. A small population (<3%) of CD14+ CD11b+ CD33+ HLA-DR− cells, characterized as myeloid derived suppressor cells (MDSCs), also expressed S100A9 to high extent. Overexpression of S100A8 and S00A9 in macrophages led to enhanced extracellular reactive oxygen species (ROS) production, as well as elevated mRNA expression of anti-inflammatory IL-10. The results suggest that the calcium-binding proteins S100A8 and S100A9 in myeloid cells have an immune regulatory effect.

Human plasmacytoid dendritic cells acquire phagocytic capacity by TLR9 ligation in the presence of soluble factors produced by renal epithelial cells

Plasmacytoid dendritic cells (pDCs) are antigen presenting cells specialized in viral recognition through Toll-like receptor (TLR)7 and TLR9, and produce vast amounts of interferon alpha upon ligation of these TLRs. We had previously demonstrated a strong influx of pDCs in the tubulointerstitium of renal biopsies at the time of acute rejection. However, the role of human pDCs in mediating acute or chronic allograft rejection remains elusive. pDCs are thought to have a limited capacity to ingest apoptotic cells, critical for inducing CD4⁺ T cell activation via indirect antigen presentation and subsequent activation of antibody producing B cells. Here we tested whether the function of pDCs is affected by their presence within the graft. Maturation and interferon alpha production by pDCs was enhanced when cells were activated in the presence of viable HK2 renal epithelial cells. Importantly, soluble factors produced by cytomegalovirus-infected (primary) epithelial or endothelial cells enhanced pDC activation and induced their capacity to phagocytose apoptotic cells. Phagocytosis was not induced by free virus or soluble factors from non-infected cells. Activated pDCs showed an enhanced CD4⁺ and CD8⁺ T cell allostimulatory capacity as well as a potent indirect alloantigen presentation. Granulocyte Macrophage-Colony Stimulating Factor is one of the soluble factors produced by renal epithelial cells that, combined with TLR9 ligation, induced this functional capacity. Thus, pDCs present in the rejecting allograft can contribute to alloimmunity and potentially act as important orchestrators in the manifestation of acute and chronic rejection.

Kidney Fibrosis: Origins and Interventions

All causes of renal allograft injury, when severe and/or sustained, can result in chronic histological damage of which interstitial fibrosis and tubular atrophy are dominant features. Unless a specific disease process can be identified, what drives interstitial fibrosis and tubular atrophy progression in individual patients is often unclear. In general, clinicopathological factors known to predict and drive allograft fibrosis include graft quality, inflammation (whether "nonspecific" or related to a specific diagnosis), infections, such as polyomavirus-associated nephropathy, calcineurin inhibitors (CNI), and genetic factors. The incidence and severity of chronic histological damage have decreased substantially over the last 3 decades, but it is difficult to disentangle what effects individual innovations (eg, better matching and preservation techniques, lower CNI dosing, BK viremia screening) may have had. There is little evidence that CNI-sparing/minimization strategies, steroid minimization or renin-angiotensin-aldosterone system blockade result in better preservation of intermediate-term histology. Treatment of subclinical rejections has only proven beneficial to histological and functional outcome in studies in which the rate of subclinical rejection in the first 3 months was greater than 10% to 15%. Potential novel antifibrotic strategies include antagonists of transforming growth factor-β, connective tissue growth factor, several tyrosine kinase ligands (epidermal growth factor, platelet-derived growth factor, vascular endothelial growth factor), endothelin and inhibitors of chemotaxis. Although many of these drugs are mainly being developed and marketed for oncological indications and diseases, such as idiopathic pulmonary fibrosis, a number may hold promise in the treatment of diabetic nephropathy, which could eventually lead to applications in renal transplantation.

Sensitivity of Dendritic Cells to Microenvironment Signals

Dendritic cells are antigen-presenting cells capable of either activating the immune response or inducing and maintaining immune tolerance. They do this by integrating stimuli from the environment and changing their functional status as a result of plasticity. The modifications suffered by these cells have consequences in the way the organism may respond. In the present work two opposing situations known to affect dendritic cells are analyzed: tumor growth, leading to a microenvironment that favors the induction of a tolerogenic profile, and organ transplantation, which leads to a proinflammatory profile. Lessons learned from these situations may help to understand the mechanisms of modulation resulting not only from the above circumstances, but also from other pathologies.

The Phenotypic Characterization of the Human Renal Mononuclear Phagocytes Reveal a Co-Ordinated Response to Injury

Mammalian tissues contain networks of mononuclear phagocytes (MPh) that sense injury and orchestrate the response to it. In mice, this is affected by distinct populations of dendritic cells (DC), monocytes and macrophages and recent studies suggest the same is true for human skin and intestine but little is known about the kidney. Here we describe the analysis of MPh populations in five human kidneys and show they are highly heterogeneous and contain discrete populations of DC, monocytes and macrophages. These include: plasmacytoid DC (CD303⁺) and both types of conventional DC—cDC1 (CD141⁺ cells) and CD2 (CD1c⁺ cells); classical, non-classical and intermediate monocytes; and macrophages including a novel population of CD141⁺ macrophages clearly distinguishable from cDC1 cells. The relative size of the MPh populations differed between kidneys: the pDC population was bi-modally distributed being less than 2% of DC in two kidneys without severe injury and over 35% in the remaining three with low grade injury in the absence of morphological evidence of inflammation. There were profound differences in the other MPh populations in kidneys with high and low numbers of pDC. Thus, cDC1 cells were abundant (55 and 52.3%) when pDC were sparse and sparse (12.8–12.5%) when pDC were abundant, whereas the proportions of cDC2 cells and classical monocytes increased slightly in pDC high kidneys. We conclude that MPh are highly heterogeneous in human kidneys and that pDC infiltration indicative of low-grade injury does not occur in isolation but is part of a co-ordinated response affecting all renal DC, monocyte and macrophage populations.

Intragraft Blood Dendritic Cell Antigen-1-Positive Myeloid Dendritic Cells Increase during BK Polyomavirus-Associated Nephropathy

Although both polyomavirus infection and T cell-mediated rejection (TCMR) are characterized by tubulointerstitial inflammation in the renal allograft, these conditions are treated with opposing therapeutic regimens. To gain more insight into the differences between antiviral and alloimmune responses, we performed a case-control study, in which we immunophenotyped the inflammatory infiltrates in renal biopsy specimens with BK polyomavirus-associated nephropathy (BKPyVAN) and specimens with TCMR. Compared with TCMR, BKPyVAN was diagnosed later after transplantation; therefore, BKPyVAN specimens showed more chronic damage than TCMR specimens showed. However, TCMR and BKPyVAN specimens had comparable levels of tubulointerstitial inflammation. Adjustment for confounders in various multivariable models revealed more blood dendritic cell antigen-1(+) (BDCA-1(+)) myeloid dendritic cells (mDCs) present during BKPyVAN (odds ratio, 2.31; 95% confidence interval, 1.03 to 5.16; P=0.04) than during TCMR. Double immunostaining for SV40 and BDCA-1 showed that, during BKPyVAN, BDCA-1(+) mDCs localized in proximity to the polyomavirus-infected tubular epithelial cells. We ensured that time of biopsy after transplantation was not a confounding factor by including additional specimens with late TCMR and protocol biopsy specimens matched for biopsy time. These additional specimens showed amounts of BDCA-1(+) mDCs comparable with amounts in the early TCMR specimens. These results suggest that BDCA-1(+) mDCs, known to be involved in the antiviral immune response during various viral infections, might have a pivotal role during BKPyVAN infection in the grafted kidney.

Dendritic Cells and Macrophages: Sentinels in the Kidney

The mononuclear phagocytes (dendritic cells and macrophages) are closely related immune cells with central roles in anti-infectious defense and maintenance of organ integrity. The canonical function of dendritic cells is the activation of T cells, whereas macrophages remove apoptotic cells and microbes by phagocytosis. In the kidney, these cell types form an intricate system of mononuclear phagocytes that surveys against injury and infection and contributes to organ homeostasis and tissue repair but may also promote progression of CKD. This review summarizes the general functions and classification of dendritic cells and macrophages in the immune system and recapitulates why overlapping definitions and historically separate research have created controversy about their tasks. Their roles in acute kidney disease, CKD, and renal transplantation are described, and therapeutic strategy to modify these cells for therapeutic purposes is discussed.

DC-SIGN: The Strange Case of Dr. Jekyll and Mr. Hyde

In this issue of Immunity, Conde et al. (2015) showed that a costimulatory blockade favors the accumulation of CD209a(+) macrophages which, upon interaction with fucosylated tissue ligands, promotes the expansion of CD4(+)Foxp3(+) Treg cell number.

Dendritic Cells in Kidney Transplant Biopsy Samples Are Associated with T Cell Infiltration and Poor Allograft Survival

Progress in long-term renal allograft survival continues to lag behind the progress in short-term transplant outcomes. Dendritic cells are the most efficient antigen-presenting cells, but surprisingly little attention has been paid to their presence in transplanted kidneys. We used dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin as a marker of dendritic cells in 105 allograft biopsy samples from 105 kidney transplant recipients. High dendritic cell density was associated with poor allograft survival independent of clinical variables. Moreover, high dendritic cell density correlated with greater T cell proliferation and poor outcomes in patients with high total inflammation scores, including inflammation in areas of tubular atrophy. We then explored the association between dendritic cells and histologic variables associated with poor prognosis. Multivariate analysis revealed an independent association between the densities of dendritic cells and T cells. In biopsy samples with high dendritic cell density, electron microscopy showed direct physical contact between infiltrating lymphocytes and cells that have the ultrastructural morphologic characteristics of dendritic cells. The origin of graft dendritic cells was sought in nine sex-mismatched recipients using XY fluorescence in situ hybridization. Whereas donor dendritic cells predominated initially, the majority of dendritic cells in late allograft biopsy samples were of recipient origin. Our data highlight the prognostic value of dendritic cell density in allograft biopsy samples, suggest a new role for these cells in shaping graft inflammation, and provide a rationale for targeting dendritic cell recruitment to promote long-term allograft survival.

Renal F4/80+ CD11c+ mononuclear phagocytes display phenotypic and functional characteristics of macrophages in health and in adriamycin nephropathy

Conventional markers of macrophages (Mфs) and dendritic cells (DCs) lack specificity and often overlap, leading to confusion and controversy regarding the precise function of these cells in kidney and other diseases. This study aimed to identify the phenotype and function of renal mononuclear phagocytes (rMPs) expressing key markers of both Mфs and DCs. F4/80(+)CD11c(+) cells accounted for 45% of total rMPs in normal kidneys and in those from mice with Adriamycin nephropathy (AN). Despite expression of the DC marker CD11c, these double-positive rMPs displayed the features of Mфs, including Mф-like morphology, high expression of CD68, CD204, and CD206, and high phagocytic ability but low antigen-presenting ability. F4/80(+)CD11c(+) cells were found in the cortex but not in the medulla of the kidney. In AN, F4/80(+)CD11c(+) cells displayed an M1 Mф phenotype with high expression of inflammatory mediators and costimulatory factors. Adoptive transfer of F4/80(+)CD11c(+) cells separated from diseased kidney aggravated renal injury in AN mice. Furthermore, adoptive transfer of common progenitors revealed that kidney F4/80(+)CD11c(+) cells were derived predominantly from monocytes, but not from pre-DCs. In conclusion, renal F4/80(+)CD11c(+) cells are a major subset of rMPs and display Mф-like phenotypic and functional characteristics in health and in AN.

Glomerular inflammation correlates with endothelial injury and with IL-6 and IL-1β secretion in the peripheral blood

BACKGROUND

Transplant glomerulitis is an active form of glomerular injury associated with suboptimal graft outcome, inadequate histologic reproducibility, and poorly understood pathogenesis. Using a modified pathologic schema where glomerular inflammation is defined by the presence of five or more leukocytes per glomerulus, we sought to assess the reproducibility of transplant glomerulitis and to prospectively investigate the pathogenesis of glomerular inflammation.

METHODS

Our cohort includes 59 kidney transplant recipients who underwent 60 "for cause" allograft biopsies. In addition to light microscopy, the majority of the biopsies were assessed using immunohistochemistry, immunofluorescence, and electron microscopy studies. Biopsies were classified as noninflamed (n=21), inflamed (borderline changes or above) without glomerulitis (n=21), and transplant glomerulitis (n=18). Peripheral blood was collected on the day of biopsy and cytokines secreted by peripheral blood mononuclear cells (PBMCs) were measured ex vivo.

RESULTS

Our modified schema had higher inter-observer agreement for detecting glomerulitis than that of the current Banff schema. Biopsies with glomerulitis showed ultrastructural signs of glomerular capillary wall remodeling. In contrast to other anatomic compartments, intraglomerular leukocytes in glomerulitis group consisted largely of monocytes. Patients with glomerulitis had high levels of IL-6 and IL-1β secreted by PBMCs. Furthermore, the percentage of inflamed glomeruli and the number of intraglomerular monocytes showed independent association with IL-6 and IL-1β levels, which tended to correlate with subsequent estimated glomerular filtration rate decline.

CONCLUSIONS

Inter-observer reproducibility of transplant glomerulitis can be improved by using more stringent histologic criteria. Glomerular inflammation correlates with endothelial injury, monocyte influx, and IL-6 and IL-β secretion by circulating immune cells.

Inflammatory processes in renal fibrosis

Many types of kidney injury induce inflammation as a protective response. However, unresolved inflammation promotes progressive renal fibrosis, which can culminate in end-stage renal disease. Kidney inflammation involves cells of the immune system as well as activation of intrinsic renal cells, with the consequent production and release of profibrotic cytokines and growth factors that drive the fibrotic process. In glomerular diseases, the development of glomerular inflammation precedes interstitial fibrosis; although the mechanisms linking these events are poorly understood, an important role for tubular epithelial cells in mediating this link is gaining support. Data have implicated macrophages in promoting both glomerular and interstitial fibrosis, whereas limited evidence suggests that CD4(+) T cells and mast cells are involved in interstitial fibrosis. However, macrophages can also promote renal repair when the cause of renal injury can be resolved, highlighting their plasticity. Understanding the mechanisms by which inflammation drives renal fibrosis is necessary to facilitate the development of therapeutics to halt the progression of chronic kidney disease.

Spatial organization of dendritic cells within tumor draining lymph nodes impacts clinical outcome in breast cancer patients

BACKGROUND

Dendritic cells (DCs) are important mediators of anti-tumor immune responses. We hypothesized that an in-depth analysis of dendritic cells and their spatial relationships to each other as well as to other immune cells within tumor draining lymph nodes (TDLNs) could provide a better understanding of immune function and dysregulation in cancer.

METHODS

We analyzed immune cells within TDLNs from 59 breast cancer patients with at least 5 years of clinical follow-up using immunohistochemical staining with a novel quantitative image analysis system. We developed algorithms to analyze spatial distribution patterns of immune cells in cancer versus healthy intra-mammary lymph nodes (HLNs) to derive information about possible mechanisms underlying immune-dysregulation in breast cancer. We used the non-parametric Mann-Whitney test for inter-group comparisons, Wilcoxon Matched-Pairs Signed Ranks test for intra-group comparisons and log-rank (Mantel-Cox) test for Kaplan Maier analyses.

RESULTS

Degree of clustering of DCs (in terms of spatial proximity of the cells to each other) was reduced in TDLNs compared to HLNs. While there were more numerous DC clusters in TDLNs compared to HLNs,DC clusters within TDLNs tended to have fewer member DCs and also consisted of fewer cells displaying the DC maturity marker CD83. The average number of T cells within a standardized radius of a clustered DC was increased compared to that of an unclustered DC, suggesting that DC clustering was associated with T cell interaction. Furthermore, the number of T cells within the radius of a clustered DC was reduced in tumor-positive TDLNs compared to HLNs. Importantly, clinical outcome analysis revealed that DC clustering in tumor-positive TDLNs correlated with the duration of disease-free survival in breast cancer patients.

CONCLUSIONS

These findings are the first to describe the spatial organization of DCs within TDLNs and their association with survival outcome. In addition, we characterized specific changes in number, size, maturity, and T cell co-localization of such clusters. Strategies to enhance DC function in-vivo, including maturation and clustering, may provide additional tools for developing more efficacious DC cancer vaccines.

Analysis of FOXP3 gene and protein expressions in renal allograft biopsies and their association with graft outcomes

BACKGROUND

The transcription factor FOXP3 is increased in acute renal rejection, but its influence on graft outcomes is unclear. This study correlated FOXP3 with dendritic cells and graft outcomes.

METHODS

We assessed 96 kidney transplants undergoing allograft biopsy for cause. FOXP3 mRNA was analyzed by real-time polymerase chain reaction (PCR) and FOXP3 protein and DCsCD83(+) by immunohistochemistry. Graft function and survival were assessed at 5 years post-transplantation, as well as by independent predictors of graft loss.

RESULTS

Intragraft FOXP3 gene and protein expression were significantly correlated (r = 0.541, p < 0.001). Both FOXP3 mRNA and protein were increased in patients with acute rejection (AR). High expression of FOXP3 mRNA or protein in biopsies did not correlate with clinical variables, but there was a trend to higher positive variation in the glomerular filtration rate (GFR) from biopsy to last follow-up. Patients with FOXP3-mRNA(high) had more DCsCD83(+) in biopsy, but these cells did not associate with AR. Five-year graft survival was not influenced by either FOXP3 mRNA or protein expressions.

CONCLUSIONS

FOXP3 mRNA and protein had a good correlation in archival renal graft tissue. Increased FOXP3 expression was found in AR and FOXP3 associated with high numbers of DCs. However, both FOXP3 mRNA and protein was not associated with better allograft outcomes.