Bone-marrow-derived macrophages genetically modified to produce IL-10 reduce injury in experimental glomerulonephritis

Gene therapy and kidney diseases

Chronic kidney disease (CKD) poses a significant global health challenge, projected to become one of the leading causes of death by 2040. Current treatments primarily manage complications and slow progression, highlighting the urgent need for personalized therapies targeting the disease-causing genes. Our increased understanding of the underlying genomic changes that lead to kidney diseases coupled with recent successful gene therapies targeting specific kidney cells have turned gene therapy and genome editing into a promising therapeutic approach for treating kidney disease. This review paper reflects on different delivery routes and systems that can be exploited to target specific kidney cells and the ways that gene therapy can be used to improve kidney health.

Macrophages regulate plaque progression in diabetic Apoe-/- mice dependent on Pi4p/Nlrp3 signaling pathway

BACKGROUND AND AIMS

Atherosclerotic cardiovascular disease complicated by diabetes mellitus (DM) is the leading cause of death in diabetic patients, and it is strongly associated with macrophages and inflammasomes. It has been found that activation of NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome is closely associated with phosphatidylinositol 4-phosphate (PI4P) on the trans-Golgi. However, how PI4P and NLRP3 regulate macrophage function and its role in diabetic atherosclerotic plaques is unclear.

METHODS

The expression of Pi4p and Nlrp3-inflammasome-related proteins in atherosclerosis in apolipoprotein E-deficient (Apoe-/-) and Apoe-/- DM mice was investigated. Then, Pi4p levels were affected by shRNA-Pi4kb or cDNA-Sac1 plasmid to investigate the effects of changes in Pi4p-related metabolic enzymes on macrophage function. Finally, genetically modified macrophages were injected into diabetic Apoe-/- mice to explore the effects on atherosclerosis.

RESULTS

DM promoted plaque progression in atherosclerotic mice and increased expression of Pi4p and Nlrp3 in plaques. In addition, impaired macrophage function induced by high glucose was reversed by transfected shRNA-Pi4kb or cDNA-Sac1 plasmid. Furthermore, decreased levels of Pi4p reduced plaque area in diabetic Apoe-/- mice.

CONCLUSIONS

Our data suggests that Pi4p/Nlrp3 in macrophages play an important role in the exacerbation of atherosclerosis in diabetic mice. Pi4p-related metabolizing enzymes (PI4KB and SAC1) may be a potential therapeutic strategy for diabetic atherosclerosis, and macrophage therapy is also a potential treatment.

Metalloporphyrins as Tools for Deciphering the Role of Heme Oxygenase in Renal Immune Injury

Renal immune injury is a frequent cause of end-stage renal disease, and, despite the progress made in understanding underlying pathogenetic mechanisms, current treatments to preserve renal function continue to be based mainly on systemic immunosuppression. Small molecules, naturally occurring biologic agents, show considerable promise in acting as disease modifiers and may provide novel therapeutic leads. Certain naturally occurring or synthetic Metalloporphyrins (Mps) can act as disease modifiers by increasing heme oxygenase (HO) enzymatic activity and/or synthesis of the inducible HO isoform (HO-1). Depending on the metal moiety of the Mp employed, these effects may occur in tandem or can be discordant (increased HO-1 synthesis but inhibition of enzyme activity). This review discusses effects of Mps, with varying redox-active transitional metals and cyclic porphyrin cores, on mechanisms underlying pathogenesis and outcomes of renal immune injury.

Inflammation in kidney repair: Mechanism and therapeutic potential

The kidney has a remarkable ability of repair after acute kidney injury (AKI). However, when injury is severe or persistent, the repair is incomplete or maladaptive and may lead to chronic kidney disease (CKD). Maladaptive kidney repair involves multiple cell types and multifactorial processes, of which inflammation is a key component. In the process of inflammation, there is a bidirectional interplay between kidney parenchymal cells and the immune system. The extensive and complex crosstalk between renal tubular epithelial cells and interstitial cells, including immune cells, fibroblasts, and endothelial cells, governs the repair and recovery of the injured kidney. Further research in this field is imperative for the discovery of biomarkers and promising therapeutic targets for kidney repair. In this review, we summarize the latest progress in the immune response and inflammation during maladaptive kidney repair, analyzing the interaction between immune cells and intrinsic kidney cells, pointing out the potentialities of inflammation-related pathways as therapeutic targets, and discussing the challenges and future research prospects in this field.

Driving role of macrophages in transition from acute kidney injury to chronic kidney disease

Acute kidney injury (AKI), characterized by acute renal dysfunction, is an increasingly common clinical problem and an important risk factor in the subsequent development of chronic kidney disease (CKD). Regardless of the initial insults, the progression of CKD after AKI involves multiple types of cells, including renal resident cells and immune cells such as macrophages. Recently, the involvements of macrophages in AKI-to-CKD transition have garnered significant attention. Furthermore, substantial progress has also been made in elucidating the pathophysiological functions of macrophages from the acute kidney to repair or fibrosis. In this review, we highlight current knowledge regarding the roles and mechanisms of macrophage activation and phenotypic polarization, and transdifferentiation in the development of AKI-to-CKD transition. In addition, the potential of macrophage-based therapy for preventing AKI-to-CKD transition is also discussed.

Macrophages in the kidney in health, injury and repair

Macrophages are a key component of the renal mononuclear phagocyte system, playing a major role in defense against infection, renal injury and repair. Yolk sac macrophage precursors seed the early embryonic kidney and are important for renal development. Later, renal macrophages are derived from hematopoietic stem cells and in adult life, there is a significant contribution from circulating monocytes, which is enhanced in response to infection or injury. Macrophages are highly plastic and can alter their phenotype in response to cues from parenchymal renal cells. Danger-associated molecules released from injured kidney cells may activate macrophages toward a pro-inflammatory phenotype, mediating further recruitment of inflammatory cells, exacerbating renal injury and activating renal fibroblasts to promote scarring. In acute kidney injury, once the injury stimulus has abated, macrophages may adopt a more reparative phenotype, dampening the immune response and promoting repair of renal tissue. However, in chronic kidney disease ongoing activation of pro-inflammatory monocytes and persistence of reparative macrophages leads to glomerulosclerosis and tubulointerstitial fibrosis, the hallmarks of end-stage kidney disease. Several strategies to inhibit the recruitment, activation and secretory products of pro-inflammatory macrophages have proven beneficial in pre-clinical models and are now undergoing clinical trials in patients with kidney disease. In addition, macrophages may be utilized in cell therapy as a "Trojan Horse" to deliver targeted therapies to the kidney. Single-cell RNA sequencing has identified a previously unappreciated spectrum of macrophage phenotypes, which may be selectively present in injury or repair, and ongoing functional analyses of these subsets may identify more specific targets for therapeutic intervention.

Hacking macrophages to combat cancer and inflammatory diseases-Current advances and challenges

Recently, immunotherapy has been served as the treatment of choice for various human pathophysiologies, including inflammatory diseases and cancer. Though most of the current approaches target the lymphoid compartment, macrophages intimately implicated in the induction or resolution of inflammation have rationally gained their place into the therapeutics arena. In this review, I discuss the past and novel groundbreaking strategies focusing on macrophages in different human diseases and highlight the current challenges and considerations underlying their translational potentials.

Role of Macrophages and Related Cytokines in Kidney Disease

Inflammation is a key characteristic of kidney disease, but this immune response is two-faced. In the acute phase of kidney injury, there is an activation of the immune cells to fight against the insult, contributing to kidney repair and regeneration. However, in chronic kidney diseases (CKD), immune cells that infiltrate the kidney play a deleterious role, actively participating in disease progression, and contributing to nephron loss and fibrosis. Importantly, CKD is a chronic inflammatory disease. In early CKD stages, patients present sub-clinical inflammation, activation of immune circulating cells and therefore, anti-inflammatory strategies have been proposed as a common therapeutic target for renal diseases. Recent studies have highlighted the plasticity of immune cells and the complexity of their functions. Among immune cells, monocytes/macrophages play an important role in all steps of kidney injury. However, the phenotype characterization between human and mice immune cells showed different markers; therefore the extrapolation of experimental studies in mice could not reflect human renal diseases. Here we will review the current information about the characteristics of different macrophage phenotypes, mainly focused on macrophage-related cytokines, with special attention to the chemokine CCL18, and its murine functional homolog CCL8, and the macrophage marker CD163, and their role in kidney pathology.

Glomerular Macrophages in Human Auto- and Allo-Immune Nephritis

Macrophages are involved in tissue homeostasis. They participate in inflammatory episodes and are involved in tissue repair. Macrophages are characterized by a phenotypic heterogeneity and a profound cell plasticity. In the kidney, and more particularly within glomeruli, macrophages are thought to play a maintenance role that is potentially critical for preserving a normal glomerular structure. Literature on the glomerular macrophage role in human crescentic glomerulonephritis and renal transplantation rejection with glomerulitis, is sparse. Evidence from preclinical models indicates that macrophages profoundly modulate disease progression, both in terms of number-where depletion has resulted in a reduced glomerular lesion-and sub-phenotype-M1 being more profoundly detrimental than M2. This evidence is corroborated by better outcomes in patients with a lower number of glomerular macrophages. However, due to the very limited biopsy sample size, the type and role of macrophage subpopulations involved in human proliferative lesions is more difficult to precisely define and synthesize. Therefore, specific biomarkers of macrophage activation may enhance our ability to assess their role, potentially enabling improved monitoring of drug activity and ultimately allowing the development of novel therapeutic strategies to target these elusive cellular players.

Targeting the progression of chronic kidney disease

Chronic kidney disease (CKD) is a devastating condition that is reaching epidemic levels owing to the increasing prevalence of diabetes mellitus, hypertension and obesity, as well as ageing of the population. Regardless of the underlying aetiology, CKD is slowly progressive and leads to irreversible nephron loss, end-stage renal disease and/or premature death. Factors that contribute to CKD progression include parenchymal cell loss, chronic inflammation, fibrosis and reduced regenerative capacity of the kidney. Current therapies have limited effectiveness and only delay disease progression, underscoring the need to develop novel therapeutic approaches to either stop or reverse progression. Preclinical studies have identified several approaches that reduce fibrosis in experimental models, including targeting cytokines, transcription factors, developmental and signalling pathways and epigenetic modulators, particularly microRNAs. Some of these nephroprotective strategies are now being tested in clinical trials. Lessons learned from the failure of clinical studies of transforming growth factor β1 (TGFβ1) blockade underscore the need for alternative approaches to CKD therapy, as strategies that target a single pathogenic process may result in unexpected negative effects on simultaneously occurring processes. Additional promising avenues include preventing tubular cell injury and anti-fibrotic therapies that target activated myofibroblasts, the main collagen-producing cells.

Macrophage polarization in chronic kidney disease: a balancing act between renal recovery and decline?

Macrophages are heterogenous cells of the innate immune system that can fluidly modulate their phenotype to respond to their local microenvironment. They are found throughout the renal compartments, where they contribute to homeostasis and function. However, renal injury activates molecular pathways that initially stimulate differentiation of macrophages into a proinflammatory M1 phenotype. Later in the course of healing, abundant apoptotic debris and anti-inflammatory cytokines induce the production of anti-inflammatory M2 macrophages, which contribute to tissue regeneration and repair. Thus, the dynamic balance of M1 and M2 populations may outline the burden of inflammation and process of tissue repair that define renal outcomes, which has been the impetus for therapeutic efforts targeting macrophages. This review will discuss the role of these phenotypes in the progression of chronic renal injury, potential pathogenic mechanisms, and the promise of macrophage-based therapeutic applications for chronic kidney disease.

The Impact of Versatile Macrophage Functions on Acute Kidney Injury and Its Outcomes

Acute kidney injury (AKI) is a common and devastating clinical condition with a high morbidity and mortality rate and is associated with a rapid decline of kidney function mostly resulting from the injury of proximal tubules. AKI is typically accompanied by inflammation and immune activation and involves macrophages (Mϕ) from the beginning: The inflamed kidney recruits “classically” activated (M1) Mϕ, which are initially poised to destroy potential pathogens, exacerbating inflammation. Of note, they soon turn into “alternatively” activated (M2) Mϕ and promote immunosuppression and tissue regeneration. Based on their roles in kidney recovery, there is a growing interest to use M2 Mϕ and Mϕ-modulating agents therapeutically against AKI. However, it is pertinent to note that the clinical translation of Mϕ-based therapies needs to be critically reviewed and questioned since Mϕ are functionally plastic with versatile roles in AKI and some Mϕ functions are detrimental to the kidney during AKI. In this review, we discuss the current state of knowledge on the biology of different Mϕ subtypes during AKI and, especially, on their role in AKI and assess the impact of versatile Mϕ functions on AKI based on the findings from translational AKI studies.

M2 macrophages in kidney disease: biology, therapies, and perspectives

Tissue macrophages are crucial players in homeostasis, inflammation, and immunity. They are characterized by heterogeneity and plasticity, due to which they display a continuum of phenotypes with M1/M2 presenting 2 extremes of this continuum. M2 macrophages are usually termed in the literature as anti-inflammatory and wound healing. Substantial progress has been made in elucidating the biology of M2 macrophages and their potential for clinical translation. In this review we discuss the current state of knowledge in M2 macrophage research with an emphasis on kidney disease. We explore their therapeutic potential and the challenges in using them as cellular therapies. Some new regulators that shape macrophage polarization and potential areas for future research are also examined.

Granulocyte macrophage-colony stimulating factor: A key modulator of renal mononuclear phagocyte plasticity

Macrophage-colony stimulating factor (M-CSF) and granulocyte macrophage-colony stimulating factor (GM-CSF) play key roles in the differentiation of macrophages and dendritic cells (DCs). We examined the effect of treatment with M-CSF-containing macrophage medium or GM-CSF-containing DC medium upon the phenotype of murine bone marrow-derived macrophages and DCs. Culture of macrophages for 5 days in DC medium reduced F4/80 expression and increased CD11c expression with cells effectively stimulating T cell proliferation in a mixed lymphocyte reaction. DC medium treatment of macrophages significantly reduced phagocytosis of both apoptotic cells and latex beads and strongly induced the expression of the chemokine receptor CCR7 known to be involved in DC trafficking to lymph nodes. Lysates of obstructed murine kidneys expressed both M-CSF and GM-CSF though M-CSF expression was dominant (M-CSF:GM-CSF ratio ∼30:1). However, combination treatment with both M-CSF and GM-CSF (ratio 30:1) indicated that small amounts of GM-CSF skewed macrophages towards a DC-like phenotype. To determine whether macrophage phenotype might be modulated in vivo we tracked CD45.1⁺ bone marrow-derived macrophages intravenously administered to CD45.2⁺ mice with unilateral ureteric obstruction. Flow cytometry of enzyme dissociated kidneys harvested 3 days later indicated CD11c and MHC Class II upregulation by adoptively transferred CD45.1⁺ cells with CD45.1⁺ cells evident in draining renal lymph nodes. Our data suggests that GM-CSF modulates mononuclear phagocyte plasticity, which likely promotes resolution of injury and healing in the injured kidney.

Lipocalin 2 enhances mesenchymal stem cell-based cell therapy in acute kidney injury rat model

Acute kidney injury (AKI) is one of the most common health-threatening diseases in the world. There is still no effective medical treatment for AKI. Recently, Mesenchymal stem cell (MSC)-based therapy has been proposed for treatment of AKI. However, the microenvironment of damaged kidney tissue is not favorable for survival of MSCs which would be used for therapeutic intervention. In this study, we genetically manipulated MSCs to up-regulate lipocalin-2 (Lcn2) and investigated whether the engineered MSCs (MSC-Lcn2) could improve cisplatin-induced AKI in a rat model. Our results revealed that up-regulation of Lcn2 in MSCs efficiently enhanced renal function. MSC Lcn2 up-regulates expression of HGF, IGF, FGF and VEGF growth factors. In addition, they reduced molecular biomarkers of kidney injury such as KIM-1 and Cystatin C, while increased the markers of proximal tubular epithelium such as AQP-1 and CK18 following cisplatin-induced AKI. Overall, here we over-expressed Lcn2, a well-known cytoprotective factor against acute ischemic renal injury, in MSCs. This not only potentiated beneficial roles of MSCs for cell therapy purposes but also suggested a new modality for treatment of AKI.

Macrophage in chronic kidney disease

Chronic kidney disease (CKD) has become a major health problem worldwide. This review describes the role of macrophages in CKD and highlights the importance of anti-inflammatory M2 macrophage activation in both renal fibrosis and wound healing processes. Furthermore, the mechanisms by which M2 macrophages induce renal repair and regeneration are still under debate and currently demand more attention. The M1/M2 macrophage balance is related to the renal microenvironment and could influence CKD progression. In fact, an inflammatory renal environment and M2 plasticity can be the major hurdles to establishing macrophage cell-based therapies in CKD. M2 macrophage cell-based therapy is promising if the M2 phenotype remains stable and is 'fixed' by in vitro manipulation. However, a greater understanding of phenotype polarization is still required. Moreover, better strategies and targets to induce reparative macrophages in vivo should guide future investigations in order to abate kidney diseases.

Transfusion of CD206+ M2 Macrophages Ameliorates Antibody-Mediated Glomerulonephritis in Mice

Macrophages are multifunctional immune cells that may either drive or modulate disease pathogenesis, depending on the activated phenotype. In this study, we investigated the protective effects of CD206⁺ M2 macrophages against nephrotoxic serum nephritis in mice. We found that these immunosuppressive macrophages, derived from bone marrow and stimulated with IL-4/IL-13 [CD206⁺ M2 bone marrow-derived macrophages (M2BMMs)], protected against renal injury, decreased proteinuria, and diminished the infiltration of CD68⁺ macrophages, neutrophils, and T cells into glomerular tissue. Comparable therapeutic results were obtained with CD206⁺ M2 cells derived from induced pluripotent stem cells. Notably, CD206⁺ M2BMMs, which retained an M2 signature, could elicit a switch of M1 to M2 phenotype in co-cultured macrophages. Moreover, these cells were found to induce the production of regulatory T cells in the spleen and renal draining lymph node. Accordingly, mRNA expression of the T helper 1 cytokines tumor necrosis factor-α, interferon-β, interferon-γ, and IL-12 was significantly reduced in kidneys from mice treated with CD206⁺ M2BMMs. Taken together, the data suggest that CD206⁺ M2 may have therapeutic potential against antibody-mediated glomerular injury and presents its therapeutic value for the treatment of crescentic nephritis in humans.

Kupffer Cell Transplantation in Mice for Elucidating Monocyte/Macrophage Biology and for Potential in Cell or Gene Therapy

Kupffer cells (KC) play major roles in immunity and tissue injury or repair. Because recapitulation of KC biology and function within liver will allow superior insights into their functional repertoire, we studied the efficacy of the cell transplantation approach for this purpose. Mouse KC were isolated from donor livers, characterized, and transplanted into syngeneic recipients. To promote cell engraftment through impairments in native KC, recipients were preconditioned with gadolinium chloride. The targeting, fate, and functionality of transplanted cells were evaluated. The findings indicated that transplanted KC engrafted and survived in recipient livers throughout the study period of 3 months. Transplanted KC expressed macrophage functions, including phagocytosis and cytokine expression, with or without genetic modifications using lentiviral vectors. This permitted studies of whether transplanted KC could affect outcomes in the context of acetaminophen hepatotoxicity or hepatic ischemia-reperfusion injury. Transplanted KC exerted beneficial effects in these injury settings. The benefits resulted from cytoprotective factors including vascular endothelial growth factor. In conclusion, transplanted adult KC were successfully targeted and engrafted in the liver with retention of innate immune and tissue repair functions over the long term. This will provide excellent opportunities to address critical aspects in the biogenesis, fate, and function of KC within their native liver microenvironment and to develop the cell and gene therapy potential of KC transplantation.

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.

A critical role for suppressor of cytokine signalling 3 in promoting M1 macrophage activation and function in vitro and in vivo

Macrophages respond to their microenvironment and develop polarized functions critical for orchestrating appropriate inflammatory responses. Classical (M1) activation eliminates pathogens while alternative (M2) activation promotes regulation and repair. M1 macrophage activation is strongly associated with suppressor of cytokine signalling 3 (SOCS3) expression in vitro, but the functional consequences of this are unclear and the role of SOCS3 in M1-macrophage polarization in vivo remains controversial. To address these questions, we defined the characteristics and function of SOCS3-expressing macrophages in vivo and identified potential mechanisms of SOCS3 action. Macrophages infiltrating inflamed glomeruli in a model of acute nephritis show significant up-regulation of SOCS3 that co-localizes with the M1-activation marker, inducible nitric oxide synthase. Numbers of SOCS3(hi) -expressing, but not SOCS1(hi) -expressing, macrophages correlate strongly with the severity of renal injury, supporting their inflammatory role in vivo. Adoptive transfer of SOCS3-short interfering RNA-silenced macrophages into a peritonitis model demonstrated the importance of SOCS3 in driving production of pro-inflammatory IL-6 and nitric oxide, while curtailing expression of anti-inflammatory IL-10 and SOCS1. SOCS3-induced pro-inflammatory effects were due, at least in part, to its role in controlling activation and nuclear accumulation of nuclear factor-κB and activity of phosphatidylinositol 3-kinase. We show for the first time that SOCS3 also directs the functions of human monocyte-derived macrophages, including efficient M1-induced cytokine production (IL-1β, IL-6, IL-23, IL-12), attenuated signal transducer and activator of transcription 3 activity and ability of antigen-loaded macrophages to drive T-cell responses. Hence, M1-associated SOCS3 was a positive regulator of pro-inflammatory responses in our rodent models and up-regulated SOCS3 is essential for effective M1-macrophage activation and function in human macrophages.

Regulatory T cell-derived IL-10 ameliorates crescentic GN

Regulatory T cells (Tregs) exert their immunosuppressive activity through several immunoregulatory mechanisms, including the production of anti-inflammatory cytokines such as IL-10. Although several studies suggest a role for Tregs in modulating crescentic GN, the underlying mechanisms are not well understood. Here, using IL-10 reporter mice, we detected IL-10-producing Foxp3(+) T cells in the kidney, blood, and secondary lymphoid tissue in a mouse model of crescentic GN. Specific inactivation of Il10 in Foxp3(+) Tregs eliminated the ability of these cells to suppress renal and systemic production of IFNγ and IL-17; these IL-10-deficient Tregs lost their capacity to attenuate renal tissue injury. These data highlight the suppressive functions of Tregs in crescentic GN and suggest the importance of Treg-derived IL-10 in ameliorating disease severity and in modulating both the Th1 and most notably Th17 immune response.

Pathogenic and protective role of macrophages in kidney disease

Macrophages (MΦ) are located throughout kidney tissue, where they play important roles in homeostasis, surveillance, tolerance, and cytoprotection. MΦ are highly heterogeneous cells and exhibit distinct phenotypic and functional characteristics depending on their microenvironment and the disease type and stage. Recent studies have identified a dual role for MΦ in several murine models of kidney disease. In this review, we discuss the pathogenic and protective roles of the various MΦ subsets in experimental and human kidney diseases and summarize current progress toward the therapeutic use of MΦ in kidney diseases.

Sialoadhesin - a macrophage-restricted marker of immunoregulation and inflammation

Sialoadhesin (Sn, also known as Siglec-1 and CD169) is a macrophage-restricted cell surface receptor that is conserved across mammals. Sn is a member of the sialic acid-binding IgG-like lectin (Siglec) family of proteins characterized by affinity to specifically sialylated ligands, and under normal conditions is expressed on subsets of macrophages in secondary lymphoid tissues, such as lymph node and spleen. However, Sn-positive macrophages can also be found in a variety of pathological conditions, including (autoimmune) inflammatory infiltrates and tumours. Sn has been shown to contribute to sialylated pathogen uptake, antigen presentation and lymphocyte proliferation, and to influence both immunity and tolerance. This review presents Sn as a macrophage-specific marker of inflammation and immunoregulation with the potential to becoming an important biomarker for immunologically active macrophages and a target for therapy.

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.

Programmed anti-inflammatory macrophages protect against AKI and promote repair through trophic actions

Because pharmacological interventions for the treatment of acute kidney injury (AKI) have remained ineffective, cell-based therapies have been developed. Marrow stromal cells have been found to be safe and potentially effective in study subjects. Jung et al. demonstrate that macrophages made to overexpress anti-inflammatory interleukin-10 protect rats with AKI through iron-mediated upregulation of lipocalin-2 and its receptors, eliciting both anti-inflammatory and proliferative responses. These data further advance our understanding of cell-based therapies for AKI.

Human proximal tubule epithelial cells modulate autologous dendritic cell function

BACKGROUND

We have previously demonstrated that human kidney proximal tubule epithelial cells (PTEC) are able to modulate autologous T and B lymphocyte responses. It is well established that dendritic cells (DC) are responsible for the initiation and direction of adaptive immune responses and that these cells occur in the renal interstitium in close apposition to PTEC under inflammatory disease settings. However, there is no information regarding the interaction of PTEC with DC in an autologous human context.

METHODS

Human monocytes were differentiated into monocyte-derived DC (MoDC) in the absence or presence of primary autologous activated PTEC and matured with polyinosinic:polycytidylic acid [poly(I:C)], while purified, pre-formed myeloid blood DC (CD1c(+) BDC) were cultured with autologous activated PTEC in the absence or presence of poly(I:C) stimulation. DC responses were monitored by surface antigen expression, cytokine secretion, antigen uptake capacity and allogeneic T-cell-stimulatory ability.

RESULTS

The presence of autologous activated PTEC inhibited the differentiation of monocytes to MoDC. Furthermore, MoDC differentiated in the presence of PTEC displayed an immature surface phenotype, efficient phagocytic capacity and, upon poly(I:C) stimulation, secreted low levels of pro-inflammatory cytokine interleukin (IL)-12p70, high levels of anti-inflammatory cytokine IL-10 and induced weak Th1 responses. Similarly, pre-formed CD1c(+) BDC matured in the presence of PTEC exhibited an immature tolerogenic surface phenotype, strong endocytic and phagocytic ability and stimulated significantly attenuated T-cell proliferative responses.

CONCLUSIONS

Our data suggest that activated PTEC regulate human autologous immunity via complex interactions with DC. The ability of PTEC to modulate autologous DC function has important implications for the dampening of pro-inflammatory immune responses within the tubulointerstitium in renal injuries. Further dissection of the mechanisms of PTEC modulation of autologous immune responses may offer targets for therapeutic intervention in renal medicine.

Infusion of IL-10-expressing cells protects against renal ischemia through induction of lipocalin-2

Ischemia/reperfusion injury is a leading cause of acute renal failure triggering an inflammatory response associated with infiltrating macrophages, which determine disease outcome. To repair the inflammation we designed a procedure whereby macrophages that overexpress the anti-inflammatory agent interleukin (IL)-10 were adoptively transferred. These bone marrow-derived macrophages were able to increase their intracellular iron pool that, in turn, augmented the expression of lipocalin-2 and its receptors. Infusion of these macrophages into rats after 1 h of reperfusion resulted in localization of the cells to injured kidney tissue, caused increases in regenerative markers, and a notable reduction in both blood urea nitrogen and creatinine. Furthermore, IL-10 therapy decreased the local inflammatory profile and upregulated the expression of pro-regenerative lipocalin-2 and its receptors. IL-10-mediated protection and subsequent renal repair were dependent on the presence of iron and lipocalin-2, since the administration of a neutralizing antibody for lipocalin-2 or administration of IL-10 macrophages pretreated with the iron chelating agent deferoxamine abrogated IL-10-mediated protective effects. Thus, adoptive transfer of IL-10 macrophages to ischemic kidneys blunts acute kidney injury. These effects are mediated through the action of intracellular iron to induce lipocalin-2.

Suppressor of cytokine signaling (SOCS)1 is a key determinant of differential macrophage activation and function

Macrophages become activated by their environment and develop polarized functions: classically activated (M1) macrophages eliminate pathogens but can cause tissue injury, whereas alternatively activated (M2) macrophages promote healing and repair. Mechanisms directing polarized activation, especially in vivo, are not understood completely, and here, we examined the role of SOCS proteins. M2 macrophages activated in vitro or elicited by implanting mice i.p. with the parasitic nematode Brugia malayi display a selective and IL-4-dependent up-regulation of SOCS1 but not SOCS3. Using siRNA-targeted knockdown in BMDM, we reveal that the enhanced SOCS1 is crucial for IL-4-induced M2 characteristics, including a high arginase I:iNOS activity ratio, suppression of T cell proliferation, attenuated responses to IFN-γ/LPS, and curtailed SOCS3 expression. Importantly, SOCS1 was essential in sustaining the enhanced PI3K activity that drives M2 activation, defining a new regulatory mechanism by which SOCS1 controls M2 polarization. By contrast, for M1 macrophages, SOCS1 was not only an important regulator of proinflammatory mediators (IL-6, IL-12, MHC class II, NO), but critically, for M1, we show that SOCS1 also restricted IL-10 secretion and arginase I activity, which otherwise would limit the efficiency of M1 macrophage proinflammatory responses. Together, our results uncover SOCS1, not only as a feedback inhibitor of inflammation but also as a critical molecular switch that tunes key signaling pathways to effectively program different sides of the macrophage balance.

Transfused macrophages ameliorate pancreatic and renal injury in murine diabetes mellitus

BACKGROUND

Alternatively activated macrophages (M2 macrophages) are able to reduce renal injury in murine adriamycin nephropathy. However, the effect of M2 macrophages in other renal diseases such as diabetic nephropathy remains unknown.

METHODS

Macrophages were separated from splenocytes and polarized with IL-4 and IL-13 into a protective phenotype. Mice underwent adoptive transfer with M2 macrophages, and then diabetes was induced by tail vein injection with streptozotocin (STZ). Blood glucose levels were monitored daily. Mice were sacrificed at week 10 after STZ. Renal function and histopathological injury were assessed quantitatively.

RESULTS

Transfused M2 macrophages accumulated progressively in kidneys for up to 10 weeks after STZ. Kidneys from diabetic mice transfused with M2 macrophages had less tubular atrophy, glomerular hypertrophy and interstitial expansion than did control diabetic mice. M2 macrophages suppressed the development of interstitial fibrosis. In addition, the degree of pancreatic islet injury, as assessed by insulin staining, haemoglobin A1c and blood glucose was reduced after transfusion of M2 macrophages. In vivo, activation of kidney endogenous macrophage cytokine expression was inhibited by M2 macrophages.

CONCLUSION

Our findings show that M2 macrophages can protect against islet and renal injury in streptozotocin-induced diabetes, providing a potential therapeutic strategy for diabetes and diabetic nephropathy.

Native macrophages genetically modified to express heme oxygenase 1 protect rat liver transplants from ischemia/reperfusion injury

We investigated whether native macrophages overexpressing heme oxygenase 1 (HO-1) could protect rat orthotopic liver transplant (OLT) against cold ischemia/reperfusion injury (IRI). Livers from Sprague-Dawley rats were stored at 4°C in University of Wisconsin solution for 24 hours, and then they were transplanted into syngeneic recipients. Bone marrow-derived macrophages (BMMs) that were transfected ex vivo with heme oxygenase 1 adenovirus (Ad-HO-1), β-galactosidase adenovirus (Ad-β-gal), or HO-1 small interfering RNA (siRNA) were infused directly into the OLT before reperfusion. Controls were OLT conditioned with unmodified or scrambled siRNA-transfected cells. The transfer of Ad-HO-1/BMMs increased the survival of OLT to 100% (versus 40%-50% for controls) and decreased serum alanine aminotransferase levels and histological features of hepatocellular damage. In contrast, an infusion of macrophages transfected with HO-1 siRNA/Ad-β-gal failed to affect IRI. Gene therapy-induced HO-1 suppressed toll-like receptor 4 expression, decreased expression of proinflammatory tumor necrosis factor α, interleukin-1β, monocyte chemoattractant protein 1, and chemokine (C-X-C motif) ligand 10, and attenuated endothelial intercellular cell adhesion molecule 1 expression with resultant diminished OLT leukocyte sequestration. Although Ad-HO-1/BMMs decreased the frequency of apoptotic cells positive for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and ameliorated caspase-3 activity, the expression of interleukin-10 and antiapoptotic B cell lymphoma 2/B cell lymphoma extra large increased in well-functioning OLT. Thus, the transfer of native macrophages transfected ex vivo with HO-1 can rescue rat iso-OLT from IRI. Our study validates a novel and clinically attractive concept: native macrophages transfected ex vivo with the antioxidant HO-1 can be applied at the time of transplantation to mitigate otherwise damaging antigen-independent liver inflammation and injury resulting from the peritransplant harvesting insult. If this new, refined strategy is proven to be effective in allo-OLT recipients, it should be considered in clinical settings to increase the supply of usable donor organs and ultimately improve the overall success of liver transplantation.

The in silico macrophage: toward a better understanding of inflammatory disease

Macrophages function as sentinel, cell-regulatory 'hubs' capable of initiating, perpetuating and contributing to the resolution of an inflammatory response, following their activation from a resting state. Highly complex and varied gene expression programs within the macrophage enable such functional diversity. To investigate how programs of gene expression relate to the phenotypic attributes of the macrophage, the development of in silico modeling methods is needed. Such models need to cover multiple scales, from molecular pathways in cell-autonomous immunity and intercellular communication pathways in tissue inflammation to whole organism response pathways in systemic disease. Here, we highlight the potential of in silico macrophage modeling as an amenable and important yet under-exploited tool in aiding in our understanding of the immune inflammatory response. We also discuss how in silico macrophage modeling can help in future therapeutic strategies for modulating both the acute protective effects of inflammation (such as host defense and tissue repair) and the harmful chronic effects (such as autoimmune diseases).

Kidney Dendritic Cells Become Pathogenic during Crescentic Glomerulonephritis with Proteinuria

It is unclear why kidney dendritic cells attenuate some models of kidney disease but aggravate others. Kidney dendritic cells ameliorate the early phase of nonaccelerated nephrotoxic nephritis, a murine model of crescentic glomerulonephritis, but their effect on the later phase is unknown. Here, we report that kidney dendritic cells at later stages of nephrotoxic nephritis expressed higher levels of costimulatory molecules but lower levels of the cosuppressor molecule ICOS-L and started production of IL-12/23p40 and TNF-α. Furthermore, we noted that kidney dendritic cells captured more filterable antigen in proteinuric mice at late time points of nephrotoxic nephritis and started to capture molecules that were too large for filtration by a healthy kidney. They presented filtered antigen to Th cells, which responded by producing the proinflammatory cytokines IL-2, IFN-γ, TNF-α, IL-6, and IL-17. Notably, production of the suppressive cytokine IL-10 further increased in late nephrotoxic nephritis. Depletion of kidney dendritic cells at a late stage attenuated nephrotoxic nephritis, in contrast to the exacerbation observed with depletion at an early stage, indicating that their acquired proinflammatory phenotype adversely affected disease. These findings indicate that the intrarenal inflammatory microenvironment determines how kidney dendritic cells affect nephritis. In addition, proteinuria may harm the kidney by providing dendritic cells with more antigens to stimulate potentially pathogenic Th cells.

Macrophage signaling pathways: a novel target in renal disease

Monocytes/macrophages are a heterogeneous cell population that play a critical role in host defense and tissue homeostasis. However, macrophage activation during acute and chronic inflammation can result in macrophage-mediated renal injury in a variety of settings, including proliferative glomerulonephritis. Macrophages can be activated via a number of intracellular signaling pathways (eg, c-Jun amino terminal kinase, p38 mitogen-activated protein kinase, FcR/Syk, Janus kinase/signal transducer and activator of transcription) that induce production of mediators of renal injury. Thus, targeting selected macrophage signaling pathways is a potential therapeutic strategy to suppress macrophage-mediated renal injury while leaving intact the desirable macrophage functions of host defense and tissue repair.

Macrophages expressing heme oxygenase-1 improve renal function in ischemia/reperfusion injury

Acute kidney injury has a high mortality and lacks specific therapies, with ischemia/reperfusion injury (IRI) being the predominant cause. Macrophages (M phi) have been used successfully in cell therapy to deliver targeted therapeutic genes in models of inflammatory kidney disease. Heme oxygenase-1 (HO-1) catalyzes heme breakdown and has important cytoprotective functions. We hypothesized that administration of M phi modified to overexpress HO-1 would protect from renal IRI. Using an adenoviral construct (Ad-HO-1), HO-1 was overexpressed in primary bone marrow-derived M phi (BMDM). In vitro Ad-HO-1 M phi showed an anti-inflammatory phenotype with increased phagocytosis of apoptotic cells (ACs) and increased interleukin (IL)-10 but reduced TNF-alpha and nitric oxide (NO) following lipopolysaccharide/interferon-gamma (IFN gamma) stimulation compared to control transduced or unmodified M phi. In vivo, intravenously (IV) injected M phi homed preferentially to the post-IRI kidney compared to uninjured control following experimental IRI. At 24 hours postinjury, despite equivalent levels of tubular necrosis, apoptosis, and capillary density between groups, the injection of Ad-HO-1 M phi resulted in preserved renal function (serum creatinine reduced by 46%), and reduced microvascular platelet deposition. These data demonstrate that genetically modified M phi improve the outcomes in IRI when administered after the establishment of structural injury, raising the prospect of targeted cell therapy to support the function of the acutely injured kidney.

Macrophages heterogeneity in atherosclerosis - implications for therapy

Atherosclerosis is a chronic inflammatory disease occurring within the artery wall and is an underlying cause of cardiovascular complications, including myocardial infarction, stroke and peripheral vascular disease. Its pathogenesis involves many immune cell types with a well accepted role for monocyte/macrophages. Cholesterol-loaded macrophages are a characteristic feature of plaques and are major players in all stages of plaque development. As well as modulating lipid metabolism, macrophages secrete inflammatory cytokines, chemokines and reactive oxygen and nitrogen species that drive pathogenesis. They also produce proteases and tissue factor that contribute to plaque rupture and thrombosis. Macrophages are however heterogeneous cells and when appropriately activated, they phagocytose cytotoxic lipoproteins, clear apoptotic bodies, secrete anti-inflammatory cytokines and synthesize matrix repair proteins that stabilize vulnerable plaques. Pharmacological modulation of macrophage activity therefore represents a potential therapeutic strategy for atherosclerosis. The aim of this review is to provide an overview of the current understanding of the different macrophage subsets and their monocyte precursors, and, the implications of these subsets for atherosclerosis. This will present a foundation for highlighting novel opportunities to exploit the heterogeneity of macrophages as important diagnostic and therapeutic targets for atherosclerosis and its associated diseases.

Macrophage cell therapy in renal disease

Macrophages play an important role in many aspects of tissue injury, inflammation, and repair. Macrophage accumulation is found in most forms of renal disease and depletion studies have shown that they contribute to injury. However, it is also clear that monocytes and macrophages can develop reparative properties that are critical to disease resolution. A number of studies have now shown that macrophages can be transduced or stimulated ex vivo, injected after the initiation of disease, and localize preferentially to the site of renal inflammation. Such macrophage cell therapy can result in reduced inflammation and fibrosis and lead to improved renal function and attenuation of proteinuria. These studies provide a platform for future translational approaches in human renal disease.

Adoptive transfer of ex vivo HO-1 modified bone marrow-derived macrophages prevents liver ischemia and reperfusion injury

Macrophages play a critical role in the pathophysiology of liver ischemia and reperfusion (IR) injury (IRI). However, macrophages that overexpress antioxidant heme oxygenase-1 (HO-1) may exert profound anti-inflammatory functions. This study explores the cytoprotective effects and mechanisms of ex vivo modified HO-1-expressing bone marrow-derived macrophages (BMDMs) in well-defined mouse model of liver warm ischemia followed by reperfusion. Adoptive transfer of Ad-HO-1-transduced macrophages prevented IR-induced hepatocellular damage, as evidenced by depressed serum glutamic-oxaloacetic transaminase (sGOT) levels and preserved liver histology (Suzuki scores), compared to Ad-beta-gal controls. This beneficial effect was reversed following concomitant treatment with HO-1 siRNA. Ad-HO-1-transfected macrophages significantly decreased local neutrophil accumulation, TNF-alpha/IL-1beta, IFN-gamma/E-selectin, and IP-10/MCP-1 expression, caspase-3 activity, and the frequency of apoptotic cells, as compared with controls. Unlike in controls, Ad-HO-1-transfected macrophages markedly increased hepatic expression of antiapoptotic Bcl-2/Bcl-xl and depressed caspase-3 activity. These results establish the precedent for a novel investigative tool and provide the rationale for a clinically attractive new strategy in which native macrophages can be transfected ex vivo with cytoprotective HO-1 and then infused, if needed, to prospective recipients exposed to hepatic IR-mediated local inflammation, such as during liver transplantation, resection, or trauma.

Reversibility of liver fibrosis

Liver cirrhosis is a major cause of morbidity and mortality worldwide and has very limited therapeutic options. Regardless of the aetiology, hepatic fibrosis is a characteristic feature of chronic liver disease. Our knowledge regarding the pathogenesis of this scarring has grown exponentially in the past 25 years. It has now clear that this is a highly dynamic process and the long-held dogma that it is irreversible and relentlessly progressive is now being challenged. In this review, we will summarise the key pathogenic mechanisms at play and will focus on the evidence demonstrating that liver fibrosis is reversible in humans and animal models. In particular, we will examine the role of hepatic stellate cells, MMPs, TIMPs and macrophages in this process. Finally, we will discuss some of the studies aimed to therapeutically target the resolution of fibrosis and their potential for translation into a badly-needed treatment modality in the clinical setting.

Poly(ADP-ribose) polymerase-1 regulates the progression of autoimmune nephritis in males by inducing necrotic cell death and modulating inflammation

Necrotic lesions and necrotic cell death characterize severe autoimmune nephritides, and contribute to local inflammation and to progression of the disease. Poly(ADP-ribose) polymerase-1 (PARP-1), a DNA repair enzyme, is involved in the induction of necrosis and is a key player in the acute and chronic inflammation. Therefore, we hypothesized that PARP-1 controls the severity of nephritis by mediating the induction of necrosis in the kidney. We used lupus and anti-glomerular basement membrane models of nephritis to determine the effects of PARP-1 on the inflammatory response in the kidney. We show in this study that PARP-1 is indeed activated during the course of glomerulonephritis. We also show that the absence of PARP-1 or its pharmacological inhibition results in milder nephritis, with lower blood urea nitrogen levels, reduced necrotic lesions, and higher survival rates. The relevance of PARP-1 showed a strong male sex specificity, and treatment of male mice with 17beta-estradiol prolonged their survival during the course of nephritis. PARP-1 also regulated TNF-alpha expression and up-regulation of adhesion molecules, further supporting a role of PARP-1 in the inflammatory process within the kidney. Our results demonstrate that PARP-1 activation and consequent necrotic cell death play an important role in the pathogenesis of male nephritis, and suggest that PARP-1 can be a novel therapeutic target in glomerulonephritis.

Macrophage diversity in renal injury and repair

Monocyte-derived macrophages can determine the outcome of the immune response and whether this response contributes to tissue repair or mediates tissue destruction. In addition to their important role in immune-mediated renal disease and host defense, macrophages play a fundamental role in tissue remodeling during embryonic development, acquired kidney disease, and renal allograft responses. This review summarizes macrophage phenotype and function in the orchestration of kidney repair and replacement of specialized renal cells following injury. Recent advances in our understanding of macrophage heterogeneity in response to their microenvironment raise new and exciting therapeutic possibilities to attenuate or conceivably reverse progressive renal disease in the context of fibrosis. Furthermore, parallels with pathological processes in many other organs also exist.

Regulatory immune cells in kidney disease

Lymphocytes and macrophages act as effector immune cells in the initiation and progression of renal injury. Recent data have shown that subpopulations of these immune cells (regulatory T lymphocytes and alternately-activated or regulatory macrophages) are potent modulators of tissue injury and repair in renal disease. Recent animal studies examining the therapeutic effect of these cells raise the exciting possibility that strategies targeting these cell types may be effective in treating and preventing kidney disease in humans. This review will describe their biological role in experimental kidney disease and therapeutic potential in clinical nephrology.

By homing to the kidney, activated macrophages potently exacerbate renal injury

Macrophages are important mediators of injury in most types of human kidney diseases; however, the pathogenic importance of both macrophage number and activation status is unknown. To examine this question, severe-combined immunodeficient mice with adriamycin nephrosis, an experimental model of human focal segmental glomerulosclerosis, were treated intravenously with either resting (1 x 10(6) to 5 x 10(6)) or activated (1 x 10(3) to 1 x 10(6)) macrophages on day 6 postadriamycin administration, and the effects on kidney injury were examined. On day 28, renal injury was worse in the group that received activated macrophages at doses as low as 1 x 10(4) macrophages per mouse compared with control adriamycin nephrotic mice. However, treatment with resting macrophages at doses as high as 5 x 10(6) macrophages per mouse had no significant effect on either renal histology or function. The transferred activated macrophages homed to inflamed kidneys during the middle-to-late stages of the disease, but such homing was not observed for resting macrophages. This study of in vivo cell adoptive transfer supports the importance of macrophage activation status over macrophage number in causing renal injury. These data suggest that therapeutic strategies for treating progressive kidney diseases should target activated macrophages.

Unique expression of suppressor of cytokine signaling 3 is essential for classical macrophage activation in rodents in vitro and in vivo

On infiltrating inflamed tissue, macrophages respond to the local microenvironment and develop one of two broad phenotypes: classically activated (M1) macrophages that cause tissue injury and alternatively activated macrophages that promote repair. Understanding how this polarization occurs in vivo is far from complete, and in this study, using a Th1-mediated macrophage-dependent model of acute glomerulonephritis, nephrotoxic nephritis, we examine the role of suppressor of cytokine signaling (SOCS)1 and SOCS3. Macrophages in normal kidneys did not express detectable SOCS proteins but those infiltrating inflamed glomeruli were rapidly polarized to express either SOCS1 (27 +/- 6%) or SOCS3 (54 +/- 12%) but rarely both (10 +/- 3%). Rat bone marrow-derived macrophages incubated with IFN-gamma or LPS expressed SOCS1 and SOCS3, whereas IL-4 stimulated macrophages expressed SOCS1 exclusively. By contrast, incubation with IFN-gamma and LPS together suppressed SOCS1 while uniquely polarizing macrophages to SOCS3 expressing cells. Macrophages in which SOCS3 was knocked down by short interfering RNA responded to IFN-gamma and LPS very differently: they had enhanced STAT3 activity; induction of macrophage mannose receptor, arginase and SOCS1; restoration of IL-4 responsiveness that is inhibited in M1 macrophages; and decreased synthesis of inflammatory mediators (NO and IL-6) and costimulatory molecule CD86, demonstrating that SOCS3 is essential for M1 activation. Without it, macrophages develop characteristic alternatively activated markers when exposed to classical activating stimuli. Lastly, increased glomerular IL-4 in nephrotoxic nephritis inhibits infiltrating macrophages from expressing SOCS3 and was associated with attenuated glomerular injury. Consequently, we propose that SOCS3 is essential for development of M1 macrophages in vitro and in vivo.

Renal dendritic cells stimulate IL-10 production and attenuate nephrotoxic nephritis

The role of renal dendritic cells (DCs) in glomerulonephritis is unknown. This question was addressed in nephrotoxic nephritis, a murine model of human necrotizing glomerulonephritis, which is dependent on CD4(+) Th1 cells and macrophages. DCs in nephritic kidneys showed signs of activation, accumulated in the tubulo-interstitium, and infiltrated the periglomerular space surrounding inflamed glomeruli. In ex vivo coculture experiments with antigen-specific CD4(+) T cells, DCs stimulated the secretion of IL-10, which is known to attenuate nephrotoxic nephritis, and the Th1 cytokine IFNgamma. Endogenous renal CD4(+) T cells produced both of these cytokines as well, but those from nephritic mice secreted increased amounts of IL-10. Renal DCs were found to express ICOS-L, an inducer of IL-10. To evaluate the in vivo role of renal DCs in disease, CD11c(+) DCs were depleted on days 4 and 10 after the induction of nephritis by injecting CD11c-DTR/GFP mice with diphtheria toxin. Sparing DCs until day 4 did not affect the autologous phase of nephritis. The number of renal DCs was reduced by 70% to 80%, the number of renal macrophages was unchanged, and periglomerular infiltrates were eliminated. On days 11 to 14, we observed aggravated tubulointerstitial and glomerular damage, reduced creatinine clearance, and increased proteinuria. These findings demonstrate that renal DCs exert a renoprotective effect in nephrotoxic nephritis, possibly by expressing ICOS-L and/or by inducing IL-10 in infiltrating CD4(+) Th1 cells.