Dendritic cells facilitate accumulation of IL-17 T cells in the kidney following acute renal obstruction

Lymphocytes and innate immune cells in acute kidney injury and repair

Acute kidney injury (AKI) is a common and serious disease entity that affects native kidneys and allografts but for which no specific treatments exist. Complex intrarenal inflammatory processes driven by lymphocytes and innate immune cells have key roles in the development and progression of AKI. Many studies have focused on prevention of early injury in AKI. However, most patients with AKI present after injury is already established. Increasing research is therefore focusing on mechanisms of renal repair following AKI and prevention of progression from AKI to chronic kidney disease. CD4+ and CD8+ T cells, B cells and neutrophils are probably involved in the development and progression of AKI, whereas regulatory T cells, double-negative T cells and type 2 innate lymphoid cells have protective roles. Several immune cells, such as macrophages and natural killer T cells, can have both deleterious and protective effects, depending on their subtype and/or the stage of AKI. The immune system not only participates in injury and repair processes during AKI but also has a role in mediating AKI-induced distant organ dysfunction. Targeted manipulation of immune cells is a promising therapeutic strategy to improve AKI outcomes.

Corneal dendritic cells in diabetes mellitus: A narrative review

Diabetes mellitus is a global public health problem with both macrovascular and microvascular complications, such as diabetic corneal neuropathy (DCN). Using in-vivo confocal microscopy, corneal nerve changes in DCN patients can be examined. Additionally, changes in the morphology and quantity of corneal dendritic cells (DCs) in diabetic corneas have also been observed. DCs are bone marrow-derived antigen-presenting cells that serve both immunological and non-immunological roles in human corneas. However, the role and pathogenesis of corneal DC in diabetic corneas have not been well understood. In this article, we provide a comprehensive review of both animal and clinical studies that report changes in DCs, including the DC density, maturation stages, as well as relationships between the corneal DCs, corneal nerves, and corneal epithelium, in diabetic corneas. We have also discussed the associations between the changes in corneal DCs and various clinical or imaging parameters, including age, corneal nerve status, and blood metabolic parameters. Such information would provide valuable insight into the development of diagnostic, preventive, and therapeutic strategies for DM-associated ocular surface complications.

The Th17/IL-17 Axis and Kidney Diseases, With Focus on Lupus Nephritis

Systemic lupus erythematosus (SLE) is a disease characterized by dysregulation and hyperreactivity of the immune response at various levels, including hyperactivation of effector cell subtypes, autoantibodies production, immune complex formation, and deposition in tissues. The consequences of hyperreactivity to the self are systemic and local inflammation and tissue damage in multiple organs. Lupus nephritis (LN) is one of the most worrying manifestations of SLE, and most patients have this involvement at some point in the course of the disease. Among the effector cells involved, the Th17, a subtype of T helper cells (CD4+), has shown significant hyperactivation and participates in kidney damage and many other organs. Th17 cells have IL-17A and IL-17F as main cytokines with receptors expressed in most renal cells, being involved in the activation of many proinflammatory and profibrotic pathways. The Th17/IL-17 axis promotes and maintains repetitive tissue damage and maladaptive repair; leading to fibrosis, loss of organ architecture and function. In the podocytes, the Th17/IL-17 axis effects include changes of the cytoskeleton with increased motility, decreased expression of health proteins, increased oxidative stress, and activation of the inflammasome and caspases resulting in podocytes apoptosis. In renal tubular epithelial cells, the Th17/IL-17 axis promotes the activation of profibrotic pathways such as increased TGF-β expression and epithelial-mesenchymal transition (EMT) with consequent increase of extracellular matrix proteins. In addition, the IL-17 promotes a proinflammatory environment by stimulating the synthesis of inflammatory cytokines by intrinsic renal cells and immune cells, and the synthesis of growth factors and chemokines, which together result in granulopoiesis/myelopoiesis, and further recruitment of immune cells to the kidney. The purpose of this work is to present the prognostic and immunopathologic role of the Th17/IL-17 axis in Kidney diseases, with a special focus on LN, including its exploration as a potential immunotherapeutic target in this complication.

Deletion of delta-like 1 homologue accelerates renal inflammation by modulating the Th17 immune response

Preclinical studies have demonstrated that activation of the NOTCH pathway plays a key role in the pathogenesis of kidney damage. There is currently no information on the role of the Delta-like homologue 1 (DLK1), a NOTCH inhibitor, in the regulation of renal damage. Here, we investigated the contribution of DLK1 to experimental renal damage and the underlying molecular mechanisms. Using a Dlk1-null mouse model in the experimental renal damage of unilateral ureteral obstruction, we found activation of NOTCH, as shown by increased nuclear translocation of the NOTCH1 intracellular domain, and upregulation of Dlk2/hey-1 expression compared to wild-type (WT) littermates. NOTCH1 over-activation in Dlk1-null injured kidneys was associated with a higher inflammatory response, characterized by infiltration of inflammatory cells, mainly CD4/IL17A + lymphocytes, and activation of the Th17 immune response. Furthermore, pharmacological NOTCH blockade inhibited the transcription factors controlling Th17 differentiation and gene expression of the Th17 effector cytokine IL-17A and other related-inflammatory factors, linked to a diminution of inflammation in the injured kidneys. We propose that the non-canonical NOTCH ligand DLK1 acts as a NOTCH antagonist in renal injury regulating the Th17-mediated inflammatory response.

Separated parabiont reveals the fate and lifespan of peripheral-derived immune cells in normal and ischaemia-induced injured kidneys

Immune cell infiltration plays a key role in acute kidney injury (AKI) to chronic kidney disease (CKD) progression. T lymphocytes, neutrophils, monocytes/macrophages and other immune cells regulate inflammation, tissue remodelling and repair. To determine the kinetics of accumulation of various immune cell populations, we established an animal model combining parabiosis and separation surgery to explore the fate and lifespan of peripheral leucocytes that migrate to the kidney. We found that peripheral T lymphocytes could survive for a long time (more than 14 days), whereas peripheral neutrophils survived for a short time in both healthy and ischaemia-induced damaged kidneys. Nearly half of the peripheral-derived macrophages disappeared after 14 days in normal kidneys, while their existing time in the inflammatory kidneys was prolonged. A fraction of F4/80^high macrophages were renewed from the circulating monocyte pool. In addition, we found that after renal ischaemia reperfusion, neutrophils increased significantly in the early phase, and T lymphocytes mainly accumulated in the late stage, whereas macrophages infiltrated throughout AKI-CKD progression and were sustained longer in injured as opposed to normal kidneys. In conclusion, peripheral-derived macrophages, T lymphocytes and neutrophils exhibit different lifespans in the kidney, which may play different roles during AKI-CKD progression.

Evaluation of Neutrophil Dynamics Change by Protective Effect of Tadalafil After Renal Ischemia/Reperfusion Using In Vivo Real-time Imaging

BACKGROUND

Neutrophils play a major role in ischemia/reperfusion injury (IRI) in renal transplantation and acute kidney injury. However, it has been difficult to observe changes in neutrophil dynamics over time in living mice kidney. We investigate neutrophil dynamics in IRI in living mice using novel in vivo multiphoton microscope imaging techniques and characterize the renoprotective effects of a selective phosphodiesterase (PDE) 5 inhibitor, tadalafil.

METHODS

Wild-type (WT) and eNOS knockout (eNOS-KO) mice, a model of endothelial dysfunction, were used to establish in vivo real-time imaging in living mouse kidneys. Neutrophils were labeled green with Ly-6G monoclonal antibody, and plasma flow was labeled red with bovine serum albumin. Tadalafil was administered orally 1 h before surgery. Both kidney pedicles were reperfused after 37° warm ischemia for 45 min.

RESULTS

Our novel approach revealed that neutrophils were trapped in glomerulus within a few minutes after reperfusion. They gradually increased over time and Infiltrated neutrophils were observed in the tubular lumen and peritubular capillary. The neutrophils were clearly visualized rolling on peritubular capillary plexus at 3 μm/min. The administration of tadalafil significantly reduced neutrophil influx into the glomerulus in both WT and eNOS-KO mice. Reduced neutrophil infiltration in tadalafil groups, which was confirmed by flow cytometry, resulted in histopathologically decreased tubular injury. The expression of VCAM-1 and KIM-1 was partially prevented by tadalafil.

CONCLUSIONS

Use of a novel technique contributed to elucidation of neutrophil dynamics after reperfusion. Tadalafil has a potential for inhibiting neutrophil infiltration in renal IRI.Supplemental Visual Abstract; http://links.lww.com/TP/C223.

Interleukin -17 Serum Levels and Polymorphisms in Acute Kidney Injury Patients

BACKGROUND

Cardiopulmonary bypass (CPB) has been demonstrated to provoke a systemic inflammatory response believed to be responsible for some of the serious postoperative complications such as renal dysfunction. Therefore, we tested the hypothesis suggesting that the serum levels of IL- 17A (IL-17), as an inflammatory cytokine, and its gene variants are associated with acute kidney injury after CPB (AKI-CPB).

METHODS

A total of 135 Iranian patients undergoing cardiopulmonary bypass were included in this study, of whom 65 (48.1%) developed AKI. Blood specimens were collected preoperatively and at 12 hours postoperatively. The IL-17 gene polymorphisms (rs2275913 and rs3819024) were determined using sequence-specific primers (PCR-SSP) technique.Pre- and postoperative IL-17 levels were measured and analyzed in relation to polymorphisms.

RESULTS

IL-17 concentrations in CBP subjects, were increased after cardiopulmonary bypass (P<0.00001)but there were no statistically significant differences in IL-17 serum level between AKI and non-AKI groups. Different genotypes of IL-17 rs2275913 SNP (G→A) were associated with different circulating IL-17 levels before bypass and also after AKI development. There were no associations between gene polymorphisms (rs2275913and rs3819024) and incidence of AKI- CPB. There was an association between thers2275913 SNP and the severity of AKI.

CONCLUSION

This study clarified that the rs2275913 SNP to some extent determines plasma IL-17 concentrations in CPB patients. No significant association was found between IL-17 levels or gene polymorphisms (rs2275913and rs3819024) and incidence of AKI-CPB. Our results suggest that there is an association between rs2275913 and the severity of AKI- CPB.

Brain-kidney interaction: Renal dysfunction following ischemic stroke

Stroke is a leading cause of mortality and morbidity, with long-term debilitating effects. Accumulating evidence from experimental studies as well as observational studies in patients suggests a cross talk between the brain and kidney after stroke. Stroke may lead to kidney dysfunction which can adversely impact patient outcome. In this review article, we discuss the epidemiology and mechanisms of brain–kidney interaction following ischemic stroke. Specifically, we discuss the role of the central autonomic network, autoregulation, inflammatory and immune responses, the role of extracellular vesicles and their cargo microRNA, in mediating brain–kidney interaction following stroke. Understanding the bidirectional nature of interaction between the brain and kidney after cerebral injury would have clinical implications for the treatment of stroke and overall patient outcome.

Interleukin-17A induces renal fibrosis through the ERK and Smad signaling pathways

Interleukin (IL)-17A is upregulated in several renal diseases and plays a crucial role in renal inflammation. However, it remains unclear how IL-17A contributes to renal fibrosis. Our result demonstrated that IL-17A expression was upregulated in the obstructed kidney of unilateral ureter obstruction (UUO) mice when compared to the contralateral control kidney. Inhibition of IL-17A functions by the intravenous administration of an anti-IL-17A receptor antibody (100 μg) 2 h prior to UUO and on post-UUO day 1 and 3 significantly reduced fibronectin expression in the UUO kidney. The addition of IL-17A (25-100 μg) to human renal proximal tubular cells or renal fibroblasts caused an increase in fibronectin production and extracellular signal-regulated kinase (ERK)1/2 activation, which were reduced upon pretreatment with the ERK inhibitor U0126. The level of phosphorylated (p)-ERK1/2 was increased in the UUO kidney, but reduced by the administration of the anti-IL-17A receptor antibody, verifying the importance of the ERK pathway in vivo. TGF-β1 mRNA expression and protein were increased in the UUO kidney and in IL-17A-stimulated cultured cells. The administration of an anti-TGF-β1 neutralizing antibody or TGF-β1 receptor I inhibitor (SB431542) to cells abrogated the IL-17A-mediated increase of fibronectin production. IL-17A induced an increase in p-Smad2 and p-Smad3 expression at 7.5 min and 24 h and pretreatment with the anti-TGF-β1 neutralizing antibody, and SB431542 reduced the IL-17A-stimulated increase of p-Smad2. Knockdown of Smad2 or Smad3 expression inhibited the IL-17A-enhanced production of fibronectin. These results suggest an essential role for the TGF-β/Smad pathway in the IL-17A-mediated increase of fibronectin production. This study demonstrates that IL-17A contributes to the production of extracellular matrix, and targeting its associated signaling pathways could provide a therapeutic target for preventing renal fibrosis.

Lymphangiogenesis in kidney and lymph node mediates renal inflammation and fibrosis

Lymphangiogenesis is associated with chronic kidney disease (CKD) and occurs following kidney transplant. Here, we demonstrate that expanding lymphatic vessels (LVs) in kidneys and corresponding renal draining lymph nodes (RDLNs) play critical roles in promoting intrarenal inflammation and fibrosis following renal injury. Our studies show that lymphangiogenesis in the kidney and RDLN is driven by proliferation of preexisting lymphatic endothelium expressing the essential C-C chemokine ligand 21 (CCL21). New injury-induced LVs also express CCL21, stimulating recruitment of more CCR7⁺ dendritic cells (DCs) and lymphocytes into both RDLNs and spleen, resulting in a systemic lymphocyte expansion. Injury-induced intrarenal inflammation and fibrosis could be attenuated by blocking the recruitment of CCR7⁺ cells into RDLN and spleen or inhibiting lymphangiogenesis. Elucidating the role of lymphangiogenesis in promoting intrarenal inflammation and fibrosis provides a key insight that can facilitate the development of novel therapeutic strategies to prevent progression of CKD-associated fibrosis.

Renal fibrosis: Primacy of the proximal tubule

Tubulointerstitial fibrosis (TIF) is the hallmark of chronic kidney disease and best predictor of renal survival. Many different cell types contribute to TIF progression including tubular epithelial cells, myofibroblasts, endothelia, and inflammatory cells. Previously, most of the attention has centered on myofibroblasts given their central importance in extracellular matrix production. However, emerging data focuses on how the response of the proximal tubule, a specialized epithelial segment vulnerable to injury, plays a central role in TIF progression. Several proximal tubular responses such as de-differentiation, cell cycle changes, autophagy, and metabolic changes may be adaptive initially, but can lead to maladaptive responses that promote TIF both through autocrine and paracrine effects. This review discusses the current paradigm of TIF progression and the increasingly important role of the proximal tubule in promoting TIF both in tubulointerstitial and glomerular injuries. A better understanding and appreciation of the role of the proximal tubule in TIF has important implications for therapeutic strategies to halt chronic kidney disease progression.

Activated Renal Dendritic Cells Cross Present Intrarenal Antigens After Ischemia-Reperfusion Injury

BACKGROUND

The healthy kidney contains an extensive population of renal mononuclear phagocytes (RMPs), with substantial phenotypic and functional diversity. However, how this diverse population is affected by ischemia-reperfusion injury (IRI), an obligate part of renal transplantation, is not yet well understood. The aim of this study was to characterize the phenotypic and functional alterations in RMPs induced by IRI.

METHODS

Renal mononuclear phagocytes were studied 24 and 72 hours after 30 minutes of renal ischemia or sham operation. Kidneys were digested and the phenotypes of renal leukocyte populations were analyzed via flow cytometry. Multiphoton microscopy was used to image renal dendritic cells (DCs) in vivo using CD11c reporter mice. The capacity of renal DCs to present antigen was examined by assessment of proliferation of ovalbumin-specific T cells in rat insulin promoter-membrane-bound ovalbumin transgenic mice after sham or IRI procedures.

RESULTS

Ischemia-reperfusion injury induced influx of monocytes, DCs, macrophages, and neutrophils into the kidney. Classification of RMP subpopulations based on CD11b/CD11c expression demonstrated that the RMPs that increased in response to IRI were predominantly newly recruited monocyte-derived inflammatory DCs. In vivo multiphoton imaging of CD11c-EYFP mice revealed that intrarenal DCs exhibited increased number and activity of dendrites in the postischemic period. Ischemia-reperfusion injury also promoted DC-dependent cross-presentation of renal antigens to CD8 T cells in the draining lymph node.

CONCLUSIONS

In response to renal IRI, RMP populations are skewed toward those derived from inflammatory monocyte precursors. In addition, renal DCs undergo functional activation, increasing their capacity to activate antigen-specific CD8 T cells in renal draining lymph nodes.

T helper type 17 cells in immune-mediated glomerular disease

CD4⁺ T cells are important drivers of tissue damage in immune-mediated renal diseases, such as anti-glomerular basement membrane glomerulonephritis, anti-neutrophil cytoplasmic antibody-associated glomerulonephritis, and lupus nephritis. The discovery of a distinct, IL-17-producing CD4⁺ T-cell lineage termed T helper type 17 (T_H17) cells has markedly advanced current understanding of the pathogenic mechanisms of organ-specific immunity and the pathways that lead to target organ damage. T_H17 cells are characterized by the expression of the transcription factor RORγt, the production of the pro-inflammatory cytokines IL-17A, IL-17F, IL-22, and high expression of the chemokine receptor C-C-motif chemokine receptor 6 (CCR6). An emerging body of evidence from experimental models and human studies supports a key role for these cells in the development of renal damage, and has led to the identification of targets to inhibit the production of T_H17 cells in the intestine, their migration, or their actions within the kidney. Here, we describe the identification, regulation, and function of T_H17 cells and their associated pathways in immune-mediated kidney diseases, with a particular focus on the mechanisms underlying renal tissue injury. We also discuss the rationale for the translation of these findings into new therapeutic approaches in patients with autoimmune kidney disease.

The attenuation of renal fibrosis by histone deacetylase inhibitors is associated with the plasticity of FOXP3+IL-17+ T cells

BACKGROUND

The histone deacetylase (HDAC) inhibitor, which has potential effects on epigenetic modifications, had been reported to attenuate renal fibrosis. CD4⁺ forkhead box P3 (FOXP3)⁺ T regulatory (Treg) cells may be converted to inflammation-associated T helper 17 cells (Th17) with tissue fibrosis properties. The association between FOXP3⁺IL-17⁺ T cells and the attenuation of renal fibrosis by the HDAC inhibitor is not clear.

METHODS

This study evaluated the roles of the HDAC inhibitor, Treg cells and their differentiation into Th17 cells, which aggravate chronic inflammation and renal fibrosis in a unilateral ureteral obstruction (UUO) mouse model. The study groups included control and UUO mice that were monitored for 7, 14 or 21 days.

RESULTS

Juxtaglomerular (JG) hyperplasia, angiotensin II type 1 receptor (AT1R) expression and lymphocyte infiltration were observed in renal tissues after UUO but were decreased after trichostatin A (TSA) treatment, a HDAC inhibitor. The number of CD4⁺FOXP3⁺ T cells increased progressively, along with the number of FOXP3⁺interleukin (IL)-17⁺ T cells, after 14 days, and their numbers then progressively decreased with increasing CD4⁺IL-17⁺ T cell numbers, as demonstrated by double immunohistochemistry. Progressive renal fibrosis was associated with the loss of CD4⁺FOXP3⁺IL-17⁺ T cells in splenic single-cell suspensions. FOXP3⁺IL-17⁺ T cells expressed TGF-β1 both in vitro and in vivo, and TGF-β1 expression was significantly knockdown by IL-17 siRNA in vitro. These cells were found to play a role in converting Tregs into IL-17- and TGF-β1-producing cells.

CONCLUSIONS

TSA treatment decreased JG hyperplasia, the percentage of FOXP3⁺IL-17⁺ cells and the degree of fibrosis, suggesting that therapeutic benefits may result from epigenetic modifications.

Dependence of Glomerulonephritis Induction on Novel Intraglomerular Alternatively Activated Bone Marrow-Derived Macrophages and Mac-1 and PD-L1 in Lupus-Prone NZM2328 Mice

Glomerular damage mediated by glomerulus-infiltrating myeloid-derived cells is a key pathogenic event in lupus nephritis (LN), but the process is poorly understood. Confocal microscopy of kidney sections and flow cytometry analysis of glomerular cells from magnetic bead-purified glomeruli have identified glomerulus-infiltrating leukocyte populations in NZM2328 (NZM) lupus-prone mice with spontaneous chronic glomerulonephritis (GN) and anti-glomerular basement membrane-induced nephritis. The occurrence of a major glomerulus-infiltrating CD11b⁺F4/80^-I-A^- macrophage population exhibiting the markers programmed death ligand-1 (PD-L1), Mac-2, and macrophage mannose receptor (CD206) and producing Klf4, Il10, Retnla, Tnf, and Il6 mRNA, which are known to be expressed by alternatively activated (M2b) macrophages, correlated with proteinuria status. In NZM mice with spontaneous LN, glomerular macrophage infiltration is predominant. CD11b⁺F4/80^-I-A^- intraglomerular macrophages and polymorphonuclear neutrophils (PMN) are important in inducing GN, as anti-CD11b and -ICAM-1 mAb inhibited both proteinuria and macrophage and PMN infiltration. The predominant and high expression of PD-L1 by CD11b⁺F4/80^-I-A^- glomerular macrophages in kidneys of mice with GN and the inhibition of proteinuria by anti-PD-L1 mAb supported the pathogenic role of these macrophages but not the PD-L1^- PMN in GN development and in inducing podocyte damage. In NZM mice with spontaneous chronic GN and severe proteinuria, few glomerulus-infiltrating PMN were found, leaving macrophages and, to a less extent, dendritic cells as the major infiltrating leukocytes. Taken together, these data support the important pathogenic effect of CD11b⁺F4/80^-I-A^- M2b-like glomerulus-infiltrating macrophages in LN and reinforce macrophages as a promising target for GN treatment.

Overview of pathophysiology and treatment of human lupus nephritis

PURPOSE OF REVIEW

Despite recent developments and treatment successes, the outcome, and prognosis of patients with lupus nephritis (LuN) have not greatly changed since the 1980s. This review covers the application of new concepts to the understanding of renal inflammation and the study of new pharmacologic agents to improve patient outcomes.

RECENT FINDINGS

Studies have shown that the presence of anti-vimentin antibodies and T follicular helper cells in patient biopsies is associated with more severe interstitial inflammation, which has been tied to faster disease progression and onset of end-stage renal disease. Additionally, data regarding the role of serum IgE antidouble-stranded DNA antibodies in LuN by means of mediating IFN1 production by plasmacytoid dendritic cells are highlighted. Finally, a thorough review of completed and currently open clinical trials of therapeutic agents is provided.

SUMMARY

Current management of LuN is guided almost exclusively by glomerular involvement. Based on the data provided in this review, we argue that renal tubulointerstitial inflammation is no less important and represents an overlooked feature in the current clinical approach to patients. Tubulointerstitial inflammation is driven by both adaptive and innate immune mechanisms that are still poorly understood. Studying these pathogenic processes promises to reveal new therapeutic opportunities for those LuN patients with the worst prognosis.

VIDEO ABSTRACT

Alternate video abstract introduction (see Video, Supplemental Digital Content 1, with introduction by two of the authors - VL and KT). Abstract Video: http://links.lww.com/COR/A35.

Knockout of interleukin-17A protects against sepsis-associated acute kidney injury

Background

Sepsis-associated acute kidney injury (SA-AKI) is an independent risk factor for death in patients with sepsis, but treatment for it is limited. To improve the diagnosis and treatment of SA-AKI, we must first understand its pathogenesis. Recently, interleukin (IL)-17A has been shown to be associated with the pathogenesis of acute kidney injury and sepsis, but its role in SA-AKI remains unclear.

Methods

SA-AKI was induced in male C57BL/6 and IL-17A^−/− mice using cecal ligation and puncture (CLP) operations for 24 h.

Results

At 7 days, only seven mice survived in the wild-type septic group, but nine survived in the IL-17A^−/− septic group, corresponding to survival rates of 25 % and 45 %, respectively. At 24 h after CLP operations, both wild-type and IL-17A^−/− septic mice developed kidney injury. The IL-17A^−/− septic mice exhibited decreased serum creatinine and blood urea nitrogen levels and an improved acute tubular necrosis score. The IL-17A^−/− septic mice exhibited decreased IL-6, interferon-γ, tumor necrosis factor-α, CXCL1, CXCL2, and CXCL5 expression in kidney tissue, but increased IL-10 expression. In addition, renal neutrophil infiltration was attenuated significantly in the IL-17A^−/− septic group. Moreover, IL-17A^−/− septic mice showed significantly decreased apoptosis of tubular epithelial cells, including decreased TUNEL-positive tubular cell number and cleaved caspase-3 level, compared with the wild-type CLP group. Their Bax/Bcl-2 expression ratio was also increased.

Conclusions

Our study demonstrates that IL-17A knockout could protect against SA-AKI. We show that IL-17A plays a pathogenic role in SA-AKI by increasing the levels of proinflammatory cytokines and chemokines, and by inducing neutrophil infiltration and apoptosis of tubular epithelial cells. Accordingly, IL-17A may be a novel target in SA-AKI.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0157-1) contains supplementary material, which is available to authorized users.

CD103+ Kidney Dendritic Cells Protect against Crescentic GN by Maintaining IL-10-Producing Regulatory T Cells

Kidney dendritic cells (DCs) regulate nephritogenic T cell responses. Most kidney DCs belong to the CD11b⁺ subset and promote crescentic GN (cGN). The function of the CD103⁺ subset, which represents <5% of kidney DCs, is poorly understood. We studied the role of CD103⁺ DCs in cGN using several lines of genetically modified mice that allowed us to reduce the number of these cells. In all lines, we detected a reduction of FoxP3⁺ intrarenal regulatory T cells (T_regs), which protect against cGN. Mice lacking the transcription factor Batf3 had a more profound reduction of CD103⁺ DCs and T_regs than did the other lines used, and showed the most profound aggravation of cGN. The conditional reduction of CD103⁺ DC numbers by 50% in Langerin-DTR mice halved T_reg numbers, which did not suffice to significantly aggravate cGN. Mice lacking the cytokine Flt3L had fewer CD103⁺ DCs and T_regs than Langerin-DTR mice but exhibited milder cGN than did Batf3^-/- mice presumably because proinflammatory CD11b⁺ DCs were somewhat depleted as well. Conversely, Flt3L supplementation increased the number of CD103⁺ DCs and T_regs, but also of proinflammatory CD11b⁺ DCs. On antibody-mediated removal of CD11b⁺ DCs, Flt3L supplementation ameliorated cGN. Mechanistically, CD103⁺ DCs caused cocultured T cells to differentiate into T_regs and produced the chemokine CCL20, which is known to attract T_regs into the kidney. Our findings show that CD103⁺ DCs foster intrarenal FoxP3⁺ T_reg accumulation, thereby antagonizing proinflammatory CD11b⁺ DCs. Thus, increasing CD103⁺ DC numbers or functionality might be advantageous in cGN.

Lipopolysaccharide-induced inflammation or unilateral ureteral obstruction yielded multiple types of glycosylated Lipocalin 2

Background

The amount of urinary glycoprotein lipocalin 2 (LCN2) has been known to increase after kidney injury because of failed reabsorption by the proximal tubules or direct secretion from injured tissues. However, the relationship between urinary tract obstruction and the isoform diversity of LCN2 has not been examined.

Methods

The urinary levels of LCN2 isoforms were examined in male mice after an intraperitoneal injection of lipopolysaccharide (LPS) or in a mouse model of unilateral ureter obstruction (UUO). The LCN2 levels in sera, bladder urine, renal pelvic urine, and tissue samples were also analyzed. Endo- and exoglycosidases were used to investigate the different N-glycan patterns of LCN2.

Results

Two isoforms of urinary LCN2 with different molecular weights were identified in an immunoblotting analysis, and the levels of both isoforms were increased 6 h after LPS administration. The primary LCN2 isoform was the lower molecular weight 22-kDa isoform, which was detected in the serum, urine, liver and kidney. In contrast, the 24-kDa LCN2 isoform was detected only in urine. In the UUO experiments, the levels of the 24-kDa LCN2 were increased in the bladder urine but not in the urine accumulated in the renal pelvis due to UUO. The 22-kDa LCN2 was identified in the renal pelvic urine from UUO mice. The peptide-N glycosidase F digestion of the two urinary LCN2 isoforms generated a single protein. Moreover, the two urinary LCN2 proteins were sensitive to neuraminidase and resistant to endoglycosidase H (Endo H). The LCN2 in the serum, lung and kidney was resistant to Endo H, as observed in urine, whereas the LCN2 in the liver and the ureter were degraded by this enzyme.

Conclusions

These results suggest that the difference in the molecular weights of the LCN2 proteins was due to their N-glycan structure. The high molecular weight LCN2 in urine could be detected after the inflammatory response to LPS and UUO. Furthermore, the sensitivity to Endo H identified the presence of two types of carbohydrate moieties, depending on the tissue in which the LCN2 was produced. These findings are useful for widening the clinical applicability of urinary LCN2 analyses.

Chronically Elevated Levels of Short-Chain Fatty Acids Induce T Cell-Mediated Ureteritis and Hydronephrosis

Short-chain fatty acids (SCFAs) are major products of gut microbial fermentation and profoundly affect host health and disease. SCFAs generate IL-10(+) regulatory T cells, which may promote immune tolerance. However, SCFAs can also induce Th1 and Th17 cells upon immunological challenges and, therefore, also have the potential to induce inflammatory responses. Because of the seemingly paradoxical SCFA activities in regulating T cells, we investigated, in depth, the impact of elevated SCFA levels on T cells and tissue inflammation in mice. Orally administered SCFAs induced effector (Th1 and Th17) and regulatory T cells in ureter and kidney tissues, and they induced T cell-mediated ureteritis, leading to kidney hydronephrosis (hereafter called acetate-induced renal disease, or C2RD). Kidney hydronephrosis in C2RD was caused by ureteral obstruction, which was, in turn, induced by SCFA-induced inflammation in the ureteropelvic junction and proximal ureter. Oral administration of all major SCFAs, such as acetate, propionate, and butyrate, induced the disease. We found that C2RD development is dependent on mammalian target of rapamycin activation, T cell-derived inflammatory cytokines such as IFN-γ and IL-17, and gut microbiota. Young or male animals were more susceptible than old or female animals, respectively. However, SCFA receptor (GPR41 or GPR43) deficiency did not affect C2RD development. Thus, SCFAs, when systemically administered at levels higher than physiological levels, cause dysregulated T cell responses and tissue inflammation in the renal system. The results provide insights into the immunological and pathological effects of chronically elevated SCFAs.

The Changing Landscape of Renal Inflammation

Kidney inflammation is a major contributor to progressive renal injury, leading to glomerulonephritis (GN) and chronic kidney disease. We review recent advances in our understanding of leukocyte accumulation in the kidney, emphasizing key chemokines involved in GN. We discuss features of renal inflammation such as the evolving concept of immune cell plasticity. We also describe certain aspects of organ-specific tissue microenvironments in shaping immune cell responses, as well as the current knowledge of how regulatory T lymphocytes impact on other immune effector cell populations to control inflammation. It is clear that present and future research in these areas may contribute to the development of novel targeted therapeutics, with the hope of alleviating the burden of end-stage renal disease (ESRD).

NF-κB in inflammation and renal diseases

Nuclear factor κB (NF-κB) is a family of inducible transcription factors that plays a vital role in different aspects of immune responses. NF-κB is normally sequestered in the cytoplasm as inactive complexes via physical association with inhibitory proteins termed IκBs. In response to immune and stress stimuli, NF-κB members become activated via two major signaling pathways, the canonical and noncanonical pathways, and move to the nucleus to exert transcriptional functions. NF-κB is vital for normal immune responses against infections, but deregulated NF-κB activation is a major cause of inflammatory diseases. Accumulated studies suggest the involvement of NF-κB in the pathogenesis of renal inflammation caused by infection, injury, or autoimmune factors. In this review, we discuss the current understanding regarding the activation and function of NF-κB in different types of kidney diseases.

The Pathogenesis and Therapeutic Implications of Tubulointerstitial Inflammation in Human Lupus Nephritis

Nephritis is a common complication of systemic lupus erythematosus for which current therapies often prove inadequate. Current lupus nephritis classification systems emphasize glomerular acuity and scarring. However, tubulointerstitial inflammation (TII) and scarring are much better predictors of progression to renal failure. It now is becoming clear that the immunologic features, and probable underlying mechanisms, are very different in lupus glomerulonephritis and TII at the time of biopsy. Although glomerulonephritis is a manifestation of systemic autoimmunity, TII is associated with local in situ adaptive immune cell networks predicted to amplify local inflammation and tissue damage. In addition, poorly defined networks of innate immune cells and effectors likely contribute to the severity of local inflammation. Defining these in situ immune mechanisms should lead to a better understanding of prognostically meaningful lupus nephritis subsets and show novel therapeutic opportunities.

The Debate about Dendritic Cells and Macrophages in the Kidney

The mononuclear phagocyte system includes macrophages and dendritic cells (DCs), which are usually classified by morphology, phenotypical characteristics, and function. In the last decades, large research communities have gathered substantial knowledge on the roles of these cells in immune homeostasis and anti-infectious defense. However, these communities developed to a degree independent from each other, so that the nomenclature and functions of the numerous DC and macrophage subsets overlap, resulting in the present intense debate about the correct nomenclature. This controversy has also reached the field of experimental nephrology. At present, no mutually accepted way to distinguish renal DC and macrophages is available, so that many important roles in acute and chronic kidney disease have been ascribed to both DCs and macrophages. In this perspective article, we discuss the causes and consequences of the overlapping DC-macrophage classification systems, functional roles of DCs and macrophages, and the transferability of recent findings from other disciplines to the renal mononuclear phagocyte system from the nephrologist's point of view.

Double-Negative αβ T Cells Are Early Responders to AKI and Are Found in Human Kidney

Ischemia-reperfusion injury (IRI) is a major cause of AKI, and previous studies established important roles for conventional CD4(+) T cells, natural killer T cells, and CD4(+)CD25(+)FoxP3(+) Tregs in AKI pathogenesis. We recently identified CD4(-)CD8(-) (double-negative; DN) T cells as an important subset of αβ T cell receptor-positive cells residing in mouse kidney. However, little is known about the pathophysiologic functions of kidney DN T cells. In this study, we phenotypically and functionally characterized murine kidney DN T cells in the steady state and in response to IRI. Unlike CD4(+) and CD8(+) T cells, DN T cells in the steady state expressed high levels of CD69, CD28, and CD40L; differentially expressed IL-27 and IL-10 anti-inflammatory cytokines; spontaneously proliferated at a very high rate; and suppressed in vitro proliferation of activated CD4(+) T cells. Within the first 3-24 hours after IRI, kidney DN T cells expanded significantly and upregulated expression of IL-10. In adoptive transfer experiments, DN T cells significantly protected recipients from AKI by an IL-10-dependent mechanism. DN T cells also made up a large fraction of the T cell compartment in human kidneys. Our results indicate that DN T cells are an important subset of the resident αβ(+) T cell population in the mammalian kidney and are early responders to AKI that have anti-inflammatory properties.

T Lymphocyte-Specific Activation of Nrf2 Protects from AKI

T lymphocytes are established mediators of ischemia reperfusion (IR)-induced AKI, but traditional immune principles do not explain their mechanism of early action in the absence of alloantigen. Nrf2 is a transcription factor that is crucial for cytoprotective gene expression and is generally thought to have a key role in dampening IR-induced AKI through protective effects on epithelial cells. We proposed an alternative hypothesis that augmentation of Nrf2 in T cells is essential to mitigate oxidative stress during IR-induced AKI. We therefore generated mice with genetically amplified levels of Nrf2 specifically in T cells and examined the effect on antioxidant gene expression, T cell activation, cytokine production, and IR-induced AKI. T cell-specific augmentation of Nrf2 significantly increased baseline antioxidant gene expression. These mice had a high frequency of intrarenal CD25(+)Foxp3(+) regulatory T cells and decreased frequencies of CD11b(+)CD11c(+) and F4/80(+) cells. Intracellular levels of TNF-α, IFN-γ, and IL-17 were significantly lower in CD4(+) T cells with high Nrf2 expression. Mice with increased T cell expression of Nrf2 were significantly protected from functional and histologic consequences of AKI. Furthermore, adoptive transfer of high-Nrf2 T cells protected wild-type mice from IR injury and significantly improved their survival. These data demonstrate that T cell-specific activation of Nrf2 protects from IR-induced AKI, revealing a novel mechanism of tissue protection during acute injury responses.

The significance of macrophage polarization subtypes for animal models of tissue fibrosis and human fibrotic diseases

The systemic and organ-specific human fibrotic disorders collectively represent one of the most serious health problems world-wide causing a large proportion of the total world population mortality. The molecular pathways involved in their pathogenesis are complex and despite intensive investigations have not been fully elucidated. Whereas chronic inflammatory cell infiltration is universally present in fibrotic lesions, the central role of monocytes and macrophages as regulators of inflammation and fibrosis has only recently become apparent. However, the precise mechanisms involved in the contribution of monocytes/macrophages to the initiation, establishment, or progression of the fibrotic process remain largely unknown. Several monocyte and macrophage subpopulations have been identified, with certain phenotypes promoting inflammation whereas others display profibrotic effects. Given the unmet need for effective treatments for fibroproliferative diseases and the crucial regulatory role of monocyte/macrophage subpopulations in fibrogenesis, the development of therapeutic strategies that target specific monocyte/macrophage subpopulations has become increasingly attractive. We will provide here an overview of the current understanding of the role of monocyte/macrophage phenotype subpopulations in animal models of tissue fibrosis and in various systemic and organ-specific human fibrotic diseases. Furthermore, we will discuss recent approaches to the design of effective anti-fibrotic therapeutic interventions by targeting the phenotypic differences identified between the various monocyte and macrophage subpopulations.

Mesenchymal stem cells and a vitamin D receptor agonist additively suppress T helper 17 cells and the related inflammatory response in the kidney

Mesenchymal stem cells (MSCs) suppress T helper (Th)17 cell differentiation and are being clinically pursued for conditions associated with aberrant Th17 responses. Whether such immunomodulatory effects are enhanced by coadministration of MSCs with other agents is not well known. In the present study, individual and combined effects of MSCs and the vitamin D receptor (VDR) agonist paricalcitol on Th17 induction were investigated in vitro and in a mouse model of sterile kidney inflammation (unilateral ureteral obstruction). In vitro, MSCs and paricalcitol additively suppressed Th17 differentiation, although only MSCs suppressed expression of Th17-associated transcriptions factors. Combined administration of MSCs and paricalcitol resulted in an early ( day 3) reduction of intrarenal CD4+ and CD8+ T cells, CD11b+/lymphocyte antigen 6G+ neutrophils, and inflammatory (lymphocyte antigen 6Chi) monocytes as well as reduced transcript for IL-17 compared with untreated animals. Later ( day 8), obstructed kidneys of MSC/paricalcitol double-treated mice, but not mice treated with either intervention alone, had reduced tubular injury and interstitial fibrosis as well as lower numbers of neutrophils and inflammatory monocytes and an increase in the ratio between M2 (CD206+) and M1 (CD206−) macrophages compared with control mice. Adjunctive therapy with VDR agonists may enhance the immunosuppressive properties of MSCs in the setting of pathogenic Th17-type immune responses and related inflammatory responses.

Macrophage depletion ameliorates glycerol-induced acute kidney injury in mice

BACKGROUND

This study was conducted to elucidate the role of renal macrophages in the development of acute kidney injury (AKI) in a glycerol (Gly)-induced rhabdomyolysis mouse model.

METHODS

The experimental model of rhabdomyolysis requires injecting 50% Gly (10 ml/kg) intramuscularly into mice. Control mice were injected into the tail vein with the liposomal vehicle. Liposome-encapsulated clodronate (LEC)-only mice were injected with LEC. Gly-only mice were injected with Gly into a hind limb. LEC+Gly-treated mice were injected intravenously with 100 μl of LEC 24 h prior to Gly injection. Mice were sacrificed 24 h after Gly injection.

RESULTS

Gly injection increased the serum creatinine level, and induced tubular damage. Renal CD45(+)CD11b(+)Ly6c(+) or CD45(+)CD11b(+)Ly6c(+)F4/80(+) macrophages were decreased by pretreatment with LEC in both normal and injured kidneys. Macrophage depletion prevented Gly-induced apoptotic death of tubular epithelial cells by decreasing caspase-9, ERK and p53, while increasing Bcl-2 expression. Expression of the inflammatory mediators NF-κB, MCP-1, ICAM-1, iNOS and COX-2 were also decreased with LEC pretreatment of mice injected with Gly.

CONCLUSION

These results support the hypothesis that depletion of macrophages prevents renal dysfunction by abrogating apoptosis and attenuating inflammation during AKI.

Dendritic cells and macrophages in the kidney: a spectrum of good and evil

Renal dendritic cells (DCs) and macrophages represent a constitutive, extensive and contiguous network of innate immune cells that provide sentinel and immune-intelligence activity; they induce and regulate inflammatory responses to freely filtered antigenic material and protect the kidney from infection. Tissue-resident or infiltrating DCs and macrophages are key factors in the initiation and propagation of renal disease, as well as essential contributors to subsequent tissue regeneration, regardless of the aetiological and pathogenetic mechanisms. The identification, and functional and phenotypic distinction of these cell types is complex and incompletely understood, and the same is true of their interplay and relationships with effector and regulatory cells of the adaptive immune system. In this Review, we discuss the common and distinct characteristics of DCs and macrophages, as well as key advances that have identified the renal-specific functions of these important phagocytic, antigen-presenting cells, and their roles in potentiating or mitigating intrinsic kidney disease. We also identify remaining issues that are of priority for further investigation, and highlight the prospects for translational and therapeutic application of the knowledge acquired.

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.

CXCL5 drives neutrophil recruitment in TH17-mediated GN

Neutrophil trafficking to sites of inflammation is essential for the defense against bacterial and fungal infections, but also contributes to tissue damage in TH17-mediated autoimmunity. This process is regulated by chemokines, which often show an overlapping expression pattern and function in pathogen- and autoimmune-induced inflammatory reactions. Using a murine model of crescentic GN, we show that the pathogenic TH17/IL-17 immune response induces chemokine (C-X-C motif) ligand 5 (CXCL5) expression in kidney tubular cells, which recruits destructive neutrophils that contribute to renal tissue injury. By contrast, CXCL5 was dispensable for neutrophil recruitment and effective bacterial clearance in a murine model of acute bacterial pyelonephritis. In line with these findings, CXCL5 expression was highly upregulated in the kidneys of patients with ANCA-associated crescentic GN as opposed to patients with acute bacterial pyelonephritis. Our data therefore identify CXCL5 as a potential therapeutic target for the restriction of pathogenic neutrophil infiltration in TH17-mediated autoimmune diseases while leaving intact the neutrophil function in protective immunity against invading pathogens.

Guidance cue netrin-1 and the regulation of inflammation in acute and chronic kidney disease

Acute kidney injury (AKI) is a common problem in the hospital setting and intensive care unit. Despite improved understanding, there are no effective therapies available to treat AKI. A large body of evidence strongly suggests that ischemia reperfusion injury is an inflammatory disease mediated by both adaptive and innate immune systems. Cell migration also plays an important role in embryonic development and inflammation, and this process is highly regulated to ensure tissue homeostasis. One such paradigm exists in the developing nervous system, where neuronal migration is mediated by a balance between chemoattractive and chemorepulsive signals. The ability of the guidance molecule netrin-1 to repulse or abolish attraction of neuronal cells expressing the UNC5B receptor makes it an attractive candidate for the regulation of inflammatory cell migration. Recent identification of netrin-1 as regulators of immune cell migration has led to a large number of studies looking into how netrin-1 controls inflammation and inflammatory cell migration. This review will focus on recent advances in understanding netrin-1 mediated regulation of inflammation during acute and chronic kidney disease and whether netrin-1 and its receptor activation can be used to treat acute and chronic kidney disease.

Immune Components of Liver Damage Associated with Connective Tissue Diseases

Autoimmune connective tissue diseases are associated with liver abnormalities and often have overlapping pathological and clinical manifestations. As a result, they can present great clinical challenges and evoke questions about diagnostic criteria for liver diseases. Moreover, discriminating between liver involvement as a manifestation of connective tissue disease and primary liver disease can be challenging since they share a similar immunological mechanism. Most patients with connective tissue diseases exhibit liver test abnormalities that likely result from coexisting, primary liver diseases, such as fatty liver disease, viral hepatitis, primary biliary cirrhosis, autoimmune hepatitis, and drug-related liver toxicity. Liver damage can be progressive, leading to cirrhosis, complications of portal hypertension, and liver-related death, and, therefore, must be accurately identified. In this review, we highlight the challenges facing the diagnosis of liver damage associated with connective tissue disease and identify immune mechanisms involved in liver damage associated with connective tissue diseases.

Exclusive CX3CR1 dependence of kidney DCs impacts glomerulonephritis progression

DCs and macrophages both express the chemokine receptor CX3CR1. Here we demonstrate that its ligand, CX3CL1, is highly expressed in the murine kidney and intestine. CX3CR1 deficiency markedly reduced DC numbers in the healthy and inflamed kidney cortex, and to a lesser degree in the kidney medulla and intestine, but not in other organs. CX3CR1 also promoted influx of DC precursors in crescentic glomerulonephritis, a DC-dependent aggressive type of nephritis. Disease severity was strongly attenuated in CX3CR1-deficient mice. Primarily CX3CR1-dependent DCs in the kidney cortex processed antigen for the intrarenal stimulation of T helper cells, a function important for glomerulonephritis progression. In contrast, medullary DCs played a specialized role in inducing innate immunity against bacterial pyelonephritis by recruiting neutrophils through rapid chemokine production. CX3CR1 deficiency had little effect on the immune defense against pyelonephritis, as medullary DCs were less CX3CR1 dependent than cortical DCs and because recruited neutrophils produced chemokines to compensate for the DC paucity. These findings demonstrate that cortical and medullary DCs play specialized roles in their respective kidney compartments. We identify CX3CR1 as a potential therapeutic target in glomerulonephritis that may involve fewer adverse side effects, such as impaired anti-infectious defense or compromised DC functions in other organs.

Pivotal roles of T-helper 17-related cytokines, IL-17, IL-22, and IL-23, in inflammatory diseases

T-helper 17 (Th17) cells are characterized by producing interleukin-17 (IL-17, also called IL-17A), IL-17F, IL-21, and IL-22 and potentially TNF- α and IL-6 upon certain stimulation. IL-23, which promotes Th17 cell development, as well as IL-17 and IL-22 produced by the Th17 cells plays essential roles in various inflammatory diseases, such as experimental autoimmune encephalomyelitis, rheumatoid arthritis, colitis, and Concanavalin A-induced hepatitis. In this review, we summarize the characteristics of the functional role of Th17 cells, with particular focus on the Th17 cell-related cytokines such as IL-17, IL-22, and IL-23, in mouse models and human inflammatory diseases.

Mononuclear phagocyte depletion strategies in models of acute kidney disease: what are they trying to tell us?

Mononuclear phagocytes (macrophages, dendritic cells, and monocytes) play a complex role in kidney disease. Techniques for selectively depleting them in rodents have made important contributions but have also generated some contradictory results. Ferenbach et al. report that two widely used mononuclear phagocyte depletion techniques differentially affect early severity of renal ischemia/reperfusion injury and provide evidence that this may be due to a residual, protective subset that persists in the kidney after one of the two techniques.

The C-terminal module IV of connective tissue growth factor is a novel immune modulator of the Th17 response

Connective tissue growth factor (CTGF/CCN2) is a matricellular protein susceptible to proteolytic degradation. CCN2 levels have been suggested as a potential risk biomarker in several chronic diseases. In body fluids, CCN2 full-length and its degradation fragments can be found; however, their in vivo effects are far from being elucidated. CCN2 was described as a profibrotic mediator, but this concept is changing to a proinflammatory cytokine. In vitro, CCN2 full-length and its C-terminal module IV (CCN2(IV)) exert proinflammatory properties. Emerging evidence suggest that Th17 cells, and its effector cytokine IL-17A, participate in chronic inflammatory diseases. Our aim was to explore whether CCN2(IV) could regulate the Th17 response. In vitro, stimulation of human naive CD4+ T lymphocytes with CCN2(IV) resulted in differentiation to Th17 phenotype. The in vivo effects of CCN2(IV) were studied in C57BL/6 mice. Intraperitoneal administration of recombinant CCN2(IV) did not change serum IL-17A levels, but caused an activation of the Th17 response in the kidney, characterized by interstitial infiltration of Th17 (IL17A+/CD4+) cells and upregulation of proinflammatory mediators. In CCN2(IV)-injected mice, elevated renal levels of Th17-related factors (IL-17A, IL-6, STAT3 and RORγt) were found, whereas Th1/Th2 cytokines or Treg-related factors (TGF-β and Foxp-3) were not modified. Treatment with an anti-IL-17A neutralizing antibody diminished CCN2(IV)-induced renal inflammation. Our findings unveil that the C-terminal module of CCN2 induces the Th17 differentiation of human Th17 cells and causes a renal Th17 inflammatory response. Furthermore, these data bear out that IL-17A targeting is a promising tool for chronic inflammatory diseases, including renal pathologies.

Epithelial cell TGFβ signaling induces acute tubular injury and interstitial inflammation

TGFβ signaling plays a central role in the development of acute and chronic kidney diseases. Previous in vivo studies involved systemic alteration of TGFβ signaling, however, limiting conclusions about the direct role of TGFβ in tubular cell injury. Here, we generated a double transgenic mouse that inducibly expresses a ligand-independent constitutively active TGFβ receptor type 1 (TβR1) kinase specifically in tubular epithelial cells, with expression restricted by the Pax8 promoter. In this model, activation of TGFβ signaling in the tubular epithelium alone was sufficient to cause AKI characterized by marked tubular cell apoptosis and necrosis, oxidative stress, dedifferentiation and regenerative cell proliferation, reduced renal function, and interstitial accumulation of inflammatory cells. This tubular injury was associated with mitochondrial-derived generation of reactive oxygen species (ROS), but cell damage and apoptosis were partially independent of mitochondrial-derived ROS. TβR1 signaling-induced tubular injury also associated with significant leukocyte infiltration consisting of F4/80(+) macrophages, CD11c(+) F4/80(+) dendritic cells, CD11c(+) F4/80(-) Ly6C(high) dendritic cells/monocytes, and T cells. Inhibition of mitochondrial-derived ROS significantly reduced accumulation of CD11c(+) F4/80(+) dendritic cells and T cells, suggesting a role for ROS in the activation and recruitment of the adaptive immune response to tubular injury. Taken together, these results suggest that TGFβ signaling in the tubular epithelium alone is sufficient to cause acute tubular injury and inflammation; therefore, TGFβ may be a mechanistic link between acute injury and chronic progression of kidney disease.

Isolation of functional dendritic cells from murine kidneys for immunological characterization

AIM

The kidney is a complex organ, requiring the contributions of multiple cell types to perform its various functions. Within this system the dendritic cell has been demonstrated to play a key role in maintaining the immunological balance of the kidney. In this methods paper we aim to identify the best method for isolating murine renal dendritic cells.

METHODS

The efficiency of isolating dendritic cells from enzymatically digested renal parenchyma by density centrifugation, MACS and FACS was compared.

RESULTS

Density centrifugation enriched dendritic cells by only approximately two fold. However, MACS and FACS resulted in a much higher purity (80% versus 95% respectively).

CONCLUSIONS

Although FACS gave the highest purity, MACS is the optimal method for isolating dendritic cells given cost and time factors. Isolation of a homogeneous population of renal dendritic cells will enable the molecular and functional dissection of these cells in both homeostasis and disease models.

IL-17A production by renal γδ T cells promotes kidney injury in crescentic GN

The Th17 immune response appears to contribute to the pathogenesis of human and experimental crescentic GN, but the cell types that produce IL-17A in the kidney, the mechanisms involved in its induction, and the IL-17A-mediated effector functions that promote renal tissue injury are incompletely understood. Here, using a murine model of crescentic GN, we found that CD4(+) T cells, γδ T cells, and a population of CD3(+)CD4(-)CD8(-)γδT cell receptor(-)NK1.1(-) T cells all produce IL-17A in the kidney. A time course analysis identified γδ T cells as a major source of IL-17A in the early phase of disease, before the first CD4(+) Th17 cells arrived. The production of IL-17A by renal γδ T cells depended on IL-23p19 signaling and retinoic acid-related orphan receptor-γt but not on IL-1β or IL-6. In addition, depletion of dendritic cells, which produce IL-23 in the kidney, reduced IL-17A production by renal γδ T cells. Furthermore, the lack of IL-17A production in γδ T cells, as well as the absence of all γδ T cells, reduced neutrophil recruitment into the kidney and ameliorated renal injury. Taken together, these data suggest that γδ T cells produce IL-17A in the kidney, induced by IL-23, promoting neutrophil recruitment, and contributing to the immunopathogenesis of crescentic GN.

Dendritic cells: novel players in fibrosis and scleroderma

Dendritic cells are professional antigen-presenting cells that are most studied for their function in mediating T-cell tolerance and T-cell activation. In addition, recent evidence indicates that dendritic cells can regulate the vasculature and function of fibroblast-type cells. The potential contribution of dendritic cells to scleroderma and fibrosis is not well-understood. In this article, we review recent studies as well as describe our own ongoing work that points toward a role for dendritic cells in scleroderma and fibrosis.

Chemokines play a critical role in the cross-regulation of Th1 and Th17 immune responses in murine crescentic glomerulonephritis

Th1 and Th17 subtype effector CD4(+) T cells are thought to play a critical role in the pathogenesis of human and experimental crescentic glomerulonephritis. The time course, mechanism, and functions of Th1 and Th17 cell recruitment, and their potential interaction in glomerulonephritis, however, remain to be elucidated. We performed interventional studies using IL-17- and IFN-γ-gene-deficient mice, as well as neutralizing antibodies that demonstrated the importance of the Th17-mediated immune response during the early phase of the disease. At a later stage, we found that Th1 cells were critical mediators of renal tissue injury. Early recruitment of IL-17-producing Th17 cells triggered expression of the chemokine CXCL9 in the kidney that drove the infiltration of Th1 cells bearing its receptor CXCR3. At a later stage, Th1 cell-derived IFN-γ was found to inhibit local chemokine CCL20 expression, acting through its receptor CCR6 on Th17 cells, thereby limiting the renal Th17 immune response. Thus, our findings provide mechanistic evidence for a cytokine-chemokine-driven feedback loop that orchestrates the observed differential Th1 and Th17 cell infiltration into the inflamed kidney. This contributes to the observed time-dependent function of these two major pathogenic effector CD4(+) T cell subsets in crescentic glomerulonephritis.