Regulatory T cells suppress innate immunity in kidney ischemia-reperfusion injury

Glucocorticoid-Induced Leucine Zipper Promotes Neutrophil and T-Cell Polarization with Protective Effects in Acute Kidney Injury

The glucocorticoid-induced leucine zipper (GILZ) mediates anti-inflammatory effects of glucocorticoids. Acute kidney injury (AKI) mobilizes immune/inflammatory mechanisms, causing tissue injury, but the impact of GILZ in AKI is not known. Neutrophils play context-specific proinflammatory [type 1 neutrophil (N1)] and anti-inflammatory [type 2 neutrophil (N2)] functional roles. Also, regulatory T lymphocytes (Tregs) and regulatory T-17 (Treg17) cells exert counterinflammatory effects, including the suppression of effector T lymphocytes [e.g., T-helper (Th) 17 cells]. Thus, utilizing cell preparations of mice kidneys subjected to AKI or sham operation, we determined the effects of GILZ on T cells and neutrophil subtypes in the context of its renoprotective effect; these studies used the transactivator of transcription (TAT)-GILZ or the TAT peptide. AKI increased N1 and Th-17 cells but reduced N2, Tregs, and Treg17 cells in association with increased interleukin (IL)-17⁺ but reduced IL-10⁺ cells accompanied with the disruption of mitochondrial membrane potential (ψ _m) and increased apoptosis/necrosis compared with sham kidneys. TAT-GILZ, compared with TAT, treatment reduced N1 and Th-17 cells but increased N2 and Tregs, without affecting Treg17 cells, in association with a reduction in IL-17⁺ cells but an increase in IL-10⁺ cells; TAT-GILZ caused less disruption of ψ _m and reduced cell death in AKI. Importantly, TAT-GILZ increased perfusion of the ischemic-reperfused kidney but reduced tissue edema compared with TAT. Utilizing splenic T cells and bone marrow-derived neutrophils, we further showed marked reduction in the proliferation of Th cells in response to TAT-GILZ compared with response to TAT. Collectively, the results indicate that GILZ exerts renoprotection accompanied by the upregulation of the regulatory/suppressive arm of immunity in AKI, likely via regulating cross talk between T cells and neutrophils.

A review of the role of immune cells in acute kidney injury

Acute kidney injury (AKI) is a systemic disease occurring commonly in patients who are critically ill. Etiologies of AKI can be septic or aseptic (nephrotoxic, or ischemia-reperfusion injury). Recent evidence reveals that innate and adaptive immune responses are involved in mediating damage to renal tubular cells and in recovery from AKI. Dendritic cells, monocytes/macrophages, neutrophils, T lymphocytes, and B lymphocytes all contribute to kidney injury. Conversely, M2 macrophages and regulatory T cells are essential in suppressing inflammation, tissue remodeling and repair following kidney injury. AKI itself confers an increased risk for developing infection owing to increased production and decreased clearance of cytokines, in addition to dysfunction of immune cells themselves. Neutrophils are the predominant cell type rendered dysfunctional by AKI. In this review, we describe the bi-directional interplay between the immune system and AKI and summarize recent developments in this field of research.

Immune mechanisms in the different phases of acute tubular necrosis

Acute kidney injury is a clinical syndrome that can be caused by numerous diseases including acute tubular necrosis (ATN). ATN evolves in several phases, all of which are accompanied by different immune mechanisms as an integral component of the disease process. In the early injury phase, regulated necrosis, damage-associated molecular patterns, danger sensing, and neutrophil-driven sterile inflammation enhance each other and contribute to the crescendo of necroinflammation and tissue injury. In the late injury phase, renal dysfunction becomes clinically apparent, and M1 macrophage-driven sterile inflammation contributes to ongoing necroinflammation and renal dysfunction. In the recovery phase, M2-macrophages and anti-inflammatory mediators counteract the inflammatory process, and compensatory remnant nephron and cell hypertrophy promote an early functional recovery of renal function, while some tubules are still badly injured and necrotic material is removed by phagocytes. The resolution of inflammation is required to promote the intrinsic regenerative capacity of tubules to replace at least some of the necrotic cells. Several immune mechanisms support this wound-healing-like re-epithelialization process. Similar to wound healing, this response is associated with mesenchymal healing, with a profound immune cell contribution in terms of collagen production and secretion of profibrotic mediators. These and numerous other factors determine whether, in the chronic phase, persistent loss of nephrons and hyperfunction of remnant nephrons will result in stable renal function or progress to decline of renal function such as progressive chronic kidney disease.

Neutrophil-lymphocyte ratio is associated with all-cause mortality among critically ill patients with acute kidney injury

BACKGROUND

Inflammation plays a critical role in the development of acute kidney injury (AKI). Neutrophil-lymphocyte ratio (NLR) is a biomarker of systemic inflammation used to predict the prognostic outcome of several diseases. We conducted a retrospective cohort study to investigate if NLR can be used as a biomarker to predict the mortality of AKI.

METHODS AND RESULTS

Records of critically ill patients with AKI were extracted from the Medical Information Mart for Intensive Care Database III version 1.3 (MIMIC-III v1.3). The primary outcome was 30-day mortality and the two secondary outcomes were in hospital and 90-day mortality. We used the Cox proportional hazards models to assess the association between different categories of NLR and outcomes. This analysis included data for 13,678 eligible subjects, with a total of 2,588 30-day, 2,224 in-hospital and 3,545 90-day deaths during the follow-up period. For 30-day mortality, an increased risk of mortality was associated with a higher level of NLR. The HR (95% confidence interval [CI]) of upper tertile (NLR > 12.14) was 1.37 (1.17-1.60) in a multivariate model when compared with that of the lower tertile (NLR < 5.55). In the quintile analysis, we confirmed the upward trend with HR (95% CI) of the fifth quintile (NLR > 17.4) of 1.35 (1.08, 1.69) in a multivariate model compared to the first quintile (NLR < 3.82). A similar tendency was observed for 90-day mortality. In the analysis of in-hospital mortality, the HR of fifth quintile (NLR > 17.4) showed a slight decrease.

CONCLUSIONS

Our analysis indicates that a higher level of NLR is associated with increased risk of 30-day and 90-day mortality in AKI patients. The similar upward trend is not detected in analysis of in-hospital mortality.

ETA receptor activation contributes to T cell accumulation in the kidney following ischemia-reperfusion injury

Renal ischemia-reperfusion (IR) injury and acute kidney injury (AKI) increase the risk of developing hypertension, with T cells suspected as a possible mechanistic link. Endothelin promotes renal T cell infiltration in several diseases, predominantly via the ETA receptor, but its contribution to renal T cell infiltration following renal IR injury is poorly understood. To test whether ETA receptor activation promotes T cell infiltration of the kidney following IR injury, male C57BL/6 mice were treated with the ETA receptor antagonist ABT-627 or vehicle, commencing 2 days prior to unilateral renal IR injury. Mice were sacrificed at 24 h or 10 days post-IR for assessment of the initial renal injury and subsequent infiltration of T cells. Vehicle and ABT-627-treated mice displayed significant upregulation of endothelin-1 (ET-1) in the IR compared to contralateral kidney at both 24 h and 10 days post-IR (P < 0.001). Renal CD3+ T cell numbers were increased in the IR compared to contralateral kidneys at 10 days, but ABT-627-treated mice displayed a 35% reduction in this effect in the outer medulla (P < 0.05 vs. vehicle) and a nonsignificant 23% reduction in the cortex compared to vehicle-treated mice. Whether specific T cell subsets were affected awaits confirmation by flow cytometry, but outer medullary expression of the T helper 17 transcription factor RORγt was reduced by ABT-627 (P = 0.06). These data indicate that ET-1 acting via the ETA receptor contributes to renal T cell infiltration post-IR injury. This may have important implications for immune system-mediated long-term consequences of AKI, an area which awaits further investigation.

CCL20 blockade increases the severity of nephrotoxic folic acid-induced acute kidney injury

The chemokine CCL20 activates the CCR6 receptor and has been implicated in the pathogenesis of glomerular injury. However, it is unknown whether it contributes to acute kidney injury (AKI). We identified CCL20 as upregulated in a systems biology strategy combining transcriptomics of kidney tissue from experimental toxic folic acid-induced AKI and from stressed cultured tubular cells and have explored the expression and function of CCL20 in experimental and clinical AKI. CCL20 upregulation was confirmed in three models of kidney injury induced by a folic acid overdose, cisplatin or unilateral ureteral obstruction. In injured kidneys, CCL20 was expressed by tubular, endothelial, and interstitial cells, and was also upregulated in human kidneys with AKI. Urinary CCL20 was increased in human AKI and was associated with severity. The function of CCL20 in nephrotoxic folic acid-induced AKI was assessed by using neutralising anti-CCL20 antibodies or CCR6-deficient mice. CCL20/CCR6 targeting increased the severity of kidney failure and mortality. This was associated with more severe histological injury, nephrocalcinosis, capillary rarefaction, and fibrosis, as well as higher expression of tubular injury-associated genes. Surprisingly, mice with CCL20 blockade had a lower tubular proliferative response and a higher number of cells in the G2/M phase, suggesting impaired repair mechanisms. This may be related to a lower influx of Tregs, despite a milder inflammatory response in terms of chemokine expression and infiltration by IL-17⁺ cells and neutrophils. In conclusion, CCL20 has a nephroprotective role during AKI, both by decreasing tissue injury and by facilitating repair. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Defective Treg response in acute kidney injury was caused by a reduction in TIM-3+ Treg cells

BACKGROUND

Despite years of research, the treatment of acute kidney injury (AKI) remains a significant challenge. Animal studies presented causal links between elevated regulatory T cell (Treg) response and better prognosis in AKI. Previous studies in mice and humans showed that TIM-3+ Treg cells were more potent than TIM-3- Treg cells. In this study, we investigated the role of TIM-3 in Treg in AKI patients.

METHODS

Peripheral blood from AKI patients and healthy controls were gathered, and TIM-3+ Treg subset was examined.

RESULTS

Compared to healthy controls, the AKI patients presented a significant upregulation in the frequency of circulating CD4+CD25+ T cells; however, the majority of this increase was from the CD4+CD25+TIM-3- subset, and the frequency of CD4+CD25+TIM-3+ T cells was downregulated in AKI patients. In both healthy controls and AKI patients, the CD4+CD25+TIM-3+ T cells expressed higher levels of Foxp3, and were more potent at expressing LFA-1, LAG-3, CTLA-4, IL-10 and TGF-β. In addition, the CD4+CD25+TIM-3+ T cells from both healthy controls and AKI patients presented higher capacity to suppress CD4+CD25- T cell proliferation than the CD4+CD25+TIM-3- T cells. Interestingly, the total CD4+CD25+ T cells from AKI patients presented significantly lower inhibitory capacity than those from healthy controls, indicating that the low frequency of CD4+CD25+TIM-3+ T cells was restricting the efficacy of the Treg responses in AKI patients.

CONCLUSIONS

We demonstrated that TIM-3 downregulation impaired the function of Treg cells in AKI. The therapeutic potential of CD4+CD25+TIM-3+ T cells in AKI should be investigated in future studies.

CD39-adenosinergic axis in renal pathophysiology and therapeutics

Extracellular ATP interacts with purinergic type 2 (P2) receptors and elicits many crucial biological functions. Extracellular ATP is sequentially hydrolyzed to ADP and AMP by the actions of defined nucleotidases, such as CD39, and AMP is converted to adenosine, largely by CD73, an ecto-5'-nucleotidase. Extracellular adenosine interacts with P1 receptors and often opposes the effects of P2 receptor activation. The balance between extracellular ATP and adenosine in the blood and extracellular fluid is regulated chiefly by the activities of CD39 and CD73, which constitute the CD39-adenosinergic axis. In recent years, several studies have shown this axis to play critical roles in transport of water/sodium, tubuloglomerular feedback, renin secretion, ischemia reperfusion injury, renal fibrosis, hypertension, diabetic nephropathy, transplantation, inflammation, and macrophage transformation. Important developments include global and targeted gene knockout and/or transgenic mouse models of CD39 or CD73, biological or small molecule inhibitors, and soluble engineered ectonucleotidases to directly impact the CD39-adenosinergic axis. This review presents a comprehensive picture of the multiple roles of CD39-adenosinergic axis in renal physiology, pathophysiology, and therapeutics. Scientific advances and greater understanding of the role of this axis in the kidney, in both health and illness, will direct development of innovative therapies for renal diseases.

Preliminary Report on the Association Between STAT3 Polymorphisms and Susceptibility to Acute Kidney Injury After Cardiopulmonary Bypass

Cardiopulmonary bypass-associated acute kidney injury (CPB-AKI) is a well-recognized complication which is clearly linked to increased morbidity and mortality. Due to important role of inflammation in CPB-AKI pathogenesis, we explored the association between polymorphisms in STAT3, an inflammation-associated transcription factor, and the risk of CPB-AKI. In this study, STAT3 rs1053004 and rs744166 polymorphisms were analyzed in 129 patients undergoing coronary artery bypass grafting in Jorjani heart center, Bandar Abbas, Iran. The genotypes were determined using sequence-specific primers (PCR-SSP). Sixty-three patients met the criteria for AKI after cardiac surgery (AKI group). The remaining 66 patients did not develop AKI (non-AKI group). Rs1053004 GG genotype was significantly associated with a decreased risk (OR 0.4, 95% CI 0.17-0.9, P = 0.03) of CPB-AKI. Subgroup analyses revealed that GG genotype has also a protective effect in older patients (Age ≥ 60) (OR 0.19, 95% CI 0.04-0.8, P = 0.01). However, rs744166 did not show any difference between AKI and non-AKI groups. The result of our study for the first time provides evidence that rs1053004 polymorphism is significantly associated with a decreased risk of CPB-AKI in Iranian population, especially in older subjects.

T cells and their immunometabolism: A novel way to understanding sepsis immunopathogenesis and future therapeutics

Sepsis has always been considered as a big challenge for pharmaceutical companies in terms of discovering and designing new therapeutics. The pathogenesis of sepsis involves aberrant activation of innate immune cells (i.e. macrophages, neutrophils etc.) at early stages. However, a stage of immunosuppression is also observed during sepsis even in the patients who have recovered from it. This stage of immunosuppression is observed due to the loss of conventional (i.e. CD4⁺, CD8⁺) T cells, Th17 cells and an upregulation of regulatory T cells (Tregs). This process also impacts metabolic processes controlling immune cell metabolism called immunometabolism. The present review is focused on the T cell-mediated immune response, their immunometabolism and targeting T cell immunometabolism during sepsis as future therapeutic approach. The first part of the manuscripts describes an impact of sepsis on conventional T cells, Th17 cells and Tregs along with their impact on sepsis. The subsequent section further describes the immunometabolism of these cells (CD4⁺, CD8⁺, Th17, and Tregs) under normal conditions and during sepsis-induced immunosuppression. The article ends with the therapeutic targeting of T cell immunometabolism (both conventional T cells and Tregs) during sepsis as a future immunomodulatory approach for its management.

Antigen-specific Helios- , Neuropilin-1- Tregs induce apoptosis of autoreactive B cells via PD-L1

Regulatory T cells (Tregs) maintain self-tolerance and prevent autoimmunity by controlling autoreactive T cells. We recently demonstrated in vivo that Tregs can directly suppress auto-reactive B cells via programmed death ligand 1 (PD-L1) that ligated PD-1 on B cells and caused them to undergo apoptosis. Here, we asked whether this mechanism is utilized by thymus-derived natural Tregs and/or by peripheral lymphoid tissue-induced Tregs. We first demonstrated that antigen-specific PD-L1-expressing Tregs were induced in the draining lymph node of autoantigen-expressing tissue and characterized them by their lack of the transcription factor Helios and of the surface marker Neuropilin-1 (Nrp-1). Next, we established an in vitro co-culture system to study the interaction between B cells and Treg subsets under controlled conditions. We found that Nrp^- Treg, but not Nrp⁺ Treg suppressed autoreactive B cells, whereas both were able to suppress T-helper cells. Such suppression was antigen-specific and was facilitated by PD-L1/PD-1-induced apoptosis. Furthermore, it required physical cell contact and was MHC II-restricted, providing an explanation for the antigen-specificity of peripherally-induced Tregs. These findings identify a role for peripherally induced Helios^- Nrp-1^- inducible Treg in controlling peripheral B-cell tolerance against tissue auto-antigens.

Regulatory T cells in acute and chronic kidney diseases

Foxp3-expressing CD4+ regulatory T cells (Tregs) make up one subset of the helper T cells (Th) and are one of the major mechanisms of peripheral tolerance. Tregs prevent abnormal activation of the immune system throughout the lifespan, thus protecting from autoimmune and inflammatory diseases. Recent studies have elucidated the role of Tregs beyond autoimmunity. Tregs play important functions in controlling not only innate and adaptive immune cell activation, but also regulate nonimmune cell function during insults and injury. Inflammation contributes to a multitude of acute and chronic diseases affecting the kidneys. This review examines the role of Tregs in pathogenesis of renal inflammatory diseases and explores the approaches for enhancing Tregs for prevention and therapy of renal inflammation.

The Costimulatory Pathways and T Regulatory Cells in Ischemia-Reperfusion Injury: A Strong Arm in the Inflammatory Response?

Costimulatory molecules have been identified as crucial regulators in the inflammatory response in various immunologic disease models. These molecules are classified into four different families depending on their structure. Here, we will focus on various ischemia studies that use costimulatory molecules as a target to reduce the inherent inflammatory status. Furthermore, we will discuss the relevant role of T regulatory cells in these inflammatory mechanisms and the costimulatory pathways in which they are involved.

CD4+ and CD8+ T Cells Exert Regulatory Properties During Experimental Acute Aristolochic Acid Nephropathy

Experimental aristolochic acid nephropathy is characterized by transient acute proximal tubule necrosis and inflammatory cell infiltrates followed by interstitial fibrosis and tubular atrophy. The respective role of T-cell subpopulations has never been studied in the acute phase of the mouse model, and was heretofore exclusively investigated by the use of several depletion protocols. As compared to mice injected with aristolochic acids alone, more severe acute kidney injury was observed after CD4⁺ or CD8⁺ T-cells depletion. TNF-alpha and MCP-1 mRNA renal expressions were also increased. In contrast, regulatory T-cells depletion did not modify the severity of the aristolochic acids induced acute kidney injury, suggesting an independent mechanism. Aristolochic acids nephropathy was also associated with an increased proportion of myeloid CD11b^highF4/80^mid and a decreased proportion of their counterpart CD11b^lowF4/80^high population. After CD4⁺ T-cell depletion the increase in the CD11b^highF4/80^mid population was even higher whereas the decrease in the CD11b^lowF4/80^high population was more marked after CD8+ T cells depletion. Our results suggest that CD4⁺ and CD8⁺ T-cells provide protection against AA-induced acute tubular necrosis. Interestingly, T-cell depletion was associated with an imbalance of the CD11b^highF4/80^mid and CD11b^lowF4/80^high populations.

Regulatory T-Cells: Potential Regulator of Tissue Repair and Regeneration

The identification of stem cells and growth factors as well as the development of biomaterials hold great promise for regenerative medicine applications. However, the therapeutic efficacy of regenerative therapies can be greatly influenced by the host immune system, which plays a pivotal role during tissue repair and regeneration. Therefore, understanding how the immune system modulates tissue healing is critical to design efficient regenerative strategies. While the innate immune system is well known to be involved in the tissue healing process, the adaptive immune system has recently emerged as a key player. T-cells, in particular, regulatory T-cells (Treg), have been shown to promote repair and regeneration of various organ systems. In this review, we discuss the mechanisms by which Treg participate in the repair and regeneration of skeletal and heart muscle, skin, lung, bone, and the central nervous system.

Parabiosis reveals leukocyte dynamics in the kidney

The immune cellular compartment of the kidney is involved in organ development and homeostasis, as well as in many pathological conditions. Little is known about the mechanisms that drive intrarenal immune responses in the presence of renal tubular and interstitial cell death. However, it is known that tissue-resident leukocytes have the potential to have distinct roles compared with circulating cells. We used a parabiosis model in C57BL/6 CD45 congenic and green fluorescent protein transgenic mice to better understand the dynamics of immune cells in the kidney. We found F4/80^Hi intrarenal macrophages exhibit minimal exchange with the peripheral circulation in two models of parabiosis, whether mice were attached for 4 or 16 weeks. Other intrarenal inflammatory cells demonstrate near total exchange with the circulating immune cell pool in healthy kidneys, indicating that innate and adaptive immune cells extensively traffic through the kidney interstitium during normal physiology. Neutrophils, dendritic cells, F4/80^Low macrophages, T cells, B cells, and NK cells are renewed from the circulating immune cell pool. However, a fraction of double-negative T (CD4^- CD8^-) and NKT cells are long-lived or tissue resident. This study provides direct evidence of leukocyte sub-populations that are resident in the renal tissue, cells which demonstrate minimal to no exchange with the peripheral blood. In addition, the data demonstrate continual exchange of other sub-populations through uninflamed tissue.

Role of Calcium Sensing Receptor in Streptozotocin-Induced Diabetic Rats Exposed to Renal Ischemia Reperfusion Injury

BACKGROUND/AIMS

Renal ischemia/reperfusion (I/R) injury (RI/RI) is a common complication of diabetes, and it may be involved in altering intracellular calcium concentrations at its onset, which can result in inflammation, abnormal lipid metabolism, the production of reactive oxygen species (ROS), and nitroso-redox imbalance. The calcium-sensing receptor (CaSR) is a G-protein coupled receptor, however, the functional involvement of CaSR in diabetic RI/ RI remains unclear. The present study was intended to investigate the role of CaSR on RI/RI in diabetes mellitus (DM).

METHODS

The bilateral renal arteries and veins of streptozotocin (STZ)-induced diabetic rats were subjected to 45-min ischemia followed by 2-h reperfusion with or without R-568 (agonist of CaSR) and NPS-2143 (antagonist of CaSR) at the beginning of I/R procedure. DM without renal I/R rats served as control group. The expressions of CaSR, calmodulin (CaM), and p47phox in the renal tissue were analyzed by qRT-PCR and Western blot. The renal pathomorphology, renal function, oxidative stress, inflammatory response, and calcium disorder were evaluated by detection of a series of indices by hematoxylin-eosin (HE) staining, transmission electron microscope (TEM), commercial kits, enzyme-linked immunosorbent assay (ELISA), and spectrophotofluorometry, respectively.

RESULTS

Results showed that the expressions of CaSR, CaM, and p47phox in I/R group were significantly up-regulated as compared with those in DM group, which were accompanied by renal tissue injury, increased calcium, oxidative stress, inflammation, and nitroso-redox imbalance.

CONCLUSION

These results suggest that activation of CaSR is involved in the induction of damage of renal tubular epithelial cell during diabetic RI/RI, resulting in lipid peroxidation, inflammatory response, nitroso-redox imbalance, and apoptosis.

Ischemia-Reperfusion Injury Reduces Long Term Renal Graft Survival: Mechanism and Beyond

Ischemia-reperfusion injury (IRI) during renal transplantation often initiates non-specific inflammatory responses that can result in the loss of kidney graft viability. However, the long-term consequence of IRI on renal grafts survival is uncertain. Here we review clinical evidence and laboratory studies, and elucidate the association between early IRI and later graft loss. Our critical analysis of previous publications indicates that early IRI does contribute to later graft loss through reduction of renal functional mass, graft vascular injury, and chronic hypoxia, as well as subsequent fibrosis. IRI is also known to induce kidney allograft dysfunction and acute rejection, reducing graft survival. Therefore, attempts have been made to substitute traditional preserving solutions with novel agents, yielding promising results.

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Ischaemia reperfusion injury (IRI) potentiates delayed renal graft function and causes reduction in renal graft survival

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IRI causes innate immune system activation, hypoxic injury, inflammation and graft vascular disease

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Reducing prolonged cold ischaemic time improves graft survival

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Novel protective strategies include mesenchymal stem cells, machine perfusion, and ex vivo preservation solution saturated with gas.

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Further studies are needed to investigate the long-term effects of novel ex vivo preservation agents

Regulatory T cells in renal disease

The kidney is vulnerable to injury, both acute and chronic from a variety of immune and metabolic insults, all of which at least to some degree involve inflammation. Regulatory T cells modulate systemic autoimmune and allogenic responses in glomerulonephritis and transplantation. Intrarenal regulatory T cells (Tregs), including those recruited to the kidney, have suppressive effects on both adaptive and innate immune cells, and probably also intrinsic kidney cells. Evidence from autoimmune glomerulonephritis implicates antigen-specific Tregs in HLA-mediated dominant protection, while in several human renal diseases Tregs are abnormal in number or phenotype. Experimentally, Tregs can protect the kidney from injury in a variety of renal diseases. Mechanisms of Treg recruitment to the kidney include via the chemokine receptors CCR6 and CXCR3 and potentially, at least in innate injury TLR9. The effects of Tregs may be context dependent, with evidence for roles for immunoregulatory roles both for endogenous Tbet-expressing Tregs and STAT-3-expressing Tregs in experimental glomerulonephritis. Most experimental work and some of the ongoing human trials in renal transplantation have focussed on unfractionated thymically derived Tregs (tTregs). However, induced Tregs (iTregs), type 1 regulatory T (Tr1) cells and in particular antigen-specific Tregs also have therapeutic potential not only in renal transplantation, but also in other kidney diseases.

Cellular and molecular pathways of renal repair after acute kidney injury

The acutely injured mammalian kidney mounts a cellular and molecular response to repair itself. However, in patchy regions such intrinsic processes are impaired and dysregulated leading to chronic kidney disease. Currently, no therapy exists to treat established acute kidney injury per se. Strategies to augment human endogenous repair processes and retard associated profibrotic responses are urgently required. Recent studies have identified injury-induced activation of the intrinsic molecular driver of epithelial regeneration and induction of partial epithelial to the mesenchymal state, respectively. Activation of key developmental transcription factors drive such processes; however, whether these recruit comparable gene regulatory networks with target genes similar to those in nephrogenesis is unclear. Extensive complex molecular cross-talk between the nephron epithelia and immune, interstitial, and endothelial cells regulate renal recovery. In vitro-based M1/M2 macrophage subtypes have been increasingly linked to renal repair; however, the precise contribution of in vivo macrophage plasticity to repair responses is poorly understood. Endothelial cell-pericyte intimacy, balance of the angiocrine/antiangiocrine system, and endothelial cell-regulated inflammatory processes have an impact on renal recovery and fibrosis. Close scrutiny of cellular and molecular pathways in repairing human kidneys is imperative for the identification of promising therapeutic targets and biomarker of human renal repair processes.

Clinical Applications of Regulatory T cells in Adoptive Cell Therapies

Interest in adoptive T-cell therapies has been ignited by the recent clinical success of genetically-modified T cells in the cancer immunotherapy space. In addition to immune targeting for malignancies, this approach is now being explored for the establishment of immune tolerance with regulatory T cells (Tregs). Herein, we will summarize the basic science and clinical results emanating from trials directed at inducing durable immune regulation through administration of Tregs. We will discuss some of the current challenges facing the field in terms of maximizing cell purity, stability and expansion capacity, while also achieving feasibility and GMP production. Indeed, recent advances in methodologies for Treg isolation, expansion, and optimal source materials represent important strides toward these considerations. Finally, we will review the emerging genetic and biomaterial-based approaches on the horizon for directing Treg specificity to augment tissue-targeting and regenerative medicine.

Role of immune cells in crystal-induced kidney fibrosis

Chronic kidney diseases can lead to kidney fibrosis, which can be considered a futile attempt of tissue healing to replaces functional kidney tissue with connective tissue, basically forming a scar. Chronic inflammation is a frequent cause of kidney fibrosis. Classical as well as recently discovered immune cell subsets and their molecular mediators have been intensively investigated for their contribution to kidney fibrosis and their potential as therapeutic targets. Here we review the current knowledge about the role of immune cells in crystal-induced renal fibrosis.

Redirecting TGF-β Signaling through the β-Catenin/Foxo Complex Prevents Kidney Fibrosis

TGF-β is a key profibrotic factor, but targeting TGF-β to prevent fibrosis also abolishes its protective anti-inflammatory effects. Here, we investigated the hypothesis that we can redirect TGF-β signaling by preventing downstream profibrotic interaction of β-catenin with T cell factor (TCF), thereby enhancing the interaction of β-catenin with Foxo, a transcription factor that controls differentiation of TGF-β induced regulatory T cells (iTregs), and thus, enhance anti-inflammatory effects of TGF-β In iTregs derived from EL4 T cells treated with recombinant human TGF-β1 (rhTGF-β1) in vitro, inhibition of β-catenin/TCF transcription with ICG-001 increased Foxp3 expression, interaction of β-catenin and Foxo1, binding of Foxo1 to the Foxp3 promoter, and Foxo transcriptional activity. Moreover, the level of β-catenin expression positively correlated with the level of Foxo1 binding to the Foxp3 promoter and Foxo transcriptional activity. T cell fate mapping in Foxp3^gfp Ly5.1/5.2 mice revealed that coadministration of rhTGF-β1 and ICG-001 further enhanced the expansion of iTregs and natural Tregs observed with rhTGF-β1 treatment alone. Coadministration of rhTGF-β1 with ICG-001 also increased the number of Tregs and reduced inflammation and fibrosis in the kidney fibrosis models of unilateral ureteric obstruction and ischemia-reperfusion injury. Notably, ICG-001 prevented the fibrosis in distant organs (lung and liver) caused by rhTGF-β1. Together, our results show that diversion of β-catenin from TCF- to Foxo-mediated transcription inhibits the β-catenin/TCF-mediated profibrotic effects of TGF-β while enhancing the β-catenin/Foxo-mediated anti-inflammatory effects. Targeting β-catenin/Foxo may be a novel therapeutic strategy in the treatment of fibrotic diseases that lead to organ failure.

IL-17A improves the efficacy of mesenchymal stem cells in ischemic-reperfusion renal injury by increasing Treg percentages by the COX-2/PGE2 pathway

Mesenchymal stem cells (MSCs) are effective for the management of experimental ischemia-reperfusion acute kidney injury (IRI-AKI). Immune modulation is one of the important mechanisms of MSCs treatment. Interleukin-17A (IL-17A) pretreated MSCs are more immunosuppressive with minimal changes in immunogenicity in vitro. Here, we demonstrated that administration of IL-17A-pretreated MSCs resulted in significantly lower acute tubular necrosis scores, serum creatinine, and BUN of mice with IRI-AKI, compared with the administration of MSCs. Of the co-cultured splenocytes, IL-17A-pretreated MSCs significantly increased the percentages of CD4⁺Foxp3⁺ Tregs and decreased concanavalin A-induced T cell proliferation. Furthermore, mice with IRI-AKI that underwent IL-17A-pretreated MSC therapy had significantly lower serum IL-6, TNF-α, and IFN-γ levels, a higher serum IL-10 level, and higher spleen and kidney Treg percentages than the mice that underwent MSCs treatment. Additionally, the depletion of Tregs by PC61 (anti-CD25 antibody) reversed the enhanced treatment efficacy of the IL-17A-pretreatedMSCs on mice with IRI-AKI. Additionally, IL-17A upregulated COX-2 expression and increased PGE2 production. The blockage of COX-2 by celecoxib reversed the benefit of IL-pretreated 17A-MSCs on the serum PGE2 concentration, spleen and kidney Tregs percentages, serum creatinine and BUN levels, renal acute tubular necrosis scores, and serum IL-6, TNF-α, IFN-γ, and IL-10 levels of IRI-pretreated mice with AKI, compared with MSCs. Thus, our results suggest that IL-17A pretreatment enhances the efficacy of MSCs on mice with IRI-AKI by increasing the Treg percentages through the COX-2/PGE2 pathway.

Sex and gender differences in hypertensive kidney injury

Hypertension is a complex, multifaceted disorder, affecting ~1 in 3 adults in the United States. Although hypertension occurs in both men and women, there are distinct sex differences in the way in which they develop hypertension, with women having a lower incidence of hypertension until the sixth decade of life. Despite observed sex differences in hypertension, little is known about the molecular mechanisms underlying the development of hypertension in females, primarily because of their underrepresentation in both clinical and experimental animal studies. The first goal of this review is to provide a concise overview of the participation of women in clinical trials, including a discussion of the importance of including females in basic science research, as recently mandated by the National Institutes of Health. The remaining portion of the review is dedicated to identifying clinical and experimental animal studies that concentrate on gender and sex differences in hypertensive kidney disease, ending with a proposed role for T cells in mediating sex differences in blood pressure.

Macrophages in Renal Injury and Repair

Acute kidney injury (AKI) is a growing global health concern, yet no treatment is currently available to prevent it or to promote kidney repair after injury. Animal models demonstrate that the macrophage is a major contributor to the inflammatory response to AKI. Emerging data from human biopsies also corroborate the presence of macrophages in AKI and their persistence in progressive chronic kidney disease. Macrophages are phagocytic innate immune cells that are important mediators of tissue homeostasis and host defense. In response to tissue injury, macrophages become activated based on specific signals from the damaged microenvironment. The activation and functional state of the macrophage depends on the stage of tissue injury and repair, reflecting a dynamic and diverse spectrum of macrophage phenotypes. In this review, we highlight our current understanding of the mechanisms by which macrophages contribute to injury and repair after AKI.

Pathophysiology of AKI

Acute kidney injury (AKI) is common in the perioperative and intensive care setting. Although AKI is usually multifactorial, haemodynamic instability, sepsis and drug toxicity are commonly implicated. Independent of the exact aetiology, several different pathophysiologic processes occur simultaneously and in sequence, including endothelial dysfunction, alteration of the microcirculation, tubular injury, venous congestion and intrarenal inflammation. A multitude of different immune cells from within the kidney and the systemic circulation play a role in the development, maintenance and recovery phase of AKI. In this review, we describe the common processes involved in AKI and their connections, with particular emphasis on the perioperative and critical care setting.

YB-1 orchestrates onset and resolution of renal inflammation via IL10 gene regulation

The Y‐box‐binding protein (YB)‐1 plays a non‐redundant role in both systemic and local inflammatory response. We analysed YB‐1‐mediated expression of the immune regulatory cytokine IL‐10 in both LPS and sterile inflammation induced by unilateral renal ischaemia–reperfusion (I/R) and found an important role of YB‐1 not only in the onset but also in the resolution of inflammation in kidneys. Within a decisive cis‐regulatory region of the IL10 gene locus, the fourth intron, we identified and characterized an operative YB‐1 binding site via gel shift experiments and reporter assays in immune and different renal cells. In vivo, YB‐1 phosphorylated at serine 102 localized to the fourth intron, which was paralleled by enhanced IL‐10 mRNA expression in mice following LPS challenge and in I/R. Mice with half‐maximal expression of YB‐1 (Yb1^+/−) had diminished IL‐10 expression upon LPS challenge. In I/R, Yb1^+/− mice exhibited ameliorated kidney injury/inflammation in the early‐phase (days 1 and 5), however showed aggravated long‐term damage (day 21) with increased expression of IL‐10 and other known mediators of renal injury and inflammation.

In conclusion, these data support the notion that there are context‐specific decisions concerning YB‐1 function and that a fine‐tuning of YB‐1, for example, via a post‐translational modification regulates its activity and/or localization that is crucial for systemic processes such as inflammation.

IL233, A Novel IL-2 and IL-33 Hybrid Cytokine, Ameliorates Renal Injury

CD4⁺Foxp3⁺ regulatory T cells (Tregs) protect the kidney during AKI. We previously found that IL-2, which is critical for Treg homeostasis, upregulates the IL-33 receptor (ST2) on CD4⁺ T cells, thus we hypothesized that IL-2 and IL-33 cooperate to enhance Treg function. We found that a major subset of Tregs in mice express ST2, and coinjection of IL-2 and IL-33 increased the number of Tregs in lymphoid organs and protected mice from ischemia-reperfusion injury (IRI) more efficiently than either cytokine alone. Accordingly, we generated a novel hybrid cytokine (IL233) bearing the activities of IL-2 and IL-33 for efficient targeting to Tregs. IL233 treatment increased the number of Tregs in blood and spleen and prevented IRI more efficiently than a mixture of IL-2 and IL-33. Injection of IL233 also increased the numbers of Tregs in renal compartments. Moreover, IL233-treated mice had fewer splenic Tregs and more Tregs in kidneys after IRI. In vitro, splenic Tregs from IL233-treated mice suppressed CD4⁺ T cell proliferation better than Tregs from saline-treated controls. IL233 treatment also improved the ability of isolated Tregs to inhibit IRI in adoptive transfer experiments and protected mice from cisplatin- and doxorubicin-induced nephrotoxic injury. Finally, treatment with IL233 increased the proportion of ST2-bearing innate lymphoid cells (ILC2) in blood and kidneys, and adoptive transfer of ILC2 also protected mice from IRI. Thus, the novel IL233 hybrid cytokine, which utilizes the cooperation of IL-2 and IL-33 to enhance Treg- and ILC2-mediated protection from AKI, bears strong therapeutic potential.

Exacerbation of spontaneous autoimmune nephritis following regulatory T cell depletion in B cell lymphoma 2-interacting mediator knock-out mice

Regulatory T cells (Tregs ) have been recognized as central mediators for maintaining peripheral tolerance and limiting autoimmune diseases. The loss of Tregs or their function has been associated with exacerbation of autoimmune disease. However, the temporary loss of Tregs in the chronic spontaneous disease model has not been investigated. In this study, we evaluated the role of Tregs in a novel chronic spontaneous glomerulonephritis model of B cell lymphoma 2-interacting mediator (Bim) knock-out mice by transient depleting Tregs . Bim is a pro-apoptotic member of the B cell lymphoma 2 (Bcl-2) family. Bim knock-out (Bim-/- ) mice fail to delete autoreactive T cells in thymus, leading to chronic spontaneous autoimmune kidney disease. We found that Treg depletion in Bim-/- mice exacerbated the kidney injury with increased proteinuria, impaired kidney function, weight loss and greater histological injury compared with wild-type mice. There was a significant increase in interstitial infiltrate of inflammatory cells, antibody deposition and tubular damage. Furthermore, the serum levels of cytokines interleukin (IL)-2, IL-4, IL-6, IL-10, IL-17α, interferon (IFN)-γ and tumour necrosis factor (TNF)-α were increased significantly after Treg depletion in Bim-/- mice. This study demonstrates that transient depletion of Tregs leads to enhanced self-reactive T effector cell function followed by exacerbation of kidney disease in the chronic spontaneous kidney disease model of Bim-deficient mice.

Early, but not late, treatment with human umbilical cord blood-derived mesenchymal stem cells attenuates cisplatin nephrotoxicity through immunomodulation

Preemptive treatment with mesenchymal stem cells (MSCs) can attenuate cisplatin-induced acute kidney injury (AKI). However, it is uncertain whether MSC treatment after the development of renal dysfunction prevents AKI progression or if MSC immunomodulatory properties contribute to MSC therapy. In this study, human umbilical cord blood (hUCB)-derived MSCs were used to compare the effects and mechanisms of early and late MSC therapy in a murine model. After cisplatin injection into C57BL/6 mice, hUCB-MSCs were administered on day 1 (early treatment) or day 3 (late treatment). With early treatment, cisplatin nephrotoxicity was attenuated as evidenced by decreased blood urea nitrogen (BUN) and reduced apoptosis and tubular injury scores on day 3 Early treatment resulted in downregulation of intrarenal monocyte chemotactic protein-1 and IL-6 expression and upregulation of IL-10 and VEGF expression. Flow cytometric analysis showed similar populations of infiltrated immune cells in both groups; however, regulatory T-cell (Treg) infiltration was 2.5-fold higher in the early treatment group. The role of Tregs was confirmed by the blunted effect of early treatment on renal injury after Treg depletion. In contrast, late treatment (at a time when BUN levels were 2-fold higher than baseline levels) showed no renoprotective effects on day 6 Neither the populations of intrarenal infiltrating immune cells (including Tregs) nor cytokine expression levels were affected by late treatment. Our results suggest that early MSC treatment attenuates renal injury by Treg induction and immunomodulation, whereas a late treatment (i.e., after the development of renal dysfunction) does not prevent AKI progression or alter the intrarenal inflammatory micromilieu.

Superagonistic CD28 Protects against Renal Ischemic Injury by Expansion of Regulatory T-Cell

BACKGROUND

Regulatory T (Treg) cells are a highly suppressive subset of CD4+ lymphocytes and have recently been proved to be crucial to suppress the inflammatory responses of ischemic kidney injury. CD28 superagonists (CD28sa) are monoclonal antibodies that preferentially expand Treg cells without a T-cell receptor and a costimulatory signal. This study aims to test the protection and discover the mechanisms of CD28sa treatment against renal ischemia-reperfusion (IR) injury (IRI).

METHODS

Male C57BL/6N mice were treated with CD28sa via peritoneal injection (0.1 mg) 6 days before the induction of IRI, or with 18-min ischemic precondition (IPC). IRI was induced by bilateral clamping of renal pedicles for 35 min followed by reperfusion. The role of Treg expansion in renal protection conferred by CD28sa treatment was examined using anti-CD25 antibody.

RESULTS

CD28sa treatment alone significantly increased the percentage of Treg cells in the spleen (18.10 ± 2.00 vs. 6.64 ± 0.86%, p < 0.01), peripheral blood (16.43 ± 5.94 vs. 2.57 ± 1.09%, p < 0.01), and kidney (2.69 ± 0.90 vs. 0.53 ± 0.14%, p < 0.01) of C57BL/6N mice 6 days after the administration. Mice pretreated with CD28sa or IPC had less renal injury at 24 h after IRI with attenuation of renal tubular damage and lower serum creatinine compared with the mice that underwent renal IRI alone. The number of infiltrating macrophages in the kidney and IFN-γ secreting CD4+ T cells in peripheral blood were diminished in the CD28sa-IR group and the IPC-IR group. The renal protection bestowed by CD28sa or IPC was abolished by anti-CD25 antibody administration.

CONCLUSIONS

Treg expansion induced by CD28sa ameliorated renal IRI.

Kidney and innate immunity

Innate immune system is an important modulator of the inflammatory response during infection and tissue injury/repair. The kidney as a vital organ with high energy demand plays a key role in regulating the disease related metabolic process. Increasing research interest has focused on the immune pathogenesis of many kidney diseases. However, innate immune cells such as dendritic cells, macrophages, NK cells and a few innate lymphocytes, as well as the complement system are essential for renal immune homeostasis and ensure a coordinated balance between tissue injury and regeneration. The innate immune response provides the first line of host defense initiated by several classes of pattern recognition receptors (PRRs), such as membrane-bound Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs), together with inflammasomes responsible for early innate immune response. Although the innate immune system is well studied, the research on the detailed relationship between innate immunity and kidney is still very limited. In this review, we will focus on the innate immune sensing system in renal immune homeostasis, as well as the corresponding pathogenesis of many kidney diseases. The pivotal roles of innate immunity in renal injury and regeneration with special emphasis on kidney disease related immunoregulatory mechanism are also discussed.

Mononuclear phagocyte subpopulations in the mouse kidney

Mononuclear phagocytes are the most common cells in the kidney associated with immunity and inflammation. Although the presence of these cells in the kidney has been known for decades, the study of mononuclear phagocytes in the context of kidney function and dysfunction is still at an early stage. The purpose of this review is to summarize the present knowledge regarding classification of these cells in the mouse kidney and to identify relevant questions that would further advance the field and potentially lead to new opportunities for treatment of acute kidney injury and other kidney diseases.

Targeting Inflammation in So-Called Acute Kidney Injury

The clinical category of acute kidney injury includes a wide range of completely different disorders, many with their own pathomechanisms and treatment targets. In this review we focus on the role of inflammation in the pathogenesis of acute tubular necrosis (ATN). We approach this topic by first discussing the role of the immune system in the different phases of ATN (ie, early and late injury phase, recovery phase, and the long-term outcome phase of an ATN episode). A more detailed discussion focuses on putative therapeutic targets among the following mechanisms and mediators: oxidative stress and reactive oxygen species-related necroinflammation, regulated cell death-related necroinflammation, immunoregulatory lipid mediators, cytokines and cytokine signaling, chemokines and chemokine signaling, neutrophils and neutrophils extracellular traps (NETs) associated neutrophil cell death, called NETosis, extracellular histones, proinflammatory mononuclear phagocytes, humoral mediators such as complement, pentraxins, and natural antibodies. Any prioritization of these targets has to take into account the intrinsic differences between rodent models and human ATN, the current acute kidney injury definitions, and the timing of clinical decision making. Several conceptual problems need to be solved before anti-inflammatory drugs that are efficacious in rodent ATN may become useful therapeutics for human ATN.

Prophylactic orthosteric inhibition of leukocyte integrin CD11b/CD18 prevents long-term fibrotic kidney failure in cynomolgus monkeys

Ischaemic acute kidney injury (AKI), an inflammatory disease process, often progresses to chronic kidney disease (CKD), with no available effective prophylaxis. This is in part due to lack of clinically relevant CKD models in non-human primates. Here we demonstrate that inhibition of the archetypal innate immune receptor CD11b/CD18 prevents progression of AKI to CKD in cynomolgus monkeys. Severe ischaemia-reperfusion injury of the right kidney, with subsequent periods of the left ureter ligation, causes irreversible right kidney failure 3, 6 or 9 months after AKI. Moreover, prophylactic inactivation of CD11b/CD18, using the orthosteric CD11b/CD18 inhibitor mAb107, improves microvascular perfusion and histopathology, reduces intrarenal pro-inflammatory mediators and salvages kidney function long term. These studies reveal an important early role of CD11b⁺ leukocytes in post-ischaemic kidney fibrosis and failure, and suggest a potential early therapeutic intervention to mitigate progression of ischaemic AKI to CKD in humans.

Relationship Between Different Subpopulations of Circulating CD4+ T-lymphocytes and Microvascular Structural Alterations in Humans

BACKGROUND

Different components of the immune system, including innate and adaptive immunity (T-effector lymphocytes and T-regulatory lymphocytes-TREGs) may be involved in the development of hypertension. In addition, it was demonstrated in animal models that TREGs may prevent angiotensin II-induced hypertension and vascular injury/inflammation. However, no data are presently available in humans about possible relationships between T-lymphocyte subtypes and microvascular structural alterations.

METHODS

For this purpose, in the present study, we enrolled 24 normotensive subjects and 12 hypertensive patients undergoing an elective surgical intervention. No sign of local or systemic inflammation was present. All patients underwent a biopsy of subcutaneous fat during surgery. Subcutaneous small resistance arteries were dissected and mounted on a wire myograph and the media to lumen ratio (M/L) was calculated. In addition, retinal arteriolar structure was evaluated noninvasively by scanning laser Doppler flowmetry. Capillary density in the nailfold, dorsum of the finger, and forearm were evaluated by videomicroscopy. A peripheral blood sample was obtained before surgery for assessment of T-lymphocyte subpopulations by flow cytometry.

RESULTS

Significant negative correlations were observed between indices of microvascular structure (M/L of subcutaneous small arteries and wall to lumen ratio of retinal arterioles) and circulating TREG lymphocytes. A direct correlation was observed between M/L of subcutaneous small arteries and circulating Th17 lymphocytes. In addition, total capillary density was correlated with a TREG effector memory subpopulation.

CONCLUSION

Our data suggest that some lymphocyte subpopulations may be related to microvascular remodeling, confirming previous animal data, and opening therapeutic possibilities.

Role of Natural IgM Autoantibodies (IgM-NAA) and IgM Anti-Leukocyte Antibodies (IgM-ALA) in Regulating Inflammation

Natural IgM autoantibodies (IgM-NAA) are rapidly produced to inhibit pathogens and abrogate inflammation mediated by invading microorganisms and host neoantigens. IgM-NAA achieve this difficult task by being polyreactive with low binding affinity but with high avidity, characteristics that allow these antibodies to bind antigenic determinants shared by pathogens and neoantigens. Hence the same clones of natural IgM can bind and mask host neoantigens as well as inhibit microorganisms. In addition, IgM-NAA regulate the inflammatory response via mechanisms involving binding of IgM to apoptotic cells to enhance their removal and binding of IgM to live leukocytes to regulate their function. Secondly, we review how natural IgM prevents autoimmune disorders arising from pathogenic IgG autoantibodies as well as by autoreactive B and T cells that have escaped tolerance mechanisms. Thirdly, using IgM knockout mice, we show that regulatory B and T cells require IgM to effectively regulate inflammation mediated by innate, adaptive and autoimmune mechanisms. It is therefore not surprising why the host positively selects such autoreactive B1 cells that generate protective IgM-NAA, which are also evolutionarily conserved. Fourthly, we show that IgM anti-leukocyte autoantibodies (IgM-ALA) levels and their repertoire can vary in normal humans and disease states and this variation may partly explain the observed differences in the inflammatory response after infection, ischemic injury or after a transplant. Finally we also show how protective IgM-NAA can be rendered pathogenic under non-physiological conditions. IgM-NAA have therapeutic potential. Polyclonal IgM infusions can be used to abrogate ongoing inflammation. Additionally, inflammation arising after ischemic kidney injury, e.g., during high-risk elective cardiac surgery or after allograft transplantation, can be prevented by pre-emptively infusing polyclonal IgM, or DC pretreated ex vivo with IgM, or by increasing in vivo IgM with a vaccine approach. Cell therapy with IgM pretreated cells, is appealing as less IgM will be required.

Regulatory T cells in immune-mediated renal disease

Regulatory T cells (Tregs) are CD4+ T cells that can suppress immune responses by effector T cells, B cells and innate immune cells. This review discusses the role that Tregs play in murine models of immune-mediated renal diseases and acute kidney injury and in human autoimmune kidney disease (such as systemic lupus erythematosus, anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody-associated vasculitis). Current research suggests that Tregs may be reduced in number and/or have impaired regulatory function in these diseases. Tregs possess several mechanisms by which they can limit renal and systemic inflammatory immune responses. Potential therapeutic applications involving Tregs include in vivo induction of Tregs or inducing Tregs from naïve CD4+ T cells or expanding natural Tregs ex vivo, to use as a cellular therapy. At present, the optimal method of generating a phenotypically stable pool of Tregs with long-lasting suppressive effects is not established, but human studies in renal transplantation are underway exploring the therapeutic potential of Tregs as a cellular therapy, and if successful may have a role as a novel therapy in immune-mediated renal diseases.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Rescue therapy with Tanshinone IIA hinders transition of acute kidney injury to chronic kidney disease via targeting GSK3β

Acute kidney injury (AKI) remains challenging for clinical practice and poses a risk of developing progressive chronic kidney disease (CKD) with no definitive treatment available yet. Tanshinone IIA, an active ingredient of Chinese herbal Salvia miltiorrhiza, has been widely used in Asia for the remarkable organoprotective activities. Its effect on established AKI, however, remains unknown. In mice with folic acid-induced AKI, delayed treatment with Tanshinone IIA, commenced early or late after injury, diminished renal expression of kidney injury markers, reduced apoptosis and improved kidney dysfunction, concomitant with mitigated histologic signs of AKI to CKD transition, including interstitial fibrosis and tubular atrophy, and with an ameliorated inflammatory infiltration in tubulointerstitium and a favored M2-skewed macrophage polarization. Mechanistically, Tanshinone IIA blunted glycogen synthase kinase (GSK)3β overactivity and hyperactivation of its downstream mitogen-activated protein kinases that are centrally implicated in renal fibrogenesis and inflammation. Inhibition of GSK3β is likely a key mechanism mediating the therapeutic activity of Tanshinone IIA, because sodium nitroprusside, a GSK3β activator, largely offset its renoprotective effect. In confirmatory studies, rescue treatment with Tanshinone IIA likewise ameliorated ischemia/reperfusion-induced kidney destruction in mice. Our data suggest that Tanshinone IIA represents a valuable treatment that improves post-AKI kidney salvage via targeting GSK3β.

IL-17 mediates neutrophil infiltration and renal fibrosis following recovery from ischemia reperfusion: compensatory role of natural killer cells in athymic rats

T cells have been implicated in the pathogenesis of acute kidney injury (AKI) and its progression to chronic kidney disease (CKD). Previous studies suggest that Th17 cells participate during the AKI-to-CKD transition, and inhibition of T cell activity by mycophenolate mofetil (MMF) or losartan attenuates the development of fibrosis following AKI. We hypothesized that T cell-deficient rats may have reduced levels of IL-17 cytokine leading to decreased fibrosis following AKI. Renal ischemis-reperfusion (I/R) was performed on T cell-deficient athymic rats (Foxn1^rnu-/rnu-) and control euthymic rats (Foxn1^rnu-/+), and CKD progression was hastened by unilateral nephrectomy at day 33 and subsequent exposure to 4.0% sodium diet. Renal fibrosis developed in euthymic rats and was reduced by MMF treatment. Athymic rats exhibited a similar degree of fibrosis, but this was unaffected by MMF treatment. FACS analysis demonstrated that the number of IL-17⁺ cells was similar between postischemic athymic vs. euthymic rats. The source of IL-17 production in euthymic rats was predominately from conventional T cells (CD3⁺/CD161^-). In the absence of conventional T cells in athymic rats, a compensatory pathway involving natural killer cells (CD3^-/CD161⁺) was the primary source of IL-17. Blockade of IL-17 activity using IL-17Rc receptor significantly decreased fibrosis and neutrophil recruitment in both euthymic and athymic rats compared with vehicle-treated controls. Taken together, these data suggest that IL-17 secretion participates in the pathogenesis of AKI-induced fibrosis possibly via the recruitment of neutrophils and that the source of IL-17 may be from either conventional T cells or NK cells.

Ischemia as a factor affecting innate immune responses in kidney transplantation

PURPOSE OF REVIEW

Ischemic injury inevitably occurs during the procurement of organs for transplantation, and the injury is worsened by inflammation following reperfusion. The purpose of this review is to describe the role of the innate immune system in ischemia-induced renal injury in kidneys procured for transplantation. The key role of pattern recognition receptors in immune responses to ischemia is described. Innate immune receptors are emerging novel targets for the amelioration of ischemic injury of donor kidneys.

RECENT FINDINGS

Several families of pattern recognition receptors are direct mediators of early injurious events during kidney procurement, and also innate and adaptive immune responses after transplantation. The deleterious events associated with the activation of the innate immune system in donor kidneys significantly contribute to short and long-term allograft outcomes.

SUMMARY

Although a number of therapies have been proposed to decrease ischemic donor kidney injury, targeting the innate immune system is an exciting new area that is gaining significant interest in transplantation. As we learn more about how these important receptors are regulated by ischemia, strategies will likely evolve to allow their modulation in ischemic renal injury.

Atorvastatin Modulates Regulatory T Cells and Attenuates Cerebral Damage in a Model of Transient Middle Cerebral Artery Occlusion in Rats

Regulatory T cells (Tregs) inhibit the activation of the immune response which could down-regulate the systemic and focal activation observed during ischemic stroke. In fact, in animal models, Tregs infiltrate the infarcted brain and reduce the pro-inflammatory cytokine production and infarct volume, mainly in late stages of ischemia. Recently, an expansion and greater suppressive capacity of circulating Tregs after treatment with statins was observed, in addition to their cardio- and neuroprotective actions demonstrated previously. Thus, to determine whether Treg modulation mediated by statins can also be beneficial during stroke, cerebral ischemia was artificially induced in Wistar rats by transient middle cerebral artery occlusion (tMCAO) during 60 minutes with subsequent reperfusion for 7 days. Six hours after surgery, some animals were treated with atorvastatin (ATV, 10 mg/kg) or carboxymethylcellulose as vehicle at the same concentration every other day during 7 days. Some animals were sham operated as control group of surgery. Interestingly, ATV treatment prevented the development of infarct volume, reduced the neurological deficits, and the circulating and cervical lymph node CD25⁺FoxP3⁺ Treg population. Moreover, there was a reduction of glial cell activation, which correlated with decreased circulating Tregs. Remarkably, treatment with ATV induced an increase in the frequency of CD4⁺CD25⁺ T cells, in particular of those expressing CTLA-4, in brain samples. Together, these results suggest that ATV can modulate Tregs in peripheral tissue and favor their accumulation in the brain, where they can exert neuroprotective actions maybe by the reduction of glial cell activation.

The multifaceted role of the renal microvasculature during acute kidney injury

Pediatric acute kidney injury (AKI) represents a complex disease process for clinicians as it is multifactorial in cause and only limited treatment or preventatives are available. The renal microvasculature has recently been implicated in AKI as a strong therapeutic candidate involved in both injury and recovery. Significant progress has been made in the ability to study the renal microvasculature following ischemic AKI and its role in repair. Advances have also been made in elucidating cell-cell interactions and the molecular mechanisms involved in these interactions. The ability of the kidney to repair post AKI is closely linked to alterations in hypoxia, and these studies are elucidated in this review. Injury to the microvasculature following AKI plays an integral role in mediating the inflammatory response, thereby complicating potential therapeutics. However, recent work with experimental animal models suggests that the endothelium and its cellular and molecular interactions are attractive targets to prevent injury or hasten repair following AKI. Here, we review the cellular and molecular mechanisms of the renal endothelium in AKI, as well as repair and recovery, and potential therapeutics to prevent or ameliorate injury and hasten repair.

Deficiency of T-regulatory cells exaggerates angiotensin II-induced microvascular injury by enhancing immune responses

AIMS

T-regulatory lymphocyte (Treg) adoptive transfer prevented angiotensin (Ang) II-induced hypertension and microvascular injury. Scurfy mice are deficient in Treg because of a mutation in the transcription factor forkhead box P3 (Foxp3) gene. Enhanced Ang II effects in the absence of Treg would unambiguously demonstrate their vascular protective role. We hypothesized that adoptive transfer of Scurfy vs. wild-type T cells will exacerbate Ang II-induced microvascular damage in T and B-cell-deficient recombination-activating gene 1 (Rag1) knockout mice.

METHODS AND RESULTS

Rag1 knockout mice were injected with vehicle, 10(7) T cells from wild-type or Scurfy mice or 10 (6)wild-type Treg alone or in combination with Scurfy T cells, and then infused or not with Ang II (490 ng/kg per min, subcutaneous) for 14 days. Ang II increased SBP in all the groups, but DBP only in wild-type and Scurfy T-cell groups. Ang II-induced endothelial dysfunction and oxidative stress in perivascular adipose tissue (PVAT) of mesenteric arteries of the wild-type T-cell group, whereas these were exaggerated in the Scurfy T-cell group. Ang II enhanced microvascular remodeling and stiffness in vehicle and Scurfy T-cell groups. Ang II increased monocyte chemotactic protein-1 expression in the vascular wall and PVAT, monocyte/macrophage infiltration and proinflammatory polarization in PVAT and the renal cortex, and T-cell infiltration in the renal cortex only in the Scurfy T-cell group. Treg coinjection in the vehicle and Scurfy T-cell groups prevented or reduced the effects of Ang II.

CONCLUSION

FOXP3+ Treg deficiency exaggerates Ang II-induced microvascular injury by modulating innate and adaptive immune responses.