T cells in crescentic glomerulonephritis

Animal models of lupus nephritis: the past, present and a future outlook

Lupus nephritis (LN) is the most severe end-organ pathology in Systemic Lupus Erythematosus (SLE). Research has enhanced our understanding of immune effectors and inflammatory pathways in LN. However, even with the best available therapy, the rate of complete remission for proliferative LN remains below 50%. A deeper understanding of the resistance or susceptibility of renal cells to injury during the progression of SLE is critical for identifying new targets and developing effective long-term therapies. The complex and heterogeneous nature of LN, combined with the limitations of clinical research, make it challenging to investigate the aetiology of this disease directly in patients. Hence, multiple murine models resembling SLE-driven nephritis are utilised to dissect LN's cellular and genetic mechanisms, identify therapeutic targets, and screen novel compounds. This review discusses commonly used spontaneous and inducible mouse models that have provided insights into pathogenic mechanisms and long-term maintenance therapies in LN.

Macrophage-derived macrophage migration inhibitory factor mediates renal injury in anti-glomerular basement membrane glomerulonephritis

Macrophages are a rich source of macrophage migration inhibitory factor (MIF). It is well established that macrophages and MIF play a pathogenic role in anti-glomerular basement membrane crescentic glomerulonephritis (anti-GBM CGN). However, whether macrophages mediate anti-GBM CGN via MIF-dependent mechanism remains unexplored, which was investigated in this study by specifically deleting MIF from macrophages in MIFf/f-lysM-cre mice. We found that compared to anti-GBM CGN induced in MIFf/f control mice, conditional ablation of MIF in macrophages significantly suppressed anti-GBM CGN by inhibiting glomerular crescent formation and reducing serum creatinine and proteinuria while improving creatine clearance. Mechanistically, selective MIF depletion in macrophages largely inhibited renal macrophage and T cell recruitment, promoted the polarization of macrophage from M1 towards M2 via the CD74/NF-κB/p38MAPK-dependent mechanism. Unexpectedly, selective depletion of macrophage MIF also significantly promoted Treg while inhibiting Th1 and Th17 immune responses. In summary, MIF produced by macrophages plays a pathogenic role in anti-GBM CGN. Targeting macrophage-derived MIF may represent a novel and promising therapeutic approach for the treatment of immune-mediated kidney diseases.

Mucosal-associated invariant T cells contribute to suppression of inflammatory myeloid cells in immune-mediated kidney disease

Mucosal-associated invariant T (MAIT) cells have been implicated in various inflammatory diseases of barrier organs, but so far, their role in kidney disease is unclear. Here we report that MAIT cells that recognize their prototypical ligand, the vitamin B2 intermediate 5-OP-RU presented by MR1, reside in human and mouse kidneys. Single cell RNAseq analysis reveals several intrarenal MAIT subsets, and one, carrying the genetic fingerprint of tissue-resident MAIT17 cells, is activated and expanded in a murine model of crescentic glomerulonephritis (cGN). An equivalent subset is also present in kidney biopsies of patients with anti-neutrophil cytoplasmatic antibody (ANCA)-associated cGN. MAIT cell-deficient MR1 mice show aggravated disease, whereas B6-MAITCAST mice, harboring higher MAIT cell numbers, are protected from cGN. The expanded MAIT17 cells express anti-inflammatory mediators known to suppress cGN, such as CTLA-4, PD-1, and TGF-β. Interactome analysis predicts CXCR6 - CXCL16-mediated cross-talk with renal mononuclear phagocytes, known to drive cGN progression. In line, we find that cGN is aggravated upon CXCL16 blockade. Finally, we present an optimized 5-OP-RU synthesis method which we apply to attenuating cGN in mice. In summary, we propose that CXCR6+ MAIT cells might play a protective role in cGN, implicating them as a potential target for anti-inflammatory therapies.

Three Diseases Mediated by Different Immunopathologic Mechanisms-ANCA-Associated Vasculitis, Anti-Glomerular Basement Membrane Disease, and Immune Complex-Mediated Glomerulonephritis-A Common Clinical and Histopathologic Picture: Rapidly Progressive Crescentic Glomerulonephritis

Immune mechanisms play an important role in the pathogenesis of glomerulonephritis (GN), with autoimmunity being the main underlying pathogenetic process of both primary and secondary GN. We present three autoimmune diseases mediated by different autoimmune mechanisms: glomerulonephritis in vasculitis mediated by anti-neutrophil cytoplasmic antibodies (ANCAs), glomerulonephritis mediated by anti-glomerular basement membrane antibodies (anti-GBM antibodies), and immune complex-mediated glomerulonephritis. Some of these diseases represent a common clinical and histopathologic scenario, namely rapidly progressive crescentic glomerulonephritis. This is a severe illness requiring complex therapy, with the main role being played by therapy aimed at targeting immune mechanisms. In the absence of immune therapy, the crescents, the characteristic histopathologic lesions of this common presentation, progress toward fibrosis, which is accompanied by end-stage renal disease (ESRD). The fact that three diseases mediated by different immunopathologic mechanisms have a common clinical and histopathologic picture reveals the complexity of the relationship between immunopathologic mechanisms and their clinical expression. Whereas most glomerular diseases progress by a slow process of sclerosis and fibrosis, the glomerular diseases accompanied by glomerular crescent formation can progress, if untreated, in a couple of months into whole-nephron glomerulosclerosis and fibrosis. The outcome of different immune processes in a common clinical and histopathologic phenotype reveals the complexity of the relationship of the kidney with the immune system. The aim of this review is to present different immune processes that lead to a common clinical and histopathologic phenotype, such as rapidly progressive crescentic glomerulonephritis.

Diminished PD-L1 regulation along with dysregulated T lymphocyte subsets and chemokine in ANCA-associated vasculitis

ANCA-associated vasculitis (AAV) is a life-threatening disease characterized by small vessel inflammation and pathogenic self-directed antibodies. Programmed death-ligand 1 receptor (PD-1) and programmed cell death ligand-1 (PD-L1) are immune checkpoint molecules crucial for maintaining tolerance and immune homeostasis. After checkpoint inhibition therapy, development of various autoimmune diseases and immune-related adverse events (irAEs) have been observed. Here, we investigated the immunomodulatory roles of neutrophils through the expression of immune checkpoint molecule (PD-L1), migratory molecules (CXCR2), chemotactic chemokines (CXCL5) and other important molecules (BAFF and HMGB1) in development of AAV. We also scrutinized the immune mechanism responsible for development of pauci-immune crescentic GN (PICGN). We demonstrate for the first time that the frequency of PD-L1 expressing neutrophils was significantly reduced in AAV patients compared to healthy controls and correlated negatively with disease severity (BVASv3). Further, in renal biopsy, reduced PD-L1 immune checkpoint expression provides a microenvironment that unleashes uncontrolled activated CD4 + T cells, B cells, neutrophils and macrophages and ultimately causes engulfment of immune complexes leading to PICGN. Furthermore, during remission, reduced neutrophils PD-L1 and CXCR2 expression, increased neutrophils CXCL5 expression and increased peripheral effector memory T cells and increased HMGB1 and BAFF levels in serum, demonstrate the propensity for the persistence of sub-clinical inflammation, which could explain relapse, in this group of diseases.

EGF-Receptor-Dependent TLR7 Signaling in Macrophages Promotes Glomerular Injury in Crescentic Glomerulonephritis

Glomerulonephritis (GN) is a group of inflammatory diseases and an important cause of morbidity and mortality worldwide. The initiation of the inflammatory process is quite different for each type of GN; however, each GN is characterized commonly and variably by acute inflammation with neutrophils and macrophages and crescent formation, leading to glomerular death. Toll-like receptor (TLR) 7 is a sensor for self-RNA and implicated in the pathogenesis of human and murine GN. Here, we show that TLR7 exacerbates glomerular injury in nephrotoxic serum nephritis (NTN), a murine model of severe crescentic GN. TLR7-/- mice were resistant to NTN, although TLR7-/- mice manifested comparable immune-complex deposition to wild-type mice without significant defects in humoral immunity, suggesting that endogenous TLR7 ligands accelerate glomerular injury. TLR7 was expressed exclusively in macrophages in glomeruli in GN but not in glomerular resident cells or neutrophils. Furthermore, we discovered that epidermal growth factor receptor (EGFR), a receptor-type tyrosine kinase, is essential for TLR7 signaling in macrophages. Mechanistically, EGFR physically interacted with TLR7 upon TLR7 stimulation, and EGFR inhibitor completely blocked the phosphorylation of TLR7 tyrosine residue(s). EGFR inhibitor attenuated glomerular damage in wild-type mice, and no additional glomerular protective effects by EGFR inhibitor were observed in TLR7-/- mice. Finally, mice lacking EGFR in macrophages were resistant to NTN. This study clearly demonstrated that EGFR-dependent TLR7 signaling in macrophages is essential for glomerular injury in crescentic GN.

Stimulation of Immune Checkpoint Molecule B and T-Lymphocyte Attenuator Alleviates Experimental Crescentic Glomerulonephritis

SIGNIFICANCE STATEMENT

Treatment of acute, crescentic glomerulonephritis (GN) consists of unspecific and potentially toxic immunosuppression. T cells are central in the pathogenesis of GN, and various checkpoint molecules control their activation. The immune checkpoint molecule B and T-lymphocyte attenuator (BTLA) has shown potential for restraining inflammation in other T-cell-mediated disease models. To investigate its role in GN in a murine model of crescentic nephritis, the authors induced nephrotoxic nephritis in BTLA-deficient mice and wild-type mice. They found that BTLA has a renoprotective role through suppression of local Th1-driven inflammation and expansion of T regulatory cells and that administration of an agonistic anti-BTLA antibody attenuated experimental GN. These findings suggest that antibody-based modulation of BTLA may represent a treatment strategy in human glomerular disease.

BACKGROUND

Modulating T-lymphocytes represents a promising targeted therapeutic option for glomerulonephritis (GN) because these cells mediate damage in various experimental and human GN types. The immune checkpoint molecule B and T-lymphocyte attenuator (BTLA) has shown its potential to restrain inflammation in other T-cell-mediated disease models. Its role in GN, however, has not been investigated.

METHODS

We induced nephrotoxic nephritis (NTN), a mouse model of crescentic GN, in Btla -deficient ( BtlaKO ) mice and wild-type littermate controls and assessed disease severity using functional and histologic parameters at different time points after disease induction. Immunologic changes were comprehensively evaluated by flow cytometry, RNA sequencing, and in vitro assays for dendritic cell and T-cell function. Transfer experiments into Rag1KO mice confirmed the observed in vitro findings. In addition, we evaluated the potential of an agonistic anti-BTLA antibody to treat NTN in vivo .

RESULTS

The BtlaKO mice developed aggravated NTN, driven by an increase of infiltrating renal Th1 cells. Single-cell RNA sequencing showed increased renal T-cell activation and positive regulation of the immune response. Although BTLA-deficient regulatory T cells (Tregs) exhibited preserved suppressive function in vitro and in vivo , BtlaKO T effector cells evaded Treg suppression. Administration of an agonistic anti-BTLA antibody robustly attenuated NTN by suppressing nephritogenic T effector cells and promoting Treg expansion.

CONCLUSIONS

In a model of crescentic GN, BTLA signaling effectively restrained nephritogenic Th1 cells and promoted regulatory T cells. Suppression of T-cell-mediated inflammation by BTLA stimulation may prove relevant for a broad range of conditions involving acute GN.

Androgen-Induced Cardiovascular Risk in Polycystic Ovary Syndrome: The Role of T Lymphocytes

An estimated 15-20% of reproductive-age women are affected by polycystic ovary syndrome (PCOS). PCOS is associated with substantial metabolic and cardiovascular long-term consequences. In young women with PCOS, several cardiovascular risk factors may be found, including chronic inflammation, high blood pressure, and elevated leukocytes. These women are at an increased risk of cardiovascular diseases (CVD), not only during the reproductive years, but also with aging and menopause; therefore, the early prevention and treatment of future cardiovascular adverse effects are necessary. The fundamental characteristic of PCOS is hyperandrogenemia, which is associated with increased pro-inflammatory cytokines and T lymphocytes. Whether these factors play a role in the pathophysiology of hypertension, a risk factor of CVD, due to PCOS is not well established. This review will briefly discuss how a modest increase in androgens in females is linked to the development of hypertension through pro-inflammatory cytokines and T lymphocyte subsets and the promotion of renal injury. Moreover, it reveals a few existing research gaps in this area, including the lack of specific therapy directed at androgen-induced inflammation and immune activation, thus emphasizing the necessity to explore the systemic inflammation in women with PCOS to halt the inevitable inflammatory process targeting the underlying abnormalities of CVD.

Therapeutic effects of traditional Chinese medicine on gouty nephropathy: Based on NF-κB signalingpathways

As the final product of purine metabolism, excess serum uric acid (SUA) aggravates the process of some metabolic diseases. SUA causes renal tubule damage, interstitial fibrosis, and glomerular hardening, leading to gouty nephropathy (GN). A growing number of investigations have shown that NF-κB mediated inflammation and oxidative stress have been directly involved in the pathogenesis of GN. Traditional Chinese medicine's treatment methods of GN have amassed a wealth of treatment experience. In this review, we first describe the mechanism of NF-κB signaling pathways in GN. Subsequently, we highlight traditional Chinese medicine that can treat GN through NF-κB pathways. Finally, commenting on promising candidate targets of herbal medicine for GN treatment via suppressing NF-κB signaling pathways was summarized.

Differentiation of crescent-forming kidney progenitor cells into podocytes attenuates severe glomerulonephritis in mice

Crescentic glomerulonephritis is characterized by vascular necrosis and parietal epithelial cell hyperplasia in the space surrounding the glomerulus, resulting in the formation of crescents. Little is known about the molecular mechanisms driving this process. Inducing crescentic glomerulonephritis in two Pax2Cre reporter mouse models revealed that crescents derive from clonal expansion of single immature parietal epithelial cells. Preemptive and delayed histone deacetylase inhibition with panobinostat, a drug used to treat hematopoietic stem cell disorders, attenuated crescentic glomerulonephritis with recovery of kidney function in the two mouse models. Three-dimensional confocal microscopy and stimulated emission depletion superresolution imaging of mouse glomeruli showed that, in addition to exerting an anti-inflammatory and immunosuppressive effect, panobinostat induced differentiation of an immature hyperplastic parietal epithelial cell subset into podocytes, thereby restoring the glomerular filtration barrier. Single-cell RNA sequencing of human renal progenitor cells in vitro identified an immature stratifin-positive cell subset and revealed that expansion of this stratifin-expressing progenitor cell subset was associated with a poor outcome in human crescentic glomerulonephritis. Treatment of human parietal epithelial cells in vitro with panobinostat attenuated stratifin expression in renal progenitor cells, reduced their proliferation, and promoted their differentiation into podocytes. These results offer mechanistic insights into the formation of glomerular crescents and demonstrate that selective targeting of renal progenitor cells can attenuate crescent formation and the deterioration of kidney function in crescentic glomerulonephritis in mice.

Clinical value of urinary cytokines/chemokines as prognostic markers in patients with crescentic glomerulonephritis

Crescentic glomerulonephritis (CrGN) usually requires urgent immunosuppressive treatment. However, aggressive immunosuppressive treatment is often difficult because of the patients' medical conditions or comorbidities. Prognostic markers including urinary cytokines/chemokines as noninvasive biomarkers were explored in CrGN patients. This prospective cohort study included 82 patients with biopsy-confirmed CrGN from 2002 to 2015 who were followed up for 5 years. Urine and serum cytokines/chemokines on the day of kidney biopsy were analyzed in 36 patients. The median age was 65 years and 47.6% were male. Baseline estimated glomerular filtration rate (eGFR) and interstitial fibrosis and tubular atrophy (IFTA) scores were identified as significant prognostic factors. Among patients with cytokines/chemokines measurement, increased IL-10 level was identified as an independent predictor of good prognosis, and increased levels of urinary MCP-1 and fractalkine tended to be associated with good prognosis after adjusting for baseline eGFR and IFTA score. However, semiquantitative analysis of intrarenal leukocytes did not show prognostic value predicting renal outcome or correlation with urinary cytokines/chemokines. This study supports the clinical importance of baseline eGFR and IFTA scores and suggests potential usefulness of urinary IL-10, MCP-1, and fractalkine as prognostic markers for predicting renal outcomes in patients with CrGN.

Pathogenic T-Cell Responses in Immune-Mediated Glomerulonephritis

Glomerulonephritis (GN) comprises a group of immune-mediated kidney diseases affecting glomeruli and the tubulointerstitium. Glomerular crescent formation is a histopathological characteristic of severe forms of GN, also referred to as crescentic GN (cGN). Based on histological findings, cGN includes anti-neutrophil cytoplasmic antibody (ANCA)-associated GN, a severe form of ANCA-associated vasculitis, lupus nephritis associated with systemic lupus erythematosus, Goodpasture’s disease, and IgA nephropathy. The immunopathogenesis of cGN is associated with activation of CD4+ and CD8+ T cells, which particularly accumulate in the periglomerular and tubulointerstitial space but also infiltrate glomeruli. Clinical observations and functional studies in pre-clinical animal models provide evidence for a pathogenic role of Th1 and Th17 cell-mediated immune responses in cGN. Emerging evidence further argues that CD8+ T cells have a role in disease pathology and the mechanisms of activation and function of recently identified tissue-resident CD4+ and CD8+ T cells in cGN are currently under investigation. This review summarizes the mechanisms of pathogenic T-cell responses leading to glomerular damage and renal inflammation in cGN. Advanced knowledge of the underlying immune mechanisms involved with cGN will enable the identification of novel therapeutic targets for the replacement or reduction in standard immunosuppressive therapy or the treatment of refractory disease.

Conventional NK Cells and Type 1 Innate Lymphoid Cells Do Not Influence Pathogenesis of Experimental Glomerulonephritis

Innate lymphoid cells (ILCs) that express NK cell receptors (NCRs) and the transcription factor T-bet populate nonlymphoid tissues and are crucial in immune responses against viral infections and malignancies. Recent studies highlighted the heterogeneity of this ILC population and extended their functional spectrum to include important roles in tissue homeostasis and autoimmunity. In this article, we provide detailed profiling of NCR+T-bet+ ILC populations in the murine kidney, identifying conventional NK (cNK) cells and type 1 ILCs (ILC1s) as the two major subsets. Induction of renal inflammation in a mouse model of glomerulonephritis did not substantially influence abundance or phenotype of cNK cells or ILC1s in the kidney. For functional analyses in this model, widely used depletion strategies for total NCR+ ILCs (anti-NK1.1 Ab application) and cNK cells (anti-asialoGM1 serum application) were unreliable tools, because they were accompanied by significant off-target depletion of kidney NKT cells and CD8+ T cells, respectively. However, neither depletion of cNK cells and ILC1s in NKT cell–deficient mice nor specific genetic deletion of cNK cells in Ncr1Cre/wt × Eomesfl/fl mice altered the clinical course of experimental glomerulonephritis. In summary, we show in this article that cNK cells and ILC1s are dispensable for initiation and progression of immune-mediated glomerular disease and advise caution in the use of standard Ab depletion methods to study NCR+ ILC function in mouse models.

Disease activity prediction and prognosis of anti-GBM nephritis based on T lymphocyte subset ratios

Introduction

Cell-mediated autoimmunity, especially the autoreactivity of T cells, is known to underlie the initiation of anti-glomerular basement membrane disease. However, the T lymphocyte subsets that determine the disease activity, renal fibrosis, and prognosis of anti-GBM disease have not been clearly elucidated.

Methods

The T lymphocyte subsets (CD4+ and CD8+) were examined on peripheral blood and renal biopsy tissues from 65 patients with biopsy proven anti-GBM disease. Patients were divided into the high ratio group and low ratio group according to the cutoff values in the receiver operating characteristic curve analysis. The correlations of T lymphocyte subsets with clinical, pathological data, and renal outcome were analyzed.

Results

By the end of follow-up, 45 patients (69.2%) developed end-stage renal disease (ESRD). In peripheral blood, the CD4+/CD8+ ratio showed a predictive ability with a sensitivity and specificity of 91.3% and 52.9%, respectively, which gave rise to a cutoff value of 0.89. There was a significant difference in the activity index between these two groups (3.91 ± 1.38 vs. 2.89 ± 1.13, p = 0.007). In the renal tissues, the CD4+/CD8+ ratio had the optimal cutoff point of 0.82 with a sensitivity of 57.8% and specificity of 85%. The renal activity index was higher for the renal tissues with high CD4+/CD8+ ratios than that of tissues with low CD4+/CD8+ ratios (4.32 ± 1.55 vs. 3.37 ± 1.41, p = 0.016). Peripheral blood CD4+/CD8+ ratios of ≥0.89 or renal tissue CD4+/CD8+ ratios of < 0.82 positively correlated with poor renal prognosis in patients with anti-GBM nephritis.

Conclusions

The CD4+/CD8+ ratio was associated with renal activity index both in peripheral blood and renal tissue and predicts the renal prognosis of patients with anti-GBM nephritis.

Regulatory role and mechanisms of myeloid TLR4 in anti-GBM glomerulonephritis

Myeloid cells and TLR4 play a critical role in acute kidney injury. This study investigated the regulatory role and mechanisms of myeloid TLR4 in experimental anti-glomerular basement membrane (GBM) glomerulonephritis (GN). Anti-GBM GN was induced in tlr4^flox/flox and tlr4^{flox/flox−lysM−cre} mice by intravenous injection of the sheep anti-mouse GBM antibody. Compared to control mice, conditional disruption of tlr4 from myeloid cells, largely macrophages (> 85%), suppressed glomerular crescent formation and attenuated progressive renal injury by lowering serum creatinine and 24-h urine protein excretion while improving creatinine clearance. Mechanistically, deletion of myeloid tlr4 markedly inhibited renal infiltration of macrophages and T cells and resulted in a shift of infiltrating macrophages from F4/80⁺iNOS⁺ M1 to F4/80⁺CD206⁺ M2 phenotype and inhibited the upregulation of renal proinflammatory cytokines IL-1β and MCP-1. Importantly, deletion of myeloid tlr4 suppressed T cell-mediated immune injury by shifting Th1 (CD4⁺IFNγ⁺) and Th17 (CD4⁺IL-17a⁺) to Treg (CD4⁺CD25⁺FoxP3⁺) immune responses. Transcriptome analysis also revealed that disrupted myeloid TLR4 largely downregulated genes involving immune and cytokine-related pathways. Thus, myeloid TLR4 plays a pivotal role in anti-GBM GN by immunological switching from M1 to M2 and from Th1/Th17 to Treg and targeting myeloid TLR4 may be a novel therapeutic strategy for immune-mediated kidney diseases.

Parietal epithelial cell dysfunction in crescentic glomerulonephritis

Crescentic glomerulonephritis represents a group of kidney diseases characterized by rapid loss of kidney function and the formation of glomerular crescents. While the role of the immune system has been extensively studied in relation to the development of crescents, recent findings show that parietal epithelial cells play a key role in the pathophysiology of crescent formation, even in the absence of immune modulation. This review highlights our current understanding of parietal epithelial cell biology and the reported physiological and pathological roles that these cells play in glomerular lesion formation, especially in the context of crescentic glomerulonephritis.

T cell plasticity in renal autoimmune disease

The presence of immune cells is a morphological hallmark of rapidly progressive glomerulonephritis, a disease group that includes anti-glomerular basement membrane glomerulonephritis, lupus nephritis, and anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis. The cellular infiltrates include cells from both the innate and the adaptive immune responses. The latter includes CD4⁺ and CD8⁺ T cells. In the past, CD4⁺ T cell subsets were viewed as terminally differentiated lineages with limited flexibility. However, it is now clear that Th17 cells can in fact have a high degree of plasticity and convert, for example, into pro-inflammatory Th1 cells or anti-inflammatory Tr1 cells. Interestingly, Th17 cells in experimental GN display limited spontaneous plasticity. Here we review the literature of CD4⁺ T cell plasticity focusing on immune-mediated kidney disease. We point out the key findings of the past decade, in particular that targeting pathogenic Th17 cells by anti-CD3 injection can be a tool to modulate the CD4⁺ T cell response. This anti-CD3 treatment can trigger a regulatory phenotype in Th17 cells and transdifferentiation of Th17 cells into immunosuppressive IL-10-expressing Tr1 cells (Tr1exTh17 cells). Thus, targeting Th17 cell plasticity could be envisaged as a new therapeutic approach in patients with glomerulonephritis.

Laminin β2 variants associated with isolated nephropathy that impact matrix regulation

Mutations in LAMB2, encoding laminin β₂, cause Pierson syndrome and occasionally milder nephropathy without extrarenal abnormalities. The most deleterious missense mutations that have been identified affect primarily the N-terminus of laminin β₂. On the other hand, those associated with isolated nephropathy are distributed across the entire molecule, and variants in the β₂ LEa-LF-LEb domains are exclusively found in cases with isolated nephropathy. Here we report the clinical features of mild isolated nephropathy associated with 3 LAMB2 variants in the LEa-LF-LEb domains (p.R469Q, p.G699R, and p.R1078C) and their biochemical characterization. Although Pierson syndrome missense mutations often inhibit laminin β₂ secretion, the 3 recombinant variants were secreted as efficiently as WT. However, the β₂ variants lost pH dependency for heparin binding, resulting in aberrant binding under physiologic conditions. This suggests that the binding of laminin β₂ to negatively charged molecules is involved in glomerular basement membrane (GBM) permselectivity. Moreover, the excessive binding of the β₂ variants to other laminins appears to lead to their increased deposition in the GBM. Laminin β₂ also serves as a potentially novel cell-adhesive ligand for integrin α₄β₁. Our findings define biochemical functions of laminin β₂ variants influencing glomerular filtration that may underlie the pathogenesis of isolated nephropathy caused by LAMB2 abnormalities.

BTK inhibition modulates multiple immune cell populations involved in the pathogenesis of immune mediated nephritis

Lupus nephritis (LN) is a serious end organ complication of systemic lupus erythematosus. Nephrotoxic serum nephritis (NTN) is an inducible model of LN, which utilizes passive transfer of pre-formed nephrotoxic antibodies to initiate disease. In previous studies, we demonstrated that the Bruton's tyrosine kinase inhibitor, BI-BTK-1, prevents the development of nephritis in NTN when treatment was started prior to nephrotoxic serum transfer, and reverses established proteinuria as well. We manipulated the initiation and duration of BI-BTK-1 therapy in NTN to study its delayed therapeutic effects when treatment is given later in the disease course, as well as to further understand what effect BI-BTK-1 is having to prevent initiation of nephritis with early treatment. Early treatment and remission induction each correlated with decreased inflammatory macrophages, CD4+ and CD8+ T cells, and decreased B220+ B cells. Additionally, an increased proportion of resident macrophages within the CD45+ population favored a delay of disease onset and remission induction. We also studied the cellular processes involved in reactivation of nephritis by withdrawing BI-BTK-1 treatment at different time points. Treatment cessation led to either early or later onset of renal flares inversely dependent on the initial duration of BTK inhibition, as assessed by increased proteinuria and BUN levels and worse renal pathology. These flares were associated with an increase in kidney CD45+ infiltrates, including myeloid cell populations. IL-6, CD14, and CCL2 were also increased in mice developing late flares. These analyses point to the role of macrophages as an important contributor to the pathogenesis of immune mediated nephritis, and further support the therapeutic potential of BTK inhibition in this disease and related conditions.

Utilizing methylglyoxal and D-lactate in urine to evaluate saikosaponin C treatment in mice with accelerated nephrotoxic serum nephritis

The relationship between methylglyoxal (MGO) and D-lactate during saikosaponin C (SSC) treatment of mice with accelerated nephrotoxic serum (NTS) nephritis was investigated. NTS nephritis was induced by administration of anti-basement membrane antibodies to C57BL/6 mice and three dosages of SSC were administered for 14 days. Proteinuria, blood urea nitrogen, serum creatinine, renal histology, urinary MGO and d-lactate changes were examined. Compared to the NTS control group, the middle dosage (10 mg/kg/day) of SSC significantly alleviated the development of nephritis based on urine protein measurements (34.40 ± 6.85 vs. 17.33 ± 4.79 mg/day, p<0.05). Pathological observation of the glomerular basement membrane (GBM) revealed monocyte infiltration, hypertrophy, and crescents were alleviated, and injury scoring also showed improved efficacy for the middle dose of SSC during nephritis (7.92 ± 1.37 vs. 3.50 ± 1.14, p<0.05). Moreover, the significant decreases in urinary levels of MGO (24.71 ± 3.46 vs. 16.72 ± 2.36 μg/mg, p<0.05) and D-lactate (0.31 ± 0.04 vs. 0.23 ± 0.02 μmol/mg, p<0.05) were consistent with the biochemical and pathological examinations. This study demonstrates that MGO and D-lactate may reflect the extent of damage and the efficacy of SSC in NTS nephritis; further studies are required to enable clinical application.

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

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

Role of CD8+ T cells in crescentic glomerulonephritis

Crescentic glomerulonephritis (cGN) comprises three main types according to the pathogenesis and immunofluorescence patterns: anti-glomerular basement membrane antibody cGN, vasculitis-associated cGN and post-infectious immune complex cGN. In this brief review of the immune-pathogenesis of cGN, the focus is mainly on the role of CD8+ T cells in the progression of cGN. Under control conditions, Bowman's capsule (BC) provides a protected immunological niche by preventing access of cytotoxic CD8+ T cells to Bowman's space and thereby podocytes. Even in experimental nephrotoxic nephritis, leukocytes accumulate around the glomeruli, but remain outside of BC, as long as the latter remains intact. However, when and where breaches in BC occur, the inflammatory cells can gain access to and destroy podocytes, thus converting cGN into rapidly progressive glomerulonephritis (RPGN). These conclusions also apply to human cGN, where biopsies show that loss of BC integrity is associated with RPGN and progression to end-stage kidney disease. We propose a two-hit hypothesis for the role of cytotoxic CD8+ T cells in the progression of cGN. The initial insult occurs in response to the immune complex formation or deposition, resulting in local capillary and podocyte injury (first hit). The injured podocytes release neo-epitopes, eventually causing T-cell activation and migration to the glomerulus. Upon generation of breaches in BC, macrophages and CD8+ T cells can now gain access to the glomerular space and destroy neo-epitope expressing podocytes (second hit), resulting in RPGN. While further investigation will be required to test this hypothesis, future therapeutic trials should consider targeting of CD8+ T cells in the therapy of progressive cGN.

Protecting the kidney in systemic lupus erythematosus: from diagnosis to therapy

Lupus nephritis (LN) is a common manifestation of systemic lupus erythematosus that can lead to irreversible renal impairment. Although the prognosis of LN has improved substantially over the past 50 years, outcomes have plateaued in the USA in the past 20 years as immunosuppressive therapies have failed to reverse disease in more than half of treated patients. This failure might reflect disease complexity and heterogeneity, as well as social and economic barriers to health-care access that can delay intervention until after damage has already occurred. LN progression is still poorly understood and involves multiple cell types and both immune and non-immune mechanisms. Single-cell analysis of intrinsic renal cells and infiltrating cells from patients with LN is a new approach that will help to define the pathways of renal injury at a cellular level. Although many new immune-modulating therapies are being tested in the clinic, the development of therapies to improve regeneration of the injured kidney and to prevent fibrosis requires a better understanding of the mechanisms of LN progression. This mechanistic understanding, together with the development of clinical measures to evaluate risk and detect early disease and better access to expert health-care providers, should improve outcomes for patients with LN.

TNF-α in T lymphocytes attenuates renal injury and fibrosis during nephrotoxic nephritis

Nephrotoxic serum nephritis (NTN) models immune-mediated human glomerulonephritis and culminates in kidney inflammation and fibrosis, a process regulated by T lymphocytes. TNF-α is a key proinflammatory cytokine that contributes to diverse forms of renal injury. Therefore, we posited that TNF-α from T lymphocytes may contribute to NTN pathogenesis. Here, mice with T cell-specific deletion of TNF-α (TNF TKO) and wild-type (WT) control mice were subjected to the NTN model. At 14 days after NTN, kidney injury and fibrosis were increased in kidneys from TNF TKO mice compared with WT mice. PD1+CD4+ T cell numbers and mRNA levels of IL-17A were elevated in NTN kidneys of TNF TKO mice, suggesting that augmented local T helper 17 lymphocyte responses in the TNF TKO kidney may exaggerate renal injury and fibrosis. In turn, we found increased accumulation of neutrophils in TNF TKO kidneys during NTN. We conclude that TNF-α production in T lymphocytes mitigates NTN-induced kidney injury and fibrosis by inhibiting renal T helper 17 lymphocyte responses and infiltration of neutrophils.

Group 1 innate lymphoid cells are involved in the progression of experimental anti-glomerular basement membrane glomerulonephritis and are regulated by peroxisome proliferator-activated receptor α

Innate lymphoid cells play an important role in the early effector cytokine-mediated response. In Wistar Kyoto rats, CD8⁺ non-T lymphocytes (CD8⁺Lym) infiltrate into glomeruli during the development of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Here, we examined the profiles and roles of CD8⁺Lym in anti-GBM glomerulonephritis. The regulation of CD8⁺Lym by peroxisome proliferator-activated receptor (PPAR)-α in anti-GBM glomerulonephritis was also evaluated. Glomerular infiltrating CD8⁺Lym were lineage-negative cells that showed markedly high expression of IFN-γ and T-bet mRNAs but not Eomes, indicating these cells are group 1 innate lymphoid cells. In anti-GBM glomerulonephritis, the glomerular mRNAs of innate lymphoid cell-related cytokines (IFN-γ and TNF-α) and chemokines (CXCL9, CXCL10, and CXCL11) are significantly increased. Treatment with a PPARα agonist ameliorated renal injury, with reduced expression of these mRNAs. In vitro, enhanced IFN-γ production from innate lymphoid cells upon IL-12 and IL-18 stimulation was reduced by the PPARα agonist. Moreover, CXCL9 mRNA in glomerular endothelial cells and CXCL9, CXCL10, and CXCL11 mRNAs in podocytes and macrophages were upregulated by IFN-γ, whereas the PPARα agonist downregulated their expression. We also detected the infiltration of innate lymphoid cells into glomeruli in human anti-GBM glomerulonephritis. Thus, innate lymphoid cells are involved in the progression of anti-GBM glomerulonephritis and regulated directly or indirectly by PPARα. Our findings suggest that innate lymphoid cells could serve as novel therapeutic targets for anti-GBM glomerulonephritis.

Role of Mesangial-Podocytic-Tubular Cross-Talk in IgA Nephropathy

IgA nephropathy (IgAN), a common primary glomerulonephritis worldwide, is associated with a substantial risk of progression to end-stage renal failure. The disease runs a highly variable clinical course with frequent involvement of tubulointerstitial damage. A subgroup of IgAN with proximal tubular epithelial cells (PTECs) and tubulointerstitial damage often is associated with rapid progression to end-stage renal failure. Human mesangial cell-derived mediators lead to podocyte and tubulointerstitial injury via mesangial-podocytic-tubular cross-talk. Although mesangial-podocytic communication plays a pathogenic role in podocytic injury, the implication of a podocyte-PTEC cross-talk pathway in the progression of tubulointerstitial injury in IgAN should not be underscored. We review the role of mesangial-podocytic-tubular cross-talk in the progression of IgAN. We discuss how podocytopathy in IgAN promotes subsequent PTEC dysfunction and whether tubulointerstitial injury affects the propagation of podocytic injury in IgAN. A thorough understanding of the cross-talk mechanisms among mesangial cells, podocytes, and PTECs may lead to better design of potential therapeutic options for IgAN.

Cytomegalovirus Induced Collapsing Glomerulopathy and Necrotizing Glomerulonephritis in a Renal Allograft Recipient

In renal allograft recipients, cytomegalovirus (CMV) typically causes tubulointerstitial nephritis. Only rarely glomeruli are involved. We present a rare case of CMV with collapsing glomerulopathy, necrotizing glomerulonephritis, and crescent formation in a renal allograft recipient. Immunohistochemistry confirmed CMV infection. The patient was started on valganciclovir and his renal function remained stable. A repeat renal biopsy performed three months later showed morphologically normal glomeruli and CMV immunostaining was also negative. Nephropathologists have to carefully screen for CMV in cases with crescentic or collapsing glomerulopathy as the later lesions resolve after treating the underlying viral infection. This study will add on to the various glomerular changes associated with CMV infection.

Activation of fibroblastic reticular cells in kidney lymph node during crescentic glomerulonephritis

Crescentic glomerulonephritis is an inflammatory condition characterized by rapid deterioration of kidney function. Previous studies of crescentic glomerulonephritis have focused on immune activation in the kidney. However, the role of fibroblastic reticular cells, which reside in the stromal compartment of the kidney lymph node, has not been studied in this condition. We investigated the activation of kidney lymph node-resident fibroblastic reticular cells in nephrotoxic serum nephritis, a classic murine model of crescentic glomerulonephritis. We found that increased deposition of extracellular matrix fibers by fibroblastic reticular cells in the kidney lymph node was associated with the propagation of high endothelial venules, specialized blood vessels through which lymphocytes enter the lymph node, as well as with expansion of the lymphatic vasculature. The kidney lymph node also contained an expanding population of pro-inflammatory T cells. Removal of the kidney lymph node, depletion of fibroblastic reticular cells, and treatment with anti-podoplanin antibody each resulted in reduction of kidney injury. Our findings suggest that modulating the activity of fibroblastic reticular cells may be a novel therapeutic approach in crescentic glomerulonephritis.

Immunophenotypic profile of leukocytes in hyperandrogenemic female rat an animal model of polycystic ovary syndrome

The immune etiology of polycystic ovary syndrome (PCOS) is an intriguing area. However, whether there is alteration in the leukocyte populations in different tissues remain ambiguous.

AIM

To characterize the leukocyte populations of hyperandrogenemic female (HAF) rat tissues.

METHODS

Female Sprague Dawley rats at 3 weeks of age were implanted subcutaneously with dihydrotestosterone (DHT) or placebo pellets. The rats were aged to 14-15 weeks and tissues were collected.

RESULTS

Peripheral blood (PB) and renal CD4⁺ (P < 0.03, P < 0.007), Th17 (P < 0.05, P < 0.002), and CD4⁺CD28^null (P < 0.04, P < 0.001) were significantly increased in HAF rats compared to placebo, respectively, in spite of their lower percentage in the spleen. Although, the percentage of Treg T lymphocytes were significantly higher in the PB (P < 0.001) of HAF rats, the splenic (P < 0.01) and renal Treg cells (P < 0.03) were found to be significantly lower. Remarkably, HAF rats had higher renal mast cells (P < 0.00009) despite lower splenic (P < 0.002). The number of PB, renal, and splenic CD8⁺ T cells and IgM⁺-B cells in HAF rats remained unchanged.

CONCLUSION

Results from this study 1) provide the first evidence of significant alteration of T lymphocyte subsets and different leukocyte populations profile in a rat model of polycystic ovary syndrome, 2) demonstrate alteration of the immunological niche of blood, spleen, and kidney tissues in Hyperandrogenemia state in female rats, 3) imply potential immune system dysregulation in HAF rats which may suggest a link between excess androgen, chronic inflammation, and immune-mediated diseases in polycystic ovary syndrome patients.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

T-lymphocyte-specific knockout of IKK-2 or NEMO induces Th17 cells in an experimental nephrotoxic nephritis mouse model

Experimental nephrotoxic serum nephritis (NTN) is a model for T-cell-mediated human rapid progressive glomerulonephritis. T-cell receptor stimulation involves intracellular signaling events that ultimately lead to the activation of transcription factors, such as NF-κB. We explored the involvement of the NF-κB components IKK-2 and NEMO in NTN, by using cell-specific knockouts of IKK-2 and NEMO in CD4⁺ T lymphocytes. Our results demonstrate that although the course of disease was not grossly altered in CD4xIKK2^Δ and CD4xNEMO^Δ animals, renal regulatory T cells were significantly reduced and T helper (T_h)1 and T_h17 cells significantly increased in both knockout mouse groups. The expression of the renal cytokines and chemokines IL-1β, CCL-2, and CCL-20 was also significantly altered in both knockout mice. Lymphocyte transcriptome analysis confirmed the increased expression of T_h17-related cytokines in spleen CD4⁺ T cells. Moreover, our array data demonstrate an interrupted canonical NF-κB pathway and an increased expression of noncanonical NF-κB pathway-related genes in nephritic CD4xNEMO^Δ mice, highlighting different downstream effects of deletion of IKK-2 or NEMO in T lymphocytes. We propose that better understanding of the role of IKK-2 and NEMO in nephritis is essential for the clinical application of kinase inhibitors in patients with glomerulonephritis.-Guo, L., Huang, J., Chen, M., Piotrowski, E., Song, N., Zahner, G., Paust, H.-J., Alawi, M., Geffers, R., Thaiss, F. T-lymphocyte-specific knockout of IKK-2 or NEMO induces T_h17 cells in an experimental nephrotoxic nephritis mouse model.

Suppressor of Cytokine Signaling-1/STAT1 Regulates Renal Inflammation in Mesangial Proliferative Glomerulonephritis Models

Mesangial proliferative glomerulonephritis (MsGN) is a significant global threat to public health. Inflammation plays a crucial role in MsGN; however, the underlying mechanism remains unknown. Herein, we demonstrate that suppression of the cytokine signaling-1 (SOCS1)/signal transducer and activator of transcription 1 (STAT1) signaling pathway is associated with renal inflammation and renal injury in MsGN. Using MsGN rat (Thy1.1 GN) and mouse (Habu GN) models, renal SOCS1/STAT1 was determined to be associated with CD4+ T cell infiltration and related cytokines. In vitro, SOCS1 overexpression repressed IFN-γ-induced MHC class II and cytokine levels and STAT1 phosphorylation in mesangial cells. SOCS1 and STAT1 inhibitors significantly inhibited IFN-γ-induced CIITA promoter activity and MHC class II expression. In conclusion, our study emphasizes the pivotal role of the SOCS1/STAT1 axis in the regulation of inflammation in MsGN.

Antineutrophil cytoplasmic antibodies-associated glomerulonephritis: From bench to bedside

Antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) is a group of autoimmune disorders that predominantly affects small vessels. The onset of the disease is closely associated with ANCA. Renal involvement, also known as ANCA-associated glomerulonephritis (AGN), is one of the most common manifestations of AAV. In this mini-review, we described the clinical and pathological features of AGN. We then focused on recent studies on the mechanism of acute kidney lesions, including fibrinoid necrosis and crescent formation. Following the basic aspects of kidney injury in AGN, we demonstrated the clinical importance of kidney injury in determining the outcome of patients with AGN. The prognostic value of the 2010 Histopathological Classification of AGN and validating studies were summarized. Finally, treatment and novel therapeutic strategies were introduced addressing the importance of optimizing management of this patient population.

Bowman's capsule provides a protective niche for podocytes from cytotoxic CD8+ T cells

T cells play a key role in immune-mediated glomerulonephritis, but how cytotoxic T cells interact with podocytes remains unclear. To address this, we injected EGFP-specific CD8+ T cells from just EGFP death inducing (Jedi) mice into transgenic mice with podocyte-specific expression of EGFP. In healthy mice, Jedi T cells could not access EGFP+ podocytes. Conversely, when we induced nephrotoxic serum nephritis (NTSN) and injected Jedi T cells, EGFP+ podocyte transgenic mice showed enhanced proteinuria and higher blood urea levels. Morphometric analysis showed greater loss of EGFP+ podocytes, which was associated with severe crescentic and necrotizing glomerulonephritis. Notably, only glomeruli with disrupted Bowman's capsule displayed massive CD8+ T cell infiltrates that were in direct contact with EGFP+ podocytes, causing their apoptosis. Thus, under control conditions with intact Bowman's capsule, podocytes are not accessible to CD8+ T cells. However, breaches in Bowman's capsule, as also noted in human crescentic glomerulonephritis, allow access of CD8+ T cells to the glomerular tuft and podocytes, resulting in their destruction. Through these mechanisms, a potentially reversible glomerulonephritis undergoes an augmentation process to a rapidly progressive glomerulonephritis, leading to end-stage kidney disease. Translating these mechanistic insights to human crescentic nephritis should direct future therapeutic interventions at blocking CD8+ T cells, especially in progressive stages of rapidly progressive glomerulonephritis.

Cryoglobulinemic Glomerulonephritis Associated With Nodal and Renal Infiltration by T-Cell Lymphoma of T-Follicular Helper Phenotype: A Case Report

We present a unique case of cryoglobulinemic glomerulonephritis associated with nodal and renal infiltration by T-cell lymphoma of T-follicular helper phenotype. The patient presented with transient neurologic symptoms, severe nephritic syndrome with nephrotic-range proteinuria, and acute kidney injury. He had elevated double-stranded DNA levels, low complement levels, detectable cryoglobulin, and detectable immunoglobulin M (IgM) paraprotein. The kidney biopsy showed cryoglobulinemic glomerulonephritis with a membranoproliferative pattern and diffuse interstitial infiltrates on light microscopy; IgM, C3 but weak IgG, C1q, and negative C4d staining on immunofluorescence; and deposits with organized substructures on electron microscopy. Positron emission tomography showed diffuse uptake in bilaterally enlarged kidneys and a localized group of lymph nodes. Subsequent lymph node biopsy revealed Epstein-Barr virus-negative nodal T-cell lymphoma, which was also proven in renal tissue. The association between T-cell lymphoma, autoantibodies, and cryoglobulinemia may represent a paraneoplastic phenomenon. His renal prognosis has been excellent, but overall prognosis and survival is dictated by the clinical course of T-cell lymphoma.

(5R)-5-hydroxytriptolide ameliorates anti-glomerular basement membrane glomerulonephritis in NZW mice by regulating Fcγ receptor signaling

(5R)-5-hydroxytriptolide (LLDT-8) is a novel triptolide analog that has been identified as a promising candidate for treating autoimmune diseases and has been shown to be effective in treating murine collagen-induced arthritis and lupus nephritis. In the present study, we investigated the therapeutic effect and possible mechanism of action of LLDT-8 in a murine anti-glomerular basement membrane (GBM) glomerulonephritis model. NZW mice were injected with rabbit anti-GBM serum (500 μL, ip). The mice were orally treated with LLDT-8 (0.125 mg/kg, every other day) or a positive control prednisolone (2 mg/kg every day) for 14 d. Blood and urine samples as well as spleen and kidney tissues were collected for analyses. LLDT-8 treatment did not affect the generation of mouse anti-rabbit antibodies. LLDT-8 significantly reversed established proteinuria, improved renal histopathology and attenuated renal dysfunction in glomerulonephritis mice. Furthermore, LLDT-8 inhibited inflammation in the kidney evidenced by significantly decreasing C3 and IgG deposition, reducing the levels of the pathogenic cytokines TNF-α, IL-6, IL-17, and IFN-γ, and reducing related chemokine expression and leukocyte infiltration in kidneys. Moreover, LLDT-8 treatment significantly increased the expression of FcγRIIB in the kidney and spleen. In addition, the treatment restored the reduced expression of FcγRIIB on the surface of kidney effector cells, CD11b⁺ cells, and interfered with FcγR-dependent signaling, especially FcγRIIB-mediated downstream kinases, such as BTK. These results demonstrate that LLDT-8 ameliorates anti-GBM glomerulonephritis by regulating the Fcγ receptor signaling.

Retinoic acid improves nephrotoxic serum-induced glomerulonephritis through activation of podocyte retinoic acid receptor α

Proliferation of glomerular epithelial cells, including podocytes, is a key histologic feature of crescentic glomerulonephritis. We previously found that retinoic acid (RA) inhibits proliferation and induces differentiation of podocytes by activating RA receptor-α (RARα) in a murine model of HIV-associated nephropathy. Here, we examined whether RA would similarly protect podocytes against nephrotoxic serum-induced crescentic glomerulonephritis and whether this effect was mediated by podocyte RARα. RA treatment markedly improved renal function and reduced the number of crescentic lesions in nephritic wild-type mice, while this protection was largely lost in mice with podocyte-specific ablation of Rara (Pod-Rara knockout). At a cellular level, RA significantly restored the expression of podocyte differentiation markers in nephritic wild-type mice, but not in nephritic Pod-Rara knockout mice. Furthermore, RA suppressed the expression of cell injury, proliferation, and parietal epithelial cell markers in nephritic wild-type mice, all of which were significantly dampened in nephritic Pod-Rara knockout mice. Interestingly, RA treatment led to the coexpression of podocyte and parietal epithelial cell markers in a small subset of glomerular cells in nephritic mice, suggesting that RA may induce transdifferentiation of parietal epithelial cells toward a podocyte phenotype. In vitro, RA directly inhibited the proliferation of parietal epithelial cells and enhanced the expression of podocyte markers. In vivo lineage tracing of labeled parietal epithelial cells confirmed that RA increased the number of parietal epithelial cells expressing podocyte markers in nephritic glomeruli. Thus, RA attenuates crescentic glomerulonephritis primarily through RARα-mediated protection of podocytes and in part through the inhibition of parietal epithelial cell proliferation and induction of their transdifferentiation into podocytes.

ID3 may protect mice from anti‑GBM glomerulonephritis by regulating the differentiation of Th17 and Treg cells

Anti‑glomerular basement membrane glomerulonephritis (anti‑GBM GN) is an autoimmune disease that leads to severe and rapidly progressive renal injury. Inhibition of DNA‑binding factor 3 (ID3) serves a key role in autoimmune diseases, such as asthma and Sjögren's syndrome, and in experimental allergic encephalitis models. However, the role of ID3 in the progression of anti‑GBM GN remains unknown. In the present study, ID3 mRNA expression increased between 3‑ and 20‑fold in the renal tissues of anti‑GBM GN mice compared with the Control group, with a peak at day 14 post‑induction. In addition, ID3 protein expression was upregulated from day 7 onwards. The expression of ID3 was also examined in the spleen, and was demonstrated to be increased in the spleen of nephritic mice. T helper 17 (Th17) cells and regulatory T (Treg) cells were present throughout the entire period of observation (from day 7 to day 28) in anti‑GBM GN mice, which may vary at different time points, accompanied with the expression of ID3. In vitro, ID3 expression was increased when CD4+ T cells differentiated into Tregs; however, expression was lower in Th17 cells. Following treatment with ID3 small interfering RNA, RAR‑related orphan receptor γt, but not forkhead box P3, expression increased. Furthermore, increased expression of interleukin‑17A was also observed when ID3 was blocked. In addition, ID3 was able to interact with transcription factor E2A. A significant increase in binding between ID3 and E2A was observed in anti‑GBM GN from day 7 onwards, with a peak at day 14 in both renal tissue and spleen. In conclusion, ID3 may be involved in the differentiation of Th17 and Tregs by downregulating Th17 cells, which is probably associated with binding to E2A. The present results suggested that ID3 may offer protection against anti‑GBM GN in mice.

The Regulatory T-cell Transcription Factor Foxp3 Protects against Crescentic Glomerulonephritis

Regulatory T cells (Tregs) have been shown to play a protective role in glomerulonephritis (GN) and Foxp3 is a master transcription factor in Treg development. In this study, we examined the functional role and mechanisms of Foxp3 in a mouse model of accelerated anti-glomerular basement membrane (anti-GBM) GN induced in antigen-primed Foxp3 transgenic (Tg) mice. Compared with littermate of wildtype (WT) mice in which induced severe crescentic GN developed with progressive renal dysfunction, Foxp3 Tg mice had reduced crescent formation, urinary protein excretion, plasma creatinine and decline in creatinine clearance. The protective role of Foxp3 in crescentic GN was associated with a markedly suppressed expression of proinflammatory interleukin-1 beta (IL-1β), tumour necrosis factor-alpha (TNF-α) and monocyte chemoattractant protein 1 (MCP-1), and diminished infiltration of the kidneys by CD3⁺ T cells and F4/80⁺ macrophages. Moreover, overexpression of Foxp3 resulted in a significant increase in CD4⁺ Foxp3⁺ Tregs systemically and in the diseased kidneys, thereby blunting Th1, Th2, and Th17 responses systemically and in the kidneys. In conclusion, Foxp3 protects against kidney injury in crescentic GN through enhancement of Treg numbers and function, and suppression of Th1, Th2 and Th17 immune responses at the systemic and local tissue levels.

(5R)-5-hydroxytriptolide ameliorates lupus nephritis in MRL/lpr mice by preventing infiltration of immune cells

(5R)-5-hydroxytriptolide (LLDT-8), a triptolide derivative with low toxicity, was previously reported to have strong immunosuppressive effects both in vitro and in vivo, but it remains unknown whether LLDT-8 has a therapy effect on systemic lupus erythematosus. In this study, we aimed to investigate the therapeutic effects of LLDT-8 on lupus nephritis in MRL/lpr mice, a model of systemic lupus erythematosus. Compared with the vehicle group, different clinical parameters were improved upon LLDT-8 treatment as follows: prolonged life span of mice, decreased proteinuria, downregulated blood urea nitrogen and serum creatinine, reduced glomerular IgG deposits, and ameliorated histopathology. A decreased expression of the inflammatory cytokines IFN-γ, IL-17, IL-6, and TNF-α was also observed in the kidney of LLDT-8 treated MRL/lpr mice. Moreover, infiltration of T cells in the kidney was mitigated after LLDT-8 treatment, corresponding with decreased expression of related chemokines IP-10, Mig, and RANTES in the kidney. The proportion of macrophage and neutrophil cells and related chemokines expression was also reduced in kidneys of LLDT-8-treated mice. In the human proximal tubule epithelial cell line and mouse mesangial cell line, consistent with our in vivo experimental results, LLDT-8 suppressed the expression of related chemokines and IL-6. In summary, LLDT-8 has a therapeutic benefit for lupus nephritis via suppressing chemokine expression and inhibiting immune cell infiltration in kidneys of MRL/lpr mice.

Innate and adaptive immunity in experimental glomerulonephritis: a pathfinder tale

The role of innate and adaptive immune cells in the experimental model of nephrotoxic serum nephritis (NTS) has been rigorously studied in recent years. The model is dependent on kidney-infiltrating T helper (TH) 17 and TH1 cells, which recruit neutrophils and macrophages, respectively, and cause sustained kidney inflammation. In a later phase of disease, regulatory T cells (Tregs) infiltrate the kidney in an attempt to limit disease activity. In the early stage of NTS, lymph node drainage plays an important role in disease initiation since dendritic cells present the antigen to T cells in the T cell zones of the draining lymph nodes. This results in the differentiation and proliferation of TH17 and TH1 cells. In this setting, immune regulatory cells (Tregs), namely, CCR7-expressing Tregs and mast cells (MCs), which are recruited by Tregs via the production of interleukin-9, exert their immunosuppressive capacity. Together, these two cell populations inhibit T cell differentiation and proliferation, thereby limiting disease activity by as yet unknown mechanisms. In contrast, the spleen plays no role in immune activation in NTS, but constitutes a place of extramedullary haematopoiesis. The complex interactions of immune cells in NTS are still under investigation and might ultimately lead to targeted therapies in glomerulonephritis.

Basement membranes and autoimmune diseases

Basement membrane components are targets of autoimmune attack in diverse diseases that destroy kidneys, lungs, skin, mucous membranes, joints, and other organs in man. Epitopes on collagen and laminin, in particular, are targeted by autoantibodies and T cells in anti-glomerular basement membrane glomerulonephritis, Goodpasture's disease, rheumatoid arthritis, post-lung transplant bronchiolitis obliterans syndrome, and multiple autoimmune dermatoses. This review examines major diseases linked to basement membrane autoreactivity, with a focus on investigations in patients and animal models that advance our understanding of disease pathogenesis. Autoimmunity to glomerular basement membrane type IV is discussed in depth as a prototypic organ-specific autoimmune disease yielding novel insights into the complexity of anti-basement membrane immunity and the roles of genetic and environmental susceptibility.

Inhibitor of NFκB Kinase Subunit 2 Blockade Hinders the Initiation but Aggravates the Progression of Crescentic GN

The NFκB transcription factor family facilitates the activation of dendritic cells (DCs) and CD4(+) T helper (Th) cells, which are important for protective adaptive immunity. Inappropriate activation of these immune cells may cause inflammatory disease, and NFκB inhibitors are promising anti-inflammatory drug candidates. Here, we investigated whether inhibiting the NFκB-inducing kinase IKK2 can attenuate crescentic GN, a severe DC- and Th cell-dependent kidney inflammatory disease. Prophylactic pharmacologic IKK2 inhibition reduced DC and Th cell activation and ameliorated nephrotoxic serum-induced GN in mice. However, therapeutic IKK2 inhibition during ongoing disease aggravated the nephritogenic immune response and disease symptoms. This effect resulted from the renal loss of regulatory T cells, which have been shown to protect against crescentic GN and which require IKK2. In conclusion, although IKK2 inhibition can suppress the induction of nephritogenic immune responses in vivo, it may aggravate such responses in clinically relevant situations, because it also impairs regulatory T cells and thereby, unleashes preexisting nephritogenic responses. Our findings argue against using IKK2 inhibitors in chronic GN and perhaps, other immune-mediated diseases.

Pretransplant Recipient Circulating CD4+CD127lo/- Tumor Necrosis Factor Receptor 2+ Regulatory T Cells: A Surrogate of Regulatory T Cell-Suppressive Function and Predictor of Delayed and Slow Graft Function After Kidney Transplantation

BACKGROUND

Delayed graft function (DGF) and slow graft function (SGF) are ischemia-reperfusion-associated acute kidney injuries (AKI) that decrease long-term graft survival after kidney transplantation. Regulatory T (Treg) cells are protective in murine AKI, and their suppressive function predictive of AKI in kidney transplantation. The conventional Treg cell function coculture assay is however time-consuming and labor intensive. We sought a simpler alternative to measure Treg cell function and predict AKI.

METHODS

In this prospective observational cohort study, pretransplant recipient circulating CD4+CD25+CD127lo/- and CD4+CD127lo/- tumor necrosis factor receptor 2 (TNFR2)+ Treg cells were measured by flow cytometry in 76 deceased donor kidney transplant recipients (DGF, n = 18; SGF, n = 34; immediate graft function [IGF], n = 24). In a subset of 37 recipients, pretransplant circulating Treg cell-suppressive function was also quantified by measuring the suppression of autologous effector T-cell proliferation by Treg cell in coculture.

RESULTS

The TNFR2+ expression on CD4+CD127lo/- T cells correlated with Treg cell-suppressive function (r = 0.63, P < 0.01). In receiver operating characteristic curves, percentage and absolute number of CD4+CD127lo/-TNFR2+ Treg cell predicted DGF from non-DGF (IGF + SGF) with area under the curves of 0.75 and 0.77, respectively, and also AKI (DGF + SGF) from IGF with area under the curves of 0.76 and 0.72, respectively (P < 0.01). Prediction of AKI (DGF + SGF) from IGF remained significant in multivariate logistic regression accounting for cold ischemic time, donor age, previous transplant, and pretransplant dialysis modality.

CONCLUSIONS

Pretransplant recipient circulating CD4+CD127lo/-TNFR2+ Treg cell is potentially a simpler alternative to Treg cell function as a pretransplant recipient immune marker for AKI (DGF + SGF), independent from donor and organ procurement characteristics.

Optimizing the translational value of animal models of glomerulonephritis: insights from recent murine prototypes

Animal models are indispensable for the study of glomerulonephritis, a group of diseases that destroy kidneys but for which specific therapies do not yet exist. Novel interventions are urgently needed, but their rational design requires suitable in vivo platforms to identify and test new candidates. Animal models can recreate the complex immunologic microenvironments that foster human autoimmunity and nephritis and provide access to tissue compartments not readily examined in patients. Study of rat Heymann nephritis identified fundamental disease mechanisms that ultimately revolutionized our understanding of human membranous nephropathy. Significant species differences in expression of a major target antigen, however, and lack of spontaneous autoimmunity in animals remain roadblocks to full exploitation of preclinical models in this disease. For several glomerulonephritides, humanized models have been developed to circumvent cross-species barriers and to study the effects of human genetic risk variants. Herein we review humanized mouse prototypes that provide fresh insight into mediators of IgA nephropathy and origins of antiglomerular basement membrane nephritis and Goodpasture's disease, as well as a means to test novel therapies for ANCA vasculitis. Additional and refined model systems are needed to mirror the full spectrum of human disease in a genetically diverse population, to facilitate development of patient-specific interventions, to determine the origin of nephritogenic autoimmunity, and to define the role of environmental exposures in disease initiation and relapse.

AKAP9 regulates activation-induced retention of T lymphocytes at sites of inflammation

The mechanisms driving T cell homing to lymph nodes and migration to tissue are well described but little is known about factors that affect T cell egress from tissues. Here, we generate mice with a T cell-specific deletion of the scaffold protein A kinase anchoring protein 9 (AKAP9) and use models of inflammatory disease to demonstrate that AKAP9 is dispensable for T cell priming and migration into tissues and lymph nodes, but is required for T cell retention in tissues. AKAP9 deficiency results in increased T cell egress to draining lymph nodes, which is associated with impaired T cell re-activation in tissues and protection from organ damage. AKAP9-deficient T cells exhibit reduced microtubule-dependent recycling of TCRs back to the cell surface and this affects antigen-dependent activation, primarily by non-classical antigen-presenting cells. Thus, AKAP9-dependent TCR trafficking drives efficient T cell re-activation and extends their retention at sites of inflammation with implications for disease pathogenesis.

A-kinase anchoring protein 9 (AKAP9) is a scaffold protein that binds signalling proteins and regulates microtubules. Here the authors show that during inflammation AKAP9 in T cells is required for their reactivation and retention at the inflammation site and that its deletion protects from inflammation-induced organ damage.