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Background: Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and glomerulonephritis is uncommon in children. We sought to characterize the histological and clinical features of the disease and report on risk factors for adverse outcomes in a pediatric cohort., Methods: Retrospective single-center cohort of all pediatric (< 20 years) patients diagnosed with ANCA-associated glomerulonephritis (AAGN) by kidney biopsy between 2002 and 2022 at Johns Hopkins University. Histological and clinical features were extracted from the medical record. Clinical, laboratory, and histological findings were analyzed to determine the association with kidney failure (KF) and/or death., Results: A total of 17 patients were identified (GPA n = 7, MPA = 10) with a median age of 15 years (IQR 12-17) at presentation, a slight female predominance (59%), with seven patients reaching the composite outcome of death (n = 1) or kidney failure (n = 6). There was no difference in presenting clinical symptoms or extra-renal manifestations between the two groups. Univariable Cox regression identified several factors associated with an increased hazard of endpoint including the degree of global or segmental sclerosis, interstitial fibrosis and tubular atrophy (IFTA), C3 and C1q staining, presence of subendothelial deposits, and proteinuria. Multivariable regression was not performed due to the small sample size. We saw a trend towards increased utilization of plasma exchange and a decrease in cyclophosphamide utilization in the more recent era. There was no association between treatment modality and outcome., Conclusions: Pediatric AAGN is a rare disease associated with significant morbidity. We identified glomerulosclerosis and IFTA on histology, and proteinuria on initial presentation as risk factors for KF/death., (© 2024. The Author(s), under exclusive licence to International Pediatric Nephrology Association.)

Competing Interests: Competing interests: None declared.

T cells mediate organ injury and repair. A proportion of unconventional kidney T cells called double-negative (DN) T cells (TCR + CD4 - CD8 - ), with anti-inflammatory properties, were previously demonstrated to protect from early injury in moderate experimental acute kidney injury (AKI). However, their role in repair after AKI has not been studied. We hypothesized that DN T cells mediate repair after severe AKI. C57B6 mice underwent severe (40 min) unilateral ischemia-reperfusion injury (IRI). Kidney DN T cells were studied by flow cytometry and compared with gold-standard anti-inflammatory CD4 + regulatory T cells (Tregs). In vitro effects of DN T cells and Tregs on renal tubular epithelial cell (RTEC) repair after injury were quantified with live-cell analysis. DN T cells, Tregs, CD4, or vehicle were adoptively transferred after severe AKI. Glomerular filtration rate (GFR) was measured using fluorescein isothiocyanate (FITC)-sinistrin. Fibrosis was assessed with Masson's trichrome staining. Profibrotic genes were measured with qRT-PCR. Percentages and the numbers of DN T cells substantially decreased during repair phase after severe AKI, as well as their activation and proliferation. Both DN T cells and Tregs accelerated RTEC cell repair in vitro. Post-AKI transfer of DN T cells reduced kidney fibrosis and improved GFR, as did Treg transfer. DN T cell transfer lowered transforming growth factor (TGF)β1 and α-smooth muscle actin (αSMA) expression. DN T cells reduced effector-memory CD4 + T cells and IL-17 expression. DN T cells undergo quantitative and phenotypical changes after severe AKI, accelerate RTEC repair in vitro as well as improve GFR and renal fibrosis in vivo. DN T cells have potential as immunotherapy to accelerate repair after AKI. NEW & NOTEWORTHY Double-negative (DN) T cells (CD4 - CD8 - ) are unconventional kidney T cells with regulatory abilities. Their role in repair from acute kidney injury (AKI) is unknown. Kidney DN T cell population decreased during repair after ischemic AKI, in contrast to regulatory T cells (Tregs) which increased. DN T cell administration accelerated tubular repair in vitro, while after severe in vivo ischemic injury reduced kidney fibrosis and increased glomerular filtration rate (GFR). DN T cell infusion is a potential therapeutic agent to improve outcome from severe AKI.

Competing Interests: Declaration of interests We declare no competing interests.

Targeting gut microbiota has shown promise to prevent experimental acute kidney injury (AKI). However, this has not been studied in relation to accelerating recovery and preventing fibrosis. Here, we found that modifying gut microbiota with an antibiotic administered after severe ischemic kidney injury in mice, particularly with amoxicillin, accelerated recovery. These indices of recovery included increased glomerular filtration rate, diminution of kidney fibrosis, and reduction of kidney profibrotic gene expression. Amoxicillin was found to increase stool Alistipes, Odoribacter and Stomatobaculum species while significantly depleting Holdemanella and Anaeroplasma. Specifically, amoxicillin treatment reduced kidney CD4 + T cells, interleukin (IL)-17 + CD4 + T cells, and tumor necrosis factor-α double negative T cells while it increased CD8 + T cells and PD1 + CD8 + T cells. Amoxicillin also increased gut lamina propria CD4 + T cells while decreasing CD8 + T and IL-17 + CD4 + T cells. Amoxicillin did not accelerate repair in germ-free or CD8-deficient mice, demonstrating microbiome and CD8 + T lymphocytes dependence for amoxicillin protective effects. However, amoxicillin remained effective in CD4-deficient mice. Fecal microbiota transplantation from amoxicillin-treated to germ-free mice reduced kidney fibrosis and increased Foxp3 + CD8 + T cells. Amoxicillin pre-treatment protected mice against kidney bilateral ischemia reperfusion injury but not cisplatin-induced AKI. Thus, modification of gut bacteria with amoxicillin after severe ischemic AKI is a promising novel therapeutic approach to accelerate recovery of kidney function and mitigate the progression of AKI to chronic kidney disease., (Copyright © 2023 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Rationale & Objective: Patients hospitalized with COVID-19 are at increased risk for major adverse kidney events (MAKE). We sought to identify plasma biomarkers predictive of MAKE in patients hospitalized with COVID-19., Study Design: Prospective cohort study., Setting & Participants: A total of 576 patients hospitalized with COVID-19 between March 2020 and January 2021 across 3 academic medical centers., Exposure: Twenty-six plasma biomarkers of injury, inflammation, and repair from first available blood samples collected during hospitalization., Outcome: MAKE, defined as KDIGO stage 3 acute kidney injury (AKI), dialysis-requiring AKI, or mortality up to 60 days., Analytical Approach: Cox proportional hazards regression to associate biomarker level with MAKE. We additionally applied the least absolute shrinkage and selection operator (LASSO) and random forest regression for prediction modeling and estimated model discrimination with time-varying C index., Results: The median length of stay for COVID-19 hospitalization was 9 (IQR, 5-16) days. In total, 95 patients (16%) experienced MAKE. Each 1 SD increase in soluble tumor necrosis factor receptor 1 (sTNFR1) and sTNFR2 was significantly associated with an increased risk of MAKE (adjusted HR [AHR], 2.30 [95% CI, 1.86-2.85], and AHR, 2.26 [95% CI, 1.73-2.95], respectively). The C index of sTNFR1 alone was 0.80 (95% CI, 0.78-0.84), and the C index of sTNFR2 was 0.81 (95% CI, 0.77-0.84). LASSO and random forest regression modeling using all biomarkers yielded C indexes of 0.86 (95% CI, 0.83-0.89) and 0.84 (95% CI, 0.78-0.91), respectively., Limitations: No control group of hospitalized patients without COVID-19., Conclusions: We found that sTNFR1 and sTNFR2 are independently associated with MAKE in patients hospitalized with COVID-19 and can both also serve as predictors for adverse kidney outcomes., Plain-Language Summary: Patients hospitalized with COVID-19 are at increased risk for long-term adverse health outcomes, but not all patients suffer long-term kidney dysfunction. Identification of patients with COVID-19 who are at high risk for adverse kidney events may have important implications in terms of nephrology follow-up and patient counseling. In this study, we found that the plasma biomarkers soluble tumor necrosis factor receptor 1 (sTNFR1) and sTNFR2 measured in hospitalized patients with COVID-19 were associated with a greater risk of adverse kidney outcomes. Along with clinical variables previously shown to predict adverse kidney events in patients with COVID-19, both sTNFR1 and sTNFR2 are also strong predictors of adverse kidney outcomes., (Copyright © 2023 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Drug-induced vasculitis can rarely cause inflammation and necrosis of blood vessel walls of both kidney and lung tissue. Diagnosis is challenging because of the lack of difference between systemic and drug-induced vasculitis in clinical presentation, immunological workup and pathological findings. Tissue biopsy guides diagnosis and treatment. Pathological findings must be correlated with clinical information to arrive at a presumed diagnosis of drug-induced vasculitis. We present a patient with hydralazine-induced antineutrophil cytoplasmic antibodies-positive vasculitis with a pulmonary-renal syndrome manifesting as pauci-immune glomerulonephritis and alveolar haemorrhage., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2023. No commercial re-use. See rights and permissions. Published by BMJ.)

T cells play an important role in acute kidney injury (AKI). Metabolic programming of T cells regulates their function, is a rapidly emerging field, and is unknown in AKI. We induced ischemic AKI in C57BL/6J mice and collected kidneys and spleens at multiple time points. T cells were isolated and analyzed by an immune-metabolic assay. Unbiased machine learning analyses identified a distinct T cell subset with reduced voltage-dependent anion channel 1 and mTOR expression in post-AKI kidneys. Ischemic kidneys showed higher expression of trimethylation of histone H3 lysine 27 and glutaminase. Splenic T cells from post-AKI mice had higher expression of glucose transporter 1, hexokinase II, and carnitine palmitoyltransferase 1a. Human nonischemic and ischemic kidney tissue displayed similar findings to mouse kidneys. Given a convergent role for glutamine in T cell metabolic pathways and the availability of a relatively safe glutamine antagonist, JHU083, effects on AKI were evaluated. JHU083 attenuated renal injury and reduced T cell activation and proliferation in ischemic and nephrotoxic AKI, whereas T cell-deficient mice were not protected by glutamine blockade. In vitro hypoxia demonstrated upregulation of glycolysis-related enzymes. T cells undergo metabolic reprogramming during AKI, and reconstitution of metabolism by targeting T cell glutamine pathway could be a promising novel therapeutic approach.

Significance Statement: T cells mediate pathogenic and reparative processes during AKI, but the exact mechanisms regulating kidney T cell functions are unclear. This study identified upregulation of the novel immune checkpoint molecule, TIGIT, on mouse and human kidney T cells after AKI. TIGIT-expressing kidney T cells produced proinflammatory cytokines and had effector (EM) and central memory (CM) phenotypes. TIGIT-deficient mice had protection from both ischemic and nephrotoxic AKI. Single-cell RNA sequencing led to the discovery of possible downstream targets of TIGIT. TIGIT mediates AKI pathophysiology, is a promising novel target for AKI therapy, and is being increasingly studied in human cancer therapy trials., Background: T cells play pathogenic and reparative roles during AKI. However, mechanisms regulating T cell responses are relatively unknown. We investigated the roles of the novel immune checkpoint molecule T cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory motif domains (TIGIT) in kidney T cells and AKI outcomes., Methods: TIGIT expression and functional effects were evaluated in mouse kidney T cells using RNA sequencing (RNA-Seq) and flow cytometry. TIGIT effect on AKI outcomes was studied with TIGIT knockout (TIGIT-KO) mice in ischemia reperfusion (IR) and cisplatin AKI models. Human kidney T cells from nephrectomy samples and single cell RNA sequencing (scRNA-Seq) data from the Kidney Precision Medicine Project were used to assess TIGIT's role in humans., Results: RNA-Seq and flow cytometry analysis of mouse kidney CD4+ T cells revealed increased expression of TIGIT after IR injury. Ischemic injury also increased TIGIT expression in human kidney T cells, and TIGIT expression was restricted to T/natural killer cell subsets in patients with AKI. TIGIT-expressing kidney T cells in wild type (WT) mice had an effector/central memory phenotype and proinflammatory profile at baseline and post-IR. Kidney regulatory T cells were predominantly TIGIT+ and significantly reduced post-IR. TIGIT-KO mice had significantly reduced kidney injury after IR and nephrotoxic injury compared with WT mice. scRNA-Seq analysis showed enrichment of genes related to oxidative phosphorylation and mTORC1 signaling in Th17 cells from TIGIT-KO mice., Conclusions: TIGIT expression increases in mouse and human kidney T cells during AKI, worsens AKI outcomes, and is a novel therapeutic target for AKI., (Copyright © 2023 by the American Society of Nephrology.)

Aims: T cells play pathophysiologic roles in kidney ischemia-reperfusion injury (IRI), and the nuclear factor erythroid 2-related factor 2/kelch-like ECH-associated protein 1 (Nrf2/Keap1) pathway regulates T cell responses. We hypothesized that clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-mediated Keap1 -knockout (KO) augments Nrf2 antioxidant potential of CD4+ T cells, and that Keap1 -KO CD4+ T cell immunotherapy protects from kidney IRI. Results: CD4+ T cell Keap1 -KO resulted in significant increase of Nrf2 target genes NAD(P)H quinone dehydrogenase 1, heme oxygenase 1, glutamate-cysteine ligase catalytic subunit, and glutamate-cysteine ligase modifier subunit. Keap1 -KO cells displayed no signs of exhaustion, and had significantly lower levels of interleukin 2 (IL2) and IL6 in normoxic conditions, but increased interferon gamma in hypoxic conditions in vitro . In vivo , adoptive transfer of Keap1 -KO CD4+ T cells before IRI improved kidney function in T cell-deficient nu/nu mice compared with mice receiving unedited control CD4+ T cells. Keap1 -KO CD4+ T cells isolated from recipient kidneys 24 h post IR were less activated compared with unedited CD4+ T cells, isolated from control kidneys. Innovation: Editing Nrf2/Keap1 pathway in murine T cells using CRISPR/Cas9 is an innovative and promising immunotherapy approach for kidney IRI and possibly other solid organ IRI. Conclusion: CRISPR/Cas9-mediated Keap1 -KO increased Nrf2-regulated antioxidant gene expression in murine CD4+ T cells, modified responses to in vitro hypoxia and in vivo kidney IRI. Gene editing targeting the Nrf2/Keap1 pathway in T cells is a promising approach for immune-mediated kidney diseases.

Introduction: Proliferative lupus nephritis (LN) progresses to end-stage kidney disease (ESKD) in roughly 10% of the cases despite treatment. Other than achieving <0.8 g/24h proteinuria at 12 months after treatment, early biomarkers predicting ESKD or death are lacking. Recent studies encompassing not only LN have highlighted the central role of the alternative complement pathway (ACP), with or without histological evidence of thrombotic microangiopathy (TMA), as a key promotor of renal death., Methods: We assessed whether persistent isolated C3 hypocomplementemia (PI-LowC3), that is not accompanied by C4 hypocomplementemia, 6 months after kidney biopsy, is associated with an increased risk of death or ESKD in proliferative LN., Results: We retrospectively followed-up 197 patients with proliferative LN (51 with PI-LowC3) for a median of 4.5 years (interquartile-range: 1.9-9.0), 11 of whom died and 22 reached ESKD. After adjusting for age, gender, ethnicity, hypertension, mycophenolate, or cyclophosphamide use, PI-LowC3 was associated with a hazard ratio [HR] of the composite outcome ESKD or death of 2.46 (95% confidence interval [CI]: 1.22-4.99, P  = 0.012). These results were confirmed even after controlling for time-varying estimated glomerular filtration rate (eGFR) measurements in joint longitudinal-survival multiple regression models. After accounting for the competing risk of death, PI-LowC3 patients showed a strikingly increased risk of ESKD (adjusted HR 3.41, 95% CI: 1.31-8.88, P  = 0.012)., Conclusion: Our findings support the use of PI-LowC3 as a low-cost readily available biomarker, allowing clinicians to modify treatment strategies early in the course of disease and offering a rationale for complement blockade trials in this particularly at-risk subgroup of LN patients., (© 2022 International Society of Nephrology. Published by Elsevier Inc.)

Introduction: It has been recognized that T cells have a pathogenic role in anti-neutrophil cytoplasmic antibody- (ANCA) associated vasculitis, in addition to being dominant cells in the interstitium in ANCA glomerulonephritis (GN). Given there are differences in renal outcomes based on ANCA type, we sought to characterize the interstitial infiltrate in ANCA GN to determine differences in relation to ANCA type and renal function., Methods: Immunohistochemistry stains for CD3, CD4, CD20, C4d and FOXP3 were done in renal biopsies of patients with ANCA GN. Light microscopy was used to determine the percentage of cortical interstitium containing positive cells. Demographics, ANCA type and entry eGFR were recorded. The level of staining was compared between ANCA type and entry eGFR using Wilcoxon rank-sum test., Results: Renal biopsies of 16 patients with MPO and 14 with PR3 ANCA GN were studied. CD3 cells were the predominant cells, with all biopsies staining positive for CD4 and FOXP3. C4d staining was negative in all biopsies, with no significant difference in staining between MPO and PR3 groups for any of the identified cell types. However, regardless of ANCA type, FOXP3 staining was significantly higher in patients with baseline GFR < 10 compared with GFR > 10 mL/min/1.73 m 2 (mean 7.54, SD 6.6 versus mean 2.67, SD 3.6; p = 0.04)., Conclusion: These data confirm the role of T cells in ANCA GN and demonstrate no differences in interstitial T and B cell infiltrates between PR3 and MPO ANCA GN. Higher FOXP3 signal associates with lower renal function, suggesting a role for regulatory T cells. Further characterization of this T cell subset should be explored in future studies., (© 2021. Italian Society of Nephrology.)

Introduction: Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults and can be primary or secondary. The antigenic target of antibodies in 70% of primary cases is phospholipase A2 receptor (PLA2R). The presence or absence of mesangial electron-dense deposits has been used to distinguish between primary and secondary MN. Mesangial deposits suggest MN due to lupus, infection, or other causes, though they are reported to occur in approximately 10% of primary MN. Staining for PLA2R is now frequently used for confirming a diagnosis of primary MN. If mesangial deposits predict a secondary cause, they should be more frequent in PLA2R-negative biopsies., Methods: A review of institutional kidney biopsies between March 2017 and June 2020 identified all cases of MN. Cases with a diagnosis of lupus or near "full-house" staining by immunofluorescence microscopy (IF) were excluded. Light microscopy, IF, and electron microscopy (EM) were performed. PLA2R staining was performed by IF. EM for all cases was reviewed and electron-dense deposit location, distribution, and size were determined., Results: Ninety-three cases of MN were identified, of which 86 had both PLA2R staining and EM performed. Of these, 51 cases (59%) were positive for PLA2R and 35 (41%) were negative. Mesangial electron-dense deposits were present in 22 (25.6%) of the 86 cases, including 27.5% (14/51) of PLA2R-positive cases and 22.8% (8/35) of PLA2R-negative cases. No difference was seen in size or distribution of deposits, or other features considered suggestive of secondary MN., Conclusion: PLA2R-negative cases were not more likely to have mesangial deposits than PLA2R-positive cases. Mesangial deposits should not be used as an indicator of secondary MN., (© 2021 S. Karger AG, Basel.)

Replacing equipment and software can improve efficiency and allow updates to laboratory procedures, but has the potential to introduce changes in established values for a laboratory. Replacement of an electron microscope (EM), fitted with an updated digital camera, and use of new software for imaging and analysis prompted this QA study to ensure that new equipment, imaging, and measurement of the glomerular basement membrane (GBM) produced data consistent with the laboratory's established range of normal width. GBM measurements from 14 randomly selected human renal biopsies were compared using five different approaches. Original measurements of GBMs obtained on the laboratory's previous EM were compared to images collected on the new microscope with measurements performed using new software, as well as the original images and the new images measured using a separate software method as a control. The widths obtained by five approaches were compared to each other. While measurements showed minor variability between the approaches, significant difference in GBM width was noted in three of the paired comparisons. In some cases, these differences suggested slight diagnostic changes. Evaluation of new equipment, software, and techniques is important for a laboratory's quality assurance. While new equipment and/or procedures can introduce errors in test outcomes, we found that different EMs, cameras, and software made slight differences in our laboratory's values for kidney GBM width. However, a few cases showed enough difference in GBM width to suggest a change in diagnosis, illustrating the necessity of calibration adjustments in the setting of new equipment and software., (© 2021 Wiley Periodicals LLC.)

Inhibitors of the renin-angiotensin system (RAS) are widely used to treat hypertension. Using mice harboring fluorescent cell lineage tracers, single-cell RNA-Seq, and long-term inhibition of RAS in both mice and humans, we found that deletion of renin or inhibition of the RAS leads to concentric thickening of the intrarenal arteries and arterioles. This severe disease was caused by the multiclonal expansion and transformation of renin cells from a classical endocrine phenotype to a matrix-secretory phenotype: the cells surrounded the vessel walls and induced the accumulation of adjacent smooth muscle cells and extracellular matrix, resulting in blood flow obstruction, focal ischemia, and fibrosis. Ablation of the renin cells via conditional deletion of β1 integrin prevented arteriolar hypertrophy, indicating that renin cells are responsible for vascular disease. Given these findings, prospective morphological studies in humans are necessary to determine the extent of renal vascular damage caused by the widespread use of inhibitors of the RAS.

Background: Kidney involvement is common in patients with systemic lupus erythematosus (SLE). This study investigates the clinical and prognostic characteristics of thrombotic microangiopathy (TMA) compared to class IV lupus nephritis in SLE patients., Methods: A retrospective review of patients who underwent kidney biopsy, with a primary diagnosis of SLE and TMA between June 2006 and September 2018 was conducted. Those patients were subsequently compared to patients with class IV lupus nephritis between January 2018 and December 2018. Demographics, laboratory, and serological data at the time of biopsy were abstracted., Results: Among 214 SLE patients records screened, 27 were included in the final analysis. Eight patients had lupus-related TMA without evidence of active lupus nephritis, while 19 patients had class IV lupus nephritis without evidence of TMA. TMA patients had significantly higher lactate dehydrogenase levels (718 ± 499 vs. 264 ± 107.7 U/L, p = 0.009), serum C3 (100.6 ± 39.3 vs. 65.8 ± 27 mg/dL, p = 0.049), white blood cell count (14743.8 ± 7933.3 vs. 5807.9 ± 2053.2 × 10E3/uL, p < 0.001), and total bilirubin (0.8 ± 0.5 vs. 0.3 ± 0.1 mg/dL, p = 0.007) in addition to significantly lower platelet counts (158.4 ± 88.6 vs. 240.3 ± 100.3 × 10E3/uL, p = 0.03), and haptoglobin (68.8 ± 116.1 vs. 166.8 ± 95.4 mg/dL, p = 0.03). After a median follow-up time of 53 weeks, 3 patients with TMA were dialysis-dependent (37.5%), compared with none in class IV lupus nephritis patients (p = 0.002)., Conclusions: TMA-associated SLE has worse prognosis compared to class IV lupus nephritis. An array of laboratory and pathological findings may be of value in discriminating between those two entities., (© 2021. Italian Society of Nephrology.)