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Immune dysregulation plays a key role in the pathogenesis of steroid-dependent/frequently relapsing nephrotic syndrome (SDNS/FRNS). However, in contrast with evidence from the pediatric series, no major B- or T-cell alterations have been described for adults. In these patients, treatment with rituximab allows safe discontinuation of steroids, but long-term efficacy is variable, and some patients experience NS relapses after B cell reconstitution. In this study, we aimed to determine disease-associated changes in the B and T cell phenotype of adult patients with SDND/FRNS after steroid-induced remission. We also investigated whether any of these changes in immune cell subsets could discriminate between patients who developed NS relapses after steroid-sparing treatment with rituximab from those who did not. Lymphocyte subsets in SDNS/FRNS patients (n = 18) were compared to those from patients with steroid-resistant NS (SRNS, n = 7) and healthy volunteers (HV, n = 15). Before rituximab, SDND/FRNS patients showed increased frequencies of total and memory B cells, mainly with a CD38-negative phenotype. Within the T-cell compartment, significantly lower levels of FOXP3+ regulatory T cells (Tregs) were found, mostly due to a reduction in CD45RO+ memory Tregs compared to both SRNS and HV. The levels of CD45RO+ Tregs were significantly lower at baseline in patients who relapsed after rituximab (n = 9) compared to patients who did not (n = 9). In conclusion, patients with SDND/FRNS displayed expansion of memory B cells and reduced memory Tregs. Treg levels at baseline may help identify patients who will achieve sustained remission following rituximab infusion from those who will experience NS relapses.

Background In donor kidneys subjected to ischemia-reperfusion injury during kidney transplant, phagocytes coexpressing the F4/80 and CD11c molecules mediate proinflammatory responses and trigger adaptive immunity in transplantation through antigen presentation. After injury, however, resident renal macrophages coexpressing these surface markers acquire a proreparative phenotype, which is pivotal in controlling inflammation and fibrosis. No data are currently available regarding the effects of transplant-induced ischemia-reperfusion injury on the ability of donor-derived resident renal macrophages to act as professional antigen-presenting cells. Methods We evaluated the phenotype and function of intragraft CD11c+F4/80+ renal macrophages after cold ischemia. We also assessed the modifications of donor renal macrophages after reversible ischemia-reperfusion injury in a mouse model of congeneic renal transplantation. To investigate the role played by IL-1R8, we conducted in vitro and in vivo studies comparing cells and grafts from wild-type and IL-R8-deficient donors. Results Cold ischemia and reversible ischemia-reperfusion injury dampened antigen presentation by renal macrophages, skewed their polarization toward the M2 phenotype, and increased surface expression of IL-1R8, diminishing activation mediated by toll-like receptor 4. Ischemic IL-1R8-deficient donor renal macrophages acquired an M1 phenotype, effectively induced IFNγ and IL-17 responses, and failed to orchestrate tissue repair, resulting in severe graft fibrosis and aberrant humoral immune responses. Conclusions IL-1R8 is a key regulator of donor renal macrophage functions after ischemia-reperfusion injury, crucial to guiding the phenotype and antigen-presenting role of these cells. It may therefore represent an intriguing pathway to explore with respect to modulating responses against autoantigens and alloantigens after kidney transplant.

A membranoproliferative pattern of glomerular injury is frequently observed in patients with complement-mediated disorders, such as C3 glomerulopathies (C3G) and primary immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN). The outcomes of C3G and ­IC-MPGN are poor, independently of immunosuppressive therapy. However, two 48-week treatment periods with the anti-C5 monoclonal antibody eculizumab, divided by a ­12-week washout period, achieved remission of proteinuria and stabilization/improvement of the glomerular filtration rate (GFR), measured through iohexol plasma clearance, in 3 of 10 patients with biopsy-proven MPGN, nephrotic syndrome and terminal complement complex sC5b-9 plasma levels >1,000 mg/mL, at inclusion. Baseline and end-of-study kidney biopsies were available for 2 patients with IC-MPGN, and their baseline characteristics were similar. However, in 1 patient proteinuria and GFR did not improve during the study, whereas in the other proteinuria decreased from 4.84 to 2.12 g/24-h and GFR increased from 91.5 to 142.7 mL/min/1.73 m2. Glomerular inflammation improved and median (interquartile range) glomerular staining for C5b-9 decreased in both cases: from 23.6 to 18.2% (p = 0.021) in the patient who achieved remission and from 15.8 to 10.7% (p = 0.019) in the patient with persistent proteinuria. Chronic glomerular lesions progressed and C3 glomerular staining and electron-dense deposits did not change appreciably in either case. However, in the patient who achieved remission, ultrastructural evaluation revealed features of glomerular microangiopathy at inclusion, which fully recovered posttreatment. Podocyte foot process effacement was observed in both patients at inclusion, but recovered only in the patient with microangiopathy. Thus, in 2 patients with ­IC-MPGN, chronic glomerular changes progressed despite eculizumab-induced amelioration of glomerular inflammation and inhibition of sC5b-9 deposition, and independently of treatment effects on proteinuria and podocytes. The finding that the regression of microangiopathic changes was associated with improved clinical outcomes suggests that C5 blockade might have a therapeutic role in patients with IC-MPGN displaying microangiopathic endothelial injury.

Rationale & Objective: Primary membranoproliferative glomerulonephritis (MPGN) is a rare glomerulopathy characterized by complement dysregulation. MPGN progresses rapidly to kidney failure when it is associated with nephrotic syndrome. We assessed the effects of C5 convertase blockade in patients with MPGN and terminal complement activation. Study Design: Prospective off-on-off-on open-label clinical trial. Setting & Participants: Consenting patients with immune complex–mediated MPGN (n = 6) or C3 glomerulonephritis (n = 4) with sC5b-9 (serum complement membrane attack complex) plasma levels > 1,000 ng/mL and 24-hour proteinuria with protein excretion > 3.5 g identified from the Italian Registry of MPGN and followed up at the Istituto di Ricerche Farmacologiche Mario Negri IRCCS (Bergamo, Italy) between March 4, 2014, and January 7, 2015. Intervention: Anti-C5 monoclonal antibody eculizumab administered during 2 sequential 48-week treatment periods separated by one 12-week washout period. Outcomes: Primary outcome was change in 24-hour proteinuria (median of 3 consecutive measurements) at 24 and 48 weeks. Results: Median proteinuria decreased from protein excretion of 6.03 (interquartile range [IQR], 4.8-12.4) g/d at baseline to 3.74 (IQR, 3.2-4.4) g/d at 24 weeks (P = 0.01) and to 5.06 (IQR, 3.1-5.8) g/d (P = 0.006) at 48 weeks of treatment, recovered toward baseline during the washout period, and did not significantly decrease thereafter. Hypoalbuminemia, dyslipidemia, and glomerular sieving function improved during the first treatment period. 3 patients achieved partial remission of nephrotic syndrome and all had undetectable C3 nephritic factors before treatment. Mean measured glomerular filtration rate was 69.7 ± 35.2 versus 87.4 ± 55.1 and 75.8 ± 42.7 versus 76.6 ± 44.1 mL/min/1.73 m2 at the start versus the end of the first and second treatment periods, respectively, among all 10 study participants. Unlike C3, sC5b-9 plasma levels normalized during both treatment periods and recovered toward baseline during the washout in all patients. Limitations: Single-arm design, small sample size. Conclusions: Eculizumab blunted terminal complement activation in all patients with immune complex–mediated MPGN or C3 glomerulonephritis and nephrotic syndrome, but persistently reduced proteinuria in just a subgroup. Trial Registration: Registered in the EU Clinical Trials Register with study no. 2013-003826-10.

Background Mesenchymal stromal cells (MSCs) have protolerogenic effects in renal transplantation, but they induce long-term regulatory T cells (Treg)-dependent graft acceptance only when infused before transplantation. When given posttransplant, MSCs home to the graft where they promote engraftment syndrome and do not induce Treg. Unfortunately, pretransplant MSC administration is unfeasible in deceased-donor kidney transplantation. Methods To make MSCs a therapeutic option also for deceased organ recipients, we tested whether MSC infusion at the time of transplant (day 0) or posttransplant (day 2) together with inhibition of complement receptors prevents engraftment syndrome and allows their homing to secondary lymphoid organs for promoting tolerance. We analyzed intragraft and splenic MSC localization, graft survival, and alloimmune response in mice recipients of kidney allografts and syngeneic MSCs given on day 0 or on posttransplant day 2. C3a receptor (C3aR) or C5a receptor (C5aR) antagonists were administered to mice in combination with the cells or were used together to treat MSCs before infusion. Results Syngeneic MSCs given at day 0 homed to the spleen increased Treg numbers and induced long-term graft acceptance. Posttransplant MSC infusion, combined with a short course of C3aR or C5aR antagonist or administration of MSCs pretreated with C3aR and C5aR antagonists, prevented intragraft recruitment of MSCs and graft inflammation, inhibited antidonor T-cell reactivity, but failed to induce Treg, resulting in mild prolongation of graft survival. Conclusions These data support testing the safety/efficacy profile of administering MSCs on the day of transplant in deceased-donor transplant recipients and indicate that complement is crucial for MSC recruitment into the kidney allograft.

A 6-month-old boy presented with acute renal failure, thrombocytopenia, and severe non-immune hemolytic anemia. Infection by Shiga-like toxin-producing Escherichia coli and other causes of microangiopathic hemolysis were ruled out, leading to a diagnosis of atypical hemolytic uremic syndrome (aHUS). Neither pathogenic variants in HUS-associated genes nor anti-factor H antibodies were identified. Copy number variation analysis uncovered 4 copies of complement factor H related genes, CFHR1-CFHR4, conceivably leading to higher than normal levels of the corresponding proteins. However, this abnormality was also found in the healthy relatives, neither explaining the disease nor the excessive complement deposition on endothelial cells detected by an ex-vivo test. Whole-exome sequencing revealed a pathogenic homozygous variant in GRHPR encoding the glyoxylate and hydroxypyruvate reductase. Recessive GRHPR mutations cause primary hyperoxaluria type 2 (PH2). The presence of renal calculi in the patient and elevated oxalate levels in the urine were consistent with the genetic diagnosis of PH2. We hypothesize that, in this patient, hyperoxaluria caused by the GRHPR genetic defect triggered endothelial perturbation and complement activation, which was amplified by impaired factor H regulatory activity due to the increased ­CFHR1-CFHR4 copy numbers, resulting in aHUS.

Glomerulonephritis as well as kidney injury secondary to fulminant intravascular hemolysis are rare extrapulmonary manifestations of Mycoplasma pneumoniae infection. We describe a 50-year-old female diagnosed with M. pneumoniae infection-associated hemolytic anemia, characterized by negative cold agglutinin tests but with laboratory evidence of complement alternative pathway activation. The patient presented both with anemia and severe kidney failure and she was treated with steroids and red blood cell transfusions along with plasmapheresis. She also received a short course of antibiotics. Renal biopsy showed combined features of resolving postinfectious glomerulonephritis and hemolysis-associated extensive acute tubular injury characterized by renal hemosiderosis and intratubular hemoglobin casts. Electron microscopy revealed features of glomerular microangiopathic injury. The treatment led to complete disease remission and a favorable renal outcome at the first year follow-up.

The increasing prevalence of diabetes worldwide has led to a concomitant rise in diabetic kidney disease (DKD) as a major cause of end-stage renal disease. Glomerular lesions constitute the most striking and consistent features identified in biopsies from patients with DKD, although tubulointerstitial injury has an important and often under-recognized role in the progression to overt nephropathy. In advanced stages of the disease, podocyte detachment is a pivotal event in the loss of glomerular filtration barrier integrity and may explain, at least in part, the inability of current therapies to halt renal function decline. This chapter details the systematic method that can be used to study renal tissue samples from diabetic patients, and the specific role of different imaging techniques, such as light microscopy, immunofluorescence microscopy, and transmission and scanning electron microscopy in detecting histologic lesions specific to DKD.

BACKGROUND: In donor kidneys subjected to ischemia-reperfusion injury during kidney transplant, phagocytes coexpressing the F4/80 and CD11c molecules mediate proinflammatory responses and trigger adaptive immunity in transplantation through antigen presentation. After injury, however, resident renal macrophages coexpressing these surface markers acquire a proreparative phenotype, which is pivotal in controlling inflammation and fibrosis. No data are currently available regarding the effects of transplant-induced ischemia-reperfusion injury on the ability of donor-derived resident renal macrophages to act as professional antigen-presenting cells. METHODS: We evaluated the phenotype and function of intragraft CD11c(+)F4/80(+) renal macrophages after cold ischemia. We also assessed the modifications of donor renal macrophages after reversible ischemia-reperfusion injury in a mouse model of congeneic renal transplantation. To investigate the role played by IL-1R8, we conducted in vitro and in vivo studies comparing cells and grafts from wild-type and IL-R8–deficient donors. RESULTS: Cold ischemia and reversible ischemia-reperfusion injury dampened antigen presentation by renal macrophages, skewed their polarization toward the M(2) phenotype, and increased surface expression of IL-1R8, diminishing activation mediated by toll-like receptor 4. Ischemic IL-1R8–deficient donor renal macrophages acquired an M(1) phenotype, effectively induced IFNγ and IL-17 responses, and failed to orchestrate tissue repair, resulting in severe graft fibrosis and aberrant humoral immune responses. CONCLUSIONS: IL-1R8 is a key regulator of donor renal macrophage functions after ischemia-reperfusion injury, crucial to guiding the phenotype and antigen-presenting role of these cells. It may therefore represent an intriguing pathway to explore with respect to modulating responses against autoantigens and alloantigens after kidney transplant.

Diabetic nephropathy (DN), the single strongest predictor of mortality in patients with type 2 diabetes, is characterized by initial glomerular hyperfiltration with subsequent progressive renal function loss with or without albuminuria, greatly accelerated with the onset of overt proteinuria. Experimental and clinical studies have convincingly shown that early interventions retard disease progression, while treatment if started late in the disease course seldom modifies the slope of GFR decline. Here we assessed whether the negligible renoprotection afforded by drugs in patients with proteinuric DN could be due to loss of glomerular structural integrity, explored by scanning electron microscopy (SEM). In diabetic patients with early renal disease, glomerular structural integrity was largely preserved. At variance SEM documented that in the late stage of proteinuric DN, glomerular structure was subverted with nearly complete loss of podocytes and lobular transformation of the glomerular basement membrane. In these circumstances one can reasonably imply that any form of treatment, albeit personalized, is unlikely to reach a given cellular or molecular target. These findings should persuade physicians to start the putative renoprotective therapy soon after the diagnosis of diabetes or in an early phase of the disease before structural integrity of the glomerular filter is irreversibly compromised.

Levamisole is an antihelminthic agent widely used as an adulterant of illicit cocaine recently implicated as a cause of antineutrophil cytoplasmic antibody (ANCA)-associated microscopic polyangiitis in cocaine abusers. An isolated case of membranous nephropathy (MN) associated with levamisole exposure has also been reported. We report the first case, to our knowledge, of a patient with both microscopic polyangiitis manifest as a pauci-immune necrotizing and crescentic glomerulonephritis and concurrent MN in the setting of chronic cocaine abuse and presumed levamisole exposure, raising the hypothesis that levamisole was the causative agent in the development of this rare dual glomerulopathy.

Glomerulonephritis as well as kidney injury secondary to fulminant intravascular hemolysis are rare extrapulmonary manifestations of Mycoplasma pneumoniae infection. We describe a 50-year-old female diagnosed with M. pneumoniae infection-associated hemolytic anemia, characterized by negative cold agglutinin tests but with laboratory evidence of complement alternative pathway activation. The patient presented both with anemia and severe kidney failure and she was treated with steroids and red blood cell transfusions along with plasmapheresis. She also received a short course of antibiotics. Renal biopsy showed combined features of resolving postinfectious glomerulonephritis and hemolysis-associated extensive acute tubular injury characterized by renal hemosiderosis and intratubular hemoglobin casts. Electron microscopy revealed features of glomerular microangiopathic injury. The treatment led to complete disease remission and a favorable renal outcome at the first year follow-up.

Dabrafenib and trametinib, BRAF and MEK inhibitors, respectively, are effective targeted metastatic melanoma therapies, but little is known about their nephrotoxicity. Although tubulointerstitial injury has been the most widely reported renal side effect of targeted melanoma therapy, nephrotic syndrome has not been reported before. We report on a patient with metastatic melanoma who developed nephrotic syndrome during dabrafenib and trametinib treatment. Kidney biopsy showed diffuse loss of podocyte cytoarchitecture, extensive foot-process effacement, and glomerular endothelial injury. Kidney function and glomerular ultrastructural changes recovered fully after drug withdrawal. In vitro, BRAF inhibition decreased PLCe1 expression in podocytes, accompanied by a reduction in nephrin expression and an increase in permeability to albumin. Additionally, these drugs inhibited the podocyte–vascular endothelial growth factor (VEGF) system. In addition to implications for nephrotic syndrome pathophysiology, we suggest that patients given dabrafenib and trametinib be monitored closely for potential glomerular damage.