RORing toward immunoregulation in glomerulonephritis?

CD4+ T cells that express forkhead box protein 3 are important in maintaining tolerance and restraining effector responses. Herrnstadt et al. use a model of rapidly progressive glomerulonephritis to examine the nature and role of forkhead box protein 3-positive and retinoid acid-related orphan receptor γt-positive regulatory T cells. These cells are prominent in experimental glomerulonephritis, both locally and systemically, and are present in kidneys of people with anti-neutrophil cytoplasmic antibody-associated vasculitis. Functionally, despite their expression of retinoid acid-related orphan receptor γt, associated with T-helper cell 17 cells, they regulate cellular immunity, both systemically and within the kidney.

International Society of Nephrology first consensus guidance for preclinical animal studies in translational nephrology.

Preclinical tests in animal models are key steps in early drug development. Consequently, the International Society of Nephrology held a consensus meeting that connected experts in the global kidney community in order to provide guidance on optimal management of translational animal studies for the development of new drugs to treat kidney disease, entitled "TRANSFORM; TRAnslational Nephrology Science FOR new Medications." The meeting covered various themes, including the following: (i) selection of disease model; (ii) pharmacokinetics; (iii) interventions in late preclinical models; (iv) choice of animal; (v) statistical power; (vi) organoids and organ-on-a-chip models; and (vii) reporting of results. This guidance is the first to be provided on the optimal conduct of translational animal studies for the development of new drugs to treat kidney disease. These recommendations are designed to accelerate development of new drugs for efficacious treatment of kidney diseases, and to improve the prognosis and quality of life of patients with a variety of kidney diseases.

T-cell receptor αß+ double-negative T cells in the kidney are predominantly extravascular and increase in abundance in response to ischemia-reperfusion injury.

T-cell receptor+ CD4- CD8- double-negative (DN) T cells are a population of T cells present in low abundance in blood and lymphoid organs, but enriched in various organs including the kidney. Despite burgeoning interest in these cells, studies examining their abundance in the kidney have reported conflicting results. Here we developed a flow cytometry strategy to clearly segregate DN T cells from other immune cells in the mouse kidney and used it to characterize their phenotype and response in renal ischemia-reperfusion injury (IRI). These experiments revealed that in the healthy kidney, most DN T cells are located within the renal parenchyma and exhibit an effector memory phenotype. In response to IRI, the number of renal DN T cells is unaltered after 24 h, but significantly increased by 72 h. This increase is not related to alterations in proliferation or apoptosis. By contrast, adoptive transfer studies indicate that circulating DN T cells undergo preferential recruitment to the postischemic kidney. Furthermore, DN T cells show the capacity to upregulate CD8, both in vivo following adoptive transfer and in response to ex vivo activation. Together, these findings provide novel insights regarding the phenotype of DN T cells in the kidney, including their predominant extravascular location, and show that increases in their abundance in the kidney following IRI occur in part as a result of increased recruitment from the circulation. Furthermore, the observation that DN T cells can upregulate CD8 in vivo has important implications for detection and characterization of DN T cells in future studies.

Removal of the endothelial surface layer via hyaluronidase does not modulate monocyte and neutrophil interactions with the glomerular endothelium.

OBJECTIVE: The endothelial surface layer (ESL), a layer of macromolecules on the surface of endothelial cells, can both impede and facilitate leukocyte recruitment. However, its role in monocyte and neutrophil recruitment in glomerular capillaries is unknown. METHODS: We used multiphoton intravital microscopy to examine monocyte and neutrophil behavior in the glomerulus following ESL disruption with hyaluronidase. RESULTS: Constitutive retention and migration of monocytes and neutrophils within the glomerular microvasculature was unaltered by hyaluronidase. Consistent with this, inhibition of the hyaluronan-binding molecule CD44 also failed to modulate glomerular trafficking of these immune cells. To investigate the contribution of the ESL during acute inflammation, we induced glomerulonephritis via in situ immune complex deposition. This resulted in increases in glomerular retention of monocytes and neutrophils but did not induce marked reduction in the glomerular ESL. Furthermore, hyaluronidase treatment did not modify the prolonged retention of monocytes and neutrophils in the acutely inflamed glomerular microvasculature. CONCLUSIONS: These observations indicate that, despite evidence that the ESL has the capacity to inhibit leukocyte-endothelial cell interactions while also containing adhesive ligands for immune cells, neither of these functions modulate trafficking of monocytes and neutrophils in steady-state or acutely-inflamed glomeruli.

The five types of glomerulonephritis classified by pathogenesis, activity and chronicity (GN-AC).

Glomerulonephritis (GN) is a diverse group of immune-mediated disorders. Currently, GN is classified largely by histological patterns that are difficult to understand and teach, and most importantly, do not indicate treatment choices. Indeed, altered systemic immunity is the primary pathogenic process and the key therapeutic target in GN. Here, we apply a conceptual framework of immune-mediated disorders to GN guided by immunopathogenesis and hence immunophenotyping: (i) infection-related GN require pathogen identification and control; (ii) autoimmunity-related GN, defined by presence of autoantibodies and (iii) alloimmunity-related GN in transplant recipients both require the suppression of adaptive immunity in lymphoid organs and bone marrow; (iv) autoinflammation-related GN, e.g. inborn errors of immunity diagnosed by genetic testing, requires suppression of single cytokine or complement pathways; and (v) Monoclonal gammopathy-related GN requires B or plasma cell clone-directed therapy. A new GN classification should include disease category, immunological activity to tailor the use of the increasing number of immunomodulatory drugs, and chronicity to trigger standard chronic kidney disease care including the evolving spectrum of cardio-renoprotective drugs. Certain biomarkers allow diagnosis and the assessment of immunological activity and disease chronicity without kidney biopsy. The use of these five GN categories and a therapy-focused GN classification is likely to overcome some of the existing hurdles in GN research, management and teaching by reflecting disease pathogenesis and guiding the therapeutic approach.

Primary aldosteronism: an unsuspected culprit of hypertension in systemic lupus erythematosus?

Primary aldosteronism (PA) is the most common endocrine cause of secondary hypertension and is associated with a high risk of cardiovascular disease in the general population. Patients suffering from systemic lupus erythematosus (SLE), a multisystem and multifactorial autoimmune disease, experience a high burden of hypertension and cardiovascular disease. Importantly, cardiovascular disease is one of the leading causes of death in SLE. Very limited evidence suggests an increased proportion of autoimmune diseases such as SLE in patients with PA. However, studies evaluating the prevalence of PA in the SLE population are lacking. Despite the potential for curative or targeted treatments, guidelines for the management of hypertension in SLE do not currently recommend testing for PA. This review highlights PA as a potentially over-looked secondary cause of hypertension in SLE, and offers future directions in research to improve the detection of this highly modifiable cardiovascular risk factor in the SLE population.

Dominant protection from HLA-linked autoimmunity by antigen-specific regulatory T cells.

Susceptibility and protection against human autoimmune diseases, including type I diabetes, multiple sclerosis, and Goodpasture disease, is associated with particular human leukocyte antigen (HLA) alleles. However, the mechanisms underpinning such HLA-mediated effects on self-tolerance remain unclear. Here we investigate the molecular mechanism of Goodpasture disease, an HLA-linked autoimmune renal disorder characterized by an immunodominant CD4+ T-cell self-epitope derived from the α3 chain of type IV collagen (α3135-145). While HLA-DR15 confers a markedly increased disease risk, the protective HLA-DR1 allele is dominantly protective in trans with HLA-DR15 (ref. 2). We show that autoreactive α3135-145-specific T cells expand in patients with Goodpasture disease and, in α3135-145-immunized HLA-DR15 transgenic mice, α3135-145-specific T cells infiltrate the kidney and mice develop Goodpasture disease. HLA-DR15 and HLA-DR1 exhibit distinct peptide repertoires and binding preferences and present the α3135-145 epitope in different binding registers. HLA-DR15-α3135-145 tetramer+ T cells in HLA-DR15 transgenic mice exhibit a conventional T-cell phenotype (Tconv) that secretes pro-inflammatory cytokines. In contrast, HLA-DR1-α3135-145 tetramer+ T cells in HLA-DR1 and HLA-DR15/DR1 transgenic mice are predominantly CD4+Foxp3+ regulatory T cells (Treg cells) expressing tolerogenic cytokines. HLA-DR1-induced Treg cells confer resistance to disease in HLA-DR15/DR1 transgenic mice. HLA-DR15+ and HLA-DR1+ healthy human donors display altered α3135-145-specific T-cell antigen receptor usage, HLA-DR15-α3135-145 tetramer+ Foxp3- Tconv and HLA-DR1-α3135-145 tetramer+ Foxp3+CD25hiCD127lo Treg dominant phenotypes. Moreover, patients with Goodpasture disease display a clonally expanded α3135-145-specific CD4+ T-cell repertoire. Accordingly, we provide a mechanistic basis for the dominantly protective effect of HLA in autoimmune disease, whereby HLA polymorphism shapes the relative abundance of self-epitope specific Treg cells that leads to protection or causation of autoimmunity.

The use of belimumab in three cases of refractory lupus nephritis.

In recent trials for the treatment of systemic lupus erythematosus (SLE), belimumab (BLM), in addition to standard immunosuppression, has been shown to improve renal and nonrenal outcomes. We report our experience using BLM in three cases of refractory lupus nephritis (LN), where renal remission was not achieved using cyclophosphamide, mycophenolate mofetil and other immunosuppressive medications. In two of the three cases, BLM therapy led to a partial remission of LN, improvement in serological markers of SLE and disease activity, which permitted a reduction in prednisolone dosing. Treatment with efficacious therapies early in the course of LN is a desirable therapeutic strategy, to achieve early remission of proteinuria and curtail the development of irreversible chronic renal damage. Further studies are needed to provide information on the effectiveness of BLM for maintenance of remission, prevention of flares and monitoring for long-term complications of B-cell modulation.

Toll-like Receptor 9 Induced Dendritic Cell Activation Promotes Anti-Myeloperoxidase Autoimmunity and Glomerulonephritis.

ANCA-associated vasculitis (AAV) is intricately linked with infections. Toll-like receptors (TLR) provide a potential link between infection and anti-myeloperoxidase (MPO) autoimmunity. TLR9 ligation has been shown to promote anti-MPO autoimmunity and glomerular vasculitis in murine MPO-AAV. This study investigates dendritic cell TLR9 ligation in murine experimental anti-MPO glomerulonephritis. We analyzed autoimmune responses to MPO following transfer of TLR9 stimulated, MPO pulsed dendritic cells and kidney injury following a sub-nephritogenic dose of sheep anti-mouse glomerular basement membrane globulin. TLR9 ligation enhanced dendritic cell activation upregulating CD40 and CD80 expression, promoting systemic anti-MPO autoimmunity and T cell recall responses and exacerbating kidney injury. CD40 upregulation by TLR9 was critical for the induction of nephritogenic autoimmunity. The presence of DEC205, which transports the TLR9 ligand to TLR9 located in the endosome, also promoted kidney injury. This confirms TLR9 mediated dendritic cell activation as a mechanism of anti-MPO autoimmunity in AAV and further defines the link between infection and the generation of MPO specific autoimmune inflammation.

Collagen IVα345 dysfunction in glomerular basement membrane diseases. I. Discovery of a COL4A3 variant in familial Goodpasture's and Alport diseases.

Diseases of the glomerular basement membrane (GBM), such as Goodpasture's disease (GP) and Alport syndrome (AS), are a major cause of chronic kidney failure and an unmet medical need. Collagen IVα345 is an important architectural element of the GBM that was discovered in previous research on GP and AS. How this collagen enables GBM to function as a permselective filter and how structural defects cause renal failure remain an enigma. We found a distinctive genetic variant of collagen IVα345 in both a familial GP case and four AS kindreds that provided insights into these mechanisms. The variant is an 8-residue appendage at the C-terminus of the α3 subunit of the α345 hexamer. A knock-in mouse harboring the variant displayed GBM abnormalities and proteinuria. This pathology phenocopied AS, which pinpointed the α345 hexamer as a focal point in GBM function and dysfunction. Crystallography and assembly studies revealed underlying hexamer mechanisms, as described in Boudko et al. and Pedchenko et al. Bioactive sites on the hexamer surface were identified where pathogenic pathways of GP and AS converge and, potentially, that of diabetic nephropathy (DN). We conclude that the hexamer functions include signaling and organizing macromolecular complexes, which enable GBM assembly and function. Therapeutic modulation or replacement of α345 hexamer could therefore be a potential treatment for GBM diseases, and this knock-in mouse model is suitable for developing gene therapies.

Animal models of vasculitis.

PURPOSE OF REVIEW: Vasculitis describes a wide spectrum of rare, inflammatory, multisystem disorders. These heterogenous diseases all have inflammation of blood vessels as a central feature. However, they differ in terms of their genetic and environmental risk factors, disease pathogenesis, clinical presentations and treatment strategies. Many animal models of vasculitis exist, each resembling a different human clinical phenotype. This review provides an overview of recently published findings from experimental animal models of vasculitis. RECENT FINDINGS: Several new animal models have been described during the review period. New insights gleaned from existing animal models regarding cause, disease effector mechanisms and novel treatments identified in established animal models are discussed. SUMMARY: Animal models continue to be an important tool for understanding disease pathogenesis, especially in rare and complex diseases such as vasculitis. They also provide an invaluable platform for development and preclinical testing of new treatments.

Ageing enhances cellular immunity to myeloperoxidase and experimental anti-myeloperoxidase glomerulonephritis.

OBJECTIVES: ANCA-associated vasculitis (AAV) is an autoimmune disease characterized by small blood vessel inflammation, commonly affecting the kidneys and respiratory tract. It is unclear why the incidence of this condition increases with age. Previous studies in a passive antibody transfer system in aged mice have implicated innate effectors. To test the hypothesis that autoimmunity to myeloperoxidase (MPO), an autoantigen responsible for AAV, increases with age, anti-MPO autoimmunity was studied in murine models of active autoimmunity and disease induced by cellular immunity. METHODS: Young (8 weeks) and aged (either 15 or 22 months) mice were immunized with whole proteins or peptides from ovalbumin, as a model foreign antigen, or MPO protein or peptides. Mice were subjected to a model of active anti-MPO glomerulonephritis. Cellular and humoral immune responses, and tissue inflammation were assessed. RESULTS: While cellular immunity to ovalbumin was diminished in aged mice, cellular autoimmunity to MPO and its immunodominant CD4+ and CD8+ T cell epitopes was increased after immunization with either MPO peptides or whole MPO protein, assessed by peptide and antigen-specific production of the pro-inflammatory cytokines IFN-γ and IL-17A. MPO-ANCA titres were not increased in aged mice compared with young mice. In experimental anti-MPO glomerulonephritis, cell-mediated injury was increased, likely due to CD4+ and CD8+ T cells, innate immunity and the increased vulnerability of aged kidneys. CONCLUSION: Heightened cellular immunity to MPO develops with ageing in mice and may contribute to the increased incidence and severity of AAV in older people.

Anti-CD20 mAb-Induced B Cell Apoptosis Generates T Cell Regulation of Experimental Myeloperoxidase ANCA-Associated Vasculitis.

BACKGROUND: Myeloperoxidase ANCA-associated vasculitis is a major cause of ESKD. Efficacy of anti-CD20 mAb treatment was tested in a mouse model of the disease. METHODS: MPO immunization induced anti-MPO autoimmunity, and a subnephritogenic dose of sheep anti-mouse GBM globulin triggered GN. RESULTS: Anti-CD20 mAb treatment increased the numbers and immunomodulatory capacity of MPO-specific T regulatory cells (Tregs) and attenuated T cell-mediated and humoral anti-MPO autoimmunity and GN. Disabling of Tregs negated the therapeutic benefit of anti-CD20 treatment. The mechanism of enhancement of Treg activity could be attributed to anti-CD20 mAb effects on inducing B cell apoptosis. Administering anti-CD20 mAb-induced apoptotic splenocytes to mice developing anti-MPO GN was as effective as anti-CD20 mAb treatment in inducing Tregs and attenuating both anti-MPO autoimmunity and GN. A nonredundant role for splenic macrophages in mediating the anti-CD20 mAb-induced immunomodulation was demonstrated by showing that administration of anti-CD20 mAb ex vivo-induced apoptotic splenocytes to unmanipulated mice attenuated autoimmunity and GN, whereas deletion of splenic marginal zone macrophages prevented anti-CD20 mAb-induced immunomodulation and treatment efficacy. Six days after administering anti-CD20 mAb to mice with murine anti-MPO GN, cell-mediated anti-MPO responses and GN were attenuated, and Tregs were enhanced, but ANCA levels were unchanged, suggesting humoral autoimmunity was redundant at this time point. CONCLUSIONS: Collectively, these data suggest that, as well as reducing humoral autoimmunity, anti-CD20 mAb more rapidly induces protective anti-MPO Treg-mediated immunomodulation by splenic processing of anti-CD20-induced apoptotic B cells.

Recurrent membranous nephropathy after transplantation: donor antigen and HLA converge in defining risk.

Membranous nephropathy, like many forms of glomerulonephritis, is an HLA-associated autoimmune disease that can recur in the transplanted kidney. In this issue of Kidney International, Berchtold and colleagues publish an intriguing and important paper on risk factors for recurrent post-transplant membranous nephropathy due to autoimmunity to PLA2R1. They found that the genetics of both the autoantigen and donor HLA are important determinants of the risk of recurrent disease in the graft.

Development of an international Delphi survey to establish core outcome domains for trials in adults with glomerular disease.

Outcomes relevant to treatment decision-making are inconsistently reported in trials involving glomerular disease. Here, we sought to establish a consensus-derived set of critically important outcomes designed to be reported in all future trials by using an online, international two-round Delphi survey in English. To develop this, patients with glomerular disease, caregivers and health professionals aged 18 years and older rated the importance of outcomes using a Likert scale and a Best-Worst scale. The absolute and relative importance was assessed and comments were analyzed thematically. Of 1198 participants who completed Round 1, 734 were patients/caregivers while 464 were health care professionals from 59 countries. Of 700 participants that completed Round 2, 412 were patients/caregivers and 288 were health care professionals. Need for dialysis or transplant, kidney function, death, cardiovascular disease, remission-relapse and life participation were the most important outcomes to patients/caregivers and health professionals. Patients/caregivers rated patient-reported outcomes higher while health care professionals rated hospitalization, death and remission/relapse higher. Four themes explained the reasons for their priorities: confronting death and compounded suffering, focusing on specific targets in glomerular disease, preserving meaning in life, and fostering self-management. Thus, consistent reporting of these critically important outcomes in all trials involving glomerular disease is hoped to improve patient-centered decision-making.

Tetraspanin CD53 modulates lymphocyte trafficking but not systemic autoimmunity in Lyn-deficient mice.

The leukocyte-restricted tetraspanin CD53 has been shown to promote lymphocyte homing to lymph nodes (LNs) and myeloid cell recruitment to acutely inflamed peripheral organs, and accelerate the onset of immune-mediated disease. However, its contribution in the setting of chronic systemic autoimmunity has not been investigated. We made use of the Lyn-/- autoimmune model, generating Cd53-/- Lyn-/- mice, and compared trafficking of immune cells into secondary lymphoid organs and systemic autoimmune disease development with mice lacking either gene alone. Consistent with previous observations, absence of CD53 led to reduced LN cellularity via reductions in both B and T cells, a phenotype also observed in Cd53-/- Lyn-/- mice. In some settings, Cd53-/- Lyn-/- lymphocytes showed greater loss of surface L-selectin and CD69 upregulation above that imparted by Lyn deficiency alone, indicating that absence of these two proteins can mediate additive effects in the immune system. Conversely, prototypical effects of Lyn deficiency including splenomegaly, plasma cell expansion, elevated serum immunoglobulin M and anti-nuclear antibodies were unaffected by CD53 deficiency. Furthermore, while Lyn-/- mice developed glomerular injury and showed elevated glomerular neutrophil retention above than that in wild-type mice, absence of CD53 in Lyn-/- mice did not alter these responses. Together, these findings demonstrate that while tetraspanin CD53 promotes lymphocyte trafficking into LNs independent of Lyn, it does not make an important contribution to development of autoimmunity, plasma cell dysfunction or glomerular injury in the Lyn-/- model of systemic autoimmunity.

Increased burden of rare variants in genes of the endosomal Toll-like receptor pathway in patients with systemic lupus erythematosus.

OBJECTIVE: To compare the frequency of rare variants in genes of the pathophysiologically relevant endosomal Toll-like receptor (eTLR) pathway and any quantifiable differences in variant rarity, predicted deleteriousness, or molecular proximity in patients with systemic lupus erythematosus (SLE) and healthy controls. PATIENTS AND METHODS: 65 genes associated with the eTLR pathway were identified by literature search and pathway analysis. Using next generation sequencing techniques, these were compared in two randomised cohorts of patients with SLE (n = 114 and n = 113) with 197 healthy controls. Genetically determined ethnicity was used to normalise minor allele frequencies (MAF) for the identified genetic variants and these were then compared by their frequency: rare (MAF < 0.005), uncommon (MAF 0.005-0.02), and common (MAF >0.02). This was compared to the results for 65 randomly selected genes. RESULTS: Patients with SLE are more likely to carry a rare nonsynonymous variant affecting proteins within the eTLR pathway than healthy controls. Furthermore, individuals with SLE are more likely to have multiple rare variants in this pathway. There were no differences in rarity, Combined Annotation Dependent Depletion (CADD) score, or molecular proximity for rare eTLR pathway variants. CONCLUSIONS: Rare non-synonymous variants are enriched in patients with SLE in the eTLR pathway. This supports the hypothesis that SLE arises from several rare variants of relatively large effect rather than many common variants of small effect.

Experimental Antiglomerular Basement Membrane GN Induced by a Peptide from Actinomyces.

BACKGROUND: Antiglomerular basement membrane (anti-GBM) disease is associated with HLA-DRB1*1501 (the major predisposing genetic factor in the disease), with α3127-148 as a nephritogenic T and B cell epitope. Although the cause of disease remains unclear, the association of infections with anti-GBM disease has been long suspected. METHODS: To investigate whether microbes might activate autoreactive T and B lymphocytes via molecular mimicry in anti-GBM disease, we used bioinformatic tools, including BLAST, SYFPEITHI, and ABCpred, for peptide searching and epitope prediction. We used sera from patients with anti-GBM disease to assess peptides recognized by antibodies, and immunized WKY rats and a humanized mouse model (HLA-DR15 transgenic mice) with each of the peptide candidates to assess pathogenicity. RESULTS: On the basis of the critical motif, the bioinformatic approach identified 36 microbial peptides that mimic human α3127-148. Circulating antibodies in sera from patients with anti-GBM recognized nine of them. One peptide, B7, derived from Actinomyces species, induced proteinuria, linear IgG deposition on the GBM, and crescent formation when injected into WKY rats. The antibodies to B7 also targeted human and rat α3127-148. B7 induced T cell activation from human α3127-148-immunized rats. T cell responses to B7 were detected in rats immunized by Actinomyces lysate proteins or recombinant proteins. We confirmed B7's pathogenicity in HLA-DR15 transgenic mice that developed kidney injury similar to that observed in α3135-145-immunized mice. CONCLUSIONS: Sera from patients with anti-GBM disease recognized microbial peptides identified through a bioinformatic approach, and a peptide from Actinomyces induced experimental anti-GBM GN by T and B cell crossreactivity. These studies demonstrate that anti-GBM disease may be initiated by immunization with a microbial peptide.

Tertiary lymphoid tissue in kidneys: understanding local immunity and inflammation.

Tertiary lymphoid tissues are peripheral foci of immune activity that develop in kidneys and other peripheral organs in the context of chronic inflammation. In this issue of Kidney International, Sato and colleagues present a detailed characterization of tertiary lymphoid tissues in mouse and human kidneys in the context of acute kidney injury, chronic pyelonephritis, aging, and chronic kidney disease, showing the importance of nontraditional roles of B cells in the inflamed kidney microenvironment.

Tolerogenic Dendritic Cells Attenuate Experimental Autoimmune Antimyeloperoxidase Glomerulonephritis.

Background Because of their capacity to induce antigen-specific immunosuppression, tolerogenic dendritic cells are a promising tool for treatment of autoimmune conditions, such as GN caused by autoimmunity against myeloperoxidase (MPO). METHODS: We sought to generate tolerogenic dendritic cells to suppress anti-MPO GN by culturing bone marrow cells with an NFκB inhibitor (BAY 11-7082) and exposing them to a pulse of MPO. After administering these MPO/BAY dendritic cells or saline to mice with established anti-MPO or anti-methylated BSA (mBSA) immunity, we assessed immune responses and GN. We also examined mechanisms of action of MPO/BAY dendritic cells. RESULTS: MPO/BAY dendritic cells decreased anti-MPO immunity and GN without inhibiting immune responses against mBSA; they also induced IL-10-producing regulatory T cells in MPO-immunized mice without affecting IL-10+ CD4+Foxp3- type 1 regulatory T cells or regulatory B cells. MPO/BAY dendritic cells did not inhibit anti-MPO immunity when CD4+Foxp3+ cells were depleted in vivo, showing that regulatory T cells are required for their effects. Coculture experiments with dendritic cells and CD4+Foxp3- or CD4+Foxp3+ cells showed that MPO/BAY dendritic cells generate Foxp3+ regulatory T cells from CD4+Foxp3- cells through several pathways, and induce IL-10+ regulatory T cells via inducible costimulator (ICOS), which was confirmed in vivo. Transfer of MPO/BAY dendritic cell-induced regulatory T cells in vivo, with or without anti-IL-10 receptor antibody, demonstrated that they suppress anti-MPO immunity and GN via IL-10. CONCLUSIONS: MPO/BAY dendritic cells attenuate established anti-MPO autoimmunity and GN in an antigen-specific manner through ICOS-dependent induction of IL-10-expressing regulatory T cells. This suggests that autoantigen-loaded tolerogenic dendritic cells may represent a novel antigen-specific therapeutic option for anti-MPO GN.