Glomerular handling of immune complex in the acute phase of active in situ immune complex glomerulonephritis employing cationized ferritin in rats. Ultrastructural localization of immune complex, complements and inflammatory cells

Slowly Progressive ANCA-associated Glomerulonephritis with Strong Mesangial MPO Deposits Following a Diagnosis of Interstitial Lung Disease

An elderly woman showed positive conversion of myeloperoxidase (MPO)-antineutrophil cytoplasmic antibodies (ANCAs) following the diagnosis of interstitial lung disease (ILD) and glomerular hematuria and subsequently experienced slowly progressive glomerulonephritis. A kidney biopsy revealed chronic damage and necrotizing crescentic glomerulonephritis with mesangial MPO deposits. After corticosteroid treatment, the patient's urinalysis results and MPO-ANCA titers almost normalized and her renal function stabilized. This case is similar to recently reported cases of slowly progressive ANCA-associated glomerulonephritis. ILD likely triggered the production of MPO-ANCAs, and the accumulation of MPO deposits in the glomeruli may have contributed to the progression of her renal disease.

Extracellular vesicles and lupus nephritis - New insights into pathophysiology and clinical implications

Lupus nephritis (LN) is a major cause for overall morbidity and mortality in patients with systemic lupus erythematosus (SLE), while its pathogenic mechanisms are still not well understood. Extracellular vesicles (EVs) are membrane vesicles that are released from almost all cell types. EVs can be subdivided into exosomes, microvesicles, and apoptotic bodies. Latest studies have shown that EVs can be released during several cellular events, including cell activation, autophagy, and several types of programed cell death, i.e. apoptosis, necroptosis, pyroptosis, and NETosis. Emerging evidence demonstrates that EVs harbor different bioactive molecules, including nucleic acids, proteins, lipids, cytokines, immune complexes (ICs), complements, and other molecules, some of which may contribute to pathogenesis of autoimmune diseases. EVs can serve as novel information shuttle to mediate local autocrine or paracrine signals to nearby cells, and distant endocrine signals to cells located far away. In LN, EVs may have pathogenic effects by transportation of autoantigens or complements, promotion of IC deposition or complement activation, and stimulation of inflammatory responses, renal tissue injury, or microthrombus formation. Additionally, EVs released from kidney cells may serve as specific biomarkers for diagnosis or monitoring of disease activity and therapeutic efficacy. In this review, we will summarize the latest progress about EV generation from basic research, their potential pathologic effects on LN, and their clinical implications. The cutting-edge knowledge about EV research provides insights into novel therapeutic strategy, new tools for diagnosis or prognosis, and evaluation approaches for treatment effectiveness in LN.

Podocytes Intracytoplasmic Dense Inclusions: Are They Associated with Subepithelial Dense Deposits? An Ultrastructural Study

Introduction:

Podocytes play a crucial role in health and disease. They participate in clearing the filtration barrier by removing accumulated proteins. It is proposed that podocytes have the ability to remove immune complexes and internalize them in the cytoplasm.

Aims:

The purpose of this study is to review certain immune complex glomerulonephritis (GN) types and illustrate ultrastructural details of podocytes intracytoplasmic dense inclusions (ICDIs) if present.

Materials and Methods:

A retrospective ultrastructural study of podocytes was conducted to detect cytoplasmic inclusions. The study cases (n = 148) include GN types with subepithelial dense deposits such as membranous GN, postinfectious GN (PIGN), and lupus nephritis.

Results:

Podocytes ICDIs are detected ultrastructurally in 48 of 148 cases, mostly with PIGN; their morphology resembles the subepithelial dense deposits of the corresponding case.

Conclusions:

Podocytes ICDIs represent internalized immune complexes from the adjacent subepithelial dense deposits, suggesting a clearance method of the glomerular basement membrane by podocytes.

Possible role of complement factor H in podocytes in clearing glomerular subendothelial immune complex deposits

Podocytes are known to express various complement factors including complement factor H (CFH) and to promote the removal of both subendothelial and subepithelial immune complex (IC) deposits. Using podocyte-selective injury model NEP25 mice and an IgG3-producing hybridoma clone 2B11.3 established by MRL/lpr mice, the present study investigated the role of podocyte complement regulation in only subendothelial IC deposition. In immunotoxin (LMB2) induced fatal podocyte injury (NEP25/LMB2) at day 12, glomerular CFH and C3a receptor (C3aR) expression was decreased as compared with NEP25/vehicle mice. In contrast, in sublytic podocyte injury 5 days after LMB2, glomerular CFH and C3aR expression was increased as compared with NEP25/vehicle mice. Intra-abdominal injection of 2B11.3 hybridoma to NEP25 mice (NEP25/hybridoma) caused IC deposition limited to the subendothelial area associated with unaltered CFH expression. NEP25/hybridoma mice with sublytic podocyte injury (NEP25/hybridoma/LMB2) resulted in increased glomerular CFH expression (1.7-fold) accompanied by decreased subendothelial IC deposition, as compared with NEP25/hybridoma. Immunostaining revealed that CFH was dominantly expressed in podocytes of NEP25/hybridoma/LMB2. In addition, puromycin-induced sublytic podocyte injury promoted CFH expression in immortalized mouse podocytes in vitro. These results suggest that in response to sublytic levels of injury, podocyte induced CFH expression locally and clearance of subendothelial IC deposits.

Renal albumin filtration: alternative models to the standard physical barriers

Human kidneys produce more than 4 million litres of virtually protein-free primary urine in a lifetime. In healthy individuals, the sieving process is accomplished by the glomerular filter without the smallest sign of clogging, even in old age. How nature accomplishes this extraordinary task is a mystery, but unravelling the functioning of the glomerular filter is important. The basic principles that govern glomerular filtration are probably also true for peripheral filtering by fenestrated capillaries. In addition, understanding the sieving process is a prerequisite to understanding the pathogenesis of proteinuria (that is, the leakage of plasma proteins into the urine). Proteinuria is the hallmark of glomerular disease and a major risk factor for systemic cardiovascular complications, a fact that emphasizes the relationship between the glomerular and peripheral filtering capillaries. In this Review, we briefly summarize the major models that have been proposed for the mechanisms of glomerular filtration and discuss their strengths and limitations. A special emphasis is placed on the 'electrokinetic model' that we have proposed, a model that could potentially resolve many of the seemingly strange characteristics of the glomerular filtration barrier.

Basic and translational concepts of immune-mediated glomerular diseases

Genetically modified immune responses to infections and self-antigens initiate most forms of GN by generating pathogen- and danger-associated molecular patterns that stimulate Toll-like receptors and complement. These innate immune responses activate circulating monocytes and resident glomerular cells to release inflammatory mediators and initiate adaptive, antigen-specific immune responses that collectively damage glomerular structures. CD4 T cells are needed for B cell-driven antibody production that leads to immune complex formation in glomeruli, complement activation, and injury induced by both circulating inflammatory and resident glomerular effector cells. Th17 cells can also induce glomerular injury directly. In this review, information derived from studies in vitro, well characterized experimental models, and humans summarize and update likely pathogenic mechanisms involved in human diseases presenting as nephritis (postinfectious GN, IgA nephropathy, antiglomerular basement membrane and antineutrophil cytoplasmic antibody-mediated crescentic GN, lupus nephritis, type I membranoproliferative GN), and nephrotic syndrome (minimal change/FSGS, membranous nephropathy, and C3 glomerulopathies). Advances in understanding the immunopathogenesis of each of these entities offer many opportunities for future therapeutic interventions.

Role of the podocyte in proteinuria

In recent years, the podocyte, with its elaborate cytoarchitecture and slit diaphragm, has been the focus of extensive research, yet its precise role in the glomerular filtration barrier is still debated. There are puzzling observations indicating that a comprehensive mechanistic model for glomerular filtration is still necessary. There is no doubt that podocytes are essential for glomerular filtration barrier integrity. However, most albumin never reaches the podocyte because it is prevented from entering the glomerular filter at the endothelium level. Another puzzling observation is that the glomerular filter never clogs despite its high load of several kilograms of plasma proteins per day. Recently, we proposed a novel model in which an electrical potential difference is generated across the glomerular filtration barrier by filtration. The model offers novel potential solutions to some of the riddles regarding the glomerular filter.

Analysis of intra-GBM microstructures in a SLE case with glomerulopathy associated with podocytic infolding

BACKGROUND

Systemically podocytic infolding into the GBM which causes nonargyrophilic holes in the GBM in association with intra-GBM microstructures has been considered as a new pathological entity. However, its pathomechanisms are largely unknown.

METHODS

We analyzed intra-GBM microstructures in an SLE patient with glomerulopathy associated with podocytic infolding by immunoelectron microscopy for vimentin (a marker for both podocyte and endothelium) and C5b-9 and by 3D reconstruction of transmission electron microscopy (TEM) images by computer tomography method.

RESULTS

Immunofluorescent study showed immunoglobulin deposition in a diffuse, capillary pattern; however, electron-dense deposits like stage 3 membranous nephropathy could be found only in some capillary loops by TEM in spite of the systemic existence of podocytic infolding and the intra-GBM microstructures. Three-dimensional reconstructed images of the TEM images revealed that some of the intra-GBM microstructures made connections with the podocyte. The clustered microstructures underneath the podocyte and their surroundings looked as a whole like the degraded part of podocyte in 3D reconstructed images. Immunoelectron microscopy showed that vimentin was positive in most intra-GBM microstructures. C5b-9 was positive along the entire epithelial side of the GBM and in some microstructures, suggesting that the podocytes may be attacked by C5b-9 and that the microstructures may contain C5b-9 bound cellular membranes.

CONCLUSION

Intra-GBM microstructures may be originated mainly from the podocyte. Podotyte and GBM injuries caused by C5b-9 attack to podocytes might contribute in part to podocytic infolding and intra-GBM microstructures in this case.

Shift of C3 deposition from localization in the glomerulus into the tubulo-interstitial compartment in the absence of secreted IgM in immune complex glomerulonephritis

The role of secretory IgM in protecting kidney tissue from immune complex glomerulonephritis induced by 4 mg horse spleen apoferritin and 0.05 mg lipopolysaccharide has been investigated in mutant mice in which B cells do not secrete IgM, but are capable of expressing surface IgM and IgD and secreting other Ig isotypes. Glomerular size, number of glomeruli per cross-section, glomerular cellularity and urine content of protein and creatinine was comparable in treated secreted IgM (sIgM)-deficient and wild-type mice. Assessment of urinary proteins by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed a 30 kDa low molecular weight protein in treated sIgM-deficient animals only, reflecting dysfunction of proximal tubules. A shift of bound C3 from glomeruli to the tubulo-interstitial compartment in sIgM-deficient mice also suggests tubulo-interstitial damage. In contrast, local C3 synthesis within the kidney tissue did not differ between the two treated groups. Apoptosis physiologically present to maintain kidney cell homeostasis was increased slightly in treated wild-type mice. These results indicate that secretory IgM can protect the tubulo-interstitial compartment from immune complex-induced damage without having an effect on the glomerulus.

Role of soluble factors and three-dimensional culture in in vitro differentiation of intestinal macrophages

AIM: To examine the factor(s) involved in differentiation of intestinal macrophages (IMACs) using a recently established in vitro model.

METHODS: To test whether soluble or membrane bound factors induce IMAC-differentiation, freshly elutriated monocytes (MO) were incubated with conditioned media or cell membranes of intestinal epithelial cells (IEC) or cultured with IEC in transwell systems. To determine the importance of an active migration of MO, three-dimensional aggregates from a 1:1-mixture of MO and IEC were examined by immunohistochemistry and flow cytometry. Apoptosis was examined by caspase-3 Western blots. Extracellular matrix production in differentiation models was compared by immunohistochemistry.

RESULTS: IMAC differentiation was observed in a complex three-dimensional co-culture model (multicellular spheroid, MCS) with IEC after migration of MO into the spheroids. By co-culture of MO with conditioned media or membrane preparations of IEC no IMAC differentiation was induced. Co-culture of MO with IEC in transwell-cultures, with the two cell populations separated by a membrane also did not result in intestinal-like differentiation of MO. In contrast to IEC-spheroids with immigrating MO in mixed MCS of IEC and MO only a small subpopulation of MO was able to survive the seven day culture period.

CONCLUSION: Intestinal-like differentiation of MO in vitro is only induced in the complex three-dimensional MCS model after immigration of MO indicating a role of cell-matrix and/or cell-cell interactions during the differentiation of IMACs.

The simple design of complement factor H: Looks can be deceiving

The complement system is a powerful component of innate immunity which recognizes and facilitates the elimination of pathogens and unwanted host material. Since complement can also lead to host tissue injury and inflammation, strict regulation of its activation is important. One of the key regulators is complement factor H (CFH), a protein with an ever-expanding list of relevant functions. Inherited mutations in CFH can account for membranoproliferative glomerulonephritis (MPGN) type II, atypical hemolytic uremic syndrome, and age-related macular degeneration. The former can be associated with excessive systemic complement activation from dysfunctional CFH, while the latter two are associated with mutations affecting the ability of CFH to bind to anionic surfaces such as on endothelial cells and glomerular and retinal capillary walls. Mice with targeted deletion of CFH can spontaneously develop MPGN and have increased susceptibility to models of GN. In the rodent, CFH on platelets functions as the immune adherence receptor, analogous to CR1 on primate erythrocytes. In mice, platelets lacking CFH are unable to effectively clear immune complexes which results in their accumulation in glomeruli. The same switch also appears to be true in the rodent podocyte where CFH is present in place of CR1 in human podocytes. Thus, CFH has a variety of functions which can affect the diverse roles the complement system plays in health and disease.

A mechanism for the development of subepithelial deposits in a patient with type III membranoproliferative glomerulonephritis

We report on a patient with membranoproliferative glomerulonephritis (MPGN) type III, whose repeated renal biopsies show evolution from a type I-like pattern to a type III pattern of immune complex formation over a 1-year period. Based on the development of experimental in situ immune complex glomerulonephritis, we discuss possible mechanisms for the formation of subepithelial deposits in type III MPGN with reference to an experimental in situ immune complex model of glomerulonephritis.

Fc gamma RIII mediates neutrophil recruitment to immune complexes. a mechanism for neutrophil accumulation in immune-mediated inflammation

Neutrophil accumulation is a hallmark of immune complex-mediated inflammatory disorders. Current models of neutrophil recruitment envision the capture of circulating neutrophils by activated endothelial cells. We now demonstrate that immobilized immune complexes alone support the rapid attachment of neutrophils, under physiologic flow conditions. Initial cell tethering requires the low-affinity Fc gamma receptor IIIB (Fc gamma RIIIB), and the beta(2) integrins are additionally required for the subsequent shear-resistant adhesion. The attachment function of Fc gamma RIIIB may be facilitated by its observed presentation on neutrophil microvilli. In vivo, in a model of acute antiglomerular basement membrane nephritis in which immune complexes are accessible to circulating neutrophils, Fc gamma RIII-deficient mice had a significant reduction in neutrophil recruitment. Thus, the interaction of immune complexes with Fc gamma RIII may mediate early neutrophil recruitment in immune complex-mediated inflammation.