Immune complexes in acute adult-onset Henoch-Schonlein nephritis

Pathophysiology and clinical manifestations of immune complex vasculitides

Immune complex (IC) vasculitides present inflammations of vessel walls associated with perivascular deposition of immunoglobulins (Igs), mostly ICs. They encompass systemic and skin-limited variants of IgA vasculitis (IgAV), cryoglobulinemic vasculitis (CV), rheumatoid, lupus, and hypocomplementemic vasculitides, serum sickness cutaneous IgM/IgG (non-IgA) vasculitis, and recurrent macular (hypergammaglobulinemic or exertion-induced) vasculitis. Serum sickness and CV fulfill the criteria of a type III hypersensitivity immune reaction as large lattices of the IC precipitate at vessel walls and activate polymorphonuclear neutrophils (PMNs). Immunoglobulin-A vasculitis differs with regard to the causes of perivascular deposition of ICs since here many IgA1 molecules are hypoglycosylated (Gd-IgA1), which appears to facilitate their perivascular deposition in skin and mesangium (via e.g. CD71). The reasons for increased generation of immunoglobulins or formation of IC and their perivascular deposition in either skin or systemic organs are different and not fully explored. A common denominator of OC vasculitides is the activation of PMNs near the vessel wall via Fcy or Fcα receptors. Acute episodes of IgAV additionally require PMNs to become preactivated by IgA1 or by IC already in circulation. This intravascular priming results in increased adherence and subsequently vessel-destructive NETosis when they encounter IgA deposited at the vessel walls. Binding of IgA1 to PMNs in blood stream is associated with increased serum levels of hypogalactosidated IgA1. The characteristic clinical picture of IgAV (and also of so-called IgG/IgM vasculitis) comprises palpable or retiform purpura with a clear predilection for lower legs, probably due to stasis-related reduction in blood velocity, while in other IC vasculitides, additional factors influence the sites of vasculitides. Our knowledge of distinct forms and different pathophysiological pathways of IC vasculitides may lead to in efficacious or targeted therapies. Antibodies to complement components or intestinal budesonide for IgAV are promising agents (the latter suppresses the pathophysiologically related IgA nephropathy by reducing the generation of mucosal IgA.

Novel aspects in the pathophysiology and diagnosis of glomerular diseases

Immune deposits/complexes are detected in a multitude of tissues in autoimmune disorders, but no organ has attracted as much attention as the kidney. Several kidney diseases are characterised by the presence of specific configurations of such deposits, and many of them are under a 'shared care' between rheumatologists and nephrologists. This review focuses on five different diseases commonly encountered in rheumatological and nephrological practice, namely IgA vasculitis, lupus nephritis, cryoglobulinaemia, anti-glomerular basement membrane disease and anti-neutrophil cytoplasm-antibody glomerulonephritis. They differ in disease aetiopathogenesis, but also the potential speed of kidney function decline, the responsiveness to immunosuppression/immunomodulation and the deposition of immune deposits/complexes. To date, it remains unclear if deposits are causing a specific disease or aim to abrogate inflammatory cascades responsible for tissue damage, such as neutrophil extracellular traps or the complement system. In principle, immunosuppressive therapies have not been developed to tackle immune deposits/complexes, and repeated kidney biopsy studies found persistence of deposits despite reduction of active inflammation, again highlighting the uncertainty about their involvement in tissue damage. In these studies, a progression of active lesions to chronic changes such as glomerulosclerosis was frequently reported. Novel therapeutic approaches aim to mitigate these changes more efficiently and rapidly. Several new agents, such as avacopan, an oral C5aR1 inhibitor, or imlifidase, that dissolves IgG within minutes, are more specifically reducing inflammatory cascades in the kidney and repeat tissue sampling might help to understand their impact on immune cell deposition and finally kidney function recovery and potential impact of immune complexes/deposits.

IgA vasculitis update: Epidemiology, pathogenesis, and biomarkers

Immunoglobulin A vasculitis (IgAV), formerly known as Henoch-Schönlein purpura, is the most common systemic vasculitis in children, characterized by diverse clinical manifestations with a wide spectrum ranging from isolated cutaneous vasculitis to systemic involvement. The incidence of IgAV is geographically and ethnically variable, with a prevalence in autumn and winter, suggesting a driving role that genetic and environmental factors play in the disease. Although IgAV has a certain degree of natural remission, it varies widely among individuals. Some patients can suffer from severe renal involvement and even progress to end-stage renal disease. Its pathogenesis is complex and has not been fully elucidated. The formation of galactose-deficient IgA1 (Gd-IgA1) and related immune complexes plays a vital role in promoting the occurrence and development of IgAV nephritis. In addition, neutrophil activation is stimulated through the binding of IgA to the Fc alpha receptor I expressed on its surface, resulting in systemic vascular inflammation and tissue damage. Starting from the epidemiological characteristics, this article will review the role of immunological factors such as Gd-IgA1, autoantibodies, circulating immune complexes, complement system, cellular immunization, and the contributions of environmental and genetic factors in the pathogenesis of IgAV, and conclude with the major biomarkers for IgAV.

IgA vasculitis with nephritis: update of pathogenesis with clinical implications

IgA vasculitis with nephritis (IgAVN) shares many pathogenetic features with IgA nephropathy (IgAN). The purpose of this review is to describe our current understanding of the pathogenesis of pediatric IgAVN, particularly as it relates to the four-hit hypothesis for IgAN. These individual steps, i.e., hits, in the pathogenesis of IgAN are (1) elevated production of IgA1 glycoforms with some O-glycans deficient in galactose (galactose-deficient IgA1; Gd-IgA1), (2) generation of circulating IgG autoantibodies specific for Gd-IgA1, (3) formation of pathogenic circulating Gd-IgA1-containing immune complexes, and (4) kidney deposition of the Gd-IgA1-IgG immune complexes from the circulation and induction of glomerular injury. Evidence supporting the four-hit hypothesis in the pathogenesis of pediatric IgAVN is detailed. The genetics, pediatric outcomes, and kidney histopathologic features and the impact of these findings on future treatment and potential biomarkers are discussed. In summary, the evidence points to the critical roles of Gd-IgA1-IgG immune complexes and complement activation in the pathogenesis of IgAVN. Future studies are needed to characterize the features of the immune and autoimmune responses that enable progression of IgA vasculitis to IgAVN.

Adult-Onset Immunoglobulin A Vasculitis With Renal Involvement

A 50-year-old male presented with worsening bilateral lower extremities swelling for a month, associated with a purpuric rash over bilateral upper and lower extremities, joint pain over bilateral hands and ankles, and intermittent generalized abdominal pain. Physical examination was notable for pitting edema in bilateral lower extremities and palpable, non-blanching purpuric rashes and crusts, joint tenderness over bilateral hands/wrists/ankles, and mild generalized abdominal tenderness. Laboratory tests were remarkable for sub-nephrotic range proteinuria and microscopic hematuria. The skin biopsy revealed leukocytoclastic vasculitis. Renal biopsy showed mild mesangial expansion and immunoglobulin A (IgA)-dominant mesangial deposits. The patient was diagnosed with IgA vasculitis (IgAV) nephritis (IgAVN) and was subsequently treated with oral prednisone 80 mg daily for seven days followed by slow tapering doses, oral lisinopril 2.5 mg daily, and oral furosemide 40 mg daily. At the one-month follow-up as an outpatient, his skin rash and lower extremity swelling had resolved along with an improvement of proteinuria.

A cross-sectional analysis of clinicopathologic similarities and differences between Henoch-Schönlein purpura nephritis and IgA nephropathy

Introduction

Recent studies noted that Henoch-Schönlein purpura nephritis (HSPN) and IgA nephropathy (IgAN) share the feature of galactose-deficient IgA1 (Gd-IgA1)-oriented pathogenesis, although there are distinct clinical differences. We aimed to clarify the clinicopathologic differences between these 2 diseases.

Methods

We cross-sectionally analyzed adult patients with HSPN (n = 24) or IgAN (n = 56) who underwent renal biopsy (RB) between 2008 and 2018 at Showa University Hospital. Serum Gd-IgA1 (s-Gd-IgA1) levels at the time of RB were compared among study groups using enzyme-linked immunosorbent assay (ELISA) with anti-human Gd-IgA1-specific monoclonal antibody (KM55). We also immunohistochemically stained paraffin-embedded sections for glomerular Gd-IgA1 (g-Gd-IgA1)-deposition using KM55. Serum inflammatory cytokines were measured using ELISA.

Results

Glomerular endothelial injury with subendothelial IgA deposition was significant in patients with HSPN. Serum IL-8, MCP-1, TNF-α, and IL-6 levels were significantly higher in patients with HSPN than IgAN. Levels of s-Gd-IgA1 were comparable among patients with HSPN and IgAN, and a similar degree of g-Gd-IgA1-deposition was detected in both diseases. Furthermore, g-Gd-IgA1-deposition was evident in patients with histopathologically advanced HSPN or IgAN. In HSPN, significant positive correlations between s-Gd-IgA1 levels and crescent formation or IL-6 elevation were confirmed, and g-Gd-IgA1 intensity showed a significant positive correlation with MCP-1 and a tendency to positively correlate with IL-8. Meanwhile, patients with IgAN showed no correlation between inflammatory cytokines and both-Gd-IgA1. Moreover, most g-Gd-IgA1-positive areas were not double stained with CD31 in HSPN.

Conclusions

Although assessing both-Gd-IgA1 alone was insufficient to distinguish between HSPN and IgAN, patients with HSPN showed considerable glomerular capillaritis with subendothelial IgA deposition and significant elevation of serum inflammatory cytokines. Furthermore, such glomerular subendothelial IgA deposition might not contain Gd-IgA1, and factors associated with Gd-IgA1 were inconsistent among these 2 diseases. Thus, developmental mechanisms for IgAN might not apply to HSPN completely, and these 2 diseases still have different aspects.

Beneficial Effects of Qingzixiaoban Granule on Henoch–Schönlein Purpura Nephritis Mice through Inhibiting Immune Complex Deposition and Th2 Immunodeviation

Background

Henoch–Schönlein purpura nephritis (HSPN) is the principal cause of morbidity and mortality in Henoch–Schönlein purpura (HSP). However, there is no absolute consensus for the best management of severe HSPN till now. Qingzixiaoban Granule (QZXB GR), a traditional Chinese medicine formula, has been applied to treat HSP in clinical in China. However, the therapeutic effects and potential mechanism of QZXB GR on HSPN is still unknown.

Methods

A Gliadin plus Indian Ink-induced HSPN mice model was established. Renal histopathologic changes and the subcutaneous hemorrhage on left legs were assessed. Hematuria and proteinuria were determined using hemocytometer and bicinchoninic acid assay, respectively. The serum circular immune complex and interleukin-6 were quantified by ELISA. Using blood biochemical analyzer, the renal biochemical parameters, including serum total protein, albumin, creatinine, and blood urea nitrogen, were measured. The deposition of immune complex in renal tissues and the lymphocyte subsets in peripheral blood and spleen was investigated by immunohistochemistry and flow cytometry.

Results

QZXB GR treatment significantly ameliorated renal injury in HSPN mice, by attenuating renal histopathological changes, reducing subcutaneous hemorrhage, decreasing proteinuria/hematuria, regulating renal biochemical parameters, and inhibiting the release of serum interleukin-6. Furthermore, QZXB GR treatment significantly decreased the level of serum circular immune complex, decreased immune complex IgA and IgG deposition in renal tissue, and suppressed Th2 immunodeviation.

Conclusion

QZXB GR could prevent renal injury in HSPN mice, and its renoprotective mechanism might be exerted partly through suppressing immune complexes deposition and Th2 immune deviation.

Clinical and Pathological Characteristics of Elderly Japanese Patients with IgA Vasculitis with Nephritis: A Case Series

Objective This case series aimed to identify the clinical and pathological characteristics of elderly patients (≥60 years) with biopsy-proven IgA vasculitis with nephritis (IgAVN). Methods The clinical and pathological presentation and treatment outcomes were compared between two groups. Patients Patients with IgAVN who were ≥19 years old at the time of their renal biopsy were divided into elderly (≥60 years) and adult (19-59 years) groups. Results Of the 23 patients in our study, 13 were elderly. In the elderly group, the median age at the diagnosis was 68 years (range, 60-85 years), with a median follow-up period of 15 months (range, 3-80 months). Twelve elderly patients had comorbidities, including hypertension, diabetes mellitus, chronic kidney disease, cardiovascular disease, and malignancies. A decrease in the estimated glomerular filtration rate, as well as massive proteinuria and rapidly progressive nephritic syndrome, were more frequent in the elderly group than in the adult group. Furthermore, renal pathological changes, including cellular or fibrocellular crescents, interstitial fibrosis, tubular atrophy, and arteriosclerosis, were more severe among elderly patients than adult patients. All elderly patients were treated with glucocorticoids and had no incidence of end-stage renal disease at the final follow-up; in addition, nine elderly patients had reduced proteinuria with a preserved renal function. Adverse events, including infection, diabetes mellitus, and vascular disorders, were identified in nine patients. Three elderly patients died from severe infections. Conclusion IgAVN in elderly patients is characterized by severe renal involvement. Elderly patients are at higher risk than adults for treatment-related adverse events.

Renal Prognosis and Related Risk Factors for Henoch-Schönlein Purpura Nephritis: A Chinese Adult Patient Cohort

This study investigated the clinicopathological characteristics of Henoch-Schönlein purpura nephritis (HSPN) in Chinese adult patients and analyzed the renal outcomes and prognostic risk factors for progression to end-stage renal disease (ESRD). Adult patients who had biopsy-proven HSPN were studied. Their clinicopathological data, renal prognoses and related risk factors were assessed. A total of 698 patients were studied, including 363 men (52.0%) and 335 women (48.0%). Most of the patients had hematuria (85.8%) and/or proteinuria (82.1%). During a median follow-up of 54.0 months, 32 patients (4.6%) progressed to ESRD. The 5- and 10-year cumulative renal survival rates from ESRD were 96.4% and 88.6%, respectively. Baseline urinary protein, renal insufficiency, glomerular sclerosis and tubular atrophy/interstitial fibrosis were independent predictors of renal outcomes. Both the time-average mean arterial pressure and proteinuria during follow-up also influenced the renal prognosis. The patients with a time-average proteinuria <0.4 g/day had the lowest rates of ESRD or a 50% decline in renal function. In conclusion, identifying of clinical and histological prognostic factors may permit the prediction of renal outcomes. The optimal goal of therapy for HSPN patients may be to lower proteinuria to <0.4 g/day and control hypertension to achieve an ideal renal outcome.

Complement in ANCA-associated glomerulonephritis

Background

Anti-neutrophil cytoplasmic antibodies (ANCA) are found in pauci-immune necrotizing crescentic glomerulonephritis. In the past, the role of complement in ANCA-associated vasculitis (AAV) was assumed to be minimal. More recently, however, it was found that blocking the complement cascade in a mouse model of AAV reduces glomerular damage. Immune complex deposits have been found in biopsies from AAV patients. In this study, we questioned whether immune complex formation or deposition may result in complement activation in ANCA-associated glomerulonephritis.

Methods

ANCA-positive patients from the Limburg Renal Registry were included between 1979 and 2011. Renal histology was documented together with immunoglobulin and complement immunofluorescence. In addition, C3d, properdin, C4d and mannose-binding lectin (MBL) were stained. Electron microscopy was performed. Circulating immune complexes were determined in a subset of patients, as well as C3 allotypes.

Results

C3c was found in 78 of 187 renal biopsies (41.7%) divided over 32.3% of proteinase-3 (PR3)-AAV patients and 52.3% of myeloperoxidase (MPO)-AAV patients (P = 0.006), whereas C3d was found positive in 51.1% of PR3-AAV patients and 70.4% of MPO-AAV patients (P = 0.105). C4d was found positive in 70.8%, properdin in 38.7% and MBL in 30.4% of patients. Whereas C4d and MBL positivity was similar between the AGN groups, properdin was more common in biopsies classified as crescentic compared with biopsies classified as focal or mixed. Renal biopsies positive for C3d and/or properdin showed more cellular crescents and less normal glomeruli compared with biopsies negative for C3d and/or properdin (P < 0.05). In 3 out of 43 renal biopsies analysed by electron microscopy, small electron dense deposits were found. In 14 of 46 patients analysed, circulating immune complexes were detectable. No association between histological findings and C3 allotypes was found.

Conclusions

In the majority of AAV patients, no immune complex deposits were found in their renal biopsies. C3d, C4d and C5b-9 staining, however, was found to be positive in a majority of analysed renal biopsies. Importantly, C3d and properdin staining was associated with cellular crescents. We hypothesize that local immune complexes are quickly degraded in AAV and therefore not visible by electron microscopy. Our findings are compatible with the hypothesis that complement activation in AAV occurs predominantly via alternative pathway activation.

IgA vasculitis (formerly Henoch-Schönlein purpura) in an adult with systemic lupus erythematosus

We report a case of a 65-year-old man with systemic lupus erythematosus (SLE) and antiphospholipid syndrome, presenting palpable purpuric lesions, necrotic blisters and swelling ankles, after a previous tracheobronchitis episode. Laboratory data were remarkable for mild proteinuria and imaging studies were normal. A skin biopsy showed IgA deposits on superficial dermal capillaries and IgA vasculitis (IgAV) (former Henoch-Schönlein purpura) was assumed. The patient was treated with colchicine, deflazacort and azathioprine, but as a regression in the purpuric lesions was noted, a decline in renal function was detected. A kidney biopsy revealed mesangial proliferation with IgA deposition and IgAV nephritis was considered. Immunosuppressive treatment was adjusted, with progressive normalisation of renal function and disappearance of proteinuria over a monthly follow-up; after 6 months, total remission was achieved. To the best of our knowledge, this is the first reported case of IgAV in an adult patient with SLE.

Recent advances in the understanding of immune-mediated nephrotic syndrome: diagnostic and prognostic implications

Glomerular diseases with severe defects in glomerular permeability give rise to heavy proteinuria and can present as nephrotic syndrome. There are many different causes of the nephrotic syndrome and a renal biopsy is nearly always needed to elucidate the underlying disease. During the last decade, substantial advances have occurred in the understanding of the pathophysiological mechanisms involved in immune-mediated glomerular diseases. Here, we review the diagnostic and prognostic implications of recent progress on the understanding of membranous nephropathy, minimal change disease, focal segmental glomerulosclerosis, amyloidosis, IgA nephropathy and membranoproliferative glomerulonephritis.

Antineutrophil cytoplasmic autoantibodies: how are they detected and what is their use for diagnosis, classification and follow-up?

Antineutrophil cytoplasmic antibodies (ANCA) are traditionally detected by an indirect immunofluorescence technique. According to the international consensus on ANCA testing, ANCA should also be tested by antigen-specific tests for myeloperoxidase-ANCA and proteinase 3-ANCA. The direct noncompetitive enzyme-linked immunosorbent assay (ELISA) used to be the method of choice. Nowadays, these assays are called "first-generation" assays. Second-generation tests (capture ELISA) or third-generation tests (anchor ELISA) are more sensitive and specific for ANCA testing. We postulate that ANCA as detected by these newer ANCA tests may replace the need to perform indirect immunofluorescence-based assays. For classification of patients, ANCA serotype seems more important than classifying patients according to their clinical subtype, since genetics, clinical manifestations and response to therapy are more related to ANCA serotype than to clinical subtype. Detection of ANCA to monitor disease activity is still a controversial issue. Treatment based on ANCA levels is at present only experimentally performed in those patients who are treated with B-cell depletion therapy with rituximab. Future studies are needed to establish whether this way of monitoring patients is warranted.