BAFF, APRIL and BAFFR on the pathogenesis of Immunoglobulin-A vasculitis

A narrative review of potential drug treatments for nephritis in children with IgA vasculitis (HSP)

Immunoglobulin A (IgA) vasculitis (IgAV, also known as Henoch-Schoenlein purpura, HSP) is the most common vasculitis of childhood. It usually presents with a simple, self-limiting disease course; however, a small subset of patients may develop kidney involvement (IgAV-N) which occurs 4-12 weeks after disease onset and is the biggest contributor to long-term morbidity. Treatment currently targets patients with established kidney involvement; however; there is a desire to work towards early prevention of inflammation during the window of opportunity between disease presentation and onset of significant nephritis. There are no clinical trials evaluating drugs which may prevent or halt the progression of nephritis in children with IgAV apart from the early use of corticosteroids which have no benefit. This article summarises the latest scientific evidence and clinical trials that support potential therapeutic targets for IgAV-N that are currently being developed based on the evolving understanding of the pathophysiology of IgAV-N. These span the mucosal immunity, B-cell and T-cell modulation, RAAS inhibition, and regulation of complement pathways, amongst others. Novel drugs that may be considered for use in early nephritis include TRF-budesonide; B-cell inhibiting agents including belimumab, telitacicept, blisibimod, VIS649, and BION-1301; B-cell depleting agents such as rituximab, ofatumumab, and bortezomib; sparsentan; angiotensin converting enzyme inhibitors (ACE-Is); and complement pathway inhibitors including avacopan, iptacopan, and narsoplimab. Further clinical trials, as well as pre-clinical scientific studies, are needed to identify mechanistic pathways as there may be an opportunity to prevent nephritis in this condition. Key Points • Kidney involvement is the main cause of long-term morbidity and mortality in IgA vasculitis despite the current treatment recommendations. • The evolving understanding of the pathophysiology of IgA vasculitis is allowing exploration of novel treatment options which target underlying immune pathways. • Novel treatments currently being trialled in IgA nephropathy may have benefit in IgA vasculitis due to the similarities in the underlying pathophysiology, such as TRF-budesonide, B-cell modulators, and complement inhibitors. • Further studies, including clinical trials of novel drugs, are urgently needed to improve the long-term outcomes for children with IgA vasculitis nephritis.

Mucosal Immune Defence Gene Polymorphisms as Relevant Players in the Pathogenesis of IgA Vasculitis?

ITGAM-ITGAX (rs11150612, rs11574637), VAV3 rs17019602, CARD9 rs4077515, DEFA (rs2738048, rs10086568), and HORMAD2 rs2412971 are mucosal immune defence polymorphisms, that have an impact on IgA production, described as risk loci for IgA nephropathy (IgAN). Since IgAN and Immunoglobulin-A vasculitis (IgAV) share molecular mechanisms, with the aberrant deposit of IgA1 being the main pathophysiologic feature of both entities, we assessed the potential influence of the seven abovementioned polymorphisms on IgAV pathogenesis. These seven variants were genotyped in 381 Caucasian IgAV patients and 997 matched healthy controls. No statistically significant differences were observed in the genotype and allele frequencies of these seven polymorphisms when the whole cohort of IgAV patients and those with nephritis were compared to controls. Similar genotype and allele frequencies of all polymorphisms were disclosed when IgAV patients were stratified according to the age at disease onset or the presence/absence of gastrointestinal or renal manifestations. Likewise, no ITGAM-ITGAX and DEFA haplotype differences were observed when the whole cohort of IgAV patients, along with those with nephritis and controls, as well as IgAV patients, stratified according to the abovementioned clinical characteristics, were compared. Our results suggest that mucosal immune defence polymorphisms do not represent novel genetic risk factors for IgAV pathogenesis.

Aberrant Gut Microbiome Contributes to Barrier Dysfunction, Inflammation, and Local Immune Responses in IgA Nephropathy

INTRODUCTION

Numerous research works have shown that serum Gal-deficient (Gd) IgA1 levels are increased in IgA nephropathy (IgAN) patients and these levels are a dangerous risk factor for IgAN. A relationship between the gut microbiota and IgAN has been reported. Whether the gut microbiota participates in the pathogenesis of IgAN was still controversial.

METHODS

We evaluated changes in the gut flora and the levels of Gd-IgA1 in IgAN patients and healthy controls (HCs). We investigated the Gd-IgA1 levels in both blood and urine specimens. C57BL/6 mice were given a broad-spectrum antibiotic cocktail to deplete the endogenous gut flora. We established a model of IgAN in pseudosterile mice and investigated the expression of the markers of intestinal permeability, inflammation, and local immune responses.

RESULTS

Studies have shown that the levels of certain gut flora differ between IgAN patients and HCs. Moreover, elevated Gd-IgA1 levels were found in both the serum and urine. Interestingly, Coprococcus, Dorea, Bifidobacterium, Blautia, and Lactococcus, selected from 10 candidate biomarkers to predict risk in IgAN patients according to random forest analysis, were inversely associated with urinary Gd-IgA1 levels. Notably, the urine level of Gd-IgA1 could best distinguish IgAN patients from HCs. Additionally, the degree of kidney damage in pseudosterile mice with IgAN was more severe than that in mice with IgAN. Furthermore, the markers of intestinal permeability were significantly elevated in pseudosterile IgAN mice. Moreover, the inflammation responses (TLR4, MyD88, and NF-κB in intestinal and renal tissues; TNF-α and IL-6 in serum) and local immune responses (BAFF and APRIL in intestinal tissue) were upregulated in pseudosterile IgAN mice.

CONCLUSIONS

The urine Gd-IgA1 level may be as a biomarker for the early screening of potential IgAN, and gut microbiota dysbiosis was demonstrated in IgAN, which might involve the dysfunction of the mucosal barrier, inflammation, and local immune responses.

Urinary Protein Array Analysis to Identify Key Inflammatory Markers in Children with IgA Vasculitis Nephritis

Chronic kidney disease is a recognised complication of immunoglobulin A vasculitis, (IgAV; formerly Henoch–Schonlein purpura—HSP). The pathophysiology of IgAV and why some patients develop significant renal involvement remains largely unknown. Identifying urinary inflammatory markers could direct targets for earlier intervention. The aim of this cross-sectional exploratory study was to perform a large protein array analysis to identify urinary markers to provide insight into the mechanisms of kidney inflammation in children with established IgAV nephritis (IgAVN). Determination of the relative levels of 124 key proteins was performed using commercially available proteome profiler array kits. Twelve children were recruited: IgAVN, n = 4; IgAV without nephritis (IgAVwoN), n = 4; healthy controls (HCs), n = 4. The urinary concentrations of twenty proteins were significantly different in IgAVN compared to IgAVwoN. The largest fold changes were reported for B-cell activating factor (BAFF), Cripto-1, sex-hormone-binding globulin and angiotensinogen. The urinary levels of complement components C5/C5a and factor D were also significantly elevated in patients with IgAVN. A total of 69 urinary proteins significantly raised levels in comparisons made between IgAVN vs. HCs and nine proteins in IgAVwoN vs. HCs, respectively. This study identified key urinary proteins potentially involved in IgAVN providing new insight into the pathophysiology. Further longitudinal studies with larger cohorts are needed to quantitatively analyse these biomarkers.

Consensus evidence-based recommendations for treat-to-target management of immunoglobulin A vasculitis

IgA vasculitis (IgAV), formerly known as Henoch-Schönlein purpura, is the most common cause of systemic vasculitis in childhood. Given its potential life-threatening systemic complications, early and accurate diagnosis as well as management of IgAV represent a major challenge for health care professionals. This study was carried out to attain an evidence-based expert consensus on a treat-to-target management approach for IgAV using Delphi technique. The preliminary scientific committee identified a total of 16 key clinical questions according to the patient, intervention, comparison, and outcomes (PICO) approach. An evidence-based, systematic, literature review was conducted to compile evidence for the IgAV management. The core leadership team identified researchers and clinicians with expertise in IgAV management in Egypt upon which experts were gathered from different governorates and health centers across Egypt. Delphi process was implemented (two rounds) to reach a consensus. An online questionnaire was sent to expert panel (n = 26) who participated in the two rounds. After completing round 2, a total of 20 recommendation items, categorized into two sections were obtained. Agreement with the recommendations (rank 7-9) ranged from 91.7-100%. Consensus was reached (i.e. ⩾75% of respondents strongly agreed or agreed) on the wording of all the 20 clinical standards identified by the scientific committee. Algorithms for the diagnosis and management have been suggested. This was an expert, consensus recommendations for the diagnosis and treatment of IgAV and IgA vasculitic nephritis, based on best available evidence and expert opinion. The guideline presented a strategy of care with a pathway to achieve a state of remission as early as possible.

Plain Language Summary

Given its potential life-threatening systemic complications, early and accurate diagnosis of immunoglobulin A vasculitis represents a major challenge for health care professionals. This work provided cornerstone principles for the management of the condition. Adopting PICO approach and implementing Delphi process a consensus was reached on evidence-based treat-to-target treatment recommendations. This will endorse enhancement and consistency of care of this cohort of patients in standard practice.