Hypocomplementemia is related to elevated serum levels of IgG subclasses other than IgG4 in IgG4-related kidney disease

Pharmacological Management of IgG4-Related Disease: From Traditional to Mechanism-Based Targeted Therapies

IgG4-related disease (IgG4-RD) is an immune-mediated disorder characterized by organ enlargement and dysfunction. The formation of tertiary lymphoid tissues (TLTs) in affected organs is crucial for understanding IgG4-RD, as T follicular helper (Tfh) 2 cells within TLTs drive IgG4+B cell differentiation, contributing to mass formation. Key cytokines IL-4 and IL-10, produced by Tfh2 cells, are essential for this process. Additionally, cytotoxic T cells and M2 macrophages significantly contribute to inflammation and fibrosis in the lesions. These insights into IgG4-RD have led to the development of innovative targeted therapies. While glucocorticoids are effective in many cases, they often cause disease flares during tapering and rarely result in long-term, treatment-free remissions. Long-term glucocorticoid use poses significant challenges owing to potential side effects, particularly in older patients who may already have complications such as diabetes and atherosclerotic diseases. In contrast, targeted therapies offer a promising alternative, potentially providing more effective disease control with fewer side effects. Current research is exploring several exciting approaches, including B-cell depletion, targeted immunomodulation of B cells, Bruton's tyrosine kinase inhibition, disruption of co-stimulation pathways, targeting the SLAMF7 cytokine or its receptor blockade (BAFF, IL-4, or IL-6), and JAK-STAT signaling pathway inhibition. These emerging strategies hold the promise of improving patient outcomes and advancing the management of IgG4-RD.

Clinicopathologic Features of IgG4-Related Kidney Disease

Introduction

IgG4-related disease (IgG4-RD) is a systemic immune-mediated disease that can involve nearly any organ. IgG4-RD can affect the kidney in different disease patterns, collectively referred to as IgG4-related kidney disease (IgG4-RKD).

Methods

We conducted a tissue-based cohort study with clinicopathological correlation in 125 patients with IgG4-RKD.

Results

The mean age at biopsy (n = 120) or nephrectomy (n = 5) was 63 years; 80% were male. One hundred eighteen patients (94%) had IgG4-related tubulointerstitial nephritis (IgG4-TIN); 20 patients (16%) had IgG4-related membranous glomerulonephritis (IgG4-MGN; 13 with concurrent IgG4-TIN). The primary clinical indication for biopsy/nephrectomy was acute or chronic renal failure in 78%, proteinuria in 17%, and mass lesion(s) in 15% (with overlap in primary indication). Fifty-two percent patients (41/79) had abnormal radiographic findings, including masses in 30% (24/79). All patients with IgG4-MGN had proteinuria. Extrarenal involvement by IgG4-RD was present in 79%. Median serum creatinine at presentation was 2.5 mg/dl (range 0.7-12). Serum IgG and/or IgG4 was increased in 91% (53/58); hypocomplementemia was present in 56% (43/77). Light microscopy showed plasma cell-rich interstitial nephritis in all cases of IgG4-TIN. Ninety-two percent of patients showed increased IgG4+ plasma cells. Seven percent showed an acute interstitial nephritis (AIN) pattern, and 5% showed non-necrotizing arteritis. Tubular basement membrane immune deposits were present in 83% of IgG4-TIN. Treatment information was available for 71 patients; 62 were treated with immunosuppression. Of those with elevated creatinine, 72% (41/57) showed a treatment response.

Conclusion

This largest tissue-based series more clearly defines the disease phenotype of IgG4-RKD.

Clinical phenotypes and prognosis of IgG4-related diseases accompanied by deteriorated kidney function: a retrospective study

INTRODUCTION

IgG4-related disease (IgG4-RD) is a multiorgan autoimmune disorder that causes irreversible injury. Deteriorated kidney functions are common but easily ignored complications associated with IgG4-RD. Yet the clinical manifestations and prognosis of this specific entity have not been fully illustrated.

METHOD

Three hundred fifty patients with IgG4-RD were retrospectively enrolled and divided into 119 IgG4-RD with chronic kidney disease (IgG4-RD CKD+) and 231 IgG4-RD without CKD (IgG4-RD CKD-). Demographic clinical and laboratory characteristics and survival of two cohorts were compared using restricted cubic splines, logistic and Cox regression, and Kaplan-Meier analysis. A nomogram was generated for calculating the probability of CKD in IgG4-RD.

RESULTS

The spectrum of organ involvement was different between IgG4-RD CKD+ and CKD- cohorts (p<0.001). Lung (26.89%) and retroperitoneum (18.49%) involvement were more common in the IgG4-RD CKD+ cohort. Increased serum potassium and phosphorus, reduced calcium levels, and hypocomplementemia (all p<0.05) were observed in IgG4-RD CKD+. Restricted cubic splines revealed a U-shaped plot regarding associations between serum potassium and CKD. Kaplan-Meier analysis demonstrated significantly lower long-term survival rates in IgG4-RD patients with kidney function at CKD stages 4-5. Cox regression revealed declined kidney functions (G4 HR 6.537 (95% CI: 1.134-37.675)) associated with increased all-cause mortality in IgG4-RD patients. A nomogram was constructed to predict CKD in IgG4-RD promptly with a discrimination (C-index) of 0.846.

CONCLUSIONS

CKD in IgG4-RD was associated with poor outcomes and electrolyte disturbances. Patients with IgG4-RD should be aware of possible deterioration in kidney function. The nomogram proposed would help to identify the subtle possibility of CKD in IgG4-RD. Key points • IgG4-related diseases with deteriorated kidney function have specific clinical and laboratory characteristics. • It is crucial to recognize and address the negative impact of deteriorating kidney function in IgG4-related diseases to prevent further harm. • The nomogram proposed would help to identify subtle kidney involvement by evaluating the possibility of CKD in IgG4-related diseases.

Update on respiratory lesions in patients with IgG4-related autoimmune pancreatitis

We previously reported respiratory involvement in 25 patients with autoimmune pancreatitis, a pancreatic manifestation of IgG4-related disease that responds well to glucocorticoid treatment. However, whether all respiratory lesions in patients with autoimmune pancreatitis have genuine respiratory involvement is unclear. This study aimed to update respiratory lesions' clinical and radiological characteristics in patients with autoimmune pancreatitis. We retrospectively reviewed the clinical and radiological data of 74 consecutive patients diagnosed with autoimmune pancreatitis at Shinshu University Hospital and treated with glucocorticoid. Clinical features and chest high-resolution computed tomography findings before and after therapy were reviewed. Fifty-one patients (68.9%) had respiratory lesions. In 65 of the 74 patients, chest high-resolution computed tomography results were evaluated before and after treatment. Patients with IgG4-related disease and respiratory lesions showed significantly higher serum IgG4 levels and hypocomplementemia than those without respiratory lesions; they also had more affected organs. While most abnormal thoracic findings improved, 4 cases of 7 with reticular opacities and all 11 cases with emphysema did not improve. Therefore, these lesions with poor response to glucocorticoid treatment should not be considered due to respiratory involvement of autoimmune pancreatitis based on the current classification criteria for IgG4-related disease. Patients with autoimmune pancreatitis and respiratory lesions exhibited higher disease activity than those without. Most chest high-resolution computed tomography lesions were responsive to glucocorticoid treatment, whereas reticular opacities and emphysema were poorly responsive.

Recent advances in IgG4-related kidney disease

Recent advances in the management and understanding of immunoglobulin (Ig)G4-related kidney disease (RKD) have emphasized the importance of urgent treatment in IgG4-related tubulointerstitial nephritis. On the other hand, to avoid long-term glucocorticoid toxicity, strategies for early withdrawal of steroids or combination of immunosuppressants, such as rituximab, and the minimum dose of steroids have been pursued. However, disease recurrence after reducing or stopping steroid therapy hampers early withdrawal of glucocorticoid maintenance therapy. In addition, knowledge has accumulated in diagnostic approaches including differential diagnosis of anti-neutrophil cytoplasmic antibodies-associated vasculitis, idiopathic multicentric Castleman's disease, and Rosai-Dorfman disease with kidney lesion, which leads to earlier and precise diagnosis of IgG4-RKD. This review summarizes recent progress in the differential diagnosis of IgG4-RKD and related treatment strategies and recent topics of hypocomplementaemia, membranous glomerulonephritis, and IgG4-related pyelitis and periureteral lesion.

Correlation between serologic parameters and disease activity of IgG4-related disease: Differences between patients with normal and elevated serum IgG4 concentrations

Objective

We aimed to identify serologic parameters that correlate with the disease activity of IgG4-related disease (IgG4-RD) in patients with normal and elevated serum IgG4 concentrations, respectively.

Methods

This retrospective cohort study included 148 patients with IgG4-RD. Patients were categorized into normal (≤201 mg/dL) and elevated (>201 mg/dL) serum IgG4 concentration groups. Disease activity was assessed using the IgG4-RD responder index (RI). The correlations between IgG4-RD RI and serologic parameters (erythrocyte sedimentation rate [ESR], C-reactive protein, C3, C4, IgG4 concentration, IgG concentration, and IgG4/IgG ratio) were evaluated in each group, using Spearman’s correlation coefficient.

Results

Of the 148 patients with IgG4-RD, 38 (25.7%) and 110 (74.3%) patients were categorized into the normal and elevated serum IgG4 concentration groups, respectively. In the normal serum IgG4 concentration group, IgG concentration was the only serologic parameter that showed a significant correlation with IgG4-RD RI (rho=0.411, p=0.013). However, in the elevated serum IgG4 concentration group, ESR (rho=0.196, p=0.041), C3 (rho=-0.432, p<0.001), C4 (rho=-0.363, p=0.001), IgG4 concentration (rho=0.423, p<0.001), IgG concentration (rho=0.224, p=0.020), and IgG4/IgG ratio (rho=0.328, p=0.001) correlated with IgG4-RD RI. The combination of C3 and IgG4 concentration (rho=0.509, p<0.001) had the strongest correlation with IgG4-RD RI in this group.

Conclusion

Among the serologic parameters tested, IgG concentration was the only parameter that correlated with IgG4-RD RI in patients with normal serum IgG4 concentrations, whereas multiple parameters correlated with IgG4-RD RI in those with elevated serum IgG4 concentrations. The combination of C3 and IgG4 concentration had the strongest correlation coefficient in the latter group.

Clinical Characteristics of Patients With IgG4-Related Disease Complicated by Hypocomplementemia

Background

A proportion of patients with immunogloblin G (IgG) 4-related disease (IgG4-RD) have hypocomplementemia. We aimed to identify characteristics of such patients.

Methods

We analyzed the demographic and clinical data and complement levels of 85 patients with IgG4-RD. We defined hypocomplementemia as serum C3 and/or C4 levels below the lower limit of normal at diagnosis. We also compared the characteristics of patients with and without IgG4-RD.

Results

Thirty-two (38%) patients had hypocomplementemia at diagnosis. Patients with hypocomplementemia had more lymph node (p < 0.01), lung (p < 0.01), and kidney (p = 0.02) involvement and a higher IgG4-RD responder index than those without (p = 0.05). Additionally, patients with hypocomplementemia had significantly higher IgG (p < 0.01), IgG4 (p < 0.01), and soluble interleukin 2-receptor (sIL-2R) (p < 0.01) levels and total IgG minus IgG4 (p < 0.01). C3 and C4 levels negatively correlated with IgG, IgG4, and sIL-2R levels, total IgG minus IgG4, and number of IgG4-RD responder index: a measure of the disease activity in IgG4-RD. Patients with hypocomplementemia at diagnosis had a significantly higher frequency of relapse (p = 0.024), as determined using the log-rank test. A multivariate logistic regression analysis showed the presence of hypocomplementemia was independently associated with relapse (OR, 6.842; 95% confidence interval [95%CI], 1.684–27.79; p = 0.007).

Conclusions

Patients with IgG4-RD with hypocomplementemia have a more active clinical phenotype, suggesting contributions of the complement system in the pathophysiology of IgG4-RD.

Clinicopathological Patterns and Predictors of the Functional Restoration of Immunoglobulin G4-Related Kidney Disease: A Chinese Single-Center Cohort Study

Background: Immunoglobulin G4-related disease (IgG4-RD) is a systemic immunoreactivity-based fibro-inflammatory disease. Immunoglobulin G4-related kidney disease (IgG4-RKD) is a frequently overlooked diagnosis. This study aimed to describe IgG4-RKD and examine the factors relevant to the renal outcomes of IgG4-RD. Methods: We studied a prospective IgG4-RKD cohort between January 2012 and December 2020 with close follow-up. Clinicopathologic data at kidney biopsy were collected and analyzed. We aimed to explore independent risk factors for long-term renal outcome and disease relapse. Patients with an eGFR<45 ml/min per 1.73m2 at 12 months were defined as having poor outcomes. Results: The included 42 patients with IgG4-RKD had a mean age of 58.5 ± 8.7 years (male-to-female ratio = 5:1). The IgG4-RD responder index (RI) was 12.2 ± 3.3. A total of 66.7% of the patients presented with acute on kidney disease or acute on chronic kidney disease. Eight patients (19.0%) showed nephrotic-range proteinuria, and nine (21.4%) had high-titer IgG4-autoantibodies, including antineutrophil cytoplasmic antibody and anti-phospholipase A2 receptor. A kidney biopsy was conducted in 40 patients. Thirty-seven (90.0%) patients were diagnosed with IgG4-related tubulointerstitial nephritis, and 19 (47.5%) of them had concurrent glomerular diseases (membranous nephropathy [MN], n = 3; crescentic glomerulonephritis [CrGN], n = 11; diabetic kidney disease, n = 3; and both MN and CrGN, n = 2). IgG4-RD RI had a close relationship with serum C3 (R = -0.509, P = 0.001), C4 (R = -0.314, P = 0.049) levels, and peripheral blood eosinophil count (PBEC; R = 0.377, P = 0.024), factors that were not included in RI scores. Correlation analysis disclosed that IgG4-RD RI (R = 0.422, P = 0.007), organs involved (R = 0.452, P = 0.003), and C3 (R = -0.487, R = 0.002) were correlated with the percentage decrease of serum creatinine at 1 month. However, multivariate regression analysis failed to identify any clinicopathological parameters that could predict short-term renal restoration and IgG4-RKD relapse. Ten out of 29 variables, of most importance, were identified by the least absolute shrinkage and selection operator (LASSO) regression analysis. By multivariate logistic regression a higher serum IgG4 (OR = 0.671, P = 0.010), IgG1 (OR = 1.396, P = 0.049), IgG3 (OR = 19.154, P = 0.039), and erythrocyte sedimentation rate (ESR; OR = 1.042, P = 0.032) were found to be independent factors for poor long-term outcome. Conventional immunosuppressive medications and/or rituximab were prescribed, and in 83.3% of the patients, the kidney function improved. Repeat kidney biopsies confirmed the remission of interstitial inflammation in two patients under immunosuppressive therapy. However, the disease relapse rate was as high as 31.0%. Conclusions: We strongly recommend a kidney biopsy in active IgG4-RD, especially when there is proteinuria and renal dysfunction, because concurrent glomerular involvement and active interstitial inflammation should be assessed. A higher serum IgG1, IgG3, and ESR were independent factors for the poor long-term renal outcome; however, elevated IgG4 predicted a good renal prognosis, and appropriate and timely immunosuppressive therapy can help achieve a better prognosis.

Proteomic analyses of plasma-derived exosomes in immunoglobulin (Ig) G4-related disease and their potential roles in B cell differentiation and tissue damage

OBJECTIVE

To investigate the proteomic profiles of plasma exosomes isolated from patients with immunoglobulin (Ig) G4-related disease (IgG4-RD) and to determine their potential roles in B cell differentiation and tissue damage.

METHODS

One hundred untreated IgG4-RD patients and 135 sex- and age-matched healthy controls (HCs) were enrolled in this study. A combination of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and tandem mass tag (TMT)-label quantitation was used for proteomic profiling. Differentially expressed proteins were validated by Western blot, enzyme-linked immunosorbent assay (ELISA) and real-time quantitative PCR (RT-qPCR) analyses. B cell activation, apoptosis, differentiation and reactive oxygen species (ROS) production were analyzed by flow cytometry. We also analyzed the correlations between differentially expressed complement proteins and laboratory parameters.

RESULTS

A total of 178 differentially expressed proteins were identified in plasma exosomes in IgG4-RD patients compared with HCs, and these proteins were enriched predominantly in the complement cascade pathway. Furthermore, reduced expression levels of complement components C3 and C5 in IgG4-RD were correlated with clinical parameters. Following stimulation with IgG4-RD plasma exosomes, the percentages of naïve B cells decreased, while those of memory B cells and plasmablasts increased; the levels of cytochrome c, somatic (CYCS) and downstream complement system activation also increased. Moreover, ROS production was greater in B cells of IgG4-RD patients than in those of HCs. In affected submandibular glands, the BCR signalling pathway was activated, and exosomes were enriched.

CONCLUSION

Proteomic profiling revealed that plasma exosome proteins may participate in the pathogenesis of IgG4-RD through complement activation and may be involved in B cell differentiation and activation of the B cell auto-oxidative damage pathway.

Identification of serum IFN-α and IL-33 as novel biomarkers for type 1 autoimmune pancreatitis and IgG4-related disease

IgG4-related disease (IgG4-RD) is a multi-organ autoimmune disease characterized by elevated serum IgG4 concentration. Although serum IgG4 concentration is widely used as a biomarker for IgG4-RD and type 1 autoimmune pancreatitis (AIP), a pancreatic manifestation of IgG4-RD, a significant number of patients have normal serum IgG4 levels, even in the active phase of the disease. Recently, we reported that the development of experimental AIP and human type 1 AIP is associated with increased expression of IFN-α and IL-33 in the pancreas. In this study, we assessed the utility of serum IFN-α and IL-33 levels as biomarkers for type 1 AIP and IgG4-RD. Serum IFN-α and IL-33 concentrations in patients who met the diagnostic criteria for definite type 1 AIP and/or IgG4-RD were significantly higher than in those with chronic pancreatitis or in healthy controls. Strong correlations between serum IFN-α, IL-33, and IgG4 concentrations were observed. Diagnostic performance of serum IFN-α and IL-33 concentrations as markers of type 1 AIP and/or IgG4-RD was comparable to that of serum IgG4 concentration, as calculated by the receiver operating characteristic curve analysis. Induction of remission by prednisolone treatment markedly decreased the serum concentration of these cytokines. We conclude that serum IFN-α and IL-33 concentrations can be useful as biomarkers for type 1 AIP and IgG4-RD.