IgG4 Autoantibodies in Organ-Specific Autoimmunopathies: Reviewing Class Switching, Antibody-Producing Cells, and Specific Immunotherapies

IgG subclass shifts occurring at acute exacerbations in autoimmune nodopathies

BACKGROUND

Autoimmune nodopathy associated with anti-contactin1 (CNTN1) IgG4 antibodies frequently manifests as acute axonal degeneration in addition to detachment of the paranodal myelin loops. The acute destruction of myelinated nerve fibers does not match the function of IgG4, which cannot activate the complement pathway. IgG subclass switching from IgG1 or IgG3 to IgG4 has been observed in some patients with autoimmune diseases associated with IgG4 throughout their disease course.

METHODS

Serial changes in IgG subclasses, clinico-neurophysiological features, and nerve and renal pathology were reviewed in three patients with anti-CNTN1-associated autoimmune nodopathy and one patient with anti-contactin-associated protein1 (Caspr1) autoimmune nodopathy.

RESULTS

All four patients had predominantly IgG4 autoantibodies, whereas they showed evidence of acute axonal degeneration. The IgG1 subclass was present in all patients at their progressing stage but then disappeared at follow-up. Nerve pathology in the patients with anti-CNTN1 and anti-Caspr1 autoimmune nodopathies showed both structural changes in the paranodes and evidence of acute axonal degeneration. Renal biopsy specimens from two patients with membranous glomerulonephritis and anti-CNTN1 autoimmune nodopathy showed deposition of IgG1 and complement on the glomerular basement membrane, as well as IgG4.

DISCUSSION

In patients with autoimmune nodopathies associated with anti-CNTN1 and anti-Caspr1 IgG4 antibodies, IgG1 subclass autoantibodies were present at their acute exacerbations and might have contributed to the axonal degeneration and glomerular injury. IgG1 disappeared with the cessation of disease progression, which indicates that the IgG1 subclass is a possible biomarker of disease activity.

A retrospective multicenter study on clinical and serological parameters in patients with MuSK myasthenia gravis with and without general immunosuppression

Introduction

Muscle-specific kinase (MuSK)- myasthenia gravis (MG) is caused by pathogenic autoantibodies against MuSK that correlate with disease severity and are predominantly of the IgG4 subclass. The first-line treatment for MuSK-MG is general immunosuppression with corticosteroids, but the effect of treatment on IgG4 and MuSK IgG4 levels has not been studied.

Methods

We analyzed the clinical data and sera from 52 MuSK-MG patients (45 female, 7 male, median age 49 (range 17-79) years) from Italy, the Netherlands, Greece and Belgium, and 43 AChR-MG patients (22 female, 21 male, median age 63 (range 2-82) years) from Italy, receiving different types of immunosuppression, and sera from 46 age- and sex-matched non-disease controls (with no diagnosed diseases, 38 female, 8 male, median age 51.5 (range 20-68) years) from the Netherlands. We analyzed the disease severity (assessed by MGFA or QMG score), and measured concentrations of MuSK IgG4, MuSK IgG, total IgG4 and total IgG in the sera by ELISA, RIA and nephelometry.

Results

We observed that MuSK-MG patients showed a robust clinical improvement and reduction of MuSK IgG after therapy, and that MuSK IgG4 concentrations, but not total IgG4 concentrations, correlated with clinical severity. MuSK IgG and MuSK IgG4 concentrations were reduced after immunosuppression in 4/5 individuals with before-after data, but data from non-linked patient samples showed no difference. Total serum IgG4 levels were within the normal range, with IgG4 levels above threshold (1.35g/L) in 1/52 MuSK-MG, 2/43 AChR-MG patients and 1/45 non-disease controls. MuSK-MG patients improved within the first four years after disease onset, but no further clinical improvement or reduction of MuSK IgG4 were observed four years later, and only 14/52 (26.92%) patients in total, of which 13 (93.3%) received general immunosuppression, reached clinical remission.

Discussion

We conclude that MuSK-MG patients improve clinically with general immunosuppression but may require further treatment to reach remission. Longitudinal testing of individual patients may be clinically more useful than single measurements of MuSK IgG4. No significant differences in the serum IgG4 concentrations and IgG4/IgG ratio between AChR- and MuSK-MG patients were found during follow-up. Further studies with larger patient and control cohorts are necessary to validate the findings.

Clinical Significance of IgG4 Serum Concentration in Graves' Disease

Elevated immunoglobulin G4 (IgG4) serum antibodies are an important feature of IgG4-related disease. However, IgG4 antibodies can play a role in autoimmune thyroid disorders. In this study, we aimed to evaluate the impact of serum IgG4 levels on clinical features of Graves' disease (GD). We recruited 60 patients with GD (48 patients without thyroid eye disease, 12 patients with moderate-to-severe Graves' orbitopathy [GO], and 25 healthy control subjects). The prevalence of high IgG4 serum concentration was 4.2% among GD patients without GO and 33.33% in patients with moderate-to-severe GO. The group with GO had significantly higher median IgG4 levels (87.9 mg/dL) than the control group (41.2 mg/dL, P = 0.034) and the GD without GO group (30.75 mg/dL, P < 0.001). Patients with thyroid nodules had lower IgG4 levels than patients without thyroid nodules, but the difference was not statistically significant (35.7 [24.8; 41.53] mg/dL vs. 43 [30.1; 92.7] mg/dL, P = 0.064). IgG4 as a diagnostic tool for moderate-to-severe GO had the following parameters: area under the curve (AUC): 0.851 (P < 0.001), at the cut-off value of 49 mg/dL, negative predictive value: 100%, positive predictive value: 48%, sensitivity: 100%, specificity: 73%. There were no significant differences between the high and normal IgG4 groups in thyroid hormones, antithyroid antibodies, and ultrasound features. Serum IgG4 levels are associated with some of the clinical features of GD and can help in the diagnostic process of the disease. More research is needed to better understand the pathophysiology of IgG4 involvement in GD.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

The spectrum of B cells in the pathogenesis, diagnosis and therapeutic applications of immunoglobulin G4-related disease

Immunoglobulin G4 (IgG4)-related disease is a chronic fibroinflammatory disease mediated by immune disorders. Given the challenging clinical diagnosis and treatment, knowledge of the pathogenesis of IgG4-related disease is important. The typical elevation of serum IgG4 concentrations and infiltration of IgG4-positive plasma cells in the involved tissues indicate the involvement of B lymphocytes in the pathogenesis of IgG4-related disease. Mass production of autoantibodies reflects abnormal activation of B cells, which causes tissue damage. Circulating plasmablasts are recently discovered markers that correlate with serum IgG4 concentration, the extent of organ involvement and disease activity. B-cell depletion therapy is an emerging curative strategy that can significantly alleviate clinical manifestations and achieve remission in patients with IgG4-related disease. These findings highlight the potential role of B cells in IgG4-related disease. In this review, we discuss the pathogenic impact of B lymphocytes on IgG4-related disease and describe novel therapies targeting B cells.

Silencing of FCRLB by shRNA ameliorates MuSK-induced EAMG in mice

INTRODUCTION

Muscle specific kinase (MuSK) antibody positive myasthenia gravis (MG) often presents with a severe disease course and resistance to treatment. Treatment-refractory patients may respond to B cell depleting treatment methods. Our aim was to investigate whether inhibition of Fc receptor-like B (FCRLB) could effectively suppress autoimmunity without diminishing B cell counts in animal model of MG, a classical antibody-mediated autoimmune disease.

METHODS

Experimental autoimmune MG was induced in Balb/C mice with two s.c. immunizations with recombinant human MuSK in complete Freund's adjuvant. FCRLB was silenced with a lentiviral particle transported shRNA in myasthenic mice with a single i.p. injection during second MuSK-immunization. Control immunized mice received scrambled shRNA or saline. Mice were observed for clinical parameters for 28 days and at termination, anti-MuSK IgG, neuromuscular junction (NMJ) deposits, muscle AChR expression and lymph node B and T cell ratios were assessed by ELISA, immunofluorescence, immunoblotting and flow cytometry, respectively.

RESULTS

FCRLB shRNA-treated mice showed no muscle weakness or weight loss at termination. Also, they exhibited higher grip strength and muscle AChR levels, lower anti-MuSK IgG and NMJ IgG/C3 levels than control mice. Flow cytometry analysis showed that ratios of major effector lymph node B and T cell populations were not altered by FCRLB silencing. However, regulatory T and CD19 + CD5+ B cell ratios were decreased in FCRLB shRNA-group.

CONCLUSION

Our results provide evidence regarding involvement and therapeutic value of FCRLB in MuSK-MG. Silencing of FCRLB appears to substantially inhibit antibody production without interfering with survival of major lymphocyte populations.

Cytokine Gene Polymorphisms in Patients with Chronic Inflammatory Demyelinating Polyneuropathy

Innate and adaptive immune responses exert their role in CIDP pathogenesis through cytokine production. Single-nucleotide polymorphisms (SNPs) may alter cytokine gene expression, with a potential influence on the pathogenesis of autoimmune diseases. However, cytokine gene SNPs have not been assessed in CIDP patients yet. We assessed functional SNPs in the genes encoding IL-10 (rs1800896, rs1800871, rs1800872 and rs3024505), IL-6 (rs1800795), TNF (rs1800629 and rs361525), IL-12B (rs3212227), IFN-γ (rs2430561), GM-CSF (rs25882) and IL-17F (rs11465553) in a cohort of 88 CIDP patients and 486 healthy controls (HCs) via qPCR. We found an association of SNP in the IL10 promotor and CIDP occurrence. Major homozygotes (AA) were more frequent in the HCs compared to CIDP patients (p = 0.049), but the GA genotype prevailed among the patients (p = 0.032). A lower frequency of the C allele was observed for rs1800871 and rs1800872 in CIDP patients compared to the HCs (p = 0.048). A higher proportion of A carriers at position -1082 (rs1800896) (presumed to be a low IL-10 producer) was noted in patients with milder disability (low INCAT). All mild-INCAT patients were C carriers for rs1800871 and rs1800872 in IL10 (p = 0.038). Furthermore, the IL6 rs1800795 GG genotype was more frequent in patients (p = 0.049) and the CG heterozygote in the HCs (p = 0.013). Among the CIDP patients, being a G carrier for this SNP was associated with a higher frequency of type 2 diabetes (T2D) compared to being a non-carrier (p = 0.032). Our data indicate a possible association of the IL10 and IL6 SNPs with CIDP, but also with disease severity and T2D occurrence. Given the paucity of CIDP patients, multicentric studies are necessary to draw definite conclusions on these associations.

Interleukin-10-alveolar macrophage cell membrane-coated nanoparticles alleviate airway inflammation and regulate Th17/regulatory T cell balance in a mouse model

Background

Allergic airway disease (AAD) is a chronic disease characterized by airway inflammation, bronchoconstriction, and hyperresponsiveness. Although exogenous interleukin-10 (IL-10) alleviates allergic inflammation, it has a short half-life in vivo. Cell membrane-coated nanomaterials have been shown to protect therapeutic payloads and increase therapeutic efficacy.

Objective

This study was aimed at investigating the efficacy of a novel macrophage-based nanoparticle drug for the treatment of house dust mite (HDM)-induced allergic airway diseases.

Methods

IL-10-poly (lactic-co-glycolic acid (PLGA) nanoparticles were encapsulated in alveolar macrophage cell membranes. An allergic airway disease mouse model was established by repeated inhalation of HDM extracts. The mice were treated with free IL-10, IL-10-PLGA nanoparticles (IL10-NP), or IL-10-alveolar macrophage cell membrane-coated nanoparticles (IL10-AMNP). The therapeutic effects were evaluated by measuring airway hyperresponsiveness, lung inflammation, cytokine levels, and regulatory T cells (Treg)- T-helper 17 (Th17) cell balance.

Results

Compared to free IL-10, IL10-AMNP significantly reduced airway hyperresponsiveness and T-helper 2 (Th2)/Th17 cytokines and inhibited neutrophilia and eosinophilia recruitment into the airways of HDM-induced mouse models. Additionally, the balance between Tregs and Th17 cells was significantly improved in groups treated with IL10-AMNP.

Conclusion

This study demonstrated that PLGA nanoparticle cores coated with alveolar macrophage cell membranes can effectively deliver therapeutic cytokines to the lungs and improve the homeostatic balance between Tregs and Th17 cells. These findings suggest that macrophage-based nanoparticle drugs represent a promising approach for treating allergic airway diseases.

Sex differences in Guillain Barré syndrome, chronic inflammatory demyelinating polyradiculoneuropathy and experimental autoimmune neuritis

Guillain Barré syndrome (GBS) and its variants, and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP and its variants, are regarded as immune mediated neuropathies. Unlike in many autoimmune disorders, GBS and CIDP are more common in males than females. Sex is not a clear predictor of outcome. Experimental autoimmune neuritis (EAN) is an animal model of these diseases, but there are no studies of the effects of sex in EAN. The pathogenesis of GBS and CIDP involves immune response to non-protein antigens, antigen presentation through non-conventional T cells and, in CIDP with nodopathy, IgG4 antibody responses to antigens. There are some reported sex differences in some of these elements of the immune system and we speculate that these sex differences could contribute to the male predominance of these diseases, and suggest that sex differences in peripheral nerves is a topic worthy of further study.

SARS-CoV-2 Vaccine Booster Elicits Robust Prolonged Maternal Antibody Responses and Passive Transfer Via The Placenta And Breastmilk

Background

Infection during pregnancy can result in adverse outcomes for both pregnant persons and offspring. Maternal vaccination is an effective mechanism to protect both mother and neonate into post-partum. However, our understanding of passive transfer of antibodies elicited by maternal SARS-CoV-2 mRNA vaccination during pregnancy remains incomplete.

Objective

We aimed to evaluate the antibody responses engendered by maternal SARS-CoV-2 vaccination following initial and booster doses in maternal circulation and breastmilk to better understand passive immunization of the newborn.

Study Design

We collected longitudinal blood samples from 121 pregnant women who received SARS-CoV-2 mRNA vaccines spanning from early gestation to delivery followed by collection of blood samples and breastmilk between delivery and 12 months post-partum. During the study, 70% of the participants also received a booster post-partum. Paired maternal plasma, breastmilk, umbilical cord plasma, and newborn plasma samples were tested via enzyme-linked immunosorbent assays (ELISA) to evaluate SARS-CoV-2 specific IgG antibody levels.

Results

Vaccine-elicited maternal antibodies were detected in both cord blood and newborn blood, albeit at lower levels than maternal circulation, demonstrating transplacental passive immunization. Booster vaccination significantly increased spike specific IgG antibody titers in maternal plasma and breastmilk. Finally, SARS-CoV-2 specific IgG antibodies in newborn blood correlated negatively with days post initial maternal vaccine dose.

Conclusion

Vaccine-induced maternal SARS-CoV-2 antibodies were passively transferred to the offspring in utero via the placenta and after birth via breastfeeding. Maternal booster vaccination, regardless of gestational age at maternal vaccination, significantly increased antibody levels in breastmilk and maternal plasma, indicating the importance of this additional dose to maximize passive protection against SARS-CoV-2 infection for neonates and infants until vaccination eligibility.

Pathogenic autoantibodies in multiple sclerosis - from a simple idea to a complex concept

The role of autoantibodies in multiple sclerosis (MS) has been enigmatic since the first description, many decades ago, of intrathecal immunoglobulin production in people with this condition. Some studies have indicated that MS pathology is heterogeneous, with an antibody-associated subtype - characterized by B cells (in varying quantities), antibodies and complement - existing alongside other subtypes with different pathologies. However, subsequent evidence suggested that some cases originally diagnosed as MS with autoantibody-mediated demyelination were more likely to be neuromyelitis optica spectrum disorder or myelin oligodendrocyte glycoprotein antibody-associated disease. These findings raise the important question of whether an autoantibody-mediated MS subtype exists and whether pathogenic MS-associated autoantibodies remain to be identified. Potential roles of autoantibodies in MS could range from specific antibodies defining the disease to a non-disease-specific amplification of cellular immune responses and other pathophysiological processes. In this Perspective, we review studies that have attempted to identify MS-associated autoantibodies and provide our opinions on their possible roles in the pathophysiology of MS.

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.

A systematic review and meta-analysis of HLA class II associations in patients with IgG4 autoimmunity

Autoimmune diseases caused by pathogenic IgG4 subclass autoantibodies (IgG4-AID) include diseases like MuSK myasthenia gravis, pemphigus vulgaris or thrombotic thrombocytopenic purpura. Their etiology is still unknown. Polymorphisms in the human leukocyte antigen (HLA) gene locus, particularly in HLA-DRB1, are known genetic susceptibility factors for autoimmune diseases. We hypothesized a similar role for HLA polymorphisms in IgG4-AID and conducted a systematic review and meta-analysis with case-control studies on IgG4-AID based on MOOSE/ HuGENet guidelines. Genotype (G) and allele (A) frequencies of HLA-DQB1*05 (G: OR 3.8; 95% CI 2.44-5.9; p < 0.00001; A: OR 2.54; 95% CI 1.82-3.55; p < 0.00001) and HLA-DRB1*14 (G: OR 4.31; 95% CI 2.82-6.59; p < 0.00001; A: OR 4.78; 95% CI 3.52-6.49; p < 0.00001) and the HLA-DRB1*14-DQB1*05 haplotype (OR 6.3; 95% CI 3.28-12.09; p < 0.00001/OR 4.98; 95% CI 3.8-6.53; p < 0.00001) were increased while HLA-DRB1*13 (G: OR 0.48; 95% CI 0.34-0.68; p < 0.0001; A: OR 0.46; 95% CI 0.34-0.62; p < 0.00001) was decreased in IgG4-AID patients. In conclusion, the HLA-DQB1*05, HLA-DRB1*14 alleles and the HLA-DQB1*05-DRB1*14 haplotype could be genetic risk factors that predispose for the production of pathogenic IgG4 autoantibodies and the HLA-DRB1*13 allele may protect from IgG4 autoimmunity.