IgG4 autoantibodies are inhibitory in the autoimmune disease bullous pemphigoid

Eosinophils in Oral Disease: A Narrative Review

The prevalence of diseases characterised by eosinophilia is on the rise, emphasising the importance of understanding the role of eosinophils in these conditions. Eosinophils are a subset of granulocytes that contribute to the body's defence against bacterial, viral, and parasitic infections, but they are also implicated in haemostatic processes, including immunoregulation and allergic reactions. They contain cytoplasmic granules which can be selectively mobilised and secrete specific proteins, including chemokines, cytokines, enzymes, extracellular matrix, and growth factors. There are multiple biological and emerging functions of these specialised immune cells, including cancer surveillance, tissue remodelling and development. Several oral diseases, including oral cancer, are associated with either tissue or blood eosinophilia; however, their exact mechanism of action in the pathogenesis of these diseases remains unclear. This review presents a comprehensive synopsis of the most recent literature for both clinicians and scientists in relation to eosinophils and oral diseases and reveals a significant knowledge gap in this area of research.

Anti-interleukin 4 receptor α antibody for the treatment of Chinese bullous pemphigoid patients with diverse comorbidities and a 1-year follow-up: a monocentric real-world study

Background

Bullous pemphigoid (BP) is a common subepidermal bullous disorder that lacks adequate treatment alternatives. Dupilumab, an anti-interleukin (IL) 4 receptor α antibody blocking Th2 molecules IL-4 and 13, has been used off-label and shown to be effective in refractory BP cases.

Methods

BP patients with various disease severities and comorbidities were included in this case series. All patients received dupilumab alone or in combination with immunosuppressants in a real-world setting. Complete remission (CR) was defined as the absence of pruritus symptoms and previous BP eruptions, with only hyperpigmentation patches and without newly occurring lesions for at least 4 weeks. Disease relapse was classified as the appearance of three or more new lesions within 1 month or at least one large urticarial or eczematous lesion that did not resolve within a week.

Findings

Ten individuals were enrolled in this case series. Pruritus symptoms and BP eruptions improved significantly in nine patients (90%). Seven patients (70%) attained CR, including all mild-to-moderate (100%) cases and three of six (50%) severe BP cases. At the dupilumab monotherapy stage, eosinophilia was observed in two severe cases. One patient out of seven (14.3%) relapsed after 1 year of follow-up after CR.

Conclusion

Treatment of BP with diverse comorbidities with anti-IL-4 receptor α antibody provides further credentials to a prospective randomized study. More impressive efficacy and safety profiles were observed in patients with mild-to-moderate disease after 1 year of follow-up. Eosinophilia may occur in patients receiving dupilumab monotherapy.

[Characteristics of allergen component in dust mite-induced allergic rhinitis patients]

Objective:To investigate the characteristics of allergen component in dust mite（DM） -induced allergic rhinitis（AR） patients, and provide reference for the diagnosis and treatment of AR. Methods:DM-induced AR patients with or without allergic asthma（AA） who visited the Allergy Department of Tongji Hospital, Huazhong University of Science and Technology between 2021 and 2022 were enrolled. Patients'age, gender, and visual analog scale（VAS） for symptoms were recorded. sIgE and sIgG4 levels of allergen components such as Der f1, Der f2, Der p1, Der p2, Der p7, Der p10, Der p21, and Der p23 were detected using a protein chip method. The sensitization characteristics of the allergen components in the patients were observed, and the correlation between sIgE, sIgG of each component and VAS as well as the component differences between AR and AR with AA（AR&AA） were evaluated. Results:A total of 87 DM-induced AR patients were enrolled, with 42.5% of them were AR&AA, their VAS scores were significantly higher than those of AR patients（6.38±1.95 vs 5.25±1.85, P=0.009 8）. The order of sensitization rates for DM components was as follows: Der p2（82.8%）, Der f2（81.6%）, Der p1（74.7%）, Der f1（70.1%）, and Der p23（35.6%）. The order of positive rates for sIgG4 was: Der p2（21.8%）, Der f2（13.8%）, Der p21（8.0%）, and Der p7（6.9%）. There were no correlation between the sIgE, sIgG4 levels or positive numbers of components and VAS scores, but there were positive correlations between sIgE, sIgG4 concentrations of components. Compared with AR patients, AR&AA patients had higher levels of sIgE for Der p（60.5[7.2-91.1]vs 14.0[4.8-45.1], P=0.02）, Der f（49.8[15.7-81.6]vs 21.3[7.0-50.2], P=0.04）, Der p1（27.2[0.7-51.5]vs 2.6[0.2-24.9], P=0.02）, Der p2（20.0[1.4-60.6]vs 5.5[0.6-19.1], P=0.004）, and Der f2（58.9[16.0-89.2]vs 23.4[0.9-56.8], P=0.009）, and a higher proportion of AR with AA patients had sIgE levels of Der p1（70.3% vs 48.0%, P=0.038） and Der p23（27.0% vs 14.0%, P=0.039） that were ≥3 grades. Conclusion:Der p1/f1, Der p2/f3, and Der p23 are the major components of DM sensitized AR patients. Multiple component sensitization and sIgE, sIgG4 levels of each component are not correlated with the severity of AR. The sIgE levels of the Der p1/f1, Der p2/f3, and Der p23 components in AR&AA patients are higher than AR.

Adaptive and innate immune pathogenesis of bullous pemphigoid: A review

Bullous pemphigoid (BP) is an autoimmune blistering disease that primarily affects elderly individuals. The presentation of BP is heterogeneous, typically manifesting as microscopic subepidermal separation with a mixed inflammatory infiltrate. The mechanism of pemphigoid development is unclear. B cells play a major role in pathogenic autoantibody production, and T cells, type II inflammatory cytokines, eosinophils, mast cells, neutrophils, and keratinocytes are also implicated in the pathogenesis of BP. Here, we review the roles of and crosstalk between innate and adaptive immune cells in BP.

Roles of IgG4 and IgG4/IgG ratio to IgG4-related disease in patients with elevated serum IgG4 level

OBJECTIVE

To evaluate the performance of elevated serum IgG4 and IgG4/IgG in IgG4-related disease (IgG4-RD) and other diseases.

METHODS

Seven hundred seventy-three patients with elevated serum IgG4 level (> 2.01 g/L) were reviewed in Zhongda Hospital of Southeast University from 1 July 2016 to 31 December 2021. Demographic, disease distribution and the role of elevated serum IgG4 and IgG4/IgG in IgG4-RD and other diseases were analysed. The alteration of IgG4 and IgG4/IgG in pre-therapy and post-treatment were also assessed in IgG4-RD.

RESULTS

Patients with elevated serum IgG4 were principally observed in older males. Chronic diseases of various organs (21.7%), rheumatic immune diseases (19.4%), bacterial infection disease (11.5%) and malignant tumor (5.2%) were the common diseases with elevated serum IgG4, but only 3.2% was IgG4-RD. The level of IgG4 and IgG4/IgG in IgG4-RD was significantly higher than that in various diseases except for eosinophilia group. Serum IgG4 and IgG4/IgG manifested a similar diagnostic capacity for IgG4-RD among this study cohort and the optimal cut-off values were 3.345 g/L and 0.295 respectively. The sensitivity and specificity were 96% and 71% for the optimal cut-off value of IgG4, and 80% and 88.8% for the optimal cut-off value of IgG4/IgG4. IgG4 and IgG4/IgG both were remarkably reduced in IgG4-RD after therapy compared with prior treatment (P < 0.05).

CONCLUSIONS

Elevated serum IgG4 was found in a variety of diseases, especially in chronic diseases of various organs. IgG4 and IgG4/IgG manifest a great value for IgG4-RD diagnosis, and are available for the treatment evaluation of IgG4-RD. Key Points • Elevated serum IgG4 level was not a specific marker to IgG4-related disease and can be observed in various diseases. • Patients with IgG4-related disease or eosinophilia manifest a higher level of serum IgG4 and IgG4/IgG. • Both of IgG4 and IgG4/IgG are available for the diagnosis and the clinical treatment evaluation of IgG4-related disease.

The cytokine milieu of bullous pemphigoid: Current and novel therapeutic targets

Bullous pemphigoid (BP) is the most common autoimmune bullous disease, characterized by severe pruritus and skin blistering. The loss of tolerance against Collagen XVII, also referred to as BP180, is the main pathogenic event of BP, leading to production of IgG autoantibodies which mainly target the juxtamembranous extracellular non-collagenous 16th A (NC16A) domain of BP180. A complex inflammatory network is activated upon autoantibody binding to the basement membrane zone; this inflammatory loop involves the complement cascade and the release of several inflammatory cytokines, chemokines and proteases from keratinocytes, lymphocytes, mast cells and granulocytes. Collectively, these events disrupt the integrity of the dermal-epidermal junction, leading to subepidermal blistering. Recent advances have led to identify novel therapeutic targets for BP, whose management is mainly based on the long-term use of topical and systemic corticosteroids. As an example, targeting type-2 T-helper cell-associated cytokines, such as Interleukin-4 and interleukin-13 has shown meaningful clinical efficacy in case series and studies; targeting IL-17 and IL-23 has also been tried, owing to an important role of these cytokines in the chronic maintenance phase of BP. In this review article, we discuss the complex cytokine milieu that characterized BP inflammation, highlighting molecules, which are currently investigated as present and future therapeutic targets for this life-threatening disease.

IgG subclass and Fc glycosylation shifts are linked to the transition from pre- to inflammatory autoimmune conditions

A crucial factor for the development of inflammatory autoimmune diseases is the occurrence of antibodies directed against self-tissues and structures, which leads to damage and inflammation. While little is known about the cause of the development of mis-directed, disease-specific T and B cells and resulting IgG autoantibody responses, there is increasing evidence that their induction can occur years before disease symptoms appear. However, a certain proportion of healthy individuals express specific IgG autoantibodies without disease symptoms and not all subjects who generate autoantibodies may develop disease symptoms. Thus, the development of inflammatory autoimmune diseases seems to involve two steps. Increasing evidence suggests that harmless self-directed T and B cell and resulting IgG autoantibody responses in the pre-autoimmune disease stage might switch to more inflammatory T and B cell and IgG autoantibody responses that trigger the inflammatory autoimmune disease stage. Here, we summarize findings on the transition from the pre-disease to the disease stage and vice versa, e.g. by pregnancy and treatment, with a focus on low-/anti-inflammatory versus pro-inflammatory IgG autoantibody responses, including IgG subclass and Fc glycosylation features. Characterization of biomarkers that identify the transition from the pre-disease to the disease stage might facilitate recognition of the ideal time point of treatment initiation and the development of therapeutic strategies for re-directing inflammatory autoimmune conditions.

The relevance of complement in pemphigoid diseases: A critical appraisal

Pemphigoid diseases are autoimmune chronic inflammatory skin diseases, which are characterized by blistering of the skin and/or mucous membranes, and circulating and tissue-bound autoantibodies. The well-established pathomechanisms comprise autoantibodies targeting various structural proteins located at the dermal-epidermal junction, leading to complement factor binding and activation. Several effector cells are thus attracted and activated, which in turn inflict characteristic tissue damage and subepidermal blistering. Moreover, the detection of linear complement deposits in the skin is a diagnostic hallmark of all pemphigoid diseases. However, recent studies showed that blistering might also occur independently of complement. This review reassesses the importance of complement in pemphigoid diseases based on current research by contrasting and contextualizing data from in vitro, murine and human studies.

The Alternative Pathway Is Necessary and Sufficient for Complement Activation by Anti-THSD7A Autoantibodies, Which Are Predominantly IgG4 in Membranous Nephropathy

Membranous nephropathy (MN) is an immune kidney disease characterized by glomerular subepithelial immune complexes (ICs) containing antigen, IgG, and products of complement activation. Whereas proteinuria is caused by complement-mediated podocyte injury, the pathways of complement activation remain controversial due to the predominance of IgG4 in ICs, an IgG subclass considered unable to activate complement. THSD7A, a transmembrane protein expressed on podocytes, is the target autoantigen in ~3% of cases of primary MN. In this study, we analyzed sera from 16 patients with THSD7A-associated MN with regard to the anti-THSD7A IgG subclasses and their ability to fix complement in vitro. The serum concentration of anti-THSD7A IgG varied over two orders of magnitude (1.3-243 μg/mL). As a relative proportion of all IgG anti-THSD7A, IgG4 was by far the most abundant subclass (median 79%), followed by IgG1 (median 11%). IgG4 was the dominant subclass of anti-THSD7A antibodies in 14 sera, while IgG1 was dominant in one and co-dominant in another. One quarter of MN sera additionally contained low levels of anti-THSD7A IgA1. ICs formed by predominantly IgG4 anti-THSD7A autoantibodies with immobilized THSD7A were relatively weak activators of complement in vitro, compared to human IgG1 and IgG3 mAbs used as positive control. Complement deposition on THSD7A ICs was dose-dependent and occurred to a significant extent only at relatively high concentration of anti-THSD7A IgG. C3b fixation by THSD7A ICs was completely abolished in factor B-depleted sera, partially inhibited in C4-depleted sera, unchanged in C1q-depleted sera, and also occurred in Mg-EGTA buffer. These results imply that THSD7A ICs predominantly containing IgG4 activate complement at high IgG4 density, which strictly requires a functional alternative pathway, whereas the classical and lectin pathways are dispensable. These findings advance our understanding of how IgG4 antibodies activate complement.

Insights Into the Pathogenesis of Bullous Pemphigoid: The Role of Complement-Independent Mechanisms

Bullous pemphigoid is an autoimmune blistering disease caused by autoantibodies targeting BP180 and BP230. While deposits of IgG and/or complement along the epidermal basement membrane are typically seen suggesting complement -mediated pathogenesis, several recent lines of evidence point towards complement-independent pathways contributing to tissue damage and subepidermal blister formation. Notable pathways include macropinocytosis of IgG-BP180 complexes resulting in depletion of cellular BP180, direct induction of pro-inflammatory cytokines from keratinocytes, as well as IgE autoantibody- and eosinophil-mediated effects. We review these mechanisms which open new perspectives on novel targeted treatment modalities.

Characteristics and renal survival of patients with lupus nephritis with glomerular immunoglobulin G4 deposition: a single-centre retrospective analysis

OBJECTIVE

Renal injury is common in SLE. Immune complex deposition plays an important role in the development of lupus nephritis (LN), while little is known about glomerular IgG₄ deposition in patients with LN. This study aimed to investigate the characteristics and renal outcome of patients with LN with glomerular IgG₄ deposition.

METHODS

This is a single-centre retrospective study enrolling 89 patients with biopsy-proven LN. Clinicopathological features, treatment responses and renal outcomes were collected and compared between patients with and without glomerular IgG₄ deposition. Renal outcome events include progression of renal dysfunction and end-stage renal disease.

RESULTS

Thirty (33.7%) patients had glomerular IgG₄ deposition. Patients with glomerular IgG₄ deposition had lower serum albumin level (25.06±8.61 g/L vs 28.29±6.31 g/L, p=0.05), more class V LN (60.0% vs 35.6%, p=0.03), more positive phospholipase A2 receptor (PLA2R) staining (43.3% vs 18.6%, p=0.01), more IgG₁ deposits (96.7% vs 64.4%, p=0.01) and less C3 deposits (46.7% vs 72.9%, p=0.02) than those without glomerular IgG₄ deposition. They also had better renal survival than those without glomerular IgG₄ deposition (96.7% vs 79.7%, p=0.03). Multivariate Cox regression showed that high serum creatinine level (relative risk (RR)=1.005, 95% CI 1.002 to 1.008, p=0.01) and high Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) scores (RR=1.078, 95% CI 1.004 to 1.157, p=0.04) independently correlated with poor renal outcome, while glomerular IgG₄ deposition tended to correlate with good renal outcome (RR=5.95, 95% CI 0.759 to 45.97, p=0.09). Further, patients with both glomerular IgG₄ and PLA2R positivity (n=13) had higher levels of serum C3 and C4 and less glomerular C3 deposits compared with those with positive IgG₄ but negative PLA2R in the glomerulus (n=17), and had a tendency of low SLEDAI score (p=0.07).

CONCLUSIONS

Patients with LN with glomerular IgG₄ deposits may have better renal survival, and patients with LN with simultaneous glomerular IgG₄ and PLA2R deposits may have low disease activity.

Impact of adding an IgG4 conjugate to routine direct immunofluorescence testing for subepithelial and intraepithelial autoimmune blistering disorders

BACKGROUND

Certain autoimmune bullous dermatoses are mediated by autoantibodies of the IgG4 subclass. We determined the diagnostic impact of adding IgG4 to our conventional direct immunofluorescence (DIF) panel.

METHODS

For all cases submitted to our referral laboratory for DIF over 1 month (n = 630), we performed IgG4 testing and collected consecutive biopsy specimens showing definite or indeterminate linear or cell-surface deposition of IgG, IgG4, and/or C3. On retrospective blinded review, we classified the pattern and whether the findings were definite, indeterminate, or negative. When present, substantial background staining was recorded.

RESULTS

Seventy DIF specimens met the inclusion criteria. Of 22 (31.4%) specimens equivocal for linear or cell-surface deposition, 9 (40.9%) had definitive IgG4 findings, either linear (3 of 14 equivocal linear cases; 21.4%) or cell-surface (6 of 8 equivocal cell-surface cases; 75.0%). Background deposition was substantial in 14 cases (20.0%) for IgG but in none for C3 or IgG4.

CONCLUSION

IgG4 allowed the classification of over 40% of DIF cases that were otherwise equivocal by IgG and C3. IgG4 staining showed lower levels of non-specific background staining than IgG or C3. IgG4 appears to contribute most value in cases with cell-surface deposition or with equivocal linear IgG deposition and negative C3 results.

Thymic Stromal Lymphopoietin in Cutaneous Immune-Mediated Diseases

Thymic stromal lymphopoietin (TSLP) was initially demonstrated to be critical in regulating inflammatory responses among various allergic disorders (such as atopic dermatitis, food allergy, and asthma). Although two isoforms (short form and long form) of TSLP have been demonstrated in human tissues, the long form of TSLP (lfTSLP) is strongly implicated in the pathogenesis of allergies and cutaneous immune-mediated diseases. The immunomodulatory activity of lfTSLP varies widely, driving T helper (Th) cells polarizing Th2 and Th17 immune responses and inducing itch. Moreover, lfTSLP is closely associated with skin fibrosis, epidermal hyperplasia, angiogenesis, and homeostatic tolerogenic regulations. This review highlights significant progress from experimental and clinical studies on lfTSLP in cutaneous immune-mediated diseases (atopic dermatitis, psoriasis, bullous pemphigoid, systemic sclerosis, chronic spontaneous urticaria, Behçet's disease, vitiligo, rosacea, systemic lupus erythematosus, and alopecia areata). We also offer original insights into the pleiotropic properties of the cytokine TSLP in various pathophysiological conditions, with significant clinical implications of TSLP-targeted therapies for immune-mediated skin diseases in the future.

Risk Factors for Mucosal Involvement in Bullous Pemphigoid and the Possible Mechanism: A Review

Bullous pemphigoid (BP) is the most common type of autoimmune bullous disease and is characterized by the presence of circulating anti-BP180 and/or anti-BP230 autoantibodies. Patients with BP often present with tense blisters and erythema, mainly on the trunk and limbs, but a few patients also have mucosal involvement. In this article, we discuss the fact that BP patients with mucosal involvement tend to have more serious conditions and their disease is more difficult to control. Potential risk factors for mucous involvement include earlier age at onset, drugs such as dipeptidyl peptidase-4 inhibitors, cancer, and blood/serum biomarkers, including lower eosinophil count, higher erythrocyte sedimentation rate, IgG autoantibodies against both the NH₂- and COOH-termini of BP180, and the absence of anti-BP230 antibodies. IgA and C3 deposition at the dermo-epidermal junction may also be present. Understanding these risk factors may benefit earlier diagnosis of these patients and promote the development of novel treatments. What's more, it's helpful in deeper understanding of BP development and the relationship between BP and mucous membrane pemphigoid (MMP).

Low serum IgG4 level: a potential diagnostic biomarker for IgA nephropathy

Background

In contrast to intense investigations of galactose-deficient immunoglobulin A (IgA)1 specific immunoglobulin G (IgG), little is known about the IgG subclasses in IgA nephropathy (IgAN). Low IgG4 levels in IgAN were noticed in our preliminary experiment. We aimed to verify the low IgG4 levels and investigate the related immune mechanism in IgAN.

Methods

A total of 112 healthy controls (HC) and 112 newly diagnosed IgAN patients were enrolled in this study. Patients with idiopathic membranous nephropathy (IMN), minimal change disease (MCD), or lupus nephritis (LN) were selected as disease controls (DC) (n=122). Serum IgG4 and IgG levels were detected by enzyme-linked immunosorbent assay (ELISA). The IgG4⁺ B, T helper 1 (Th1), and Th2 cells were measured by flow cytometry. Receiver operating characteristic curves (ROC) were performed to evaluate the diagnostic value of IgG4.

Results

Both IgG4 levels and IgG4/IgG in IgAN were lower than HC and DC (all P<0.001). Severe IgAN displayed lower IgG4 levels than mild IgAN (P=0.039). Patients with higher risk of renal progression (>50%) demonstrated lower IgG4 levels than lower-risk (≤15%) patients (P=0.019). The cutoff value of IgG4 in differentiating IgAN from HC and DC was 0.26 mg/mL [sensitivity 98.2%, specificity 82.4%, area under the curve (AUC): 0.941, P<0.0001] and 0.17 mg/mL (sensitivity 90.2%, specificity 85.2%, AUC: 0.937, P<0.0001), respectively. IgG4/IgG displayed similar diagnostic and differential ability. The IgG4⁺ B/B cells (P<0.0001) and Th2/Th (P=0.042) of IgAN were lower than HC.

Conclusions

Serum IgG4 levels were low in IgAN. Lower IgG4 levels indicated more severe disease conditions and higher risk of renal progression. Low serum IgG4 seemed to be a potential diagnostic biomarker for IgAN. Decreased IgG4⁺ B cells and Th2 cells may contribute to the low IgG4 levels in IgAN.

Levels of serum IgG subclasses in patients with liver disease: A retrospective study

Viral and alcoholic liver disease, drug induced liver disease (DILD), primary biliary cirrhosis (PBC) and autoimmune hepatitis (AIH) are among the most common liver diseases observed in clinical practice. These diseases lack unique clinical characteristics at the beginning of pathogenesis, which renders specific diagnosis difficult. Immunoglobulin G (IgG) subclasses are the main isoform of antibodies that can be found in the serum that serve important protective roles in immunity. The present study aimed to investigate the serum IgG subclass distribution in patients with the five common liver diseases aforementioned. The present study retrospectively recorded and analyzed the serum IgG subclass levels of different patients, who were grouped according to their clinical diagnosis. Serum IgG subclass levels were measured using immunonephelometric assays. IgG3 levels were found to be significantly increased whereas IgG4 levels were significantly decreased in patients with PBC. In patients with AIH, IgG1 levels were significantly increased. By contrast, IgG1/IgG level ratios in patients with viral liver disease were significantly increased. No clear pattern in the distribution characteristics of IgG subclasses could be observed in cohorts with alcoholic liver disease and DILD in the present study. Additionally, model for end-stage liver disease scores regarding IgG1 in patients with AIH shared a synergistic relationship. Anti-mitochondrial antibody subtype M2 (AMA-M2) and IgG3 in patients with PBC demonstrated a synergistic relationship. These results suggested that IgG subclasses may be used as biomarkers to further the understanding of liver disease, which could allow for early diagnosis.

Thymic Stromal Lymphopoietin Is Implicated in the Pathogenesis of Bullous Pemphigoid by Dendritic Cells

Objectives

Both thymic stromal lymphopoietin (TSLP) and dendritic cells (DCs) are involved in many autoimmune diseases, but the potential roles of TSLP and DCs in bullous pemphigoid (BP) have not been clarified. We sought to explore the contributions of TSLP and DCs in patients with BP.

Methods

TSLP levels in sera and blister fluids were measured by enzyme-linked immunosorbent assay. The TSLP expression in the BP lesional skin was detected by immunohistochemical staining. Infiltration of DCs, marked by DC-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), and its relationship with TSLP and TSLP receptors was evaluated by immunofluorescence staining.

Results

We found that TSLP levels in sera and in blister fluids of patients with BP were higher compared to the control groups. In patients with BP, TSLP levels in sera correlated with TSLP levels in blisters. The expression of TSLP in the BP lesional skin was higher compared to the healthy controls' skin. Greater numbers of TSLP-positive cells were observed in the epidermis of patients with BP compared to the healthy controls. Greater numbers of DC-SIGN-positive cells were present in the BP lesional skin compared to the skin of controls. The expression of TSLP was highly upregulated in DC-SIGN-positive cells, and most DC-SIGN-positive cells expressed TSLP receptors.

Conclusions

We conclude that TSLP may activate DC-SIGN-positive DCs directly, which may be involved in the pathogenesis of BP.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Total IgE, eosinophils, and interleukins 16, 17A, and 23 correlations in severe bullous pemphigoid and treatment implications

Bullous pemphigoid (BP) patients are predominantly above 70 years of age, with limited tolerance to the side effects of the immunosuppressive drugs. Advancements in our understanding of the pathophysiology of BP have led to the development of molecules which target specific pathways involved in induction and perpetuation of disease. Patients with BP Disease Area Index above 60 and less than 100 were split into two groups-one with high and the other with normal levels of IgE. The tested parameters included eosinophils' count, total IgE serum level, and interleukins (IL) 16, 17A, and 23 counts in the peripheral blood and skin bulla serum, before any therapeutic intervention. Thirty individuals fulfilled the criteria for enrollment. Patients with high IgE blood serum levels had significantly higher levels of IL17A and normal IL23 levels in blood and bulla serum. Patients with normal serum IgE levels had slightly higher IL23 levels in blood and bulla serum. The eosinophil count was positively related to IL17 blood serum level and negatively related to IL23. IL16 did not differ in the two groups. BP patients may represent a group of patients benefiting most substantially from the introduction of nonimmunosuppressive therapeutics into the treatment regimens for their disease. Clinical criteria and immune biomarkers are needed for making the best therapeutic choice.

Basic Research and Clinical Reports Associated with Low Serum IgG4 Concentrations

Elevated IgG4 concentrations in serum have received a great deal of attention recently, whereas the significance of decreased IgG4 levels was frequently neglected in spite of its close relation with infectious and noninfectious inflammations. In this review, based on the structural and functional characteristics of IgG4, we bring together case reports and research related to low levels of IgG4 and try to scratch the importance of decreased IgG4 concentrations in serum. As with elevated IgG4 levels, low serum IgG4-related diseases can be involved in multiple systems such as infection in the respiratory system, stroke in the circulatory system, and glomerulonephritis in the urinary system. Both genetic and immune dysregulation can contribute to decreased IgG4 levels. In the light of animal experiments, we believe that the mystery of low IgG4 can be revealed as long as enough attention is acquired.

Preferential Reactivity of Dipeptidyl Peptidase-IV Inhibitor-Associated Bullous Pemphigoid Autoantibodies to the Processed Extracellular Domains of BP180

Bullous pemphigoid (BP) is a common autoimmune blistering disease in which autoantibodies target the hemidesmosomal components BP180 and/or BP230 in basal keratinocytes. In BP, 80 to 90% of autoantibodies target the juxtamembranous extracellular non-collagenous 16th A (NC16A) domain of BP180. Recently, the administration of dipeptidyl peptidase-IV inhibitors (DPP4i), which are widely used as antihyperglycemic drugs, has been recognized to be a causative factor for BP. DPP4i-associated BP (DPP4i-BP) autoantibodies tend to target epitopes on non-NC16A regions of BP180, and the pathomechanism for the development of the unique autoantibodies remains unknown. To address the characteristics of DPP4i-BP autoantibodies in detail, we performed epitope analysis of 18 DPP4i-BP autoantibodies targeting the non-NC16A domains of BP180 using various domain-specific as well as plasmin-digested polypeptides derived from recombinant BP180. Firstly, Western blotting showed that only one DPP4i-BP serum reacted with the epitopes on the intracellular domain of BP180, and no sera reacted with the C-terminal domain of the molecule. In addition, only 2 DPP4i-BP sera reacted with BP230 as determined by enzyme-linked immunosorbent assay. Thus, DPP4i-BP autoantibodies were found to mainly target the non-NC16A mid-portion of the extracellular domain of BP. Interestingly, Western blotting using plasmin-digested BP180 as a substrate revealed that all of the DPP4i-BP sera reacted more intensively with the 97-kDa processed extracellular domain of BP180, which is known as the LABD97 autoantigen, than full-length BP180 did. All of the DPP4i-BP autoantibodies targeting the LABD97 autoantigen were IgG1, and IgG4 was observed to react with the molecule in only 7 cases (38.9%). In summary, the present study suggests that IgG1-class autoantibodies targeting epitopes on the processed extracellular domain of BP180, i.e., LABD97, are the major autoantibodies in DPP4i-BP.

Characteristics of IgG subclasses and complement deposition in BP230-type bullous pemphigoid

BACKGROUND

Bullous pemphigoid (BP) is the most common autoimmune blistering disease. BP180 is the primary autoantigen of BP, and in a portion of BP cases, BP230 is the only target of autoantibodies. Such BP is called BP230-type BP. BP230-type BP tends to show milder clinical phenotypes than conventional BP, but the reason is unclear. The pathogenic roles of autoantibodies and complement activation have been shown in conventional BP, but the distribution of IgG subclasses and the degree of complement deposition in BP230-type BP remain unclear.

OBJECTIVE

To compare the distribution of IgG subclasses and the degree of complement deposition in BP230-type BP with those in conventional BP with autoantibodies to BP180 and BP230 (BP180-BP230-type BP).

METHODS

The diagnosis of BP was confirmed by the histopathology of the lesions, the deposition of IgG and complement in the perilesional skin and the presence of circulating autoantibodies to BP180 and BP230. The disease severity was determined by bullous pemphigoid disease area index. The deposition of IgG subclasses and complement deposition were examined by direct immunofluorescence of the perilesional skin in 6 BP230-type BP cases and 11 BP180-BP230-type BP cases.

RESULTS

Sixty seven percent of BP230-type BP cases show a mild clinical phenotype. All BP230-type BP cases and 82% of BP180-BP230-type BP cases were found to demonstrate the clear deposition of IgG4 at the basement membrane zone of skin specimens. Notably, the deposition of IgG1 and IgG3 was faint or negative in all of the BP230-type BP cases, whereas they were clearly detected in 91% and 64% of the BP180-BP230-type BP cases, respectively. The deposition of complement C3 tended to be weaker in BP230-type BP than in BP180-BP230-type BP.

CONCLUSION

The mild clinical phenotype of BP230-type BP may correlate with the weaker deposition of IgG1, IgG3 and complement in the skin lesions.

Bullous pemphigoid

Bullous pemphigoid is the most frequent autoimmune bullous disease and mainly affects elderly individuals. Increase in incidence rates in the past decades has been attributed to population aging, drug-induced cases and improvement in the diagnosis of the nonbullous presentations of the disease. A dysregulated T cell immune response and synthesis of IgG and IgE autoantibodies against hemidesmosomal proteins (BP180 and BP230) lead to neutrophil chemotaxis and degradation of the basement membrane zone. Bullous pemphigoid classically manifests with tense blisters over urticarial plaques on the trunk and extremities accompanied by intense pruritus. Mucosal involvement is rarely reported. Diagnosis relies on (1) the histopathological evaluation demonstrating eosinophilic spongiosis or a subepidermal detachment with eosinophils; (2) the detection of IgG and/or C3 deposition at the basement membrane zone using direct or indirect immunofluorescence assays; and (3) quantification of circulating autoantibodies against BP180 and/or BP230 using ELISA. Bullous pemphigoid is often associated with multiple comorbidities in elderly individuals, especially neurological disorders and increased thrombotic risk, reaching a 1-year mortality rate of 23%. Treatment has to be tailored according to the patient's clinical conditions and disease severity. High potency topical steroids and systemic steroids are the current mainstay of therapy. Recent randomized controlled studies have demonstrated the benefit and safety of adjuvant treatment with doxycycline, dapsone and immunosuppressants aiming a reduction in the cumulative steroid dose and mortality.

Potential of Murine IgG1 and Human IgG4 to Inhibit the Classical Complement and Fcγ Receptor Activation Pathways

IgG antibodies (Abs) mediate their effector functions through the interaction with Fcγ receptors (FcγRs) and the complement factors. The main IgG-mediated complement activation pathway is induced through the binding of complement C1q to IgG Abs. This interaction is dependent on antigen-dependent hexamer formation of human IgG1 and IgG3 to increase the affinity for the six-headed C1q molecule. By contrast, human IgG4 fails to bind to C1q. Instead, it has been suggested that human IgG4 can block IgG1 and IgG3 hexamerization required for their binding to C1q and activating the complement. Here, we show that murine IgG1, which functionally resembles human IgG4 by not interacting with C1q, inhibits the binding of IgG2a, IgG2b, and IgG3 to C1q in vitro, and suppresses IgG2a-mediated complement activation in a hemolytic assay in an antigen-dependent and IgG subclass-specific manner. From this perspective, we discuss the potential of murine IgG1 and human IgG4 to block the complement activation as well as suppressive effects of sialylated IgG subclass Abs on FcγR-mediated immune cell activation. Accumulating evidence suggests that both mechanisms seem to be responsible for preventing uncontrolled IgG (auto)Ab-induced inflammation in mice and humans. Distinct IgG subclass distributions and functionally opposite IgG Fc glycosylation patterns might explain different outcomes of IgG-mediated immune responses and provide new therapeutic options through the induction, enrichment, or application of antigen-specific sialylated human IgG4 to prevent complement and FcγR activation as well.

BP180 Is Critical in the Autoimmunity of Bullous Pemphigoid

Bullous pemphigoid (BP) is by far the most common autoimmune blistering dermatosis that mainly occurs in the elderly. The BP180 is a transmembrane glycoprotein, which is highly immunodominant in BP. The structure and location of BP180 indicate that it is a significant autoantigen and plays a key role in blister formation. Autoantibodies from BP patients react with BP180, which leads to its degradation and this has been regarded as the central event in BP pathogenesis. The consequent blister formation involves the activation of complement-dependent or -independent signals, as well as inflammatory pathways induced by BP180/anti-BP180 autoantibody interaction. As a multi-epitope molecule, BP180 can cause dermal-epidermal separation via combining each epitope with specific immunoglobulin, which also facilitates blister formation. In addition, some inflammatory factors can directly deplete BP180, thereby leading to fragility of the dermal-epidermal junction and blister formation. This review summarizes recent investigations on the role of BP180 in BP pathogenesis to determine the potential targets for the treatment of patients with BP.

Complement-independent blistering mechanisms in bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease that clinically demonstrates tense blisters with widespread erythema, histologically demonstrates subepidermal blistering and immunologically demonstrates the presence of circulating autoantibodies against hemidesmosomal molecules. Complement activation has long been regarded as necessary for the generation of the BP. However, certain evidence has recently come to support non-complemental blistering mechanisms. The story of BP blistering mechanisms is a complicated one. This review mainly focuses on a specific blistering mechanism that highlights the role of complements in BP blistering.

Glucocorticoids: The mode of action in bullous pemphigoid

Bullous pemphigoid (BP) is the most common of pemphigoid diseases caused by autoantibodies against the structures of dermoepidermal junction followed by complement activation, innate immune cell infiltration, neutrophil proteinase secretion and subepidermal blister formation. The first-line treatment of BP is topical and systemic glucocorticoids (GC). Regulation of the immune system and inflammatory cells is the main target of GC actions. GCs act through genomic and non-genomic mechanisms. The human glucocorticoid receptor (GR) mediates most of the biologic effects of GC: cytosolic GR binds GCs and is capable to bind to glucocorticoid response elements in DNA and either transactivate or transrepress genes depending on the tissue and cell type. In addition, GR exerts rapid, non-genomic effects possibly mediated by membrane-localized receptors or by translocation to mitochondria. GCs can also interact directly with several enzymes and cytokines. As a target treatment for BP, the production of autoantibodies should be discontinued. GCs, in spite of their wide immunosuppressive actions, are weak to stop immunoglobulin G (IgG) autoantibody formation. However, both systemic and topical GCs are able to reduce the clinical symptoms of BP. GCs are used to inhibit the secondary inflammation and symptoms, such as blistering and pruritus, and it is shown that GC treatment will gradually decrease also the autoantibody formation. Our review article analyses the mode of action of GC treatment in BP, as far it is possible due to paucity of modern immunological studies.

IgG4, complement, and the mechanisms of blister formation in pemphigus and bullous pemphigoid

Autoimmune bullous diseases are at the forefront of the research field on autoimmune diseases. Pemphigus and pemphigoid were historical entities in the world of descriptive dermatology for a long time. Recently, however, dermatologists and skin biologists have elegantly explained the novel pathomechanism of pemphigus and pemphigoid diseases. IgG4 is the major subclass of autoantibodies in autoimmune bullous diseases and is known to have little activity to activate complement. It is quite acceptable for pemphigus, because acantholysis in pemphigus has been demonstrated to be complement-independent. On the other hand, subepidermal blister formation in bullous pemphigoid has been believed to be complement-dependent. Therefore, the role of IgG4 autoantibodies on blister formation in bullous pemphigoid remains controversial. Here, we examine the progress of research on the mechanisms of blister formation in autoimmune bullous diseases. We focus on the complement-dependent and independent blistering in bullous pemphigoid using comparisons between pemphigus diseases. In addition, we review the current understanding of the role of IgG4 antibodies in bullous pemphigoid.

Dysregulation of mCD46 and sCD46 contribute to the pathogenesis of bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune bullous disease caused by autoantibodies against BP180 in the epidermal basement membrane. Autoantibody-mediated complement activation is an important process in BP pathogenesis. CD46, a crucial complement regulatory protein in the complement activation, has been reported to be involved in several autoimmune diseases. In the present study, we investigated whether CD46 plays a role in BP development. We found that sCD46 expression was significantly increased in the serum and blister fluids of BP patients and correlated with the levels of anti-BP180 NC16A antibody and C3a. Otherwise, the level of mCD46 was decreased in lesions of BP patients, whereas the complement activation was enhanced. We also found that CD46 knockdown in HaCaT human keratinocytes enhanced autoantibody-mediated complement activation. Importantly, exogenous CD46 blocked complement activation in both healthy skin sections and keratinocytes induced by exposure to pathogenic antibodies from BP patients. These data suggest that CD46 deficiency is an important factor in BP pathogenesis and that increasing CD46 levels might be an effective treatment for BP.

IgG4 autoantibodies against muscle-specific kinase undergo Fab-arm exchange in myasthenia gravis patients

Autoimmunity mediated by IgG4 subclass autoantibodies is an expanding field of research. Due to their structural characteristics a key feature of IgG4 antibodies is the ability to exchange Fab-arms with other, unrelated, IgG4 molecules, making the IgG4 molecule potentially monovalent for the specific antigen. However, whether those disease-associated antigen-specific IgG4 are mono- or divalent for their antigens is unknown. Myasthenia gravis (MG) with antibodies to muscle specific kinase (MuSK-MG) is a well-recognized disease in which the predominant pathogenic IgG4 antibody binds to extracellular epitopes on MuSK at the neuromuscular junction; this inhibits a pathway that clusters the acetylcholine (neurotransmitter) receptors and leads to failure of neuromuscular transmission. In vitro Fab-arm exchange-inducing conditions were applied to MuSK antibodies in sera, purified IgG4 and IgG1-3 sub-fractions. Solid-phase cross-linking assays were established to determine the extent of pre-existing and inducible Fab-arm exchange. Functional effects of the resulting populations of IgG4 antibodies were determined by measuring inhibition of agrin-induced AChR clustering in C2C12 cells. To confirm the results, κ/κ, λ/λ and hybrid κ/λ IgG4s were isolated and tested for MuSK antibodies. At least fifty percent of patients had IgG4, but not IgG1-3, MuSK antibodies that could undergo Fab-arm exchange in vitro under reducing conditions. Also MuSK antibodies were found in vivo that were divalent (monospecific for MuSK). Fab-arm exchange with normal human IgG4 did not prevent the inhibitory effect of serum derived MuSK antibodies on AChR clustering in C2C12 mouse myotubes. The results suggest that a considerable proportion of MuSK IgG4 could already be Fab-arm exchanged in vivo. This was confirmed by isolating endogenous IgG4 MuSK antibodies containing both κ and λ light chains, i.e. hybrid IgG4 molecules. These new findings demonstrate that Fab-arm exchanged antibodies are pathogenic.