Emerging Treatment Models in Rheumatology: IgG4-Related Disease: Insights Into Human Immunology and Targeted Therapies

IgG4-related disease-rare but you should not forget it

Immunoglobulin G4-related disease is a systemic immune-mediated disease with insidious evolution characterized by fibroinflammatory lesions over virtually any organ system. Despite the remarkable progression of knowledge, its etiology remains undefined. Due to its relapse-remitting pattern, it could accumulate irreversible damage, increasing comorbidities and mortality. This paper emphasizes key concepts for diagnosing and treating patients with this condition.

Granzyme K- and amphiregulin-expressing cytotoxic T cells and activated extrafollicular B cells are potential drivers of IgG4-related disease

BACKGROUND

IgG4-related disease (IgG4-RD), an example of a type I immune disease, is an immune-mediated fibrotic disorder characterized by dysregulated resolution of severe inflammation and wound healing. However, truly dominant or pathognomonic autoantibodies related to IgG4-RD are not identified.

OBJECTIVE

We sought to perform single-cell RNA sequencing and T-cell receptor and B-cell receptor sequencing to obtain a comprehensive, unbiased view of tissue-infiltrating T and B cells.

METHODS

We performed unbiased single-cell RNA-sequencing analysis for the transcriptome and T-cell receptor sequencing and B-cell receptor sequencing on sorted CD3+ T or CD19+ B cells from affected tissues of patients with IgG4-RD. We also conducted quantitative analyses of CD3+ T-cell and CD19+ B-cell subsets in 68 patients with IgG4-RD and 30 patients with Sjögren syndrome.

RESULTS

Almost all clonally expanded T cells in these lesions were either Granzyme K (GZMK)-expressing CD4+ cytotoxic T cells or GZMK+CD8+ T cells. These GZMK-expressing cytotoxic T cells also expressed amphiregulin and TGF-β but did not express immune checkpoints, and the tissue-infiltrating CD8+ T cells were phenotypically heterogeneous. MKI67+ B cells and IgD-CD27-CD11c-CXCR5- double-negative 3 B cells were clonally expanded and infiltrated affected tissue lesions. GZMK+CD4+ cytotoxic T cells colocalized with MKI67+ B cells in the extrafollicular area from affected tissue sites.

CONCLUSIONS

The above-mentioned cells likely participate in T-B collaborative events, suggesting possible avenues for targeted therapies. Our findings were validated using orthogonal approaches, including multicolor immunofluorescence and the use of comparator disease groups, to support the central role of cytotoxic CD4+ and CD8+ T cells expressing GZMK, amphiregulin, and TGF-β in the pathogenesis of inflammatory fibrotic disorders.

Myofibroblast and pro-fibrotic cytokines in fibrosis of IgG4-related disease (IgG4-RD) patients from South Asia: preliminary data

INTRODUCTION

Fibrosis is a typical pathological characteristic in IgG4-RD patients and often irreversible. There exists a lack of suitable markers for detection of earlier onset of fibrosis in various organs in IgG4-RD patients. Hence, this study aims at analysing ambispectively the myofibroblasts and the pro-fibrotic cytokines, IFN gamma and IL-33 involved in IgG4-RD associated fibrosis in South Asian patients.

METHOD

Archived biopsy samples of definite/probable/possible cases of IgG4-RD, classified according to diagnostic criteria, taken from patients who attended the OPD and IPD of our tertiary care centre during January 2015-January 2020 were chosen for this study. The paraffin sections were examined qualitatively for fibrosis and the excessive collagen deposition by Hematoxylin & Eosin and Masson's Trichrome staining. Also, the presence of alpha-Smooth muscle actin (α-SMA) expressing myofibroblasts and the involvement of pro-fibrotic cytokines (IFN-gamma, IL-33) were assessed by Immunohistochemistry and scored semi-quantitatively (+mild, ++moderate, +++ severe). Serum IL-33 levels were analysed by indirect Elisa (R & D Systems).

RESULTS

Myofibroblasts were present in 10/12 biopsy samples, in moderate levels in 4 (33%) and very high levels (+++) in 3 (25%) of the patients. IFN-gamma was expressed at low levels in 6 (50%) and absent in 6 (50%). All patients showed IL-33 expression with very high levels in tissue (6, 50%), as well as in serum samples.

CONCLUSION

The findings of this study reinforce the role of myofibroblasts and profibrotic cytokines like IL-33 in fibrosis of Ig4-RD patients, pointing to their potential as earlier predictive markers of onset and extent of fibrosis.

A Rare Case of Immunoglobulin G4-Related Disease Presenting With Coronary Artery Pseudotumor And Aneurysm

Immunoglobulin G4-related disease (IgG4-RD) is an autoimmune disease characterized by elevated serum IgG4 levels. It has the potential to affect multiple organs. Despite the diverse manifestations of IgG4-RD, the association with coronary artery disease (CAD) remains poorly understood due to limited evidence. We report the case of a 52-year-old male patient who exhibited typical angina upon exertion, accompanied by elevated serum IgG4 levels. Coronary computed tomographic angiography (CCTA) revealed the presence of pseudotumor formations surrounding and aneurysm changes affecting all coronary arteries, consistent with IgG4-RD. The patient was treated with prednisolone and azathioprine, with the possibility of additional rituximab therapy if symptomatology failed to improve. This case sheds light on the rare occurrence of IgG4-RD with coronary artery involvement and underscores the importance of recognizing this unique clinical entity for appropriate management and further research.

LEARNING POINTS

Immunoglobulin G4-related disease (IgG4-RD) is a chronic systemic disease characterized by inflammatory fibrosis and high serum IgG4 levels.IgG4-RD can involve the coronary artery, presenting as a coronary aneurysm, and may mimic coronary artery disease.Treatment of IgG4-RD with coronary artery involvement includes corticosteroid therapy, with or without other immunosuppressant, as well as surgical intervention.

Immune dysregulation in immunoglobulin G4-related disease

(IgG4-RD) is an immune-mediated fibrotic disorder characterized by severe resolution of inflammation and dysregulation of wound healing. IgG4-RD has been considered a unique disease since 2003, and significant progress has been achieved in the understanding of its essential features. The central role of B cells in IgG4-RD has been demonstrated by the robust clinical responsiveness of IgG4-RD to B cell depletion and the identification of multiple self-antigens that promote B cell expansion. Studies have increasingly revealed critical roles of these B cells and T cells in the pathogenesis of IgG4-RD, and we and other authors further identified CD4⁺ cytotoxic T lymphocytes as the main tissue-infiltrating CD4⁺ T cell subset in IgG4-RD tissues. Additionally, T follicular helper cell subsets that play a role in IgG4 isotype switching have been identified. In this review, we discuss research on IgG4-RD and the roles of B cell and T cell subsets, as well as the functions of CD4⁺ cytotoxic T cells in IgG4-RD pathogenesis. We highlight our findings from ongoing research using single-cell analysis of infiltrating CD4⁺ cytotoxic T cells, CD4⁺ follicular helper T cells, and infiltrating B cells in IgG4-RD and propose a model for the pathogenesis of IgG4-RD.

Hypertrophic pachymeningitis due to IgG4-related disease (RD-IgG4). A case report

INTRODUCTION

Hypertrophic pachymeningitis (HP) is a clinico-radiological entity characterized by a thickening of the dura mater that may be focal or diffuse and manifested by a variety of neurological syndromes. Aetiologically, it is classified as infectious, neoplastic, autoimmune, and idiopathic. Many of these formerly idiopathic cases have been shown to fall into the spectrum of IgG4-related disease.

OBJECTIVE

To describe the case of a patient attended for neurological involvement due to hypertrophic pachymeningitis with initial diagnosis of inflammatory myofibroblastic tumour and final diagnosis of IgG4-related disease.

CASE

A 25-year-old woman with neurological symptoms of 3 years' evolution characterized initially by right hypoacusis, evolving with headache and diplopia. Magnetic resonance imaging (MRI) of the encephalon showed pachymeningeal thickening with involvement of vasculo-nervous structures in the tip of the cerebellum, cavernous sinus, ragged foramen, and optic chiasm. The patient presented for consultation with the result of an incisional biopsy that reported a proliferative lesion combining fibrous elements of fascicular or swirling arrangement with collagenized streaks with dense, lymphoplasmacytic infiltrate and some macrophages, with negative staining for ALK 1, with a diagnosis of inflammatory myofibroblastic tumour. Due to suspicion of IgG4-related disease (IgG4-RD) the biopsy was sent for review and pertinent complementary studies were requested.

BIOPSY REVIEW

Non storiform fibrosis, predominantly lymphoplasmacytic infiltrate, histiocytes, and polymorphonuclear infiltrate in sectors, without granulomas or atypia. Staining for germs negative. Immunohistochemistry with 50-60 IgG4+/HPF cells and range of 15%-20%, CD68⁺ in histiocytes, CD1a^-, S100^-. The patient presented deterioration of visual acuity due to ophthalmic nerve involvement, so glucocorticoid treatment was started in pulses and rituximab with regression of symptoms and imaging improvement of the lesions.

CONCLUSION

HP is a clinical imaging syndrome with variable symptoms and aetiologies that poses a diagnostic challenge. In this case the initial diagnosis was inflammatory myofibroblastic tumour, which is a neoplasm of variable behaviour, locally aggressive, and can metastasize; it is one of the main differential diagnoses of IgG4-related disease because they share anatomopathological features, including storiform fibrosis. IgG4-RD is an immune-mediated condition that can have single or multiple involvement. Its diagnosis is complex when it presents with single organ involvement or in non-typical organs (CNS, meninges) in which data are scarce, as in the case of our patient with single organ involvement of the CNS. Although there are classification criteria to guide non-specialists in the diagnosis, the sum of the clinical picture, imaging, laboratory, pathological anatomy, and immunohistochemistry will always be evaluated together for a definitive diagnosis.

The Positive Predictive Value of a Very High Serum IgG4 Concentration for the Diagnosis of IgG4-Related Disease

OBJECTIVE

Serum IgG4 concentrations are used to evaluate a diagnosis of IgG4-related disease (IgG4-RD), but the positive predictive value (PPV) of a very high IgG4 level is uncertain. This study evaluated the PPV of a very high IgG4 concentration for diagnosing IgG4-RD.

METHODS

The data warehouses of 2 large academic healthcare systems were queried for IgG4 concentration test results. Cases with serum IgG4 concentrations > 5× the upper limit of normal (ULN) were included. Cases of IgG4-RD were determined using the American College of Rheumatology/European Alliance of Associations for Rheumatology (ACR/EULAR) classification criteria. The PPV for IgG4-RD of an IgG4 concentration > 5× ULN was estimated. Other conditions associated with very high IgG4 concentrations and specific features of IgG4-RD cases were characterized.

RESULTS

IgG4 concentrations were available in 32,206 cases. Of these, 3039 (9.4%) had elevated IgG4 concentrations, and a final cohort of 191 (0.6%) cases had IgG4 concentrations > 5× ULN (median age 66 yrs, 72% male). The PPV of an IgG4 concentration > 5× ULN for a diagnosis of IgG4-RD was 75.4% (95% CI 68.7-81.3). In the remaining cases, elevated IgG4 concentrations were observed among patients with malignancies, autoimmune diseases, and infections.

CONCLUSION

The majority of cases with serum IgG4 concentrations > 5× ULN in this study had IgG4-RD. These data support the high weight placed on very high serum IgG4 concentrations in the ACR/EULAR classification criteria. However, 25% of cases with very high IgG4 concentrations had an alternative diagnosis, underscoring the importance of considering the broad differential of etiologies associated with an elevated IgG4 concentration when evaluating a patient.

Orchestration of Immune Cells Contributes to Fibrosis in IgG4-Related Disease

This review summarizes recent progress in understanding the pathogenesis of IgG4-related disease (IgG4-RD), with a focus on fibrosis. Several studies reported that CD4+ T cells with cytotoxic activity promoted by the secretion of granzyme and perforin, cytotoxic CD4+ T cells (CD4+CTLs), and disease-specific activated B cells, infiltrated inflamed tissues and cooperated to induce tissue fibrosis in autoimmune fibrotic diseases such as IgG4-RD, systemic sclerosis, and fibrosing mediastinitis. An accumulation of cells undergoing apoptotic cell death induced by CD4+CTLs and CD8+CTLs followed by macrophage-mediated clearing and finally tissue remodeling driven by cytokines released by CD4+CTLs, activated B cells, and M2 macrophages may contribute to the activation of fibroblasts and collagen production. In IgG4-RD, this process likely involves the apoptosis of non-immune, non-endothelial cells of mesenchymal origin and subsequent tissue remodeling. In summary, CD4+CTLs infiltrate affected tissues where they may cooperate with activated B cells, CD8+CTLs, and M2 macrophages, to induce apoptosis by secreting cytotoxic cytokines. These immune cells also drive fibrosis by secreting pro-fibrotic molecules in IgG4-RD.

The association of smoking with immunoglobulin G4-related disease: a case-control study

OBJECTIVE

To evaluate the association between cigarette smoking and the odds of IgG4-related disease (IgG4-RD).

METHODS

We performed a case-control study of patients with IgG4-RD compared in a 1:5 ratio with age-, race- and sex-matched controls. We included cases evaluated at the Massachusetts General Hospital, a hospital within the Mass General Brigham (MGB) System. Controls were identified from the MGB Biobank. Smoking status at the date of IgG4-RD diagnosis or corresponding index date was determined. Conditional logistic regression was used to estimate the association between cigarette smoking and the odds of having IgG4-RD.

RESULTS

There were 234 IgG4-RD cases and 1170 controls. The mean age (59 years), sex (62% male) and race (75% white) were well balanced. IgG4-RD cases were more likely to be current smokers compared with controls [25 (11%) vs 70 (6%); odds ratio (OR) 1.79 (95% CI 1.08, 2.95)]. This association was strongest among female cases [13 (14%) vs 19 (4%);, OR 3.79 (95% CI 1.71, 8.39)] and those with retroperitoneal fibrosis [RPF; 13 (28%) vs 13 (6%);, OR 6.93 (95% CI 2.78, 17.26)] or normal IgG4 concentrations [21 (21%) vs 21 (4%); OR 6.22 (95% CI 3.09, 12.49)]. When RPF cases were excluded, there was no longer an association between current smoking and the odds of having IgG4-RD [12 (6%) vs 57 (6%); OR 0.95 (95% CI 0.49, 1.86)].

CONCLUSION

Being a current smoker is associated with greater odds of having IgG4-RD, especially among women and those with RPF or normal IgG4 concentrations. Current smoking is the first recognized modifiable risk factor for IgG4-RD.

Significance of high serum IgG4 in complete or non-full-fledged IgG4-related disease-a retrospective investigation of 845 patients and its clinical relevance

OBJECTIVE

Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized heterogeneous, subacute, and usually silent autoimmune disease involving many organs with protean manifestations. However, high IgG4 in serum is not necessarily indicating an IgG4-RD. The aims of this study were to investigate the clinical relevance of high serum IgG4 level in IgG4-RD or non IgG4-RD patients, and to see if IgG4-RD in Taiwan differs from that in other parts of the world.

METHODS

Eight hundred forty-five patients with high IgG4 were retrospectively reviewed from January 2002 to May 2020 in Taipei Veteran General Hospital. Two hundred sixty-seven patients fulfilled IgG4-RD criteria and were categorized into pancreato-hepato-biliary disease, retroperitoneal fibrosis and/or aortitis, head/neck-limited disease, classic Mikulicz syndrome with systemic involvement, CNS-limited disease, sclerosing vasculitis, skin-limited disease, and sensorineural hearing disease. These manifestations were correlated to smoking, atopy, hyper-IgE/eosinophilia, aging, malignancies, and hypocomplementemia. Five hundred seventy-eight patients were not fulfilling the criteria but were also analyzed for the prevalence of allergy, malignancy, connective tissue diseases, lung diseases, and infections.

RESULTS

In IgG4-RD patients, 124 (46.4%) smoked. Top 4 clinical subtypes included Mikulicz syndrome with systemic involvement (33.3%), pancreato-hepatobiliary disease (31.4%), head/neck disease (19.4%), and retroperitoneal fibrosis/aortitis (12.7%). Top 4 co-morbid conditions included high serum IgE/eosinophilia (46.2%), hypocomplementemia (34%), malignancies (13.4%), and allergy (13.4%). Pancreato-biliary disease was associated with high IgE/eosinophilia (r² = 0.380, P = 0.025) and malignancy (r² = 0.211, P = 0.027), Miculicz syndrome with allergy (r² = 0.396, P < 0.01) and high IgE/eosinophil (r² = 0.396, P < 0.01), CNS diseases (r² = 0.973, P = 0.035) and sclerosing vasculitis (r² = 1, P < 0.01) with advanced age respectively, with the latter being also related to atopy and high IgE/eosinophilia (r² = 1, p < 0.01).

CONCLUSION

Smoking may precipitate IgG4-RD. IgG4-RD with pancreato-hepatobiliary disease is closely related to allergy and neoplasm, and those with Mikulicz syndrome may result from atopy. Elderly IgG4-RD patients tend to develop CNS pathology parallel to advancing of age. The disease may probably be originated from an unknown mechanism that may sporadically evolve into malignancies.

The neurology of IGG4-related disease

PURPOSE OF REVIEW

IgG4-related disease (IgG4-RD) is emerging as a fibro-inflammatory entity affecting multiple organs, including manifold neurologic manifestations. This review discusses general characteristics of IgG4-RD neurologic disease including epidemiology, histology, clinical picture and treatment approaches.

RECENT FINDINGS

IgG4-RD is increasingly recognized as an important underlying pathophysiology in multiple disorders of neurologic interest, including orbital inflammation, infundibulo-hypophysitis, hypertrophic pachymeningitis, and even in rare cases CNS parenchymal disease and cranial vascular involvement. These were previously considered idiopathic and unrelated to any systemic disease but now known to share a common histopathology. New knowledge regarding the pathogenesis, clinical features and epidemiology of IgG4 is emerging, and new neurological manifestations continue to be described. Diagnostic progress includes CT-PET imaging, the use of flow cytometry for plasmablast quantification, and the use of reverse passive latex agglutination aiming to overcome the prozone phenomenon. Histopathologic confirmation of IgG4-RD remains the gold standard method of diagnosis but new diagnostic criteria for systemic and organ-specific disease are being proposed. Though glucorticoids remain the mainstay of therapy, relapses and incomplete recovery are frequent. Rituximab is a promising treatment in IgG4-RD that is severe, refractory or glucocorticoid dependent. Initiation of immunosuppression at an early stage of disease should be considered in order to avoid development of refractory fibrosis.

SUMMARY

The current review emphasizes the neurologic manifestations of IgG4-RD.

Lifetime Allergy Symptoms in IgG4-Related Disease: A Case-Control Study

OBJECTIVE

The etiology of IgG4-related disease (IgG4-RD) is unknown and there has been controversy over the significance of allergic conditions in IgG4-RD. We examined the prevalence of lifetime allergy symptoms in IgG4-RD and the association between these and IgG4-RD.

METHODS

We identified IgG4-RD patients and non-IgG4-RD controls without autoimmune conditions seen at a single center. IgG4-RD patients were classified using the ACR/EULAR classification criteria. Allergy symptoms were ascertained by questionnaire. We assessed the association of IgG4-RD features with allergy symptoms. We compared the proportion of cases and controls with allergy symptoms using conditional logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI) after matching cases and controls 1:1 by age and sex.

RESULTS

Lifetime allergy symptoms were reported by 165 (71%) of 231 IgG4-RD cases. Aero-allergen symptoms were most commonly reported (135, 58%) followed by skin allergy symptoms (97, 42%) and food allergy symptoms (47, 20%). IgG4-RD cases with a history of allergy symptoms were more likely to have head and neck involvement (OR 2.0 [95% CI: 1.1-3.6]) and peripheral eosinophilia (OR 3.3 [95% CI: 1.2-9.0]) than those without allergy symptoms. The prevalence of any allergy symptoms was similar between cases and controls (OR 0.7 [95% CI: 0.4-1.1]); this remained consistent after stratifying by head and neck involvement.

CONCLUSION

Lifetime allergy symptoms are common in IgG4-RD but are not reported more often in IgG4-RD compared to non-IgG4-RD patients without autoimmune conditions. These findings suggest that allergies are not uniquely associated with the pathogenesis or presentation of IgG4-RD.

Long-term effects of intensive B cell depletion therapy in severe cases of IgG4-related disease with renal involvement

IgG4-related disease (IgG4-RD) is an immune-mediated disorder often showing elevated serum IgG4 concentrations, dense T and B lymphocyte infiltration, and IgG4-positive plasma cells and storiform fibrosis. We prospectively evaluated for 4 years 5 patients with histologically proven IgG4-RD of whom 3 had tubulointerstitial nephritis (TIN) and 2 had retroperitoneal fibrosis (RPF). They received an intensive B depletion therapy with rituximab. The estimated glomerular filtration rate of TIN patients after 1 year increased from 9 to 24 ml/min per 1.73 m2. IgG/IgG4 dropped from 3236/665 to 706/51 mg/dl, C3/C4 went up from 49/6 to 99/27 mg/dl, and the IgG4-RD responder index fell from 10 to 1. CD20+ B cells decreased from 8.7 to 0.5%. A striking drop in interstitial plasma cell infiltrate as well as normalization of IgG4/IgG-positive plasma cells was observed at repeat biopsy. Both clinical and immunological improvement persisted over a 4-year follow-up. Treating these patients who were affected by aggressive IgG4-RD with renal involvement in an effort to induce a prolonged B cells depletion with IgG4 and cytokine production decrease resulted in a considerable rise in eGFR, with IgG4-RD RI normalization and a noteworthy improvement in clinical and histological features. Furthermore, the TIN subgroup was shown not to need for any maintenance therapy.

Combination of autoimmune pancreatitis and peripheral neuropathy on an IgG4-related disease patient with 4 years following-up

Type1 autoimmune pancreatitis (AIP) is the first recognized and the most common manifestation of IgG4-related disease. However, AIP patient presented with neuropathy in the extremities have not been reported previously. We reported a rare combination of autoimmune pancreatitis and peripheral neuropathy on an IgG4-related disease patient based on histological features to expand the clinical spectrum of IgG4-related disease.

Immune mechanisms of fibrosis and inflammation in IgG4-related disease

PURPOSE OF REVIEW

To summarize recent advances in the understanding of the pathogenesis of IgG4-related disease.

RECENT FINDINGS

Limited data exist to explain genetic susceptibility to IgG4-related disease and the underlying triggers for this disease have not yet been identified. Cytotoxic CD4 T cells and activated B cells infiltrate affected organs and express proinflammatory and profibrotic molecules. Antigen presented by activated B cells likely reactivates cytotoxic CD4 T cells in disease tissues and these T cells in turn induce the targeted apoptotic death of host cells in certain organs - which presumably present the same antigenic peptide on human leukocyte antigen class II molecules of relevance that was also presented on B cells during reactivation. A subsequent exaggerated tissue remodeling process is orchestrated by cytokines, chemokines, and enzymes secreted by both activated B cells and CD4CTLs. These molecules induce an overexuberant repair process resulting in fibrosis and loss of target organ function.

SUMMARY

In IgG4-related disease, presumably self-reactive cytotoxic CD4 T cells infiltrate tissues, are reactivated by T cells and induce apoptotic death. Molecules secreted by activated B cells and by CD4CTLs drive an exaggerated wound healing response resulting in fibrosis and compromised tissue function.

Urgent manifestations of immunoglobulin G4-related disease

Objective: Immunoglobulin G₄-related disease (IgG₄-RD) is considered a chronic condition with insidious presentation, but clinical experience suggests that disease onset prompts admission to the emergency department (ED) in a sizeable proportion of patients. We assessed the prevalence of acute manifestations associated with IgG₄-RD onset requiring referral to the ED. Method: We revised our database and identified patients admitted to the ED because of symptoms latterly attributed to IgG₄-RD onset (Group 1) and those who were referred to our outpatient clinic without previous urgent manifestations (Group 2). Acute manifestations were clustered based on the anatomical region affected by IgG₄-RD. Epidemiological, clinical, and serological features of Groups 1 and 2 were compared. Results: The study included 141 patients with IgG₄-RD. Of these, 76 (54%) presented to the ED at disease onset. The most common clinical manifestations requiring admission to the ED were jaundice (53%), abdominal pain (41%), and fever (10%). Gastrointestinal involvement was the most frequent cause of referral to the ED (71% of cases), followed by involvement of the retroperitoneum (14.5%) and the nervous system (6.6%). Pancreatobiliary involvement was significantly more frequent in Group 1 than in Group 2. Head and neck, and salivary and lacrimal gland involvement was more frequent in Group 2 than in Group 1. The diagnostic delay was significantly shorter in Group 1 than in Group 2. Conclusion: Clinical manifestations associated with IgG₄-RD onset require referral to the ED in most cases. This finding contrasts with the general view of IgG₄-RD as a condition with non-acute presentation.

Advances in the diagnosis and management of IgG4 related disease

IgG4 related disease was recognized as a unified disease entity only 15 years ago. Awareness of IgG4 related disease has increased worldwide since then, and specialists are now familiar with most of its clinical manifestations. Involvement of the pancreato-biliary tract, retroperitoneum/aorta, head and neck, and salivary glands are the most frequently observed disease phenotypes, differing in epidemiological features, serological findings, and prognostic outcomes. In view of this multifaceted presentation, IgG4 related disease represents a great mimicker of many neoplastic, inflammatory, and infectious conditions. Histopathology remains key to diagnosis because reliable biomarkers are lacking. Recently released classification criteria will be invaluable in improving early recognition of the disease. IgG4 related disease is highly treatable and responds promptly to glucocorticoids, but it can lead to end stage organ failure and even death if unrecognized. Prolonged courses of corticosteroids are often needed to maintain remission because the disease relapses in most patients. Rapid advancement in our understanding of the pathophysiology of IgG4 related disease is leading to the identification of novel therapeutic targets and possible personalized approaches to treatment.

[IgG4-related disease: what do we know after 20 years]

IgG4-related disease is immunomediated fibroinflammatory condition, characterized by tumefective lesions in different organs with distinctive pathomorphological features and IgG4 hypersecretion in serum and tissues in the majority of patients. IgG4-RD has been established as a separate clinical in the early 2000s. In the review we focus on the evolution of views on ethiopathogenesis of the disease, therapeutic and diagnostic options and classification of the disease.

Disease Severity Linked to Increase in Autoantibody Diversity in IgG4-Related Disease

OBJECTIVE

Four autoantigens have been described recently in IgG4-related disease (IgG4-RD): prohibitin, annexin A11, laminin 511-E8, and galectin-3. However, no external validation has been performed, and the possibility that some individuals break tolerance to more than 1 autoantigen has not been explored. We undertook this study to evaluate the relative frequencies of antibody responses against these autoantigens in order to explore the role of adaptive immune response in IgG4-RD.

METHODS

Autoantibody responses against prohibitin, annexin A11, and laminin 511-E8 were measured among a clinically diverse cohort of IgG4-RD patients (n = 100) using enzyme-linked immunosorbent assays. Autoantibody responses were correlated with disease severity and organ distribution.

RESULTS

The frequencies of IgG4 autoantibody responses against prohibitin (10%), annexin A11 (12%), and laminin 511-E8 (7%) were not significantly different from those of controls. A portion of the cohort (n = 86) had been analyzed previously at our center for anti-galectin-3 antibody responses, with 25 patients (29%) having IgG4 anti-galectin-3 antibodies. Of these 86 patients, 32 (37%) had IgG4 antibodies to ≥1 of the 4 autoantigens and 12 (14%) showed reactivity with ≥2 of the tested antigens. The subset of patients with ≥2 autoantibodies had higher total levels of IgG1, IgG2, IgG4, and C-reactive protein, were more commonly hypocomplementemic, and were more likely to have visceral organ involvement.

CONCLUSION

Antibodies against prohibitin, annexin A11, and laminin 511-E8 were found in only a small portion of patients with IgG4-RD. A subset of IgG4-RD patients, however, had IgG4 antibodies against ≥2 autoantigens. These patients presented with robust IgG subclass elevations, complement consumption, and visceral organ involvement. This broader break in immunologic tolerance in IgG4-RD was associated with more severe disease.

Review of a novel disease entity, immunoglobulin G4-related disease

Immunoglobulin G4 (IgG4)-related dacryoadenitis and sialoadenitis (IgG4-DS) are part of a multiorgan fibroinflammatory condition of unknown etiology termed IgG4-related disease (IgG4-RD), which has been recognized as a single diagnostic entity for less than 15 years. Histopathologic examination is critical for diagnosis of IgG4-RD. CD4+ T and B cells, including IgG4-expressing plasma cells, constitute the major inflammatory cell populations in IgG4-RD and are thought to cause organ damage and tissue fibrosis. Patients with IgG4-RD who have active, untreated disease exhibit significant increase of IgG4-secreting plasmablasts in the blood. Considerable insight into the immunologic mechanisms of IgG4-RD has been achieved in the last decade using novel molecular biology approaches, including next-generation and single-cell RNA sequencing. Exploring the interactions between CD4+ T cells and B lineage cells is critical for understanding the pathophysiology of IgG4-RD. Establishment of pathogenic T cell clones and identification of antigens specific to these clones constitutes the first steps in determining the pathogenesis of the disease. Herein, the clinical features and mechanistic insights regarding pathogenesis of IgG4-RD were reviewed.

Management of IgG4-related disease

IgG4-related disease was unrecognised as a unified disease entity until this century, yet in a short period of time the disease has been appreciated to have a worldwide distribution, and its clinical, pathological, and radiological features have been described in considerable detail. The disease has strong organ predilections, and many of the clinical presentations of disease are increasingly familiar to both generalists and specialists. Early recognition of IgG4-related disease is crucial because although the disease is highly treatable, it can lead to serious organ damage and even death if undiagnosed until advanced stages. Its indolent nature often makes diagnosis challenging, and IgG4-related disease is one of the great mimickers of other diseases in the current era. Glucocorticoids are an effective treatment for IgG4-related disease, but their long-term use is problematic in a disease that frequently affects middle-aged to elderly individuals and often leads to pancreatic dysfunction. Our understanding of the pathophysiology of the disease is surprisingly advanced given the relatively recent recognition of this condition. Insights into disease pathophysiology offer the possibility of a variety of targeted treatment approaches. Looking ahead, biological therapies could profoundly alter the way in which IgG4-related disease is managed, permitting the use of specific therapies that are tailored to patients' clinical phenotypes.

IgG4-related disease: Association with a rare gene variant expressed in cytotoxic T cells

BACKGROUND

Family screening of a 48-year-old male with recently diagnosed IgG4-related disease (IgG4-RD) revealed unanticipated elevations in plasma IgG4 in his two healthy teenaged sons.

METHODS

We performed gene sequencing, immune cell studies, HLA typing, and analyses of circulating cytotoxic CD4+ T lymphocytes and plasmablasts to seek clues to pathogenesis. DNA from a separate cohort of 99 patients with known IgG4-RD was also sequenced for the presence of genetic variants in a specific gene, FGFBP2.

RESULTS

The three share a previously unreported heterozygous single base deletion in fibroblast growth factor binding protein type 2 (FGFBP2), which causes a frameshift in the coding sequence. The FGFBP2 protein is secreted by cytotoxic T-lymphocytes and binds fibroblast growth factor. The variant sequence in the FGFBP2 protein is predicted to form a disordered random coil rather than a helical-turn-helix structure, unable to adopt a stable conformation. The proband and the two sons had 5-10-fold higher numbers of circulating cytotoxic CD4 + T cells and plasmablasts compared to matched controls. The three members also share a homozygous missense common variant in FGFBP2 found in heterozygous form in ~40% of the population. This common variant was found in 73% of an independent, well characterized IgG4-RD cohort, showing enrichment in idiopathic IgG4-RD.

CONCLUSIONS

The presence of a shared deleterious variant and homozygous common variant in FGFBP2 in the proband and sons strongly implicates this cytotoxic T cell product in the pathophysiology of IgG4-RD. The high prevalence of a common FGFBP2 variant in sporadic IgG4-RD supports the likelihood of participation in disease.

Immunoglobulin G4 related disease: a single-centre experience from South Australia

BACKGROUND

IgG₄ related disease (IgG4RD) is a newly described multisystem fibro-inflammatory disorder. There is a paucity of literature describing the Australian experience of this rare condition.

AIMS

To characterise the Royal Adelaide Hospital IgG4RD cohort with biopsy-proven disease.

METHODS

A search of the Frome Road SA Pathology database was performed for all tissue biopsies containing the phrase 'IgG₄ positive'. Case notes were reviewed for clinical details, laboratory and radiology results. Histological features according to the Boston Criteria were used. Patients with available case notes, highly suggestive or probable histology and clinical features to suggest IgG4RD were included.

RESULTS

Twenty patients had definite or probable IgG4RD and suggestive clinical features; median age 59 (20-76), male : female 1.5:1. There was considerable delay in diagnosis (median diagnosis at 64 months). Organ involvement included: 11 exocrine gland, seven pancreatobiliary, seven nodal, seven soft tissue, five retro-orbital, three retroperitoneal fibrosis and two renal. Systemic symptoms at diagnosis were seen in eight patients. Seven (35%) had an elevated serum IgG₄ (>1.35 g/L) at diagnosis. Only 12 (60%) required immunosuppressive treatment (corticosteroids); of these, four (20%) required a steroid-sparing agent and four (20%) required B-cell depleting therapy (rituximab). The median duration of follow up was 18 months.

CONCLUSIONS

This is the first characterised Australian cohort with generalised IgG4RD, a rare, relatively indolent and under-recognised multisystem disorder. Diagnosis is difficult given lack of awareness of this rare condition among physicians, its presentation as a great disease mimic, challenges with histopathological assessment and the absence of a suitable serum biomarker.

DIAGNOSIS OF ENDOCRINE DISEASE: IgG4-related thyroid autoimmune disease

IgG4-related disease (IgG4-RD) is fibro-inflammatory, immune-mediated, systemic disease recognized as a defined clinical condition only in 2001. The prevalence of IgG4-RD is 6/100 000, but it is likely to be underestimated due to insufficient awareness of the disease. The diagnostic approach is complex because of the heterogeneity of clinical presentation and because of rather variable diagnostic criteria. Indeed, high concentrations of IgG4 in tissue and serum are not a reliable diagnostic marker. The spectrum of IgG4-RD also includes well-known thyroid diseases including Riedel's thyroiditis, Hashimoto's thyroiditis and its fibrotic variant, Graves' disease and Graves' orbitopathy. Results from clinical studies indicate that a small subset of patients with the above-mentioned thyroid conditions present some features suggestive for IgG4-RD. However, according to more recent views, the use of the term thyroid disease with an elevation of IgG4 rather than IgG4-related thyroid diseases would appear more appropriate. Nevertheless, the occurrence of high IgG4 levels in patients with thyroid disease is relevant due to peculiarities of their clinical course.

Radiotherapy for parotid IgG4-related disease

We describe the use of radiotherapy for parotid IgG4-related disease (IgG4-RD), initially misdiagnosed as Kimura's disease, with sustained good partial response in a 37-year-old male. To the best of our knowledge, this is the first reported case of radiation for extra-orbital IgG4-RD, albeit inadvertently.

Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts

OBJECTIVE

IgG4-related disease (IgG4-RD) is a heterogeneous, multiorgan condition of unclear aetiology that can cause organ failure. Difficulty recognising IgG4-RD contributes to diagnostic delays. We sought to identify key IgG4-RD phenotypes.

METHODS

We used two cross-sectional studies assembled by an international, multispecialty network of IgG4-RD specialists who submitted 765 cases to derive and replicate phenotypic groups. Phenotype groups of disease manifestations and key covariate distributions across the identified groups were measured using latent class analysis.

RESULTS

In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group 1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis; Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic involvement. We replicated the identification of four phenotype groups in the replication cohort. Compared with cases in Groups 1, 2 and 4, respectively, cases in Group 3 were more likely to be female (OR 11.60 (95% CI 5.39 to 24.98), 10.35 (95% CI 4.63 to 23.15) and 9.24 (95% CI 3.53 to 24.20)) and Asian (OR 6.68 (95% CI 2.82 to 15.79), 7.43 (95% CI 2.97 to 18.56) and 6.27 (95% CI 2.27 to 17.29)). Cases in Group 4 had a higher median serum IgG4 concentration (1170 mg/dL) compared with groups 1-3 (316, 178 and 445 mg/dL, respectively, p<0.001).

CONCLUSION

We identified four distinctive IgG4-RD phenotypes according to organ involvement. Being Asian or female may predispose individuals to head and neck-limited disease. These phenotypes serve as a framework for identifying IgG4-RD and studying its aetiology and optimal treatment.

Neuro-ophthalmic complications of IgG4-related disease

PURPOSE OF REVIEW

IgG4-related disease (IgG4-RD) is increasingly recognized as a fibroinflammatory disease with a plethora of organ-specific manifestations but a particular predilection for head and neck tissues, including the nervous system. This review discusses general features and organ-specific presentations of IgG4-RD as well as treatment considerations, particularly emphasizing features of neuro-ophthalmic interest.

RECENT FINDINGS

IgG4-RD is emerging as a common cause of several fibroinflammatory disorders in the head and neck that were previously considered idiopathic, such as sclerosing orbital pseudotumor, orbital myositis, hypophysitis, and hypertrophic pachymeningitis. New and unusual presentations continue to be described, including a number of vascular manifestations. Substantial progress has been made in elucidating the cell types involved in IgG4-RD, and new pathogenic models are being proposed. Although clinicopathologic correlation remains the cornerstone of diagnosis, ancillary tests such as flow cytometry for circulating plasmablasts and PET-computed tomography have high sensitivity, and certain radiologic features are recognized to be particularly suggestive, such as infraorbital nerve enlargement in IgG4-RD orbitopathy. IgG4-RD often responds to steroids but incomplete responses and relapses are common. Rituximab is emerging as a promising new therapy.

SUMMARY

The current review summarizes manifestations of IgG4RD that are of particular relevance to neuro-ophthalmic practice.

Correlation of Lyme Disease-Associated IgG4 Autoantibodies With Synovial Pathology in Antibiotic-Refractory Lyme Arthritis

OBJECTIVE

To determine whether IgG subclasses of Borrelia burgdorferi antibodies differ from those of 3 Lyme disease (LD)-associated autoantibodies.

METHODS

IgG antibody subclasses were determined by enzyme-linked immunosorbent assay in serum samples from 215 patients with features representative of each of the 3 stages of LD. Antibody and cytokine profiles were measured in matched serum and synovial fluid (SF) samples from patients with Lyme arthritis. Synovial tissue from patients with antibiotic-refractory arthritis was examined for histologic features, IgG subclasses of plasma cells, and messenger RNA (mRNA) subclass expression.

RESULTS

B burgdorferi antibodies were primarily of the IgG1 and IgG3 subclasses, and the levels increased as the infection progressed. In contrast, LD-associated autoantibodies were mainly of the IgG2 and IgG4 subclasses, and these responses were found primarily in patients with either antibiotic-refractory or antibiotic-responsive arthritis, particularly in SF. However, compared with the responsive group, the inflammatory milieu in SF in the refractory group was enriched for cytokines representative of innate, Th1, Th2, and Th17 responses. Synovial tissue in a subgroup of patients with refractory arthritis showed marked expression of mRNA for IgG4 antibodies and large numbers of IgG4-staining plasma cells. IgG4 autoantibodies in SF to each of the 3 LD-associated autoantigens correlated with the magnitude of obliterative microvascular lesions and fibrosis in the tissue.

CONCLUSION

Our findings indicate that the subclasses of IgG antibodies to B burgdorferi differ from those of LD-associated autoantibodies. Furthermore, the correlation of IgG4 autoantibodies with specific synovial pathology in the refractory group suggests a role for these autoantibodies, either protective or pathologic, in antibiotic-refractory Lyme arthritis.

Effect of N-acetylcysteine on mucosal immunity of respiratory tract

The outcome of diseases accompanied or caused by mucostasis depends both on the restoration of drainage function of the airways and on the effectiveness of immune mechanisms against pathogens. N-acetylcysteine (NAC) is widely used as mucolytic and antioxidant remedy in clinical practice. In this regard, the data of the scientific literature on the direct and indirect effects of NAC on the mucosal immunity of the respiratory tract have been reviewed. NAC possesses pleiotropic immunomodulating properties, most of which contribute to the regression of clinical manifestations of acute and chronic inflammatory diseases of the respiratory tract. Biological and pharmacological effects of NAC include improvement in rheological properties of mucus, reduction of excess mucin production, restoration of mucociliary clearance and production of sIgA, suppression of excess production of IgE and IgG4, destruction of biofilms and inhibition of their formation, suppression of adhesion of pathogenic bacteria to epithelial cells, antioxidant activity, regulation of the production of pro-inflammatory and profibrotic cytokines. There was no convincing evidence that NAC is able to suppress any component of mucosal immunity. For final conclusions on this subject, further research are required.

Inferior vena cava thrombosis as the initial presentation of IgG4-related retroperitoneal fibrosis: Case report and literature review

IgG4-related disease is an immune-mediated deposition of fibro-inflammatory tissue with IgG4-positive plasma cells and dense fibrosis in a single or multiple organs. It often raises concern for malignancy requiring biopsy for diagnosis. Presentation may vary according to organ involved. IgG4-related retroperitoneal fibrosis accounts for two-thirds of the previously considered idiopathic retroperitoneal fibrosis cases. In IgG4-related retroperitoneal fibrosis, computed tomography scan or magnetic resonance imaging shows periaortic soft tissue that extends from below the kidneys to iliac arteries and entrap ureters causing hydronephrosis and renal failure. We present a rare case of IgG4-related retroperitoneal fibrosis presenting with leg swelling and pain due to inferior vena cava compression and thrombosis, and we review current concepts on disease pathogenesis, diagnosis and treatment.