Clinical features and mechanistic insights regarding IgG4-related dacryoadenitis and sialoadenitis: a review

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.

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.

IgG4-related sialadenitis - a rare bilateral submandibular gland enlargement: case report

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory condition of unknown etiology. Although the salivary glands are currently considered among the most commonly affected among them, oral and maxillofacial surgeons are generally not familiar with the condition. Enlargement of the major salivary glands may be the first identifiable sign of IgG4-RD. A salivary gland biopsy along with IgG4 serum level assessment may help differentiate IgG4-related sialadenitis (IgG4-RS) from malignancies, infectious diseases, and obstructive conditions. Greater knowledge and higher levels of awareness of IgG4-RS may contribute to the expansion of differential diagnostic and treatment approaches. This case report describes a patient with bilateral submandibular salivary gland swelling who was diagnosed as having IgG4-RS on the basis of the histopathologic findings of a submandibular salivary gland biopsy and subsequent IgG4 levels.

Immunoglobulin G4-related periodontitis: case report and review of the literature

BACKGROUND

Immunoglobulin G4-related disease (IgG4-RD) is a chronic inflammatory systemic disease of unknown etiology that can affect one or multiple organs. The disease can mimic many infectious and inflammatory diseases, mainly causing organ enlargement or hyperplasia. Its diagnosis primarily relies on clinical, serologic, and histological features (lymphoplasmacytic infiltrates, storiform fibrosis, and obliterative phlebitis of IgG4 + plasma cells). Here, we report a rare case of IgG4-related periodontitis, and review the relevant literatures.

CASE PRESENTATION

A 38-year-old Chinese man visited the Department of Periodontics with gingival enlargement, loose teeth, and tooth loss. The patient had very poor oral hygiene and a large amount of calculus. Gingivae were edematous with deep periodontal pockets and attachment loss. Panoramic radiography showed alveolar bone loss. Serologic examination showed that IgG was 23.70 g/L and IgG4 concentration was 2.800 g/L. There was significant lymphoplasmacytic infiltration, a storiform pattern of fibrosis, and mitotic figures with hematoxylin and eosin staining; immunohistochemical staining showed 10 scattered IgG4-positive plasma cells in a high-power field. The patient was diagnosed as IgG4-related periodontitis. He received a course of corticosteroids with periodontal therapy, and the enlargement was significantly improved without recurrence.

CONCLUSION

IgG4-RD in the oral and maxillofacial region mainly involves salivary glands, but this rare case was characterized by enlarged gingivae. The differential diagnosis of IgG4-RD should be based on the clinical features and serologic (IgG4) and histopathological examinations. Corticosteroid therapy is effective for most IgG4-RD patients. Taken together, we hope this case report and the literature review can help dentists to improve their understanding of the IgG4-RD.

CT and MR imaging findings of ocular adnexal mucosa-associated lymphoid tissue lymphoma associated with IgG4-related disease: multi-institutional case series

AIM

To report CT and MR imaging findings of ocular adnexal mucosa-associated lymphoid tissue lymphoma associated with IgG4-related disease (IgG4-MALT lymphoma), a rare but clinically important complication of ocular adnexal IgG4-related disease.

METHODS

We retrospectively reviewed all cases of histologically confirmed ocular adnexal IgG4-related disease at three tertiary and one secondary referral centers, between February 2003 and December 2016. Seven cases of histopathologically diagnosed IgG4-MALT lymphoma were identified. CT and MR images were analyzed by consensus of two experienced head and neck radiologists.

RESULTS

Lacrimal glands were the main site of involvement in all seven patients. The lesions typically showed well-demarcated margins, iso- to hyperattenuation on precontrast CT, T2 hypo- to isointensity, T1 isointensity, and homogenous internal architecture with homogenous enhancement pattern. Lesions were mostly hyperdense and isointense to normal extraocular muscles on postcontrast CT and MR images, respectively.

CONCLUSION

Unlike in typical ocular adnexal IgG4-related disease, T2 isointensity and hyperattenuation on precontrast CT images were noted in some IgG4-MALT lymphoma cases. Although the findings may be nonspecific, the possibility of accompanying MALT lymphoma may need to be considered, when ocular adnexal lesions in patients clinically suspected of having IgG4-related disease are refractory to glucocorticoids and show T2 isointensity and hyperattenuation on precontrast CT for the optimal management of the patients. However, this is a case series of a very rare complication of ocular adnexal IgG4-related disease, and thus caution is warranted to generalize the conclusion.

Clinical phenotypes of IgG4-related disease reflect different prognostic outcomes

Introduction

Four clinical phenotypes of IgG4-related disease (IgG4-RD) have been recently identified by latent class analysis (LCA): pancreato-biliary (group 1); retroperitoneum/aortitis (group 2); head and neck limited (group 3); and Mikulicz/systemic (group 4). The reproducibility of this classification in clinical practice and its relevance for patient management, however, remain unknown.

Methods

The study included 179 patients. Four IgG4-RD experts were asked to classify a validation cohort of 40 patients according to published LCA-derived phenotypes based on clinical judgement. Agreement between LCA and clinical clustering was calculated. To assess differences among disease phenotypes, the following variables were recorded on an additional 139 patients: serum IgG4 and IgE; inflammatory markers; eosinophils; plasmablasts; IgG4-RD responder index (RI); history of atopy, diabetes, osteoporosis, relapses and malignancy; cumulative dose of glucocorticoids; and use of rituximab.

Results

Clinical judgement replicated LCA classification with strong agreement among IgG4-RD experts (κ = 0.841, P < 0.0005). At disease onset, group 1 showed the highest levels of serum IgG4 and IgE. Groups 2 and 4 had the lowest and highest IgG4-RD RI, respectively. At 2 years’ follow-up, group 3 received the highest cumulative dose of glucocorticoids, but higher incidences of diabetes mellitus were observed in groups 1 and 4, consistent with the higher likelihood of pancreatic involvement in groups 1 and 4. No difference among the four groups was observed in terms of disease recurrence, time to relapse and frequency of rituximab infusion.

Conclusion

Clinical phenotypes of IgG4-RD reflect differences in epidemiological features and prognostic outcomes.

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.