Potential roles of non-lymphocytic cells in the pathogenesis of IgG4-related disease

Single-cell RNA sequencing of submandibular gland reveals collagen type XV-positive fibroblasts as a disease-characterizing cell population of IgG4-related disease

OBJECTIVES

IgG4-related disease (IgG4-RD) is a systemic autoimmune disease with an unknown etiology, affecting single/multiple organ(s). Pathological findings include the infiltration of IgG4-producing plasma cells, obliterative phlebitis, and storiform fibrosis. Although immunological studies have shed light on the dysregulation of lymphocytes in IgG4-RD pathogenesis, the role of non-immune cells remains unclear. This study aimed to investigate the demographics and characteristics of non-immune cells in IgG4-RD and explore potential biomarkers derived from non-immune cells in the sera.

METHODS

We conducted single-cell RNA sequence (scRNA-seq) on non-immune cells isolated from submandibular glands of IgG4-RD patients. We focused on fibroblasts expressing collagen type XV and confirmed the presence of those fibroblasts using immunohistochemistry. Additionally, we measured the levels of collagen type XV in the sera of IgG4-RD patients.

RESULTS

The scRNA-seq analysis revealed several distinct clusters consisting of fibroblasts, endothelial cells, ductal cells, and muscle cells. Differential gene expression analysis showed upregulation of COL15A1 in IgG4-RD fibroblasts compared to control subjects. Notably, COL15A1-positive fibroblasts exhibited a distinct transcriptome compared to COL15A1-negative counterparts. Immunohistochemical analysis confirmed a significant presence of collagen type XV-positive fibroblasts in IgG4-RD patients. Furthermore, immune-suppressive therapy in active IgG4-RD patients resulted in decreased serum levels of collagen type XV.

CONCLUSIONS

Our findings suggest that collagen type XV-producing fibroblasts may represent a disease-characterizing non-immune cell population in IgG4-RD and hold potential as a disease-monitoring marker.

IgG4-related disease with massive pericardial effusion diagnosed clinically using FDG-PETCT: a case report

Background

IgG4-related disease (IgG4-RD) is a systemic inflammatory disease which involves various organs such as the pancreas, lacrimal gland, salivary gland, retroperitoneum, and so on. These organs can be affected concomitantly. 18-Fluorodeoxyglucose positron emission tomography computed tomography (FDG-PETCT) is a systemic examination which can identify active inflammation and detect multiple organ involvement simultaneously. Pericardial involvement is rare in IgG4-RD, early detection and treatment can greatly improve the prognosis of patients.

Case summary

We reported a 82-year-old female patient referred to our department complaining of chest tightness and abdominal fullness for 8 months and massive pericardial effusion for 2 months. A large amount of pericardial effusion was found during the hospitalization of Gastroenterology. Then she was transferred to cardiology. Although infectious, tuberculous, and neoplastic pericardial effusions were excluded, there was still no diagnosis. The patients were examined by FDG-PETCT which considered IgG4-RD. After coming to our department, the results of the patient's laboratory tests showed that immunoglobulin subgroup IgG4 was 14.0 g/L. Then we performed a biopsy of the right submandibular gland. Pathological morphology and immunohistochemistry suggested IgG4-RD. Combined with level of IgG4, clinical, pathological and immunohistochemical results, we determined the final diagnosis of IgG4 related diseases. Then we gave glucocorticoid and immunosuppressant treatment. At the end, pericardial effusion was completely absorbed. As prednisone acetate was gradually reduced, no recurrence of the disease has been observed.

Conclusion

Pericardial effusion can be the initial presentation in IgG4-RD. For patients with massive pericardial effusion of unknown cause, early detection of IgG4 is recommended, and PETCT may be helpful for obtaining the diagnosis.

A Unique Adverse Event of Radiotherapy in a Patient With IgG4-related Disease: A Case Report

BACKGROUND/AIM

IgG4-related disease (IgG4RD) is a rare autoimmune proinflammatory condition that mimics other cancers and has unique pathological findings. The effects of radiotherapy in patients with IgG4RD remain unknown.

CASE REPORT

A male patient in his seventies who received radiotherapy (68 Gy/39 fr) for bladder cancer 5 months prior, presented to our hospital with fatigue and swelling in both legs. The patient had a history of IgG4-related sclerosing cholangitis, a subtype of IgG4RD. Leg edema gradually worsened despite treatment with a diuretic agent. Computed tomography showed hyperdense soft-tissue lesions in the irradiated area. The serum level of IgG4 increased to 1,380 mg/dl. One month after administration of a corticosteroid (10 mg per day) as an ex juvantibus treatment for IgG4RD, leg edema disappeared. Soft-tissue lesions in the irradiated area decreased in size. The adverse event was ultimately diagnosed as the recurrence of IgG4RD in the irradiated area. To the best of our knowledge, this is the first case report of an adverse event of radiotherapy for a patient with IgG4RD.

CONCLUSION

We experienced a unique adverse event of radiotherapy in a patient with IgG4RD. Caution is advised on radiotherapy administration in patients with IgG4RD.