Single-cell transcriptome analysis profiles cellular and molecular alterations in submandibular gland and blood in IgG4-related disease.

Objectives: The aim of this study is to profile the transcriptional landscapes of affected tissues and peripheral blood mononuclear cells (PBMCs) at the single-cell level in IgG4-related disease (IgG4-RD). Identifying the cell populations and crosstalk between immune cells and non-immune cells will assist us in understanding the aetiology of IgG4-RD.

Methods: We performed single-cell RNA sequencing analysis on submandibular glands (SMGs) and PBMCs from patients with IgG4-RD and matched controls. Additionally, bulk RNA sequencing of PBMCs was used to construct the immune repertoire. Furthermore, multiplex immunofluorescence staining was performed to validate the transcriptomic results.

Results: We identified three novel subsets of tissue-resident immune cells in the SMGs of patients with IgG4-RD. _B cells and _T cells had stemness signatures, and trajectory analysis showed that _B cells may differentiate into IgG4plasma cells and that _T cells may differentiate into T follicular helper (Tfh) cells. _B cells with Tfh-like characteristics appeared to be an intermediate state in the differentiation from B cells to IgG4plasma cells. The cellular communication patterns within immune cells and between immune cells and non-immune cells were altered in IgG4-RD compared with controls. Consistently, infection-related pathways were shared in B cells and T cells from SMGs and PBMCs. Furthermore, immune clonotype analysis of PBMC samples showed the complementary determining region 3 amino acid CQQSYSTPYTF was expanded in patients with IgG4-RD.

Conclusion: Our data revealed the cellular and molecular changes at the single-cell resolution of IgG4-RD and provide valuable insights into the aetiology and novel therapeutic targets of the autoimmune disease.