Background: Primary Sjögren disease (SjD) is characterized by B cell overactivation. However, the role of age-associated B cells (ABCs) in SjD remains largely unknow.

Objectives: To investigate the potential role of ABCs in SjD.

Methods: Peripheral blood mononuclear cells (PBMCs) and salivary gland (SG) single-cell RNA-seq datasets of SjD were analyzed [1-2]. Peripheral and salivary gland ABCs were examined using flow cytometry (FC) and immunofluorescence in an independent SjD and control cohort, respectively. ABC differentiation stimulated by SjD-related cytokines was assessed using FC. The humanized model was established by transferring SjD or healthy control (HC) PBMCs with or without ABC depletion into NOG mice [3] , salivary flow rate and SG histopathology were analyzed. Naïve CD4 ⁺ T cell differentiation stimulated with ABCs or non-ABCs were analyzed using FC. Differentially expressed genes in SjD ABCs versus non-ABCs were screened by Smart-seq, validated by FC, and confirmed by blockade.

Results: scRNA-seq analysis indicated the ABCs were expanded in SjD (Figure 1A-B). Circulating CD19 ⁺ CD11c ⁺ T-bet ⁺ and CD19 ⁺ IgD ^- CD27 ^- CD11c ⁺ CXCR5 ^- ABCs were expanded in SjD (Figure 1C-D), and ABCs infiltrated in SG of SjD (Figure 1E). IL-21 promoted ABC differentiation from naïve B cells (Figure 1F), which was suppressed by tofacitinib and STAT5 inhibitor STAT5-IN-1 (Figure 1G). Transfer of SjD but not HC PBMCs induced saliva reduction, lymphocytic infiltrates and glandular destruction in NOG mice, which were partially attenuated in mice transferred with ABC-depleted SjD PBMCs (Figure 2A-B). ABCs promoted follicular T helper cell (Tfh) differentiation in vitro (Figure 2C). Smart-seq and FC identified ABCs overexpressed PD-L1 (Figure 2D-E), and PD-1 blockade reversed Tfh differentiation mediated by ABCs (Figure 2F).

Conclusions: ABCs are expanded in SjD by IL-21 through JAK/STAT5 pathway, and promote Tfh differentiation by overexpressing PD-L1 (Figure 2G), which contributes to SG dysfunction in SjD. This finding suggests the IL-21/ABCs/Tfh axis is a key immunopathology mechanism of SjD, which might be targeted by tofacitinib.

Figure 1.

IL-21 promotes ABC expansion via JAK/STAT5 signaling in SjD.

Figure 2.

ABCs promote Tfh differentiation through overexpressing PD-L1 and cause SG dysfunction in SjD.

REFERENCES: [1] Hong X, Meng S, Tang D, et al. Single-Cell RNA Sequencing Reveals the Expansion of Cytotoxic CD4+ T Lymphocytes and a Landscape of Immune Cells in Primary Sjögren’s Syndrome. Frontiers in Immunology, 2020, 11: 594658.

[2] Xiang N, Xu H, Zhou Z, et al. Single-cell transcriptome profiling reveals immune and stromal cell heterogeneity in primary Sjögren’s syndrome. iScience, 2023, 26(10): 107943.

[3] Young N A, Wu L C, Bruss M, et al. A chimeric human-mouse model of Sjögren’s syndrome. Clinical Immunology, 2015, 156(1): 1-8.

Acknowledgments: NIL.

Disclosure of Interests: None declared.