Background: Polymyalgia Rheumatica (PMR) is a common inflammatory disease in elderly persons whose pathogenesis is unclear [1-4].

Objectives: We aimed to explore the pathogenetic features of PMR.

Methods: We analyzed the cell subsets and their gene expression profiles in peripheral blood mononuclear cells (PBMCs) from patients with newly diagnosed PMR and sex-matched healthy controls (HC) by Single-cell RNA sequencing and bioinformatic analysis. The identified cell subsets were further analyzed in additional PMR patients using flow cytometry.

Results: Single-cell RNA sequencing revealed significant differences in cell T cell, B cell, and monocyte subset densities in PBMCs from 7 newly diagnosed PMR patients compared to 5 healthy controls (HC) (Figure 1A-C). Taking a rough look, there an increase in T cells, and a decrease in moncytes from patients with PMR (Figure 1C). We further identified 26 subpopulations, consisting of 10 types of T cells, 3 types of B cells, 3 types of monocytes, 2 types of dendritic cells (DC), 4 types of natural killer (NK) cells, and 4 other cell types. Most importanly, we observed significant increases in frequencies of CD4 ⁺ central memory T Cells (CD4 ⁺ Tcm), CD8 ⁺ CD73 ⁺ Tcm, and Age associated B cells (ABCs) in PMR patients (Figure 1D-E), significant decrease in frequencie of classical moncytes (Figure 1F) in PMR patients by Single-cell RNA sequencing analysis, while other cell subsets were not significantly altered.

As PMR happens in elderly people, ABCs are related to aged immune response. Therefore, we focus on the ABCs. Flow cytometry analysis of 20 PMR patients and 23 healthy controls confirmed a significant increase in the frequency of ABCs (CD19 ⁺ IgD ^- CD27 ^- CD11c ⁺ CD21 ^- ) among B cells in PMR (Figure 2A-B). Furthermore, the frequency of ABCs was significant related to PMR-AS disease activity socre (Figure 2C). ABCs expressed high level of CD86, FCRL5, and T-bet in PMR patients (Figure 2D). This exression profile of ABCs were consistent with data from the previous publication. Furthermore, we found ABCs had a inflammatory roles with higher productions of IL-12 and IL-8 (Figure 2D). However, the IFN-γ expression was comparable between PMR and HC. Interestingly, BCR VDJ analysis domonstrated an increase in cell clonality of ABCs from PMR using Gini index.

Conclusion: Our study show increased frequencies of CD4 ⁺ Tcm, CD8 ⁺ CD73 ⁺ Tcm and ABCs, an decrease of classical moncytes in PMR patients using single-cell RNA sequencing. Furthermore, expanded ABCs exert a inflammatory role and may contribute to the pathogenesis of PMR.

REFERENCES: [1] Buttgereit F, Matteson EL, Dejaco C. Polymyalgia Rheumatica and Giant Cell Arteritis. JAMA. 2020;324(10):993-994.

[2] Cancro MP. Age-Associated B Cells. Annu Rev Immunol. 2020;38:315-340.

[3] Li ZY, Cai ML, Qin Y, Chen Z. Age/autoimmunity-associated B cells in inflammatory arthritis: An emerging therapeutic target. Front Immunol. 2023;14:1103307.

[4] Nickerson KM, Smita S, Hoehn KB, et al. Age-associated B cells are heterogeneous and dynamic drivers of autoimmunity in mice. J Exp Med. 2023;220(5):e20221346.

Figure 1.

CD4 ⁺ Tcm, CD8 ⁺ CD73 ⁺ Tcm, and ABCs were increased, classical moncytes were decreased in patients with PMR using single-cell RNA sequencing

Figure 2.

ABCs (CD19 ⁺ IgD ^- CD27 ^- CD11c ⁺ CD21 ^- ) were increased in patients with PMR using flow analysis

Acknowledgements: This work was supported in part by grants from Natural Science Foundation of China (82171768), National Key Research and Development Program of China (2022YFC3602000).

Disclosure of Interests: None declared.