Immunophenotypic analysis of tissue-resident memory T cells in rheumatoid arthritis

Seokchan Hong¹ Jae Hyung Jung^1,2, Jung Sun Lee¹, Jae Bum Won¹, Doo-Ho Lim³, Yong-Gil Kim¹, Chang-Keun Lee¹, and Bin Yoo¹

¹Division of Rheumatology, Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea ²Asan Institute for Life Science, Asan Medical Center, Seoul, Korea

³Division of Rheumatology, Department of Internal Medicine, Ulsan University Hospital, Ulsan, Korea

Background/Purpose: Rheumatoid arthritis (RA) is a chronic autoimmune disease that is characterized by an inflammation of the synovial membrane and infiltration of immune cells including T cells into the joints. Recently, discovery of tissue-resident memory T cells (Trm), which reside in peripheral tissue rather than circulation, provides a new avenue in tissue-specific immunity. However, the phenotypes and role of Trm in the patients with RA has not been investigated yet. Thus, we examined the presence and characteristics of Trm in synovial fluid cells in patients with RA.

Methods: Cells with phenotypes of Trm was identified by the expression of CD3, CD8 and CD69 but not CD45RA in the synovial fluid mononuclear cells (SFMCs) of RA patients (n=19). The expression of markers for activation, tissue-residency, pro-inflammatory cytokines and cytotoxic molecules was analyzed with or without IL-15 stimulation.

Results: A substantial portion (mean 54.98%) of the CD8⁺CD45RA^– T cells in the SFMCs showed the phenotypes of Trm (CD3⁺CD8⁺CD45RA^–CD69⁺), and the frequency was significantly increased after stimulation with IL-15 (54.98% vs 79.24%, p<0.0001). The expression of activation markers CD25 and CD38 was similar between CD69⁺ and CD69^– CD8 T cells. CD69⁺ CD8 T cells had significantly higher expression of chemokine receptor CXCR6 compared to CD69^– CD8 T cells (38.2% vs 17.3 %, p=0.017). In addition, CD69⁺ CD8 T cells showed higher expression of markers for Trm PD-1 (P<0.001) and CD101 (P=0.07) compared to CD69^– CD8 T cells. Proinflammatory cytokines IFN¥ã (0.15% vs 0.07%, p=0.0056) and TNF¥á (0.25% vs. 0.10%, p=0.0013) were upregulated in CD69⁺ CD8 T cells compare to their CD69^– counterparts. Furthermore, CD69⁺ CD8 T cells were shown to be positive for perforin (mean 35.14%) and granzyme B (mean 46.97%) and its expression was significantly increased after IL-15 stimulation.

Conclusion: These data suggest that the presence of Trm in synovial cells from patients with RA. These cells can produce cytotoxic molecules and thus possibly contribute to tissue damage in RA.