Characteristics of PD-1+CD4+ T cells in peripheral blood and synovium of rheumatoid arthritis patients

Abstract

Objectives

PD-1 plays a crucial role in the immune dysregulation of rheumatoid arthritis (RA), but the specific characteristics of PD-1⁺CD4⁺ T cells remain unclear and require further investigation.

Methods

Circulating PD-1⁺CD4⁺ T cells from RA patients were analysed using flow cytometry. Plasma levels of soluble PD-1 (sPD-1) were measured using enzyme-linked immunosorbent assay (ELISA). Single-cell RNA sequence data from peripheral blood mononuclear cells (PBMCs) and synovial tissue of patients were obtained from the GEO and the ImmPort databases. Bioinformatics analyses were performed in the R studio to characterise PD-1⁺CD4⁺ T cells. Expression of CCR7, KLF2 and IL32 in PD-1⁺CD4⁺ T cells was validated by flow cytometry.

Results

RA patients showed an elevated proportion of PD-1⁺CD4⁺ T cells in peripheral blood, along with increased plasma sPD-1 levels, which positively correlated with TNF-α and erythrocyte sedimentation rate. Bioinformatic analysis revealed PD-1 expression on CCR7⁺CD4⁺ T cells in PBMCs, and on both CCR7⁺CD4⁺ T cells and CXCL13⁺CD4⁺ T cells in RA synovium. PD-1 was co-expressed with CCR7, KLF2, and IL32 in peripheral CD4⁺ T cells. In synovium, PD-1⁺CCR7⁺CD4⁺ T cells had higher expression of TNF and LCP2, while PD-1⁺CXCL13⁺CD4⁺ T cells showed elevated levels of ARID5A and DUSP2. PD-1⁺CD4⁺ T cells in synovium also appeared to interact with B cells and fibroblasts through BTLA and TNFSF signalling pathways.

Conclusion

This study highlights the increased proportion of PD-1⁺CD4⁺ T cells and elevated sPD-1 levels in RA. The transcriptomic profiles and signalling networks of PD-1⁺CD4⁺ T cells offer new insights into their role in RA pathogenesis.