Upregulation of interferon-γ response genes in monocytes and T cells identified by single-cell transcriptomics in patients with anti-citrullinated peptide antibody-positive early rheumatoid arthritis.

Introduction: Our aim was to investigate the insufficiently understood differences in the immune system between anti-citrullinated peptide antibody (ACPA)-positive (ACPA) and ACPA-negative (ACPA) early rheumatoid arthritis (eRA) patients.

Methods: We performed multiple cytokine assays using sera from drug-naïve ACPA and ACPA eRA patients. Additionally, we conducted single-cell RNA sequencing of CD45 cells from peripheral blood samples to analyze and compare the distribution and functional characteristics of the cell subsets based on the ACPA status.

Results: Serum concentrations of interferon-γ (IFN-γ) and interleukin (IL)-12 were higher in ACPA eRA than in ACPA eRA. Single-cell transcriptome analysis of 37,318 cells identified 17 distinct cell types and revealed the expansion of IL1B proinflammatory monocytes, IL7R T cells, and CD8 CCL4 T cells in ACPA eRA. Furthermore, we observed an enrichment of IFN-γ response genes in nearly all monocytes and T cells of ACPA eRA subsets. Heightened interactions between IFN-γ and IFN-γ receptors were observed in ACPA eRA, particularly between monocytes and T cells. We examined and as potential key markers in ACPA eRA given their pronounced upregulation and association with the IFN response. Specifically, the expression of these genes was elevated in IL1B proinflammatory monocytes (likely M1 monocytes), correlating with serum IFN-γ levels.

Discussion: Compared to ACPA eRA, ACPA eRA showed higher serum IFN-γ and IL-12 levels, upregulated IFN-γ response genes, and enhanced IFN-γ-driven monocyte-T cell interactions. These distinct immune features of the peripheral circulation in ACPA eRA suggest a role for type 1 helper T cell-related immunity in its pathogenesis.