ISG15 and rheumatoid arthritis: The abundance of GZMK+ IFN-act central memory T (TCM) cells expressing central memory CD4 T cell and interferon pathway genes (including GZMK, ISG15, IFI6, CCR7, GPR183, SELL, TCF7, and IL7R) was also higher in RA patients, especially in ACPA- RA, compared to HCs (Fig. 7c, Fig. 8a).