ISG15 and rheumatoid arthritis: Analysis of myeloid cells in the PBMC on the basis of differential expression of CD14, FCGR3A, FCER1A, IRF8, IL3RA, HLA-DRB5, S100B, and IFN activation markers (ISG15, IFI6, IFI44, and STAT1) revealed no significant differences in Monocyte/Dendritic cells (Mono_DC) populations in ACPA- RA compared with ACPA+ RA and HCs, respectively (Fig. 1c, Supplementary Fig. 1b).