PRTN3 and rheumatoid arthritis: To investigate the heterogeneity of immune cell phenotype in different subtypes of RA patients, we carried out scRNA-seq on CD45+ peripheral blood mononuclear cells (PBMCs) isolated from healthy controls (HCs) (n = 4), PBMCs and synovial tissue mononuclear cells (STMCs) isolated from ACPA+ (n = 10), and ACPA- (n = 10) RA patients (Fig. 1a).