CD4 and systemic lupus erythematosus: Further supporting the correlation between protein and mRNA levels, we detected a remarkable correlation between the expression of FOXP3 and IKZF2 with the frequency of FOXP3+ cells in both total CD4+ or CD127lowCD25low T cells (Supplementary Figures 6F,G), demonstrating that the observed Treg expansion in SLE patients can also be detected through the transcription of classical Treg signature genes in circulating CD4+ T cells.