Regarding T cells, miR-21 has been shownto both promote and inhibit T-cell activation.31,32 Overexpression of miR-21 innaïve mouse T cells promotes expression of Th2 and Treg genes33 and expression of FoxP3 in human Tregs.34 Accordingly, lower expression of miR-21 has been reported in PBMCs and CD4+ Tcells of rheumatoid arthritis patients compared to controls, with low miR-21 showingstrong correlation with an increased ratio of Th17/Treg cells.35 Arguably, miR-21 may play different roles in different stages of diseasedepending on the stage of CD4+ T-cell activation and the cell subset. This evidence concerns the gene CD4 and rheumatoid arthritis.