miR-21-5p overexpression regulates T effector/Treg cell balance via STAT3. Percentages of (A) Th17, (B) Th22 and (C) Treg cells in CD4+ T cells of the control, MC+NC, M+NC, MC+STAT3 and M+STAT3 groups were measured via flow cytometry. Protein levels of (D) IL-17A and (E) IL-22 of T cells in the control, MC+NC, M+NC, MC+STAT3 and M+STAT3 groups were measured via enzyme-linked immunosorbent assay. (F) Relative Foxp3 expression in the control, MC+NC, M+NC, MC+STAT3 and M+STAT3 groups were measured via reverse transcription-quantitative PCR. GAPDH was used as the internal control. *P<0.05, **P<0.01 and ***P<0.001 vs. MC+NC; ^P<0.05 and ^^P<0.01 vs. MC+STAT3; ##P<0.01 and ###P<0.001 vs. M+NC. Th, T helper; IL, interleukin; miR, microRNA; Treg cells, regulatory T cells; M, miR-21-5p mimic; MC, mimic control; NC, negative control.