RA can block induction of Th17 T cells. CD3/CD28/CD2-stimulated CD4⁺ T cells were cocultured with CD14⁺HLA-DR⁺ monocytes for 6 days. As indicated atRA (A,E), LE540 (B,F), AM580 (C,G) or A7980 (D,H) was added to the cultures. Shown are representative dot plots for Foxp3 and IL-17 gating on CD4⁺ T cells (A-D) or single results are shown in bars (E-H; *P < .05; n.s. indicates not significant). Numbers represent percentages of events within the respective quadrants.