RAR-α signaling is important in mediating the effects of RA on T cells. B6 spleen cells (adjusted to 1 × 10⁵ T cells/well) were cocultured with 5 × 10⁴ Balb/c dendritic cells in the presence or absence of 1 μM AM80, an RAR-α agonist. Four days later, cells were harvested for flow cytometric analysis. (A) Representative contour plots of α4β7 and CCR9 expression on CD4⁺ and CD8⁺ T cells. (B) Mean (± standard error of the mean [SEM]) percentage of CD4⁺ and CD8⁺ T cells that expressed α4β7 and CCR9. Data are cumulative results from 4 independent experiments. Statistics: *P ≤ .05, ***P < .001. (C, D) B6 spleen cells (adjusted to 1 × 10⁵ T cells/well) were cocultured with 5 × 10⁴ Balb/c dendritic cells in the presence of 10 nM exogenous RA. An RAR-α antagonist, BMS195614 (1 μM), was added to some cultures 1 hour prior to the addition of RA. Cells were analyzed after 4 days in culture. Representative contour plots of CCR9, α4β7, CD62L, and CD25 expression on CD4⁺ and CD8⁺ T cells is depicted. Data are from 1 of 4 representative experiments with similar results. (E) Cells were cultured as in panels C and D with the exception of ³H-thymidine was added for the last 18 hours to assess proliferation. Data are presented as mean counts per minute ± SEM and are representative of 1 of 2 experiments with similar results. Statistics: *P ≤ .05