Retinoic acid receptor-α gene expression is modulated by dietary vitamin A and by retinoic acid in chicken T lymphocytes

The effects of dietary vitamin A and retinoic acid in vitro on the proliferative response and gene expression of retinoic acid receptor-α (RAR- α) in chicken T lymphocytes were studied. Antigen-specific proliferative responses of T lymphocytes increased with dietary vitamin A intake from 0 to 6.6 mg/kg diet; however, at high dietary vitamin A (13.2 mg/kg diet), the proliferative response declined. RAR-α mRNA expression in T lymphocytes peaked in chicks fed low levels of vitamin A (830 and 1500 μg/kg diet) and declined at higher intakes. In vitro effects of retinoic acid on the modulation of RAR-α mRNA were studied in stimulated T lymphocytes. Retinoic acid (0.01 μmol/L) increased RAR-α mRNA levels within 2 or 16 h of incubation with concanavalin A- or β-casein-stimulated T cells, respectively. This effect was transient. Expression of RAR-α mRNA in concanavalin A-stimulated T lymphocytes was up-regulated by retinoic acid in a dose-dependent manner, and maximal expression occurred in response to 1 μmol/L retinoic acid. The proliferative response of these cells was also modulated by retinoic acid in a dose-dependent manner, and highest effects were observed at 0.01 μmol/L retinoic acid. Our results indicate that RAR- α mRNA expression and antigen-specific proliferative responses of T lymphocytes are influenced by vitamin A status in vivo, and directly modulated by retinoic acid.