Influence of retinoic acid on the differentiation pathway of T cells in the thymus.

Abstract This study investigated the ability of retinoic acid (RA) to influence T cell differentiation. All- trans -RA had marked effects on T cell differentiation in murine fetal thymic organ cultures (FTOCs). The time course of the effect of all- trans -RA in FTOC of day 14 C57BL/6 embryos revealed a twofold increase in the frequency of CD4 single-positive (SP) cells and a high level of CD3-bearing cells (CD3 high cells) at a later stage of T cell development. At an earlier stage, all- trans -RA induced a twofold increase in the frequency of CD4 SP cells, but significantly suppressed the upregulation of CD3 and TCR. Reverse transcription-PCR using RA receptor (RAR) subtype-specific primers showed that RAR α but not β and γ is expressed during T cell development in the thymus and that its expression was associated with the generation of CD4/CD8 double-positive (DP) cells. In FTOC of day 16 BALB/c embryos, the level of Vβ3 high cells was greatly reduced (1.4% of the CD3 high cells) in response to the mouse mammary tumor virus-6-encoded superantigen, but Vβ3-bearing cells were rescued from the deletion in the presence of all- trans -RA (5.6% of the CD3 high cells). Further, the inhibitory effect of all- trans -RA on thymocyte deletion was observed when the deletion was induced by a low concentration of staphylococcal enterotoxin B in FTOC. Taken together, these data suggest that RA increases the frequency of mature and self-reactive T cells in the thymus, possibly by inhibiting the process of negative selection at the DP stage of T cell differentiation.