EXPRESSION OF DIVERSE AND FUNCTIONAL TCR-GAMMA AND IG HEAVY-CHAIN TRANSCRIPTS IN FETAL LIVER-CELLS CULTURED WITH INTERLEUKIN-7

We have previously shown that specific T cell receptor (TCR) gamma V r egions genes (V gamma 4 and V gamma 6) are rearranged and expressed by murine fetal liver (FL) cells cultured with IL-7. The present studies determined that the sequences of the TCR V region gene transcripts ex pressed in response to IL-7 included diverse and functional sequences expressed by thymocyte and peripheral V gamma 4(+) and V gamma 6(+) T cells, indicating that the IL-7-induced expression of these genes is f unctionally relevant and mimics normal in vivo developmental events of gamma delta T cells. We found that more than 50% of these TCR transcr ipts had N region diversity. The presence of N region diversity indica tes that these TCR rearrangements took place in vitro, presumably in r esponse to IL-7, because fresh (uncultured) FL cells do not produce de tectable terminal deoxynucleotidyl transferase (TdT) mRNA or protein. We also found that 100% of immunoglobulin (Ig) VH7183-JH4 transcripts from FL cells cultured with IL-7 had N region diversity at the V-DJ re gion, while only 40% of IgVH7183-JH4 transcripts from FL cells culture d in the absence of IL-7 had N region diversity at this region. FL cel l cultures supplemented for 7 days with IL-7 had increased TdT mRNA an d protein levels. However, since I-day culture of FL cells with or wit hout IL-7 resulted in induction of expression of TdT, IL-7 probably do es not directly stimulate TdT expression, but increases the developmen t and expansion of TdT(+) lymphoid cells. These findings implicate IL- 7 as a regulator of the molecular signals involved in controlling TCR gamma rearrangement and diversity, and provide an in vitro system for studying the regulation of TdT and N region diversity in B and T lymph oid progenitors by environmental signals.