Differential effects of T cell receptor ligation of TCR gamma delta thymocyte development in fetal thymic organ culture.

Fetal thymus organ culture system (FTOC), a well-known model used for the study of TCR alpha beta development, was employed to study TCR gamma delta cell development. It was found that different waves of TCR gamma delta cells develop from precursors within the fetal thymi at the time in vitro culture. Subsets of fetal thymocytes were analyzed by flow cytometry and 2-D gel biochemical analysis was performed. After 5 days in FTOC, V gamma 3+ and V gamma 2+ cells were dominant. By day 12 FTOC, the absolute number of V gamma 3+ cells decreased while V gamma 2+ and V gamma 4+ cells became dominant. These observations suggest that the thymic micro-environment affects the thymic waves of TCR gamma delta subsets. Furthermore, the effect of TCR/antigen interaction in the development of TCR gamma delta cells was examined with anti-TCR mAbs added into the FTOC. Anti-CD3 mAb added to day 5 and day 12 FTOC inhibited TCR gamma delta development, especially V gamma 4+ cells. On the other hand, V gamma 2+ cells were relatively resistant to the addition of anti-TCR mAb. The reduction of TCR gamma delta+ thymocytes was not due to the modulation of TCR molecules and could be reversed by Cyclosporin A (CsA). These results suggest that TCR ligation negatively regulates the development of TCR gamma delta cells in a V gamma-specific manner.