DEVELOPMENT OF T-CELL RECEPTOR-GAMMA-DELTA CELLS PHENOTYPIC AND FUNCTIONAL CORRELATIONS OF T-CELL RECEPTOR-GAMMA-DELTA THYMOCYTE MATURATION

The development of TCR-gammadelta cells during thymic ontogeny has bee n studied using fetal thymic organ cultures of normal and transgenic ( Tg) mice. The expression of the cell-surface markers-heat stable Ag (H SA), MEL-14, CD5, CD25 (IL-2R), and CD44 (Pgp-1)-correlated with TCR-g ammadelta maturation. As the fetal thymus developed, there was an incr ease in HSA-, CD5dull, and CD44+ cells for each TCR-gammadelta cell su bset. Moreover, the expression of recombination activating genes-1 and -2 (RAG-1 and RAG-2) also correlated with TCR-gammadelta maturation a s only HSA+ TCR-gammadelta cells transcribed these genes. Cyclosporin A inhibited the development of the TCR-gammadelta thymocytes if it was introduced early during thymic ontogeny by arresting the differentiat ion of TCR-gammadelta thymocytes at the HSA+ stage. Immature HSA+ TCR- gammadelta thymocytes isolated from both TCR-gammadelta Tg and normal mice did not respond to nominal Ag or anti-TCR mAb unless exogenous IL -2 was added to the cultures. In contrast, HSA- TCR-gammadelta cells f rom Tg and normal mice responded to TCR/ligand interactions in the abs ence of additional IL-2. Finally, the development of functionally matu re TCR-gammadelta cells could be induced in vitro. Interaction of the HSA+ Tg+ TCR-gammadelta cells with anti-TCR-gammadelta mAb or Ag-beari ng thymic stromal cells resulted in RAG-1 and RAG-2 down-regulation. T hese data strongly suggest that TCR-gammadelta HSA+, RAG+ thymocytes d ifferentiate into a more mature stage under the pressure of positive s election and that TCR-gammadelta cell development is regulated in a ma nner similar to TCR-alphabeta cells. In addition, the ability of Cyclo sporin A to inhibit TCR-gammadelta cell development combined with the findings that Ag-bearing stromal cells can induce Tg TCR-gammadelta ce ll development suggests that maturation and selection of TCR-gammadelt a cells depends on receptor-mediated physiologic stimuli delivered dur ing thymic development.