INVOLVEMENT OF IL-7 IN THE DEVELOPMENT OF GAMMA-DELTA T-CELLS IN THE THYMUS

The effect of IL-7 on the growth of thymic T lymphocytes was investiga ted by adding recombinant IL-7 into cell suspension cultures and subme rsion organ cultures (SOC) of murine fetal thymuses (FT) and newborn t hymuses (NBT). FT and NBT were obtained from C57BL/6 mice at day 15 of gestational age and at day 3 after birth, respectively. In both cell suspension cultures and SOC, addition of IL-7 highly improved the cell recovery. In cell suspension cultures, addition of IL-7 resulted in t he growth of gammadelta T-cells from FT-cells, whereas the same cytoki ne promoted the growth of both alphabeta and gammadelta T-cells from N BT-cells. These results may indicate that this cytokine is able to sup port the proliferation of T-cells of both alphabeta and gammadelta lin eages. In marked contrast, in SOC, addition of IL-7 resulted in the gr owth of gammadelta T-cells not only in FT but also in NBT, despite the fact that the SOC of NBT without exogenous cytokine exclusively promo ted the growth of alphabeta T-cells. A similar effect was also seen wh en IL-2 was added to NBT-SOC, though the skewing to gammadelta lineage was not so strong as in the case of IL-7. In addition, we found that IL-7 mRNA is expressed in the day 15 FT at a much higher level than in the adult thymus. These results strongly suggested that the productio n of a large amount of IL-7 synthesized in the FT is one of the major factors leading to the generation of gammadelta T-cells in FT.