CD8(+) T cells induce medullary thymic epithelium and CD4(+)CD8(+)CD25(+) TCR beta(-) thymocytes in SCID mice

During T-cell development the transition in the thymus of CD4(-)CD8(-) doub le negative (DN) progenitor T cells into CD4(+)CD8(+) double positive (DP) cells is dependent on the expression of a T-cell receptor (TCR)P-chain prot ein. In this study purified peripheral CD4(+) and CD8(+) T lymphocytes from the C.B-17 strain of mice were adoptively transferred into syngeneic, neon atal SCID mice, where donor cells resided at constant numbers in thymus fro m 2 weeks until 10 weeks post cell transfer. In the recipient thymus the CD 8(+) donor cells outnumbered the CD4(+) cells by a factor of three to five and both subsets contained a large fraction of activated cells. During the late phase of treatment, CD8(+) T cells induced high numbers of DP thymocyt es in the SCID mice, a process accompanied by the maturation of medullary e pithelial cells. Such thymic development in the SCID mouse was inhibited by coresiding CD4(+) donor T cells. These results indicate a regulatory role by mature peripheral T cells on medullary epithelial growth and thymocyte d evelopment in the treated SCID mice.