CD8+ T cells induce medullary thymic epithelium and CD4+CD8+CD25+ TCRβ- thymocytes in SCID mice

During T-cell development the transition in the thymus of CD4(-)CD8(-) double 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 protein. In this study purified peripheral CD4(+) and CD8(+) T lymphocytes from the C.B-17 strain of mice were adoptively transferred into syngeneic, neonatal SCID mice, where donor cells resided at constant numbers in thymus from 2 weeks until 10 weeks post cell transfer. In the recipient thymus the CD8(+) 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 thymocytes in the SCID mice, a process accompanied by the maturation of medullary epithelial 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 development in the treated SCID mice.