THYMOCYTES AND RELB-DEPENDENT MEDULLARY EPITHELIAL-CELLS PROVIDE GROWTH-PROMOTING AND ORGANIZATION SIGNALS, RESPECTIVELY, TO THYMIC MEDULLARY STROMAL CELLS
M. Naspetti et al., THYMOCYTES AND RELB-DEPENDENT MEDULLARY EPITHELIAL-CELLS PROVIDE GROWTH-PROMOTING AND ORGANIZATION SIGNALS, RESPECTIVELY, TO THYMIC MEDULLARY STROMAL CELLS, European Journal of Immunology, 27(6), 1997, pp. 1392-1397
The thymic medulla is composed of distinct epithelial cell subsets, de
fined in this report by the reactivity of two novel antibodies, 95 and
29, raised against mouse thymic epithelial cell lines. These antibodi
es were used to probe the development of medulla in wild-type or mutan
t thymuses. In CD3 epsilon-deficient mice where thymocyte maturation i
s arrested at the CD4(-) CD8(-) stage, few scattered 95(+) and 29(+) e
pithelial cells are found. When few mature thymocytes develop as in CD
3 zeta/eta mice, expansion and organization of 95(+) but not 29(+) cel
ls, becomes detectable. In RelB-deficient mice, T cell maturation proc
eeds normally but negative selection is inefficient due to the lack of
thymic medulla and dendritic cells. Strikingly, 29(+) epithelial cell
s are absent and 95(+) medullary epithelial cells are scattered throug
hout the thymus, intermingling with CDR1(+) cortical epithelium. In ch
imeric mice lacking only dendritic cells, the corticomedullary junctio
n persists and both 95(+) and 29(+) epithelial cells are localized in
the medulla. These results suggest that two types of signals are requi
red for development of thymic medulla. A growth signal depends upon th
e presence of maturing thymocytes, but organization of the thymic medu
lla requires the presence of activated 29(+) medullary epithelial cell
s.