Cp. Liu et al., THYMOCYTES CAN BECOME MATURE T-CELLS WITHOUT PASSING THROUGH THE CD4(-POSITIVE STAGE()CD8(+), DOUBLE), The Journal of experimental medicine, 184(5), 1996, pp. 1619-1630
T cells bearing the class II-restricted, DO-T cell receptor (TCR) are
CD4(+) if their thymocyte precursors are positively selected on the cl
ass TI protein, IA(d), but they are almost all CD4(-) after positive s
election on a class II for which they have higher avidity, IA(b). DO-T
CR(+) T cells mature in H-2(b) mice lacking CD4. CD4(-) DO-TCR(+) T ce
lls appear in H-2(b) mice at the same rate as their CD4(+) counterpart
s appear in H-2(d) animals, suggesting that the CD4(-) cells are not t
he product of some minor pathway of thymocyte development and selectio
n. In H-2(b) CD4 knock out mice expressing human CD2 under the control
of the mouse CD4 promoter, mature DO-TCR(+) cells did not express hum
an CD2. These results suggest that the CD4(-)CD8(-), DO-TCR(+) mature
T cells have developed without ever passing through the equivalent of
a CD4(+), CD8(+) stage. The early expression of alpha/beta receptors (
TCRs) on thymocytes in TCR transgenic mice may allow maturation of thi
s type. Passage through the equivalent of the CD4(+)CD8(+), double-pos
itive stage is not essential for differentiation of thymocytes into ma
ture T cells.