Arm. Almeida et al., T cell homeostasis: Thymus regeneration and peripheral T cell restoration in mice with a reduced fraction of competent precursors, J EXP MED, 194(5), 2001, pp. 591-599
We developed a novel experimental strategy to study T cell regeneration aft
er bone marrow transplantation. We assessed the fraction of competent precu
rsors required to repopulate the thymus and quantified the relationship bet
ween the size of the different T cell compartments during T cell maturation
in the thymus. The contribution of the thymus to the establishment and mai
ntenance of the peripheral T cell pools was also quantified. We found that
the degree of thymus restoration is determined by the availability of compe
tent precursors and that the number of double-positive thymus cells is not
under homeostatic control. In contrast, the sizes of the peripheral CD4 and
CD8 T cell pools are largely independent of the number of precursors and o
f the number of thymus cells. Peripheral "homeostatic" proliferation and in
creased export and/or survival of recent thymus emigrants compensate for re
duced T cell production in the thymus. In spite of these reparatory process
es, mice with a reduced number of mature T cells in the thymus have an incr
eased probability of peripheral T cell deficiency, mainly in the naive comp
artment.