T cell deletion follows chronic antigen specific T cell activation in vivo

Exposure of mice transgenic for a TCR (F5) to cognate peptideantigen results in thymic depletion of CD4⁺ CD8⁺ cells and expansionand activation of peripheral CD8⁺ TCR(tg)⁺ T cells.in the thymusapoptotic DNA ladder is evident as early as 3 h after peptideinjection. Long exposure of intact or thymectomized F5 TCR transgenicmice to peptide antigen leads to depletion of most of the peripheralCD8⁺ T cells bearing the F5 receptor, with the remaining cellshaving lower levels of transgenic TCR compared with non-treatedanimals. In the thymus of intact F5 TCR transgenic mice suchcontinuous exposure to antigen results in the reappearance ofCD4⁺CD8⁺ with lower levels of the transgenic receptor.