How alpha beta T cells deal with induced TCR alpha ablation

On deletion of the gene encoding the constant region of the T cell antigen receptor (TCR)alpha chain in mature T cells by induced Cre-mediated recombi nation, the cells lose most of their TCR from the cell surface within 7-10 days, but minute amounts of surface-bound TCR beta chains are retained for long periods of time. In a situation in which cellular influx from the thym us is blocked, TCR-deficient naive T cells decay over time, the decay rates being faster for CD8(+) cells (t(1/2) approximate to 16 days) than for CD4 (+) cells (t(1/2) approximate to 46 days). TCR+ naive cells are either main tained (CD8(+)) or decay more slowly (CD4(+); t(1/2) approximate to 78 days .) Numbers of TCR-deficient memory T cells decline very slowly (CD8(+) cell s; t(1/2) approximate to 52 days) or not at all (CD4(+) cells), but at the population level, these cells fail to expand as their TCR+ counterparts do. Together with earlier data on T cell maintenance in environments lacking a ppropriate major histocompatibility complex antigens, these data argue agai nst the possibility that spontaneous ligand-independent signaling by the al pha beta TCR contributes significantly to T-cell homeostasis.