Abstract
Blood cells are challenged by intrinsic and exogenous stress that may result in many types of damage to DNA. As a major participant in cell-mediated immunity in blood, T lymphocytes are maintained in their quiescent (resting) state for most of their lives and switch to the proliferating state once stimulated. How resting and stimulated T cells address DNA damage remains largely unknown. Here, we report that while different types of DNA damage are efficiently repaired in stimulated T cells, they result in massive apoptosis of resting T cells. Mechanistically, DNA damage in resting T cells activates the ATM/ATR/DNA-PKcs signaling pathway but fails to induce the formation of γH2AX and 53BP1 foci, leading to unrepaired DNA damage that activates apoptosis in a p53-independent but JNK/p73-dependent manner. Mice challenged with high DNA damage stress display far fewer T cells in peripheral blood, lymph nodes, and spleens. Collectively, these results reveal that resting T cells are hypersensitive to DNA damage due to defects in DNA damage repair mechanisms. These findings provide new insight into T-cell function and maintenance of immunity under highly stressed conditions.