Immune effects of low-dose radiation: short-term induction of thymocyte apoptosis and long-term augmentation of T-cell-dependent immune responses

Radiat Res. 2000 Mar;153(3):332-8. doi: 10.1667/0033-7587(2000)153[0332:ieoldr];2.


We and others have shown that low-dose X or gamma irradiation of mice leads to an increase in their survival after a subsequent lethal high-dose irradiation. The greatest increase in radioresistance appears at a fixed window of dose and time, e.g. 8 weeks after 5-10 cGy or 2 weeks after 50 cGy preirradiation. We show that low-dose irradiation induces thymocyte apoptosis with a maximal level at 6 h postirradiation that returns to background levels after 24 h. At the same time, we observed no morphological alteration of splenocytes and no early modification of the intensity of T-cell-dependent immune responses as measured by plaque-forming cell (PFC) counts. Nevertheless, we found that PFCs were increased 2 weeks after 50 cGy irradiation, which is the same time at which mice expressed the optimal increase in survival after a second lethal irradiation. We also examined thymocyte apoptosis and spleen PFCs in mice subjected to other stress-inducing pretreatments. Our results emphasize the existence of a lag time between the time of low-dose irradiation in vivo and the appearance of radioresistance. A mechanism that interconnects an environmental stimulus with the response of the animal is proposed based on the evidence presented here and reported in the literature.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / radiation effects*
  • Dose-Response Relationship, Radiation
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred ICR
  • T-Lymphocytes / cytology
  • T-Lymphocytes / immunology
  • T-Lymphocytes / radiation effects*