Murine<i>Scid</i>Cells Complement Ataxia-telangiectasia Cells and Show a Normal Post-irradiation Response of DNA Synthesis

The murine severe combined immunodeficient mutation (scid) is characterized by a lack of both B and T cells, due to a defect in lymphoid variable-(diversity)-joining (V(D)J) rearrangement. Scid cells are highly sensitive to both radiation-induced killing and chromosomal aberrations. Significantly reduced D0 and n values were demonstrated in scid cells and were similar to ataxia-telangiectasia (AT) cells (a unique human disease conferring whole body radiosensitivity). However, the kinetics of DNA synthesis after irradiation were different between the two cell types. In contrast with the radioresistant DNA synthesis of AT cells, DNA synthesis of scid cells was markedly inhibited after irradiation. The existence of different mutations was also supported by evidence of complementation in somatic cell hybrids between scid cells and AT cells. Our results indicate that the radiobiological character of scid is similar to AT but is presumably caused by different mechanisms.