Distinct modes of cell death by ionizing radiation observed in two lines of feline T-lymphocytes.

We have examined in vitro radiosensitivities and radioresponses to (60)Co gamma-rays irradiation in feline T-lymphocyte cell lines, FeT-J and FL-4. There seemed to be no significant difference in clonogenic survival between the two lines. The mean lethal dose for both was both 1.9 Gy, and surviving fraction at 2 Gy was 0.30 and 0.48 for FeT-J and FL-4 cells, respectively. However, TUNEL assay indicated much higher degrees of apoptosis induction in FeT-J cells (>40%) than in FL-4 cells (<10%) at 4 days after 15 Gy irradiation. Microscopic examination revealed a larger population of multi-nucleate cells in FL-4 cells (60.3%) than in FeT-J cells (16.0%) at 4 days after 15 Gy irradiation, suggesting that a larger ratio of mitotic catastrophe occurred in FL-4 cells. These results suggest that FeT-J is more likely to be induced into apoptosis and FL-4 is more likely to fall into mitotic catastrophe, and eventually necrosis; both of them showed a similar surviving fraction against gamma-rays. The results also indicate that FL-4 cells follow a process other than apoptosis to cell death, suggesting the presence of a regulatory mechanism that may control the relationship between mitotic catastrophe and apoptosis in feline T-lymphocytes.