Colony growth of human T-lymphocyte colony forming units (TL-CFU) after X-irradiation.

The effect of X-irradiation on growth of T-lymphocyte colony forming units (TL-CFU) from human peripheral blood was investigated. The results indicate that not the number of activated TL-CFU but the number of cell cycles of colony forming cells was reduced by X-irradiation. Therefore we presume that TL-CFU belong to a relatively radio-resistant cell population within the PHA-responsive lymphocytes. Kinetic studies revealed that colony growth following irradiation was delayed mainly during the phase of the first cell cycle. Preculture of the cells for 24 hours after irradiation with 1,200 R in the absence of PHA caused total inhibition of colony growth in the subsequent agar culture. In the presence of PHA no inhibition was observed. This finding appears to reflect a repair mechanism from radiation damage of lymphocytes stimulated by PHA.