A Mathematical Model Resolving Normal Human Blood Lymphocyte Population X-ray Survival Curves into Six Components: Radiosensitivity, Death Rate and Size of Two Responding Subpopulations

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Abstract
The analysis was based on observations of survival decrease as a function of dose (range 0-5 Gy [gray] (= 500 rad)) and time after irradiation in vitro. Since lymphocyte survival is also sensitive to culture conditions the effects of radiation were examined daily up to 3 days only, while survival of control cells remained .apprx. 90%. The time-dependent changes were resolved as the death rates (1st-order governed) of lethally-hit cells (apparent survivors), so rendering these distinguishable from the morphologically identical true (ultimate) survivors. For 12 blood donors the estimated dose permitting 37% ultimate survival (D37 value) averaged 0.72 .+-. 0.18 (SD) Gy for the more radiosensitive lymphocyte fraction and 2.50 .+-. 0.67 Gy for the less radiosensitive, each fraction proving homogeneously radiosensitive and the latter identifying substantially in kind with T-type (erythrocyte-rosetting lymphocytes). The half-life of lethally-hit members of either fraction varied widely among the donors (ranges, 25-104 h and 11-40 h, respectively). Survival curves reconstructed by summating the numerical estimates of the 6 parameters according to the theoretical model closely matched those observed experimentally (range in multiple correlation coefficient, 0.9709-0.9994 for all donors). This signified the absence of any additional, totally radioresistant cell fraction.