Effect of X-rays on Thymocytes and Its Modification by Cysteine

Summary

Sensitivity of rabbit thymocytes to X-irradiation in vitro is decreased by a constant factor over a wide dosage range when cysteine is added to the suspension. Protection depends upon cysteine concentration and time of administration but is not a simple function of the sulfhydryl level. There is a definite postirradiation effect of cysteine which can be accounted for only in part by the persistence of toxic substances in the medium. The relative resistance of packed cells and the failure of cysteine to protect them may be a consequence of hypoxia. It is suggested that the effect of cysteine on irradiated thymic cell suspensions may be a result of competition with cell substrates for oxygen, but that the binding of oxygen per se is not necessarily the decisive event in the protection. The results are discussed in connection with related observations in the intact animal.