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

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Abstract
Sensitivlty of rabbit thymocytes to X-irradlatlon in vitro is decreased by a constant factor over a wide dosage range when cystelne is added to the suspension. Protection depends upon cysteine concn. and time of admn. but is not a simple function of the sulfhydryl level. There is a definite post-irradiation 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. The effect of cysteine on irradiated thymic cell suspensions may be a result of competition with cell substrates for O2, but the binding of 02 per se is not necessarily the decisive event in the protection.