Dependency of Sister Chromatid Exchange in T- and B-Cells on the Incorporation of Deoxyribonucleosides Into Chromosomal DNA 2

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Abstract
Human T-cells (CCRF-HSB2) did not incorporate tritiated thymidine ([3H]TDR)—1.0–5.0 µCi/ml—into the nuclei, whereas they readily incorporated tritiated deoxycytidine ([3H]CDR). When contamination with pleuropneumonia-like organisms was ruled out, these findings strongly suggested a deficiency of the enzyme thymidine kinase in the cells. Human B-cells (CCRF-SB) and normal T-lymphocytes (NTL) readily incorporated [3H]CDR, [3H]TDR, and tritiated 5-bromodeoxyuridine, and they clearly exhibited differential staining of the sister chromatids (SCD). When nonisotopic bromodeoxyuridine (BUDR), 10−5-10−4M, was used with the B-cells and NTL, SCD were clearly evident and sister chromatid exchange (SCE) was relatively infrequent; when the concentration was 10−7M, SCD staining was poor but the frequency of SCE was high. SCE frequencies in NTL, measured by autoradiography after incorporation of [3H]CDR, were the same as SCE frequencies measured by staining with BUDR at 10−4M. In the case of CCRF-HSB2, 10−4M BUDR produced relatively high frequencies of SCE as did 10−7M BUDR with the former two cells. However, [3H]CDR with CCRF-HSB2 gave relatively low frequencies of SCE, of the magnitude observed after 10−4M BUDR was used with NTL and the B-cells. Thus the high frequency of SCE in CCRF-HSB2 cells may have been due to the staining property of chromosomes that had incorporated low levels of BUDR.

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