Dependency of sister chromatid exchange in T- and B-cells on the incorporation of deoxyribonucleosides into chromosomal DNA.

Human T-cells (CCRF-HSB2) did not incorporate tritiated thymidine ([3H]TDR)--1.0-5.0 muCi/ml--into the nuclei, where.as they readily incorporated tritiated deoxycytidine (E13H]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(-6)-10(-4) M, 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(-7) M, 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(-4) M. In the case of CCRF-HSB2, 10(-4) M BUDR produced relatively high frequencies of SCE as did 10(-7) M BUDR with the former two cells. However, [3H]CDR with CCRF-HSB2 gave relatively low frequencies of SCE, of the magnitude observed after 10(-4) M 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.