A higher micronucleus yield in B- versus T-cells after low-dose -irradiation is not linked with defective Ku86 protein

Purpose: To elaborate the B-cell micronucleus (MN) response in the low-dose region in detail and to investigate the postulated deficiency in DNA-PK in B-cells.

Materials and methods: Lymphocytes of five healthy volunteers were irradiated with low LET gamma -rays and high LET fast neutrons with doses ranging between 0.01 and 2 Gy. After post-irradiation incubation, B- and T-cells were isolated via CD3 and CD19 immunomagnetic microbeads. MN were analysed in both subpopulations. To study the underlying mechanism of chromosomal radiosensitivity, cell extracts prepared from purified B- and T-cells were subjected to SDS-electrophoresis and electroblotting using antibodies directed against the DNA-PK repair enzymes Ku70/86 and DNA-PKcs. Activity measurements were per formed using the SignaTECT DNA-dependent protein kinase assay. DNA double-strand break (DSB) induction and rejoining was determined using constant-field gel electrophoresis.

Results: For low LET gamma -rays a higher MN yield was observed in B-cells than in T-cells, but only in those samples exposed to doses < 1 Gy. For 1 Gy the MN yields were comparable and for 2 Gy even lower in B-cells compared with T-cells. After high LET neutron irradiation no significant differences in MN yields wt re observed between both subsets. The results of the DNA-PK experiments demonstrate that there is no difference between T- and B-cells in the basal expression and activity of DNA-PK repair proteins. No differences in DNA DSB induction and rejoining were found between T- and B-cells using constant-field gel electrophoresis.

Conclusions: From the results, it was concluded that the enhanced chromosomal radiosensitivity in B-cells is restricted to low doses (< 1 Gy) of low LET radiation and that the chromosomal behaviour of B-cells to low LET radiation cannot be attributed to aberrant forms of the DNA-PK components. A type of chromosomal induced radioresistance (IRR) may be a possible explanation for the observed effect.