Micronucleus frequencies in cytokinesis-blocked human B lymphocytes after low dose gamma-irradiation.

Purpose : To investigate (I) the radiosensitivity of B versus T lymphocytes with respect to micronucleus (MN) induction and (2) the possible application of the B cell MN assay for biological dosimetry of individuals after acute exposure to low doses of ionizing radiation. Materials and methods: MN analysis was performed in T and B lymphocytes of six healthy volunteers exposed in vitro to γ-ray doses ranging from 0.05 Gy to 1 Gy. For the MN assay on B cells, peripheral blood mononuclear cells were cultured and stimulated with pokeweed mitogen (PWM). Afterwards the B lymphocytes (characterized by the CD20+ phenotype) were separated with the FACSort flow cytometer and the number of MN in the sorted binucleate cells was scored. For T lymphocytes the standard MN protocol was applied. Results: The number of spontaneous and radiation induced MN were significantly higher in B lymphocytes compared to T lymphocytes in the low dose range up to I Gy. An analysis of the present data showed that when the spontaneous MN frequencies are not known, doses from 0.08 Gy could be detected with the B cell MN assay while the conventional MN assay only allowed detection of doses > 0.25 Gy. However, in contradiction to the linear-quadratic dose-response for T cells, for B cells the initial steep increase of the MN yield with the very low dose was followed by a flattening of the curve towards higher doses. Conclusion: This study shows that B lymphocytes express a high number of MN for doses up to I Gy γ-rays reflecting the highly radiosensitive behaviour of B cells. The results also point to the possible application of the B-cell MN assay for individual dose assessment. When blood samples can be taken within 24 h after acute accidental overexposure, the B-cell MN assay can be performed but only as a supplementary test to the conventional MN assay.