An improved micronuclear assay in lymphocytes.

We have found that by increasing the bromodeoxyuridine (BUdR) concentration to 4 X 10(-4) M in cultures and using the conventional harlequin staining procedure we can distinguish the proliferating lymphocytes by their blue color from the non-proliferating cells which have red nuclei. The micronuclei (MN) are also blue and are associated with the proliferating cells. The high BUdR concentration does not appear to affect the yield of MN. By scoring the MN only in the (blue) proliferating cells the MN assay is made less sensitive to perturbations in the lymphocyte cultures caused by radiation or by variations in the culture time on PHA concentration. Moreover, the frequency of cells with MN approximately doubles and thus comes into better agreement with the frequency of cells with chromosome aberrations. A better agreement yet can be achieved by correcting the assay for the effect of cell division.