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30 male workers exposed to piperazine and the same number of controls were investigated. Parallel lymphocyte cultures with pokeweed mitogen and phytohemagglutinin were set up and the cells were analyzed regarding frequency and size of micronuclei. There was a statistically significant effect of the occupational exposure on the micronucleus frequencies and sizes as well, but only in the cultures activated with pokeweed mitogen. The two mitogens may activate different lymphocyte subpopulations, which probably explains both the present and earlier in vitro findings. It is interesting that there is an increased frequency of B cell derived tumours (non-Hodgkin's lymphomas and myelomas) in the piperazine-producing plant.

Micronuclei were induced in human lymphocytes by mitomycin C or gamma radiation. After the incubation the cells were separated in B- and T-cells by an immunomagnetic method, i.e., Dynabeads. The cultures were stimulated by PHA. The effect of different incubation times (60-110 h) as well as different doses of mitomycin C (0-100 nmol/l) and gamma radiation (0-2 Gy) at an incubation time of 72 h were studied. There were significantly higher frequencies of micronuclei in B- than in T-cells, when micronuclei were induced by mitomycin C. This was not found with gamma radiation, probably because of a cytotoxic effect of this agent on the B-cells.