The cytochalasins are a new group of compounds which have been recently isolated from moulds. Some of their properties are of interest in the study of cytoplasmic and nuclear division since they have been shown to inhibit motility, produce nuclear extrusion and prevent cytoplasmic cleavage with the production of multinucleated cells. The present study is a report of the effects of cytochalasin B on cultured human lymphocytes.

After exposure to cytochalasin B, a proportion of the cultured human lymphocytes became multinucleate. The magnitude of this effect was related to the concentration and the length of time of exposure to the compound. Cells with from one to eight nuclei were identified. Progressive variation in nuclear morphology became apparent as the number of nuclei in a cell increased. Examination of the chromosomes showed only diploid, tetraploid and a few octaploid cells. No obvious chromosomal abnormalities were detected, except in octaploid cells. It is suggested that in multinucleated cells there may be a failure of mitotic control leading to variations in size and shape of interphase nuclei.

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