The effect of crude preparations of vaccinia on mitosis and DNA synthesis of KB cells.

A morphologic study has been made on KB cells infected with various doses of vaccinia as to DNA synthesis and mitosis. Determination of mitotic indices revealed that the mitotic cell pool depended on the proportion of infected cells and the time after infection. By cytologic examination neither mitotic lesions were found nor an accumulation of mitotic cells at any one stage of mitosis was demonstrated. Radioautographs of infected cultures have shown that the frequency of cells labeled over nuclei was significantly increased as compared with control cultures. Following the greatest dose of virus (multiplicity of 20 PFU/cell) the ratio of cells synthesizing DNA to mitotic cells increased from 45:5 at 5 hr to 50:0 at 50 hr. Concommittant with the appearance of this disparity between the DNA-synthesizing cell pool and mitotic cell pool the nuclei of cells became "lightly" labeled. Following the lowest dose of virus (multiplicity of 0.0002 PFU/cell) the increase of the fraction of mitotic cells was proportional to the increase of the fraction of cells which were labeled over nuclei.