Viral‐induced fusion of human cells. I. Quantitative studies on the fusion of human diploid fibroblasts induced by sendai virus

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Abstract
Human diploid fibroblasts in monolayer cultures underwent cyto‐plasmic fusion in the presence of UV‐inactivated Sendai virus. The proportion of nuclei in the cultures which were in polykaryocytes (“polykaryocytic index”) under the conditions used in the present study, was about 0.50. When the cells were fused by the methods developed for the present study, the polykaryocytic index was substantially higher than when the conventional method was employed. The extent of fusion obtained was dependent, up to a certain degree, on the concentration of the virus and on the cell population density. The polykaryocytic index reached a maximum four to six hours after the cells were exposed to virus, but the frequency of cells with very high numbers of nuclei continued to increase for at least two days. Evidence is presented which suggests that the population of mononucleate cells is heterogeneous as regards their ability to fuse. The distribution of multinucleate cells with various numbers of nuclei roughly fits the Poisson distribution, although the frequency of cells with very large numbers of nuclei is substantially greater than the Poisson would predict.