A line of presumed pure human liver cells (Chang) received from a commercial source was found to be mixed with cells of nonprimate origin. Chromosomal and immunologic analysis support the view that the contaminating cells were probably of mouse origin. The mixed line was segregated into its two components by virtue of the nonspecific lytic effect of unheated human serum against the nonprimate line. Serial culture of artificially remixed cells of each line in a nonselective medium containing 10% horse serum, did not appear to influence favorably one cell type over the other during eight serial passages together. The human cells could be resegregated from the artificially mixed cultures by subculture into unheated human serum medium; the nonprimate cells could be resegregated by the selective destruction of the human cells by Coe or poliovirus. Mixtures of this type may occur more frequently than is presently recognized and may provide an explanation for some examples of apparent “transformation” of cell lines.

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This investigation was conducted under the sponsorship of the Commission on Acute Respiratory Diseases, Armed Forces Epidemiological Board, and supported by the Office of the Surgeon General, Department of the Army.

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