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Effects of Heterologous Sera on the Modal Distribution of Variants in Four Strains of Human Epithelial Cells^*

( Department of Bacteriology, The University of Michigan, Ann Arbor, Michigan)

A study was made of the morphologic characteristics of compact-large (CL), compact-small (CS), diffuse-large (DL), and diffuse-small (DS) cell variants in HeLa-S3, HeLa-Gey, Chang-liver, and Maben strains of human epithelial cells. Cells of compact colonies were epithelioid, very cohesive, difficult to trypsinize or maintain in suspension, easy to grow, and formed opaque, multilayered colonies. Cells of diffuse colonies were fibroblastic, not cohesive, easy to trypsinize and maintain in suspension, but were difficult to grow. Diffuse colonies were either translucent or essentially transparent; giant cells were most common and conspicuous in DL colonies. The diameter of CL and DL colonies was approximately 2.5 times that of CS or DS colonies. By careful selection of human sera used for growth media, and by plating large numbers of cells, it was possible to analyze the modal distribution of variants in each cell population. The per cent distribution of CL, CS, DL, and DS variants in the tested cell strains was approximately 15:5:40:40, respectively.

The effects of calf and horse serum on the distribution of variants in cell strains were studied by the stepwise "adaptation" of cell populations to growth in heterologous serum. Shifts in populations were traced by quantitative cell plating technics. The results disclosed that there was a continuous increase in the ratio of compact (C) to diffuse (D) cells and a concomitant parallel increase in plating efficiency as cultures were "adapted" to growth in heterologous sera. When cloned lines of C and D cells were plated without prior adaptation in heterologous sera, a marked selective effect resulted. Tests with cloned cell lines disclosed that the rate of interconversion between C and D cells in heterologous sera was not quantitatively equivalent to the increase in the ratio of C:D cells when uncloned populations were adapted to growth in calf or horse serum media. These findings supported the conclusion that horse and calf serum exerted a significant selective effect for C cells in the populations studied. The results did not exclude the possibility that genetic changes occurred in cells during the selective process. The significance of the experimental findings to analyses of virus-cell and virus-cell population relationships was discussed.

^* These studies were supported jointly by USPHS grant E-2279 and Army Chem. Corps grant FD-GR-60-5.

Received 12/20/61.