Enhanced Efficiency of Echovirus 6 by a Transferable Factor in Cultured Human Cells. ∗

Summary

A transferable enhancer has been demonstrated in cultured human cells which increases the efficiency of infection of the m+ mutant of echo virus 6 in monkey cells. Enhancer was present in a variety of human cells but not in cells of other species. In general, presence of enhancer coincided with the greater susceptibility of human cells for m+ infection. Enhancer in AV3 cells was detected in viable and dead cells, cellular debris and subcellular fractions. Most of the enhancer activity sedimented with the micro-somal fraction. Enhancer was thermolabile and destroyed by phenol, proteolytic enzymes, acid and alkali. Debris (AV_d) obtained by homogenization of AV3 cells enhanced the m+ titer (pfu and TCD₅₀) in monkey cells by 5- to 100-fold. Plaques appeared 2 days earlier in the presence of AV_d. There was a linear relationship between enhancer activity and concentration of cells (10^4.5 to 10^6.5 cells/ml) used for preparation of AV_d. Prior in vitro contact of virus and AV_d was not required for enhancement. Full enhancement was evident when monolayers were treated before, during, or after addition of virus. The data suggest that enhancer binds rapidly and irreversibly to the cell surface and acts beyond the virus adsorption step.