Delay of poliovirus plaque formation with use of fresh bovine serum in the growth medium of host cells.

The plaque formation of poliovirus in HeLa cell monolayers was decreased upto 95% when the host cells were subcultured several times in a growth medium containing fresh bovine serum prior to their inoculation with virus. Extended incubation of infected cell monolayers indicated that the inhibition was in the form of a delay in plaque formation rather than a permanent inhibition of it. The inhibitory factor, which was found in most bovine sera, was very unstable and disappeared after storage of the serum at -20 C for a few weeks or at 36 C within a few days. In HeLa-cell monolayers, the fresh serum brought about a decrease in the plaque formation of all three poliovirus types as well as that of poliovirus ribonucleic acid. The plaque formation of poliovirus in monkey heart and HEp-2-cell monolayers was decreased irregularly by the use of fresh serum in the growth medium of these cells. Speculations were made as to the possible mode of action of the bovine serum inhibitor.