Studies on the interaction between coxsackievirus A9 and HeLa cells. II. Mode of growth of coxsackievirus A9 in HeLa cell cultures and the effect of sulfated polysaccharide on plaque formation

Strain-specific aggregation of enterovirus by dextran sulfate

Dextran sulfate aggregates several enteroviruses depending not only on the pH, the ionic strength of the medium, but also on the protein content of the fluids and on strain specificities of the viruses. The aggregation effect was measured by filtration experiments, by sedimentation in the ultracentrifuge and by electron microscopy. The well known inhibiting effect of dextran sulfate on plaque formation may be due to its aggregating effect: A very strong inhibition of the release of matured virions from the infected cells is observed in medium containing dextran sulfate, whereas the adsorption process is inhibited much less compared with PBS controls. The maximal effect on virus aggregation, plaque size and virus release is observed at the same concentration of dextran sulfate.

Variation in susceptibility of HeLa cell lines to coxsackievirus A9

In the course of serial passages for several years a line of uncloned HeLa cells (A line) showed a gradual decrease in plaquing efficiency by coxsackievirus A9 (CA9 virus), while subcultures prepared from the same line kept frozen at an early passage level (A original line) did not show any change. However, it was observed later that the plaque-forming ability of the A original line (A orig. line) also decreased after serial passages as was observed with the A line. Comparing the characteristics of the same cell line at two different passage levels, it was found that the efficiency of adsorption of virus to cells was nearly the same, while virus yield at 8 hours after infection was different. The activity of alkaline phosphatase of cells was also different between these two passage levels, suggesting that a high enzymatic activity is associated with the susceptibility of cell cultures to CA9 virus. Magnesium chloride at 25 mM enhanced plaque formation by CA9 virus in highly passaged less susceptible cell cultures, and a possible role of the chemical as a stabilizer of alkaline phosphatase was discussed.

Studies on the interaction between coxsackievirus A9 and HeLa cells. II. Mode of growth of coxsackievirus A9 in HeLa cell cultures and the effect of sulfated polysaccharide on plaque formation

For the purpose of clarifying the mechanism of plaque formation in HeLa cell cultures by coxsackievirus A9, which does not show definite CPE in fluid cultures, we investigated the growth pattern of the virus in HeLa cells, comparing plaque (HeLA)-forming and non-plaque (HeLa)-forming viruses. It was revealed that the yield of both viruses per cell was nearly the same, but non- plaque (HeLa)-forming virus was far less efficient in infecting HeLa cells. Dextran sulfate was effective in releasing more virus from cells, when HeLa cell cultures were infected with plaque (HeLa)-forming virus, but not in cultures infected with non-plaque (HeLa)-forming virus. From these experimental results, the mechanism by which plaques are formed in HeLa cell cultures by coxsackievirus A9 was discussed.