Role of Sialic Acid Receptors in Adsorption of Influenza Virus to Chick Embryo Cells

Treatment of CE cell monolayers with neuraminidase produced 2.5- to 4.7-fold inhibition of plaque formation with different myxoviruses on subsequent infection. Continued incubation in the presence of neuraminidase failed to increase appreciably the extent of inhibition. In contrast, neuraminidase at 800-, 4000- and 500-fold lower concentrations modified receptors for virus on RBC and released sialic acid from mucin and N-acetyl neuramin-lactose, respectively, under comparable conditions. Thus, a large proportion of virus receptors on CE cells were refractory or relatively resistant to enzyme action. Evidence is presented that plaque reduction which was observed was probably attributable to the neuraminidase component of the enzyme preparation. On the other hand, the action of neuraminidase on virus infection could be distinguished from that on RBC by pH effect and by lack of competitive inhibition with N-acetyl neuramin-lactose. A difference between CE and RBC receptors for the same virus was further indicated by release of significant quantities of sialic acid from CE cells by concentrations of neuraminidase which produced hemagglutination inhibition but no reduction in infectious centers. Extent of plaque inhibition by neuraminidase was reflected by decrease in virus adsorption to the cells.