Further Studies on the Activation of Influenza Virus by Proteolytic Cleavage of the Haemagglutinin

Abstract

Egg-grown virus of an influenza A strain (virus N), produces highly infectious particles in this host with its haemagglutinin glycoprotein present in the cleaved form. It also contains relatively large amounts of mucopolysaccharide. This substance cannot be detected in virus derived from cultures of chick embryo cells which has uncleaved haemagglutinin and reduced infectivity. These observations indicate that the host-dependent differences in infectivity cannot be attributed to the presence of mucopolysaccharide as a masking substance at the virus surface, and further substantiate the essential role of the cleavage of the haemagglutinin for activation of infectivity.