On the fine structure of influenza viruses

Properties of the erythrocyte receptors for influenza C virus

Properties of the receptor for influenza C virus were studied. Although the receptor for influenza C virus on chicken erythrocytes was destroyed by the homologous virion, neuraminidase activity could not be detected in any of the influenza C virus strains tested. The receptor activity of chicken erythrocytes for influenza C virus was diminished by formaldehyde treatment but not by periodate oxidation. There was a considerable variation in the pattern and the titer of hemagglutination of influenza C virus when human erythrocytes of different blood types were used; the virus agglutinated most type B erythrocytes but not type A erythrocytes. By using human type B erythrocytes, differences among strains of influenza C virus in the hemagglutinating activity were also demonstrated. These results showed that both the receptor for and the receptor-destroying activity of influenza C virus were completely different from those of influenza A or B virus and also that carbohydrates were not involved in the receptor for influenza C virus.

Absence of neuraminidase from influenza C virus

Influenza C viruses did not possess neuraminidase activity when examined using either fetuin or sialyllactose as substrate. Purified preparations of influenza C virus inhibited hemagglutination by NWS hemagglutinin. The hemagglutination inhibiting activity was abolished by treatment of influenza C virus with neuraminidase. These findings indicated the absence of neuraminidase activity on influenza C virus particles.

Lipids in Viruses

This chapter discusses lipids in viruses. Lipid forms an integral part of many viruses and exists either in the form of a continuous envelope or in lipoprotein complexes that surround a nucleoprotein core or helix. In general, the envelope can be described as a molecular container for the genetic material of the virus. Viruses are obligate intracellular parasites and are not known to carry genetic coding for enzymes involved in lipid synthesis. Hence, they generally contain the same classes of lipid as are found in the host cell or their membrane of assembly. Lipids make up 20–35% by weight of most viruses; however, there are exceptions such as vaccinia virus, which has only 5% lipid despite having a complex multimembrane envelope structure. Naked herpesvirus capsids closely resemble non-lipid-containing viruses such as adenovirus or polyoma virus, which are also assembled in the nucleus but show full infectivity without any envelope. Both naked and enveloped herpesvirus particles are found in infected cells; however, only enveloped particles are found in extracellular fluids.

Spin-labeled electron spin resonance study of the lipid-containing membrane of influenza virus

The organization of the lipid-containing membrane of influenza virus has been studied by the use of three different lipid spin labels, and the results are compared with a parallel study on human erythrocyte ghosts. The lipid phase of the viral membrane is slightly more rigid than that of the erythrocyte ghosts. The data suggest that the viral lipid is arranged in a bilayer. The data suggest that the viral lipid is arranged in a bilayer. The glycoprotein spikes covering the viral membrane were specifically removed by proteases, and no alteration in the environment of any of the three spin labels was detected. This suggests that the spikes are not involved in determining the organization of the lipid bilayer.