Electron microscopy of influenza virus. A comparison of negatively stained and ice-embedded particles.

An electron microscopical study was made of the influenza virus, type B/Hong Kong, in the unstained, frozen, hydrated state after quench-freezing in cooled liquid ethane. The results are compared with data from negatively stained specimens. It is shown that cryo-electron microscopy confirms and extends the data obtained by conventional methods. In particular, the virus is shown to be circular in projection with no indication of icosahedral symmetry, the lipid membrane is clearly resolved as a bi-layer and it is demonstrated that the distribution of material within the bi-layer is non-uniform, with a shell of more electron dense material surrounding a less dense central region. Neuraminidase spikes are not clearly distinguished from haemaglutinin spikes. The diameter of the complete B/Hong Kong virus was estimated from cryo-micrographs as 1270(+/- 70) A. Some preliminary data for influenza virus type A/X31 are presented.