Remarks on the Ultrastructure of Type A, B, and C Virus Particles

Abstract

Publisher Summary The scope of this chapter is limited to the recent findings concerning the ultrastructure of murine RNA tumor viruses, as they appear after various preparatory procedures under the electron microscope and to some implications of these observations in the continuing search for viruses of this type in human malignancies. Here attention is focused mainly on the literature that has appeared since 1968. The title of this chapter is in direct reference to the ultrastructural classification of the murine tumor viruses originally proposed by Bernhard and Guerin in 1958. The original classification contained some ambiguity in regard to the presence or absence of viral envelopes, Type A particles were originally described as having an electron-lucent center (the “doughnut-shaped” nucleoid), and as being located either within the cytoplasm (“intracellulaire”) or within the extracellular spaces (“inter-cellulaire”). When the budding process of these viruses was described, it became clear that the cytoplasmic and extracellular type A particles differ mainly by the acquisition of an envelope derived from the plasmalemma of the infected cell. Therefore, calling type A particles before or after budding by the same name would amount to ignoring an important step in the final assembly of the virus. To distinguish between the type A particles with or without an envelope, and at the same time to respect the original terminology of Bernhard and Guerin, it was later proposed to call the first “enveloped” A particles and the second “naked” A particles. It appears therefore that, in view of the uncertainties that persist on the identification of the RNA tumor viruses in human neoplasia, the results obtained by electron microscopy, which can often provide undisputed evidence for the presence of such agents, should be reviewed and the values of different preparatory procedures reevaluated.