Morphological and cytochemical analysis of human cytomegalovirus inoculum: correlation of free particles in inoculum with counterparts in infected cells

Abstract

Electron microscopic examination of human cytomegalovirus (HCMV) inoculum, as used in the laboratory and generated by infection of human fibroblasts at low multiplicity, led to the distinction of 7 different structures. Complete virions constituted 38% of the inoculum. Non-infectious enveloped particles (NIEP) were also quite numerous (4.7%). Inoculum also contained other enveloped and non-enveloped particles. Dense bodies were the most numerous (50.2%). The Feulgen-like osmium ammine/SO2 reaction applied to ultrathin sections of inoculum suggests that NIEP, considered to be lacking DNA, may contain small and varying amounts of DNA. This DNA was lightly stained and appeared as a filamentous ring in the core structure, extending to the limits of the capsid. A correlation was established between particles identifiable in HCMV-infected cells and their free counterparts in the inoculum, which revealed that all intracytoplasmic particles are present in the inoculum. All of these elements could potentially contribute to virus-induced phenomena associated with HCMV infection of cells in vitro.