MORPHOLOGICAL AND CYTOCHEMICAL ANALYSIS OF HUMAN CYTOMEGALOVIRUS INOCULUM - CORRELATION OF FREE PARTICLES IN INOCULUM WITH COUNTERPARTS IN INFECTED-CELLS

Electron microscopic examination of human cytomegalovirus (HCMV) inocu lum, as used in the laboratory and generated by infection of human fib roblasts at low multiplicity, led to the distinction of 7 different st ructures. Complete virions constituted 38 % of the inoculum. Non-infec tious enveloped particles (NIEP) were also quite numerous (4.7 %). Ino culum also contained other enveloped and non-enveloped particles. Dens e bodies were the most numerous (50.2 %). The Feulgen-like osmium ammi ne/SO2 reaction applied to ultrathin sections of inoculum suggests tha t NIEP, considered to be lacking DNA, may contain small and varying am ounts of DNA. This DNA was lightly stained and appeared as a filamento us ring in the core structure, extending to the limits of the capsid. A correlation was established between particles identifiable in HCMV-i nfected cells and their free counterparts in the inoculum, which revea led that all intracytoplasmic particles are present in the inoculum. A ll of these elements could potentially contribute to virus-induced phe nomena associated with HCMV infection of cells in vitro.