Correlation Between Infectivity and Physical Virus Particles in Human Cytomegalovirus

Abstract

Infectivity titers [measured as plaque-forming units (PFU)] and particle counts by the sedimentation pseudoreplication technique were determined for crude, unpurified, intracellular preparations of two different strains of human cytomegalovirus. Unlike the high particleinfectivity ratio of 106 to 108 previously reported for these viruses, the number of total particles per PFU ranged from 160 to 490 with strain AD-169 and from 176 to 1,050 for strain C-87. Interpretation of particle-PFU ratios of intracellular cytomegalovirus in terms of particle morphology is not conclusive at this time. The number of enveloped forms found varied between 0 and 34% of the total particles counted. However, the true proportion is probably greater, because envelopes were found to be destroyed by the enzyme treatment used in preparing the specimens for examination in the electron microscope. The number of full particles found ranged between 4 and 31% of the total particles counted. The particle per PFU ratio of extracellular virus was found to be threeto fivefold lower than that of intracellular virus.

Human cytomegalovirus final envelopment on membranes containing bothtrans-Golgi network and endosomal markers

“…In this line, we cannot rule out that the lack of staining of some viral particles with anti‐HCMV gH antibodies may be due to inaccessibility by antibodies or gold particles, or that some virions fail to incorporate HCMV gH and the normal complement of viral envelope glycoproteins into their membrane, resulting in non‐infectious viral particles. In support of this notion, it has been shown that the ratio of viral particles to infectious virus is unusually high for HCMV (Benyesh‐Melnick et al. , 1966).…”

Indirect Hemagglutination Test for Detection of Antibodies to Cytomegalovirus

“…We are investigating preliminary evidence which suggests that the CMV antigen sensitizing the sheep erythrocyte is a soluble antigen, whereas the antigen reacting in the CF test is a combination of both viral and soluble components (1). Different sera should contain different proportions of antibody to the viral and soluble antigens.…”

Neutralizing Antibodies to Cytomegaloviruses in Normal Simian and Human Sera

“…All four viruses were kept in passage in HEL fibroblasts as described elsewhere (4,11). Cellfree virus stocks were prepared as described previously (1,4,11) and kept at -90 C in the presence of 35% sorbitol (11). Virus infectivity was determined by the modified microplaque technique (11).…”