Study of Host-Virus Relationship. I. Light, Phase, and Fluorescence Microscopy of Mouse-Embryo Cells Infected With Polyoma Virus<xref ref-type="fn" rid="FN1">2</xref>

Abstract

Comparative studies by means of light, phase-contrast, and fluorescence microscopy were carried out on C3H/An/Dm mouse-embryo cell cultures infected with SE polyoma virus. The nature and sequence of changes after infection were studied. As seen by phase microscopy, inclusions appear in the nuclei of the infected cells, 4 to 5 days after infection. One type of inclusion, centrally or eccentrically located, is composed of dense, homogeneous material and is frequently surrounded by a clear zone. The other type of inclusion consists of either dense strands or amorphous, dense, scattered material. Increase and margination of chromatin material are frequently observed. The inclusions increase in size and density before the lysis of cells. Both types of inclusions stain yellow for deoxyribonucleic acid (DNA) with acridine orange fluorescent dye. The staining is not removed by treatment with deoxyribonuclease (DNase) or pepsin. Pretreatment with pepsin, followed by DNase digestion, removes the DNA stain, which indicates the possible viral nature of these inclusions. By the Feulgen method, both types of inclusions at first stain delicate pink and lavender-pink at the height of infection. Feulgen-negative material surrounds the dense areas of type-1 inclusions and is present between the dense strands or amorphous material of type-2 inclusions. During the last stages of infection, inclusions of similar staining properties are found occasionally in the cytoplasm of the infected cells. Electron microscopy of ultrathin sections of similar cells or adjacent thin sections of cells with the two types of intranuclear inclusions has revealed characteristic polyoma-virus particles within these inclusions. The chemical nature of the polyoma virus is discussed in the light of these observations.