Structure and Development of Viruses as Observed in the Electron Microscope

Abstract

The mode of development of herpes simplex virus has been the object of periodic study ever since Lipschiit2, (1) discovered that intranuclear inclusion bodies characteristically appear in the cells of tissues infected by this agent. Interest has centered chiefly on attempts to determine the nature of the nuclear changes but the results have not been concordant. Some observers have concluded that the inclusions actually represent a stage in viral multiplication and are composed at least in part of viral material. Others have inferred that they consist solely of abnormal products of cellular metabolism. The earlier work bearing on this subject has been well reviewed by Van Rooyen and Rhodes (2). More recently, Crouse et al. (3) carried out histocbemical studies which revealed a distinct accumulation of desoxyribese nucleoprotein in early nuclear inclusions. This work was confirmed by Wolman and Behar (4) who considered the findings to be corroborative of the hypothesis that the herpetic inclusion body represents a colony of virus inside a cellular matrix. Scott el al. (5) have extended these observations by a careful study wherein the development of infectious virus was followed in temporal relation to the cytologic changes. These authors concluded that the nucleus probably contains virus during the early formation of the inclusion body. In contrast, Francis and Kurtz (6) and Ackermann and Kurtz (7) reported data on the infectivity of cellular fractions obtained by differential centrifugation which they interpreted as indicating that herpes simplex virus is not associated with the nucleus.A more direct approach to this problem can be made by examining infected tissues in the electron microscope. Morgan et al. (8) have previously reported that altered nuclei could easily be identified by means of the electron micro-* This investigation was supported by grants from

Ultrastructural Analysis of Pseudorabies Virus Infection in IB-RS-2 Cell Line and with Treatment by Persea americana Extract

“…In the first few minutes of infection, virions are already found inside the cells. Morgan and Howe (1968) have also observed adsorption and penetration of the Sendai virus into the cells at 5 min of inoculation. Soon after the adsorption, the virions underwent various types of changes such as the fusion of the viral envelope in the cellular membrane, dissolution of the capsid and the consequent release of the viral core in the cytoplasm.…”

Electron Microscopic Studies of Tumor Viruses

“…A variety of stages in the process of interaction was most commonly encountered in samples taken at 30-60 min after warming the cells to 37 C, an observation also reported in studies of MuLV entry (10). This would suggest that entry occurs more slowly and less synchronously than with other ether sensitive enveloped viruses (7,11,12). The observed dissolution of the viral envelope and cell membrane could be due to the action of an enzyme (10).…”

“…It appears likely that enveloped viruses differ in the mechanism by which they gain entry, as well as their ability to cause cell fusion at early stages of infection. In contrast to the P3HR-1 strain of EBV and MuLV, fusion of the viral envelope with the cell membrane has been observed during the entry process of some enveloped viruses, such as HSV (11,14), Sendai virus (12), and vesicular stomatitis virus (7). Nii et al (18) and Morgan and Howe (12) have suggested that this entry mechanism may play a role in the process whereby cell-cell fusion occurs at early stages of infection.…”

“…Three modes of entry have been proposed; 1. viropexis (6) or pinocytotic engulfment (2), 2. direct penetration (15), and 3. fusion of ether soluble lipoprotein enveloped viruses with the cell membrane (12)(13)(14). It has been suggested that in the latter instance the process of membrane fusion is closely similar to that associated with cell fusion at early stages of infection (12,18). In the case of murine leukemia virus (MuLV), which though enveloped does not produce cell fusion, direct penetration appears to be the mode of entry (10).…”

An electron microscope study of molluscum contagiosum

“…10, fig. 5, of the paper by Morgan et al (1954a). A quarter of the capsule wall has been removed showing the enclosed central body which is rather denser than the peripheral viroplasm.…”