The relationship between host cells and members of the
Myxovirus group has been reviewed with particular reference
to the growth of these viruses in tissue culture. Virus
multiplication, incomplete virus production and the phenomenon
of interference have also been considered. It became apparent
from the literature that certain members of the group, for
example, Newcastle disease virus (NDV) and influenza, differ
significantly from each other in various growth characteristics.
It was considered advantageous to study further the differences
between these two viruses and their growth characteristics were
therefore investigated in various tissue culture systems.
The experiments were planned to study: -
(a) the cytopathic effect of these viruses on their host
cells and the relationship between this effect and the
production of new virus,
(b) cell survival following infection,
(c) the possibility of incomplete virus formation.
During the course of the study it became possible to investigate
in addition the intracellular development of influenza virus.
(a) Cytopathic effect
The cytopathic effect of NDV in HeLa cells was examined
by ordinary microscopy and by time -lapse cinematography using
interference microscopy. The changes associated with
infection could be divided into three phases, namely the
appearance in the cell monolayer of circular foci of infection
termed "microplaques ", the ensuing formation of syncytial masses
and finally complete cellular degeneration.
The cytopathic effect of influenza virus was studied in
monkey kidney and bovine embryo kidney cells. The changes
differed from those observed with NDV and included vacuolation
and granulation of the cytoplasm and the appearance of intranuclear
vacuoles. Nuclear changes were also observed with the
acridine orange technique; the extent and pattern of these
changes depended on the strain of virus used.
With both viruses, when small inocula were used, the
cytopathic effects were accompanied by an increase in infective
and haemagglutinating virus.
(b) Cell survival following infection
Cells subjected to a large dose of NDV survived better
than cells similarly treated with influenza virus. It is
suggested that this may be due to a difference in toxicity of
the viruses. In further experiments, incomplete influenza
virus, which is known to be less toxic, produced a less
extensive cytopathic effect.
Treatment of the cells with immune serum following
infection with NDV reduced cytopathic changes.
(c) Incomplete virus formation
Although infection of HeLa cells with large inocula of
NDV did not result in the production of detectable infective
virus no evidence for the formation of incomplete virus was
With influenza virus, on the other hand, evidence was
obtained for the production of incomplete virus following
undiluted serial passage in ionkey kidney cells. The phenomenon
was, however, never as striking as that observed in eggs. It
is suggested that this may be due to the lower titres obtained
in tissue cultures.
THE INTRACELLULAR DEVELOPMENT OF INFLUENZA VIRUS
By means of the fluorescent antibody technique using
specific antisera, the S and V antigens of influenza virus
could be detected in bovine embryo kidney cells and in HeLa
cells. The S antigen was first detected in the nucleus whereas
the V antigen appeared slightly later in the cytoplasm. It
seems feasible that in the case of influenza- infected bovine
embryo kidney cells the S and V antigens combine at the surface
of the cell prior to their release as complete virus. With
HeLa cells S and V antigens are produced in the cells but only
incomplete virus is released.
When large inocula were employed, nuclear fluorescence
with S antiserum was never as intense as that observed in cells
infected with a small dose of virus. This indicates that less
S antigen per cell was produced when lame inocula were
employed and suggests the formation of incomplete virus.
On the basis of these findings a hypothesis has been
put forward to explain the formation of incomplete influenza
virus. As this phenomenon is so intimately linked to the
relationship between virus and host cell it is conceivable that
NDV, which has been found to differ from influenza virus in
many growth characteristics, should not be able to induce the
production of incomplete virus.