Han Xiao PhD thesis - Research@StAndrews:FullText - University of ...

3.1.5 PIV5 could overcome the IFN-induced antiviral state in the presence of
neutralizing antibodies
In the above experiments, it was demonstrated that, in cells in a pre-existing IFN-induced
antiviral state, PIV5 could gradually overcome the inhibitory effects of IFN. There are
two explanations for this. PIV5 could initiate multiple cycles of replication with the
functional attachment and fusion proteins and thus progeny viruses released from cells
that were strongly positive for viral antigens could infect cells that were not strongly
positive for viral antigens, or in cells that NP were seen as cytoplasmic bodies the viral
genome was gradually recovered, and expressed high level of viral antigens. To address
this issue, neutralizing antibody was used to prevent PIV5 virus from initiating multiple
cycles of replication.
Firstly, the ability of neutralizing antibodies against F and HN proteins to prevent
multiple cycles of replication of PIV5 was tested. A549 cells were inoculated at low MOI
(0.1pfu/cell) of PIV5, 3 hours after virus adsoption, the inoculum was removed, cells
were washed twice with PBS and then serum free DMEM was added in the presence
(+antibody) or absence (-antibody) of neutralizing antibody. Cells were fixed at different
times p.i. and stained with anti-NP/P antibodies (Fig. 3.6). In the absence of neutralizing
antibody, only a few cells were positive for viral antigens at early times post infection (16
h; p.i; Panel A), but the virus managed to spread to neighboring cells, and by 48 hrs p.i,
all the cells were positive for viral antigens (Panel C). In contrast, in the presence of
neutralizing antibody, the virus was unable to undergo multiple cycles of replication, and
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