simplex virus type 1 (HSV-1) is a virus people get when they are young. A type
of HSV, Varicella-zoster virus (VZV), is known as chickenpox. These viruses are
both a primary infection that will get into the body at a lesion where it gains
access to neurons and transported from there. HSV-1 is latent but when activated
sores around the mouth occur. VZV is rarer but when activated in children it
creates itchy spots. The elder have a 25% chance of getting VZV in a rash form
(Kennedy et al., 2015). There are
more experiments studied on the latency of HSV-1 than on VZV in humans. For
VZV, infections are expressed by open reading frames (ORF). There are multiple
ORF that are consistent for being involved how VZV is reactivated throughout a
Varicella-zoster virus (VZV) infects and creates latency in neuron and human
ganglia cells. In human ganglia cells, VZV has been latent in around 87% of
ganglia cells (Kennedy and Cohrs, 2010). Multiple experiments show VZV almost
exclusive in neurons rather than non-neuronal cells. In a human, there can be
VZV and HSV both latent in the same ganglion and cell (Kennedy and Cohrs, 2010).
Multiple experiments showed both latencies in the ganglia.
help find out, people used Northern blot hybridization because it can detect
DNA in the ganglia. There are 68 different ORF in a ganglion. In those 68, the
latency gene expression can be found on ORF4, 62, 63, and 66 for VZV. People
consider ORF63 the hallmark of VZV latency by confirming subsequent study with
high abundance of ORF63 transcripts in VZV latency (Kennedy and Cohrs, 2010). Researchers
looked more into ORF4 and ORF62 encoding proteins that will help VZV to infect
encoding protein normally acts as an activator for promoters on ICP27 homolog (Schoonbroodt
et al., 1996). ORF62 is known as the
major regulatory protein that can transactivate immediate-early and early gene
promotors (Schoonbroodt et al., 1996).
These two ORFs will help with the enhancement of VZV reactivation life cycle. The
ORF4 and 62 were tested in Vero cells; cell cultures that are made up of linage
of cells. Out of these type of test, they found that the ORF4 and ORF62 had a
10% positive outcome of immunofluorescence for detection (Schoonbroodt et al., 1996). Under same conditions except
VZV gE promoters were used, neither of the two ORFs showed transactivating
activities (Schoonbroodt et al., 1996).
In the nucleus of infected VZV cells, ORF62 was detected by indirect
immunofluorescence which helped promote ORF 61.
researchers considered ORF63 and 31 in VZV DNA to see if this will help
discover the mystery of how VZV can reactivate. They used Taqman digital qPCR
that uses different well plates and takes couple of weeks. Observing the well
plates, researchers found that ORF63 and 31 had low levels in the negative
wells and had triple the magnitude in the positive wells (Markus et al., 2015). This explains that
transcription isn’t only in the IE but also in late genes that are expressed in
neurons. The same researchers did tests the on levels of nucleic acids in a GF withdrawing
treatment. They found that after a couple of weeks that there was an increase
in viral DNA and transcripts from ORF63 and 31. After looking at these types of
ORFs they saw that the protein expression was created by immunocytochemistry in
infected neuron cells.
stated earlier, ORF63 is the most abundant that is expressed in the latency of
VZV. Some researchers have also found a deletion of around 90% of ORF63 by
showing there has to be protein to efficiently establish latency (Cohen et al., 2005). This protein, ORF63, is
so abundant because it is found predominantly in the nucleus when the lytic
cycle for replication has occurred and in the plasmid of already infected cells
(Cohen et al., 2005). Researchers
were looking more in-depth at ORF63 in VZV infected cells and saw that
phosphorylation can occur and changes in amino acids. After further
experiments, adding a phosphate group to the VZV showed that this could stop or
damage the growth. The mutations with phosphorylating the VZV did not work on
the nuclear location site but did influence latency (Cohen et al., 2005). With ORF63 they wanted to change something with the
carboxy-terminal 70 amino acids. After a couple of months, they found that the
carboxy-terminal 70 amino acids can replicate and have latency.
reading all the articles about VZV latency and reactivation, most of the
research has been experimented on ORFs. There is a total of 68 ORFs that have
been detected but only a couple have been researched. The most abundant ORF is
63 and is found in the nucleus. Most ORFs are promoters for others. VZV can now
be a virus that is spread by direct cell to cell contact and no infectious VZV
particles are released in the cell culture (Schoonbroodt et al., 1996). This can be explained by having positive testing on
immunofluorescence detection on neighboring cells. It also helps to use human
ganglia because VZV latency can be studied in native environments and helps
with ORFs on virus genome that have been stabilized for years. After multiple
experiments from different researchers they see that VZV ORF63 can be deleted.
This can have a future impact on the mystery of reactivation. In conclusion,
researchers still haven’t come up with a reasonable description on how the VZV
from HSV-1 can reactivate from its latency. Hopefully with future experiments
new findings can be discovered connecting all the pieces together.
reading about the research that has been done there has to be more to find. The
research I would continue to look at more is the ORFs. They have so many
different amino acids on them that express proteins to the human body. The test
would be to phosphorylate not only ORF63 but a couple of other ORFs like 4, 31,
62 together. This could change expression that can change the latency. The test
will be conducted first on animals then humans that are infected with VZV. The
infected specimens would be saliva or neuron cells. The specimens will use
laboratory techniques by PCR, Northern Blotting, Southern Blotting and
immunofluorescence to figure out the mystery.