The herpessimplex virus type 1 (HSV-1) is a virus people get when they are young. A typeof HSV, Varicella-zoster virus (VZV), is known as chickenpox. These viruses areboth a primary infection that will get into the body at a lesion where it gainsaccess to neurons and transported from there.
HSV-1 is latent but when activatedsores around the mouth occur. VZV is rarer but when activated in children itcreates itchy spots. The elder have a 25% chance of getting VZV in a rash form(Kennedy et al., 2015).
There aremore experiments studied on the latency of HSV-1 than on VZV in humans. ForVZV, infections are expressed by open reading frames (ORF). There are multipleORF that are consistent for being involved how VZV is reactivated throughout alifetime. Summary TheVaricella-zoster virus (VZV) infects and creates latency in neuron and humanganglia cells. In human ganglia cells, VZV has been latent in around 87% ofganglia cells (Kennedy and Cohrs, 2010). Multiple experiments show VZV almostexclusive in neurons rather than non-neuronal cells.
In a human, there can beVZV and HSV both latent in the same ganglion and cell (Kennedy and Cohrs, 2010).Multiple experiments showed both latencies in the ganglia. Tohelp find out, people used Northern blot hybridization because it can detectDNA in the ganglia. There are 68 different ORF in a ganglion. In those 68, thelatency gene expression can be found on ORF4, 62, 63, and 66 for VZV.
Peopleconsider ORF63 the hallmark of VZV latency by confirming subsequent study withhigh abundance of ORF63 transcripts in VZV latency (Kennedy and Cohrs, 2010). Researcherslooked more into ORF4 and ORF62 encoding proteins that will help VZV to infectcell lines. ORF4encoding protein normally acts as an activator for promoters on ICP27 homolog (Schoonbroodtet al.
, 1996). ORF62 is known as themajor regulatory protein that can transactivate immediate-early and early genepromotors (Schoonbroodt et al., 1996).These two ORFs will help with the enhancement of VZV reactivation life cycle.
TheORF4 and 62 were tested in Vero cells; cell cultures that are made up of linageof cells. Out of these type of test, they found that the ORF4 and ORF62 had a10% positive outcome of immunofluorescence for detection (Schoonbroodt et al., 1996). Under same conditions exceptVZV gE promoters were used, neither of the two ORFs showed transactivatingactivities (Schoonbroodt et al., 1996).In the nucleus of infected VZV cells, ORF62 was detected by indirectimmunofluorescence which helped promote ORF 61. Otherresearchers considered ORF63 and 31 in VZV DNA to see if this will helpdiscover the mystery of how VZV can reactivate.
They used Taqman digital qPCRthat uses different well plates and takes couple of weeks. Observing the wellplates, researchers found that ORF63 and 31 had low levels in the negativewells and had triple the magnitude in the positive wells (Markus et al., 2015).
This explains thattranscription isn’t only in the IE but also in late genes that are expressed inneurons. The same researchers did tests the on levels of nucleic acids in a GF withdrawingtreatment. They found that after a couple of weeks that there was an increasein viral DNA and transcripts from ORF63 and 31. After looking at these types ofORFs they saw that the protein expression was created by immunocytochemistry ininfected neuron cells. Asstated earlier, ORF63 is the most abundant that is expressed in the latency ofVZV. Some researchers have also found a deletion of around 90% of ORF63 byshowing there has to be protein to efficiently establish latency (Cohen et al., 2005).
This protein, ORF63, isso abundant because it is found predominantly in the nucleus when the lyticcycle for replication has occurred and in the plasmid of already infected cells(Cohen et al., 2005). Researcherswere looking more in-depth at ORF63 in VZV infected cells and saw thatphosphorylation can occur and changes in amino acids.
After furtherexperiments, adding a phosphate group to the VZV showed that this could stop ordamage the growth. The mutations with phosphorylating the VZV did not work onthe nuclear location site but did influence latency (Cohen et al., 2005). With ORF63 they wanted to change something with thecarboxy-terminal 70 amino acids.
After a couple of months, they found that thecarboxy-terminal 70 amino acids can replicate and have latency.Conclusion Afterreading all the articles about VZV latency and reactivation, most of theresearch has been experimented on ORFs. There is a total of 68 ORFs that havebeen detected but only a couple have been researched. The most abundant ORF is63 and is found in the nucleus. Most ORFs are promoters for others.
VZV can nowbe a virus that is spread by direct cell to cell contact and no infectious VZVparticles are released in the cell culture (Schoonbroodt et al., 1996). This can be explained by having positive testing onimmunofluorescence detection on neighboring cells.
It also helps to use humanganglia because VZV latency can be studied in native environments and helpswith ORFs on virus genome that have been stabilized for years. After multipleexperiments 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 VZVfrom HSV-1 can reactivate from its latency.
Hopefully with future experimentsnew findings can be discovered connecting all the pieces together.Future Direction Afterreading about the research that has been done there has to be more to find. Theresearch I would continue to look at more is the ORFs. They have so manydifferent amino acids on them that express proteins to the human body. The testwould 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 testwill be conducted first on animals then humans that are infected with VZV.
Theinfected specimens would be saliva or neuron cells. The specimens will uselaboratory techniques by PCR, Northern Blotting, Southern Blotting andimmunofluorescence to figure out the mystery.