Diagnostic Virology Flashcards
Within the HTLV-1 virus particle, in which form is the genetic material?
ssDNA
What type of cell does HTLV-1 preferentially infect?
T cells
How does HTLV-1 replicate?
HTLV-1 can integrate within the chromosome of infected cells and replicate as dsDNA as part of the host cell division process
What are 3 possible routes to become infected with HTLV-1 ?
Blood transfusion
From mother to infant by breast feeding
Sexual Contact
What diseases can be caused by HTLV-1?
HTLV-1-associated myelopathy
Leukaemia
What are PCR methods used o detect HTLV-1 based on?
The presence of the tax gene
What are the three steps of the western blot method
- Separation
- Transfer
- Staining
What does the western blot method look for?
Presence of antibodies specific to the virus
Describe the separation stage of the western blot procedure?
Viral proteins separated based on size on plyacrylamide protein gel
Which proteins will migrate fastest on the polyacrylamide gel of the western blot?
The smaller proteins
What happens to the western blot after the viral proteins are separated by size and have formed bands?
Incubated with human serum - if the human serum contains antibodies it will bind to the viral proteins
What happens in the staining phase of the western blot method?
Secondary antibodies which have an enzyme attached are added - they bind to the Fc region of the already bound antibodies
Then substrate is added which reacts with the enzyme to produce a signal
What must be detected for a positive result for HTLV-1?
MTA1 p53 p24 p19 gd21
What are the five components of PCR based analysis?
- Buffer
- Nucleotides - dNTPs
- DNA POlymerases
- Primers
- DNA Template
What is the purpose of the buffer in PCR?
Provides an appropriate pH for reactions to occur / polymerase to work
What are the three steps of PCR?
- Denature
- Anneal
- Elongate
What temperature does denaturation occur at?
90 degrees - breaks H bonds between double-stranded DNA
What must the primer have?
A free hydroxyl group
What is the temperature at which annealing takes place?
50 degrees
What temperature does elongation occu at?
73-75 degrees
Allows Polymerase to work
What DNA is used for PCR analysis?
PBMC - peripheral blood mononuclear cells = mixture of T cells B cell and NK cells
What type of genetic material can by amplified by a standard PCR
dsDNA
ssDNA
HTLV-1 has a single strand RNA genome, but a standard PCR can still be used for diagnosis. What is the reason for this?
During virus replication, viral RNA is reverse transcribed to ssDNA and converted to dsDNA that integrates into the host-cell genome. Viral infection can thus be determined by standard PCR using host cell DNA as template
What 5 key components must be included in a PCR
mix
DNA Template Primers Pair Taq Polymerase reaction Buffer Deoxynucleotides
How many grams of agarose do you need to make 50 ml of a 1% (weight/volume) agarose gel solution?
0.5
How do you estimate the size of your PCR product on the agarose gel?
Run a DNA ladder alongside your PCR reactions
What is the purpose of adding a loading buffer with dye to the PCR sample before loading on an agarose gel?1.
- Makes samples sink into wells
- Visualise how far the gel has migrated
- Visualise which wells contain samples
What is the purpose of adding a loading buffer with dye to the PCR sample before loading on an agarose gel?1.
- Makes samples sink into wells
- Visualise how far the gel has migrated
- Visualise which wells contain samples
What is the typical number of repeat cycles for the three steps in a CR reaction?
30-40
What type of nucleic acid genetic material do SARS-CoV-2 virus particles contain?
ssRNA
What two types of primers are added to PCR and during what step?
During annealing step, forward and reverse primers are needed
What is assumed about the disease severity of HTLV-1?
Assumed that the number of T cells containing HTLV-1 correlate with the disease severity and also the likelihood of transmitting the virus
How long does the denaturation stage of PCR last?
1 minute
How long does the annealing stage of PCR last?
45 seconds
How long does the elongation stage of PCR last?
2 minutes
What is added during the extension stage of PCR?
deoxynucleotides - dNTPs
What is added to Quantative Real Time PCR that is not found in in normal PCR?
TaqMan Probe
What extra information for qRT-PCR provide over normal PCR?
Provides information on the amount of viral DNA present in a sample and therefore helps predict the severity of disease
What does the TaqMan probe in qRT-PCR Bind to?
Binds to only the gene being amplified, in between the forward primer and reverse primer
What does the TaqMan Probe have attached to it?
A fluorophore and a quencher
What happens in qRT-PCR when the quencher and fluorophore get separated?
Probe degrades and becomes fluorescent
How does the fluorescence relate to the DNA amplified?
They are proportional - the more fluorescence produced, the more DNA that was amplified
How does qRT-PCR provide information on the quantity of viral load?
The fewer PCR cycles that are needed in order to reach the threshold of fluorescence (which is proportional to the amount of DNA amplified hence more viral load) indicates a higher viral load
What is the relationship between CT Values and tax gene copy number?
CT Values are linear with the Log10 of tax gene copy number