Magor-Lecture 4: HIV Flashcards
Pneumocystis pneumonia
- opportunistic pathogen
- not gonna affect someone with a normal immune system
HIV/AIDS
- presented as collection of weird diseases
- presented as Kaposi’s sarcoma- also opportunistic infection (not gonna affect somebody with a normal immune system)
- they also noticed that this disease caused sever immunosuppression
- still one of the biggest plague in history (25-35M infected)
Adult prevalence of HIV
30%
HIV is transmitted in:
infected blood and bodily fluid
In central Africa, HIV is commonly transmitted in
mother-baby
In the world, a large part of HIV transmission is through ________
IN the US & Canada, most people infected are _________ and through _____________
heterosexual sex
homosexual sex and intravenous drug use
HIV virus is mostly found in _______ and _______
plasma and WBCs
First 2-6 weeks of infection of HIV
flu-like disease (sometimes)
After 6 weeks of HIV infection, _________ phase begin
asymptomatic
Seroconversion
- 6 weeks after HIV infection
- there is detectable antibodies of HIV in the blood of that person
What happens once the number of CD4 T cells drop below 500 T cells/ µL?
you start to see the symptoms of those opportunistic infection that are characteristic of HIV/AIDS (symptomatic phase)
As it continues to go lower, (<200)= AIDS
The surface of HIV carries envelope __________.
Each capsid carries two _______and _______________ (the enzyme that copies RNA into DNA
glycoproteins
RNAs and reverse transcriptase
Why does HIV package reverse transcriptase in capsid?
- so that it’s ready to go once it enters the cell
- important immune evasion strategy
What are the two surface proteins of HIV virion
gp120 (doesn’t go through the membrane)
gp41 (does go through the membrane)
What does the HIV virion use to synthesize itself?
The virus pathogens and a couple of copies of its RNA
What does the HIV virion needs when it enters the cell?
Reverse transcriptase and integrase
HIV undergoes fusion at the ___________
cell membrane
Where does HIV bind to on the T cell?
The virus attaches to CD4 and a chemokine coreceptor and enters right at the surface of the membrane.
Usually, how many retrovirus can infect a cell?
only one
Can you force more than one retrovirus into the cell? And what happens?
Yes, you can force more than one retrovirus and it usually kills the cell.
Structure of HIV-1 envelope glycoprotein
- each spike contains 3 copies of the surface proteins (gp120 & gp41)
- variable regions
- conserved regions
- huge branched glycosylation
Variable region
- obscure the conserved region, hiding them from our immune system.
gp41 contains the most important part of the surface protein which is the ____________
fusagen or fusion peptide (completely hidden from our immune system
People with a mutation in CCR5
They are resistant to infection
That showed up in a cohort of sex trade workers in Amsterdam. There were people repeatedly exposed to HIV but not infected.
What cell types are infected by HIV?
- HIV infects cells that have CD4 and chemokine receptor in a conserved way
- Dendritic cells and macrophages =are probably the cells that first encounter HIV in mucosal tissues where the virus enters.
How did Dr. Gero Hutter cure Timothy Ray Brown’s HIV?
through a bone marrow transplant.
Timothy Ray had leukemia and Dr. Gero Hutter cured it with bone marrow transplant and had an idea to cure his HIV with it too.
But it is not a way to cure everybody with HIV
CRISPR-Cas genome editing tool
provides a new means to target HIV DNA.
They aim to develop a robust and safe combinatorial CRISPR-Cas regimen, striving for an inclusive ‘HIV cure for all’ that can inactivate diverse HIV strains across various cellular contexts.
Cxcr4
This is an alternate chemokine receptor that HIV can use to enter the target cell
located on CD4 T cells
Explain how HIV binds and enters the target cell
- HIV gp120 binds to CD4
- This causes conformational change that exposes the CCR5 receptor binding site
- The binding to the co-receptor induces a second conformational change exposing the fusion peptide
- Fusion peptide enters the membrane
- Once the virus enters, reverse transcriptase copies the ssRNA into dsDNA
- Integrase inserts DNA into genome of the cell that it infects.
What is the point of making 2 contacts and having 2 conformational changes?
It hides the parts of protein that are really important
Why is it so difficult to get the HIV virus out of the cell?
Because it’s not just hanging out anywhere in the cell. It’s actually right in the genome.
Reverse transcriptase
RNA to DNA
3 enzymatic activities of reverse transcriptase
- Reverse transcriptase activity- you have to have a primer to initiate any nucleotide synthesis.
- RNase H activity- of that same reverse transcriptase will cleave out this RNA (chop in off into bits)
- DNA polymerase activity- synthesizing DNA in this direction
What does HIV use that serves as primer for first strand?
tRNA - it initiates reverse transcriptase synthesis
Polypurine tracts (PPTs)
serve as primer for second strand
_____________ is error prone
Reverse transcriptase
HIV reverse transcriptase
- it’s gonna keep going forward regardless of the mistakes
- there are a number of diff. mistakes that happen when you’re making DNA and our polymerase would chew back and delete those mistakes but HIV doesn’t.
- HIV will make 1 mistake for every 1,000 bp of sequence that it makes, which is a really high mutation rate. It’s about 5 kb long so it will make an average of 5 mistakes.
What needs to be done in order for HIV to replicate?
cells infected with HIV must be activated
NFkB
- transcription factor at the bottom of the toll signaling pathway.
- lots of things in the immune response are turned on by NFkB
- in those cells where NFkB is expressed, and it can be in the cell that’s actually actively responding to HIV, it will turn on that NFkB and start making copies of that virus & then make the proteins and assemble the virions at the surface and they bud out through the surface taking the surface membrane proteins as well.
The assembly of new viral genomes is kind of directional. What does this mean?
The virus is actually dumping virions out of the cell.
The infected T cell (dumping virions out of the cell) will be a cytotoxic T cell target and that’s how you eliminate the infected T cells from the body & this will happen over & over again.
HIV-1
- most common type of HIV
- 1x10^10 virions made/day
- 240 infectious cycles/year
- 1 mutation on average at every position of the genome everyday.
- every possible mutation at every position in the genome is predicted to occur numerous times a day
- 4x10^7 CD4+ T cells/day replaced but then over time this can’t be replaced.
- 75,000 HIV + individuals in Canada
- 5000 HIV + individuals in Alberta
Biggest problem in HIV
immunocompromised people
What happened in the early 2000s (HIV related)
mutations happened that made HIV more virulent
What are they testing in HIV tests
They are testing for the antibodies of HIV, not the presence of HIV
