HIV Part 2 Flashcards
1
Q
Histological examination of lymph nodes show?
A
Influx of CD8 T cells
2
Q
How does HIV exploit dentritic surveillance network?
A
- Hitches ride to lymph nodes, before trasfer to CD4 T cell
- Via Sialyllactose head on GM3 ganglioside (glycosphingolipid)
- On HIV membrane
- Recognised by dentritic cell
- Taken in
3
Q
Sialylactose head on GM3 ganglioside
A
- Sialyated head
- On lactose (galactose+Glucose)
4
Q
Consequence of loss of Th activity
A
mount a delayed-type hypersensitivity reaction
5
Q
HIV infected dendritic schematic diagram
A
- HIV entering vagina -> unprotected sex
- Crossing epithelial layer
- Submucosal epithelium =encounter immature dentric cell
- Lectin (dentric cell) attachment to GM3 ganglioside on HIV virus
- Movement to lymph node
- Dentric cell mature in lymph node, enter germinal centre and pass HIV -> CD4+ T cells
- How? filopodia (actin rearrangement)
6
Q
Antibody abnormalities in HIV positive patients
A
- High increase of antibodies (Ig)
- Production of autoantibodies
- Affecting RBC, sperm cells and myelin sheeth in neurons
7
Q
Define viraemia
A
High levels of viral particles in bloodstream after infection due to rapid phase of viral replication
8
Q
What is the initial immune response to HIV?
A
- Recognise gp120,p24 (nucleocapsid) and pO1(reverse transcriptase proteins)
- Mount a resonse: Increase number of CD8+ cytotoxic T cells and antibody
- Combined-> 99% clearance
- Virus enters latent/dormant stage
- Persist -> chronic infections
- Challenge: manage and treatment against HIV
9
Q
Immune response
Lower viraemia suggests?
A
Slower progression to AIDs compared to higher viraemia
10
Q
Immune response
What did advanced methods of viral RNA detection in latent phase indicate?
A
- Active replication present even in latent phase
- > Persistent level of active viral replication
- > Viraemia
- Concentrated in lymph nodes
- Physically- structural abnormalities
- Worsening as disease progressed
11
Q
Immune response
Whats the importance of treatment?
A
- Drug -> block new infections
- clears 30% viral load/day
- Without drug
- > Rapid rate of viral replication, easily replace the cleared viral load
- 2 billion CD4 T cell eliminated and replaced by immune system
- > gradual decline of CD4 T cells
12
Q
The traditional concept of the latent stage of HIV infection as a period of relative quiescence is now being redefined to what?
A
- Dynamic phase
- Intense viral replication and destruction
- Continueous of cycle of CD4 T cells being lost and replenishes
13
Q
What is latent phase indicative of?
A
- Immune activity
- Viral acitivity
- Even if infection seems less active on surface
14
Q
Why does the immune system not completely clear the virus?
A
- High replication rate- overwhems immune system
- Proviral Latency- unable to detect and recognise by immune system
- Mutation rate- changes its antigen to not match CD8+ t cells and antibodies
15
Q
Whats the dual mechanism that results in the loss of CD4 T cells?
A
- Direct killing by the virus
- Immune system-mediated destruction
- Vulnerable to recognition and attack by immune system
16
Q
Explain direct killing by the virus
A
- HIV replicated
- > damage to cell
- Reduce CD4 overtime
17
Q
Explain Immune system-mediated destruction?
A
- Infected CD4 display viral antigens
Viral Antigens
* Viral peptides presented by MHC I molecules
* soluble gp120 bound to CD4 T cell
- Viral antigens recognised by CD8+ cytotoxic killer T cells
- Killing infected CD4+
18
Q
What is present in the blood and lymph of HIV positive patients?
A
Soluble gp120
Binds to CD4 T cell
19
Q
Potential exam diagram question
Killing Mechanism of CD4 T cells diagram
A
Killing of CD4 T cells.
(a) HIV may directly causelysis of CD4 T cells.
(b), (c) Infected cells bearing HIV antigens may be killed by antibody and complement (b) or killed by **antibody-dependent cell-mediated cytoxicity **(ADCC) (c).
(d) HIV-infected cells presenting HIV peptides on their class I MHC molecules may be killed by CD8 T cells.
21
Q
CD4 T cell killing mechanism
Antibody+complement
A
- Antibody- anti-gp120
- Bind to gp120 on CD4+
- > complement fixation
- > cascade of events -> pores -> cell-lysis
21
Q
CD4 T Cell killing mechanism
Antibody-dependent cell-mediated cytotoxicity
A
- Macrophages and Natural Killer cells have Fc receptors
- Anti-gp120 antibody has Fc portion
- Anti-gp120 bound to infected CD4
- Macrophage
- > binds to Fc portion -> phagoctosis
- Natural Killer Cells (NK)
- > induced direct death
22
Q
CD4 T cell killing mechanism
CD8 cytotoxic T cells
A
- Role is to eliminate intracellar pathogens -> virus
- viral antigenic peptides presented by MCH I molecules from infected CD4 cells
- CD8+ bind to viral antigenic peptides
- Activates CD8+
- Releases chemicals to mediate killing action
- > Perforin
- > Granzymes
23
Q
What are 2 cell death killing mechanism of CD4 T cells?
A
- Apoptosis- programmed cell death
- > controlled, non-inflammatory
- Pyroptosis - highly inflammatory form of programmed cell death
24
Q
Apoptosis
A
- Permissible T cell- completed viral cycle
- Mediated by caspase-3
25
Pyroptosis
* Caspase-1
* Release of cytokines and pro-inflammatory molecules
* Non-permissible T cell- incomplete viral cycle
* >build of HIV incomplete transcripts due to incomplete reverse transcription
26
In which tissue is CD4 cell death found in?
* Lymphoid tissue
* Result of pyroptosis
* >weakens immune system
* contributes to disease progression
27
Which drug targets caspase 1 and pyroptosis of lymphoid CD4 T-cells
Drug- **VX-765** in lymphoid tissues
* Inhibits activation of caspase-1 enzyme
* main enzyme thay mediates pyroptosis
Benefits
* Preserve CD4 cells
* Reduce inflammation
28
Pyroptosis CD4 T Cell Location:Lymphoid derived
**AIDs**
* Correlated to depletion of CD4 T cells
* Prominent in lymphoid tissues
* Result from Pyroptosis
* >**Abortive viral infection**
* >>Incomplete viral replication
* >>Viral transcripts accumulated
* >>sensed by IFI16 sensors
* >>>triggers assembly of inflammasomes, activate caspase-1 >>**Pyroptosis**
29
Pyroptosis CD4 T Cell Location:**Peripheral blood derived CD4 T cell**
* Resist pyroptosis to certain extent
* why->deeper resting state
* fewer viral transcripts
* fewer expression of IFI16 sensor
30
Sensitisation of blood derived CD4 T cells to pyroptosis
* co-culture with lymphoid derived CD4 T cell
* sensitised to pyroptosis
* high Nf-kb
* high IFI16 expression
* High reverse transcription
31
Diagram of Pyroptosis CD4 T cell location
32
Why is combination drug therapy is important?
* Less chance of virus mutating to become resistant to 3 drugs at once
33
# Antiretroviral Drugs (ARVs)
Nucleoside analogue reverse transcriptase inhibitors (NRTIs)
* analogue to DNA molecule -> nucleoside
* >3-hydroxyl removed from deoxyribose sugar
* >can't form phosphodiester bonds ->backbone of DNA
* terminated DNA chain elongation
* Integrates with the viral genome
* Halts DNA synthesis
* Viral replication cycle stops
34
# Antiretroviral Drugs
Non-nucleoside analogue reverse transcriptase inhibitors (NNRTIs)
* targets reverse transcriptase enzyme
* binds to different site (not active site): allosteric site
* non-competitive
* >substrate>ssRNA
* change the conformation of enzyme
* enzyme cannot function
* Stop transcription of viral RNA->viral DNA
35
# Antiretroviral Drugs
HIV Protease inhibitors
* Targets viral protease
* binds to active site
* competitive inhibitor
* Key role: cleave precursor polypolyproteins to functional mature form - can no longer this
* loses enzymatic activity
* incomplete assembly and packaging (immature)
* leads to non functiona virions -> cannot infect
36
What does combination chemotherapy include?
* 2 reverse transcriptase inhibitors
* Protease inhibitor
**Very effective**
* reducing level of HIV
* increasing levels of CD4
* Significant clincal improvements- patients in AIDs clinic return home (improved quality of life)
37
Problems with combination therapy
* **considerable toxicity** - some people may not be able to take it
* >bone marrow and gut
* **Regime**
* > complicated and intrusive to normal lifestyle
* >taken with/without food, certain time period from each other
* **Expensive**
* $15,000/year
* Not readily available to countries that need it the most
38
HIV Vif degrades Inteferon-a JAK/STAT1 and 3 pathway
* Vif = HIV protein
* Interfers the IFN-alpha signalling pathway
* >activated by STAT 1 andn STAT 3 proteins
* >enter nucleus and regulate gene expression->antiviral defense
* Vif intefer via targeting degredation of cellular protein
* >dampen ability to respond to inteferon
* >initiating antiviral response
**indirectly suppresses the interferon-alpha (IFN-α) signaling pathway by targeting the antiviral protein APOBEC3G for degradation.**
39
New Antiviral Strategy
compound= PA-457
* Normal capsid protein is assembled **cone -shaped** assemble ssRNA and other components
* PA-457 - intefers with normal processing of capsid protein
* How: prevent cleavage of capsid protein from gag protein
* No longer cone-shaped **"leaky sphere"**
* >doesn't fully enclose viral RNA
* >>inability to replicated and infect new cells
**Potential target antiviral therapy**
40
# HIV Vaccines
Prophylactic Vaccines
* Protection for not infected individuals
41
Therapeutic vaccines
* For HIV positive patients
* Boost immune system response against HIV
* Understanding of immune respone and HIV evasion questions the certainty of the effectiveness of the drugs
42
Why is challenging to develop vaccination against HIV virus?
* High mutation rate
* Complexity of the immune response
* Virus strains,subtypes and individuals
* High cost of reserach
* Large scale clinical trials
* No good animal models
43
Logistical Issues of Prophtlactic vaccines
* Testing
* Conventional approach
* >developed against acute diseases
* >low mortality rate
* >straightforward to vaccinate section of the populaion
However...
* AIDS ->**Chronically progressive disease**
* >could take many years in development. Too long!!
Number of vaccines in clinical trials present
* Recombinant and antigen/peptide approaches
* >not convincing protection so far
44
Antibody could sterically interfere with viral attachment and/or fusion (but anti-gp120 mostly fail)
**WHY?**
* HIV rapidly mutates>diverse strains
* gp120 highly variable across different strains
* difficult to generate specific antibody that target and neutralise ALL variants of the virus
45
New strategy: naturally occurring, broadly neutralizing HIV antibodies
* broadly neutralizing antibodies mimic the structure of the CD4 binding site on the envelope spike.
* block the virus from attaching to and entering host cells
* antibodies that have been isolated from individuals infected with HIV who have developed a strong immune response.
* cloned 576 new HIV antibodies
* individuals naturally developed antibodies with the ability to neutralize a broad spectrum of HIV strains
* antibodies were then studied to understand their structure and function.
* Sequencing of these antibodies
* >originate from two independent genes
* insights into the specific features
* effective against a range of HIV strains
46
HIV-1 Epitopes Targeted by Broadly Neutralizing Human Monoclonal Antibodies
* Epitopes are specific regions-surface of the envelope proteins
* >recognized by the immune system
* >targets for antibodies
* neutralize a wide range of HIV strains
* due to their recognition of conserved epitopes
Vaccine strategy
* antibodies that can effectively target these specific epitopes on the virus.
## Footnote
The arrows indicate four areas, or epitopes, of the envelope that are the targets of human monoclonal antibodies that, in laboratory assays,have proved capable of neutralizing a wide array of virus strains.
47
Microbiocides
* glycerol monolaurate (GML)
* inhibit the growth-certain microorganisms
* >Staphylococcus and Chlamydia
**Context of HIV prevention**
* GML- specific effect on the vaginal epithelial cells
* >exposed to HIV
* >Produce inflammatory molecules
* >increase susceptibility to HIV infection
* GML- blocks molecues
* Potential - reducing vulnerability to HIV infection
Study
* Applied GML gel to vaginal area of SIV(equivalent) infected monkeys
* >blocked acute infection in all five of the monkeys
