HIV Part 2 Flashcards
Histological examination of lymph nodes show?
Influx of CD8 T cells
How does HIV exploit dentritic surveillance network?
- 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
Sialylactose head on GM3 ganglioside
- Sialyated head
- On lactose (galactose+Glucose)
Consequence of loss of Th activity
mount a delayed-type hypersensitivity reaction
HIV infected dendritic schematic diagram
- 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)
Antibody abnormalities in HIV positive patients
- High increase of antibodies (Ig)
- Production of autoantibodies
- Affecting RBC, sperm cells and myelin sheeth in neurons
Define viraemia
High levels of viral particles in bloodstream after infection due to rapid phase of viral replication
What is the initial immune response to HIV?
- 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
Immune response
Lower viraemia suggests?
Slower progression to AIDs compared to higher viraemia
Immune response
What did advanced methods of viral RNA detection in latent phase indicate?
- 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
Immune response
Whats the importance of treatment?
- 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
The traditional concept of the latent stage of HIV infection as a period of relative quiescence is now being redefined to what?
- Dynamic phase
- Intense viral replication and destruction
- Continueous of cycle of CD4 T cells being lost and replenishes
What is latent phase indicative of?
- Immune activity
- Viral acitivity
- Even if infection seems less active on surface
Why does the immune system not completely clear the virus?
- 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
Whats the dual mechanism that results in the loss of CD4 T cells?
- Direct killing by the virus
- Immune system-mediated destruction
- Vulnerable to recognition and attack by immune system
Explain direct killing by the virus
- HIV replicated
- > damage to cell
- Reduce CD4 overtime
Explain Immune system-mediated destruction?
- 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+
What is present in the blood and lymph of HIV positive patients?
Soluble gp120
Binds to CD4 T cell
Potential exam diagram question
Killing Mechanism of CD4 T cells diagram
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.
CD4 T cell killing mechanism
Antibody+complement
- Antibody- anti-gp120
- Bind to gp120 on CD4+
- > complement fixation
- > cascade of events -> pores -> cell-lysis
CD4 T Cell killing mechanism
Antibody-dependent cell-mediated cytotoxicity
- 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
CD4 T cell killing mechanism
CD8 cytotoxic T cells
- 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
What are 2 cell death killing mechanism of CD4 T cells?
- Apoptosis- programmed cell death
- > controlled, non-inflammatory
- Pyroptosis - highly inflammatory form of programmed cell death
Apoptosis
- Permissible T cell- completed viral cycle
- Mediated by caspase-3
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
In which tissue is CD4 cell death found in?
- Lymphoid tissue
- Result of pyroptosis
- > weakens immune system
- contributes to disease progression
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
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
*»_space;Incomplete viral replication
*»_space;Viral transcripts accumulated
*»_space;sensed by IFI16 sensors
*»_space;>triggers assembly of inflammasomes, activate caspase-1»_space;Pyroptosis
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
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
Diagram of Pyroptosis CD4 T cell location
Why is combination drug therapy is important?
- Less chance of virus mutating to become resistant to 3 drugs at once
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
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
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
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)
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
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.
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
*»_space;inability to replicated and infect new cells
Potential target antiviral therapy
HIV Vaccines
Prophylactic Vaccines
- Protection for not infected individuals
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
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
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
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
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
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.
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.
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
