HCV Flashcards
Worldwide distribution of HCV
185 million chronic carriers 75% of cases become chronic
HCV is the leading chronic liver disease cirrhosis and HCC and the leading indication for liver transplantation in many countries
Risk factors of HCV
Frequent exposure to blood is the most important
HCV to acute/chronic hep
Acute hepatitis (10-30%) to recovery Chronic hepatitis (70-90% dependent on county) --> HCC (2.5% of chronic patients) 100 people infected 75-85 = chronic 60-70 = CLD 5 - 29 = cirrhosis 1 - 5 = liver cancer
Time frame of HCV
Acute hepatitis 0-24 weeks
Chronic hepatitis 24-50 years
Liver cirrhosis and HCC 10-40 years
When was HCV first identified?
1989
Where did the NANB hepatitis infectious agent
Could infect chimps and cause chronic liver disease and cirrhosis
Only 5% of people realise they have it and can go 20 years undiagnosed
Acute disease, mild compared to HBV
When was the HCV genome sequenced?
1991
Sources of HCV infection
Sources of infections: Injecting drug use 60% Sexual 15% Transfusion (before screening) 10% Occupational 4% T
How many HCV genotypes are there
6
What type of virus is HCV?
An RNA virus with a very plastic genome and is prone to change
Lots of research done genotype 1 (drugs etc specific to genotype) however more recent drugs against the majority of the genotypes
Replication of HCV
HCV infections are generally Parenteral
HCV spreads through the bloodstream to the liver - the primary target for replication
Viral half life is around 2-3 hours/1012 visions/ day if chronic
Liver contains the highest levels of HCV RNA
But only 5-19% of hepatocytes HCV RNA positive
1-5% of liver mononuclear cells express HCV antigens
The hepatic HCV innate immune response fails to mount
A productive immune rapidness that clears the infection. HCV has several mechanisms to evade the immune response - chronic infection
Therapy for HCV
Pegylated IFN α + ribavirun 40-50% curative
The HCV virion morphology
Associations with LDL
HCV infections does what to IFNL3 (IL28β)
Leads to polymorphisms which can influence the outcome of infection and therapy response
HCV genome has what elements?
IRES
Component of HCV genome and how is it transcribed?
As a polyprotein
C - core immediately wraps around genome, E1 & E2 - envelope protein (heavily glycosylated), p7 associates with NS2 in the membrane, NS2 - protease, NS3(A serine protease cofactor) - serine protease and a helicase, NS4B - membranous web, NS5A - ?, NS5B - RdepRpol
How is the HCV viral positive sense RNA genomes translated?
As a single polyprotein that is co and post translationly modified by host peptidases and 2 virally encoded proteases
What do HCV no structural proteins do?
They assemble as a peplication complex onto modified intracellular membranes
What intermediates are made in HCV
Anti genomic replication intermediate RNA and likely accumulation of dsRNA intermediates
How is HCV recognised by the immune system
HCV is recognised as non-self by PRRs that bind to PAMPs of the viral products - adaptive and innate immune activation (although this does not self like self)
What is HCV virus associated with when it leaves the cell?
In association with host lipoproteins so HCV is present as a lipoprotein coated virus
How does HCV enter into the cell
Via heparin sulphate proteoglycans Low density lipoprotein receptor SRBP1 - scavenger receptor class B member 1 Claudin 1 Occludins
Lots of receptors to help the entry of the virus into the cell. Initially receptors are not specific to the virus, no single one lets the virus into the cell but a whole group of them together.
Enters via clatherin mediated endocytosis
Look at the early and late events in the virus lifecycle and learn the images
Page 22/23 HCV
What can be used as a selectable market in an engineered viral cDNA plasmid and what is removed?
Neomycin resistance
Removal of structural genes
What’s a very virulent strain of HCV?
SGR-JFH1
HCV clinical features
Incubation period - 6-7 weeks Acute illness - mild Case fatality rate - low Chronic infection - 75-85% Chronic hepatitis - 70% Cirrhosis - 10-20% Mortality from chronic liver disease 1-5% (occasional very aggressive strain)
What marker can be used to view clinical response and liver damage to HCV?
ALT
alanine amino- transferase
Market of liver damage
What factors promote progression or severity of chronic HCV
Infection from blood transfusion Increase alcohol intake Age >40 at time of infection HIV co-infection Genetic background Others? Male gender or other co-infection HBV
In the UK HOW MANY HCC cases are caused by HCV?
30%
In HCV what does HCC follow?
Chronic inflammation, necrosis, regeneration and cirrhosis
In vivo the mechanisms of oncogenesis in HCV has not been discovered. How is it described in vitro
Core: can protect cells against apoptosis (transgenic mice expressing core developed primary liver cancer)
NS3: expression can lead to cellular transformation
NS5A: contains a transcription transactivation domain
HCV suppresses and evades the immune system: innate:
In the cell Infection blocks IFNα release which normally activates the innate immune response. (No NKT cell act)
Extra cellular: HCV directly inhibits NK cells as well as DCs that promote adaptive immunity
HCV suppresses and evades the immune system: adaptive
DCs are inhibited and the overall B and T cell response is weakened.
B cells: Mutant HCV strains elude antibody recognition
HCV elicits interfering antibodies that prevent binding of neutralising antibodies
T cells:
HCV directly and indirectly suppresses activation of killer T cells
HCV mutation yields epitopes that escape recognition
HCV transmission from liver cell to liver cell evades antibodies
HCV induces what what in the innate response?
Interferon response and also attenuate the IFN response
How does HCV affect the IFN response?
Core: inhibition of stat1 and increased expression of SOCa proteins
NS5A: General attenuation of IFN expression
inhibitors of PKR
NS3/4A cleaves the polyprotein and also cleaves MAVs and TRIF preventing IRF3 pathway activation and as a result no IFNα/β production
What TLR does HCV bind to and what other mechanism is it recognised by?
TLR3 binding
And dsRNA
Acutely infected HCV patients produces antibodies against?
Epitopes that are structural and non structural but most have no relevant antiviral activity and only a small number inhibit binding, entry of uncoating
What is associated with spontaneous resolution of acute hcv?
Certain defined HLA I alleles
HLA -A3, -B27 and -Cw*01 - clear
HLA-B8 - persistence
What does the protective effect of HLA-b27 require?
Presence of genotype specific immuno dominant CD8 T cell epitope. Thus preventing the viruses dominant role of a specific CD8 T cell response (elicited through IFNγ non cytopathic effector function)
What may lead to HCV escape from antibody?
Quasispecies development
Interaction with HDL and SCARB1
What is the role of CD4 cells in HCV infection?
They are central regulators
Acute infections associated with a vigorous multi-specific helper T cell response intensity, epitope specifics and cytokine profile of the T cell response during early infection appear to be predictive of viral clearance and recovery
In acute HCV infection what type of cd4 response is there?
Strong multi specific and sustained associated with limited course of infection
What HLA II are assoc with positive outcome of acute HCV?
DRB11101 and DRB10301
If cd8s are depleted by antibodies in chinos what happens in HCV?
Persistence until HCV response is recovered and an HCV specific cd8 T cell response emerges showing cd8 cells are most like the key effectors in HCV control
Th2 response is predominant in what type of HCV infection?
Chronic
What th1 cytokines are required for HCV clearance?
Il2 and IFNγ
CD8 in HCV pathogenisis (4)
Vigorous multi specific CTL response in acute infection
CTL epitopes identified of all viral proteins
Frequent of CTL epitopes much higher in the liver than the peripheral blood but still not enough to clear the virus in chronic infections
Balance between stronger CTL response and liver damage
When do HCV antibodies appear?
7-31 weeks after infection
What viral protein is the major target for neutralising antibodies and for vaccine?
HVR of E2 which has high sequence variability influenced by host immune pressure
Are antibodies protective against HCV?
Difficult to tell without routine cell culture
Early response to E2 HRV may be assoc with clearance of HCV
Resolution on HCV can occur without antibody production (chimps) and seroconversion (humans)
Patients who recover do not seem to be immune from reinfection
How does the immune response to HCV cause liver damage?
By immune recognition and destruction of infected hepatocytes
Persistent HCV infection triggers an active T cell response & liver lesions over time. (FasL induced apop of hepatocytes, TNFα and perforin based mechanisms of cells destruction)
What are preferentially attracted to HCV infected livers?
Th1 cells - cytokines may enhance necro-inflammatory lesions
What is the mutation rate of HCV?
1 in 10 euros every time it replicates
Which results in the rapid evolution of viral quasispecies
Consensus sequence is?
The average sequence of all the viral quasispecies with all the varying mutations in the genome.
If you develop a drug against a specific consensus sequence what happens?
There will be a shift in the viral quasispecies that exist.
Three hypotheses as to why HCV persists
- Once a persistent infection is established, the immune response is too weak to clear the infection
- HCV proteins may actively suppress the immune response
- Viral genetic variation
Treatment of HCV involves
Pegylates IFNα and ribavrin for those at risk of progression to cirrhosis
What does the success of the anti-HCV therapeutics rely on?
HCV genotype, initial viral load, prior liver damage, age, gender. Patients may feel fine and then get very ill
