Lecture 35 Flashcards
(35 cards)
1
Q
Why is Hep B special?
A
- RT step in life cycle though is a DNA virus
- Infects large population worldwide
2
Q
What is HDV and how is it special?
A
- Virus that needs help from HBV to replicate/cannot do it on its own
- however, it IS an RNA virus with ribozyme activity which means that the RNA folds in special structures to cleave itself in the cell
3
Q
Who are the three humans involved in HBV discovery?
A
- Blumberg discovered the Australia antigen in 1963 and got Nobel prize in 1976 (Ag important indicator of viral infection)
- Dane discovered the Dane particle in 1970 (only infectious HBV particle)
- Hilleman created the HBV vaccine in 1981 based on the work by blumberg
4
Q
The different hepatitis viruses
A
- HAV: enteral (causes diarrhea cause infects gut then liver cells, transmitted through fecal-oral route contaminated food and water), picornavirus like polio (small virus), +ssRNA, acute infection, yes vaccine
- HBV: blood, sexual, orthohepadnavirus, DNA (only hepatitis with DNA genome), chronic infection, and there is a vaccine
- HCV: blood, hepacivirus, +ssRNA, chronic infection, no vaccine
- HDV: blood, sexual, delta virus, -ssRNA, chronic infection with HBV
- HEV: enteral, hepevirus, +ssRNA, acute infection, vaccine but only approved in China
All different but cause similar disease
5
Q
What does an acute infection imply for hepatitis?
A
- cleared after a week or two and the patient is expected to Make a complete recovery
6
Q
What does a chronic infection imply for hepatitis?
A
Persists for years and years and can lead to cirrhosis and then even carcinoma
7
Q
Prevalence of HBV
A
- 248 million chronic HBV carries (3.6% of the population
- 750k die of hep B each year
- Causes liver cirrhosis and hepatocellular carcinoma
- Transmitted primarily through blood and sexual contact and some mother to newborn
8
Q
Geographic distribution of chronic HBV?
A
- Epidemic
- over 8% is considered high and mostly in Africa, china, south eats Asia and some South America, Indigenous land in Canada
- Quite low, less than 2% in Canada => good and promising
9
Q
Geopgraohic distribution of HBV genotypes?
A
- highly diversified, A to J genotypes
- South America is mostly F some H
- Africa is A and E some D
- Asia mostly B, some C
10
Q
What other viruses show this type of distribution?
A
- HIV, Dengue, Hep C
11
Q
What are some implications for prevention and treatment?
A
- So many genotypes so a lot of factors to consider
12
Q
Describe the natural course of HBV infection
A
- Time scale is in years and decades, but there are 4 phases of chronic infection with differing levels of DNA and protein
- Immune tolerant phase: high level of HBeAg and HBV DNA, low levels of ALT because liver not damaged yet, virus is replication quite fast
- Immune clearance: HBeAg positive chronic hepatitis, Ag starts to go down sit immune system is clearing and start to see some Anti-HBe, ALT starts to go up and DNA starts to go down, some liver damage
- Inactive carrier phase: low levels of DNA and ALT, virus is dormant but the body can’t clear the virus due to the cccDNA, Ag very low at this phase
- Reactivation: antigen not present but varying levels of DNA and ALT, this happens when the immune system goes down or we are weak
13
Q
What are the viral factors associated with HBV disease progression?
A
- Persistent presence of Ag => body has hard time clearing the virus, not good
- Persistent high levels of HBV DNA
- HBV genotype C rather than B can cause longer chronic infection and worse outcomes
- Core promoter mutations may worsen disease outcome as well as other mutations
14
Q
What are the host factors associated with HBV disease progression?
A
- Male gender (seems to get more sick)
- Increasing age like in many diseases like SARS-Cov-2
- Recurrent ALT means liver is under attack and it is hard to recover
- Cirrhosis and other preexisting liver conditions could worsen the outcome
- Diabetes and other health problems could worsen disease outcome
15
Q
What are the environment factors associated with HBV disease progression?
A
- Heavy drinking, cigarette smoking and aflatoxin all in high and frequent doses contribute to liver disease progression (cirrhosis or carcinoma) and obvi not great for HBV
- Co-infection with HIV, HDV or HCV contribute to worsening HBV infection
=> Prevent and survive disease by living a good and healthy life
16
Q
What are the three types of HBV particles?
A
- Filament and sphere/small particles => no electron dense material, no genome, not infectious, both have 22 nm diameter
- Dane particle is the only infectious particle and is 42 nm in diameter
17
Q
Structure of the DNA particle?
A
- partially circular HBV DNA with RT/Pol surrounded b core protein to package and protect viral DNA and then also has a host acquired lipid bilayer wig the surface proteins which are antigens and immunogène for HBV vaccine
18
Q
What is the ratio of infectious and non-infectious particles?
A
In 1 ml of serum of highly viremic chronically infected HBV carrier => 10^9 Dane, 10^10 filaments and 10^13 spheres
Way more non-infectious than infectious and they will serve as particle decoys to attract immune response and CTL
19
Q
How is the large amount of non-Dane particles a challenge?
A
viral titer is low when transfecting in the lab so it can be hard to study
20
Q
Describe the viral life cycle of HBV?
A
Attachment and entry, viral core is released onto the cytoplasm then DNA is transported into the nucleus where it can get repaired since it is not completed closed and then it is ready for transcription. The viral RNAs leave the nucleus for translation. The core protein goes to package the one copy of viral RNA, not the DNA, the pre genomic RNA. It can then be RT and the 3 s proteins (small, middle, large) made at the ER will attract the core with DNA to ER/Golgi where the particle will bud into it and will be released through exocytosis. It is the Large s protein that when facing inward will pick up the core containing the genome to make the Dane particle. Some s proteins can form the sphere and filament non-infectious particles by not packaging the genome and this is the formulation for the HBV vaccine. Gift of nature to humans.
21
Q
What is the path of nucleic acid with HBV?
A
- Starts off as RC-DNA (relaxed circular since not completely closes
- then can enter nucleus to make cccDNA (covalently closed circular DNA which can persist in the cell for a very long time though not integrated into the genome
The cccDNA will then be transcribed into the subgenomic RNAs for translation, not genomic and the pre genomic RNA which can be taken up by the core and polymerase protein to make an immature RNA nucleocapsid. - RNA can then get RT to form the RC-DNA and this mature nucleocapsid can either continue its merry way to leave the cell and infect other cells or will reenter the nucleus to make more cccDNA
22
Q
What are the step for DNA repair in the nucleus?
A
- The cellular DNA polymerase will fill out the gap and then a cellular nuclease will cleave the extra Strongs and finally a DNA ligase will close the tiny gaps and then we get cccDNA
- ALL of the steps of DNA repair are mediated by cellular enzymes
23
Q
How does gene expression happen for HBV?
A
- DNA ready for transcription and there are 4 promoters with only one terminator
- The cellular RNA pol II will do transcription to make 4 transcripts, the smallest one is for the X protein, and then there are two for the surface proteins and then the longest one is the pre genomic RNA which helps synthesize the genome, but it also translates viral core and polymerase proteins for genome replication, it is 3.5 kb and so two sub species one precore-core to make HBeAg (secreted protein detected in the serum and the 5’ sequence is a little longer) there is the second subspecies the pre genomic which translated the core and polymerase, the polymerase is translated through leaky scanning
24
Q
What does the X protein?
A
- Mot in the structure of the particle
- Function not really known
25
Special sequences in HBV genome
- Stem loop which will be present at two spots on the RNA and this is where RT starts
- DR1 and DR2 direct repeats which will be helpful for RT
- Enh1 and Enh2 enhancers important for pgRNA transcription
- Genomic RNA start around 1818,1819 and poly A signal at 1916-1921 that really serves as the terminator sequence
- Promoter with the help of enhancers starts transcription at about 1818 which includes DR1 and stemloop and then continues transcription until it passes DR2 and DR1 and stemloop again
26
Structure of HBV pol vs HIV pol?
HIV-1: PR protease, RT, RH domain to remove RNA portion of DNA/RNA complex made during RT, and IN integrase
HBV and HDV: TP terminal protein hick will recognize the stemloop to start RT, has RT and RH
27
How does reverse transcription start in HBV vs HIV?
- HIV: primer is tRNA and Dif retroviruses use Dif tRNAs
- HBV: TP binds stemloop and RT starts copying viral RNA -> DNA, protein initiated/primed so the 1st nt is bound to 1 aa in a protein, not RNA or DNA
28
Explain the process of HBV reverse transcription
- Starts with the 3.5 kb RNA template, TP binds stemloop and copies DR1, then can template switch or jump to other DR1 copy and continues the synthesis of the (-) strand viral DNA and viral RNA is degraded by RNAse H and whole viral RNA is copied into (-) strand DNA
- One little part is resistant to RH to prime +strand DNA synthesis and we end up with the 3.2 kb partially circular DNA product, loss of some of the RNA sequence that is redundant like double DR1 and stemploop
29
How can we prevent HBV infection?
- Using vaccines
- After viral infection, some antibodies detected for surface proteins
- antiHBs confer protective immunity and vaccines used in humans have been designed accordingly, current vaccine involves the injection of recombinant proteins derived from the PreS/S region
- Another method of HBV prevention is trough injection of the Ab post-exposure to offer some protection from mother-child transmission
30
About HBV vaccines?
- Non-infectious particles are the basis of HBV vaccine
- 1st approved in 1981 by FDA, was blood derived as in from the immunogène/Ags of patient serum but this is limited and expensive and risk of infection by other blood viruses like HIV, discontinued in 1986 when yeast-produced recombinant HBV vaccine became available (first vaccine using recombinant DNA technology)
- Common brands are recombivax HB (Merck) Engerix-B (GSK), Slovak B (human biologicals institute_, Geneva B (serum institute), shanvac B
- Vaccines given intramuscularly like covid mRNA vaccine
- Three injections, one and 6 months apart, provide long-term immunity/protection
31
What are some HBV treatments?
- Used to use IFN in early days and used in other viruses like HCV
- Now have some nucleoside analogues from HIV but can also be used for HBV thanks to RT: Lamivudine (cytosine), entecavir (guanosine), adenovirus dipivoxil and tenofovir disoproxil (adenosine), telbivudine (thymidine)
32
How can HBV develop drug resistance?
- Mutations in RT region of HBV are associated with nucleoside analogue therapy
33
Difference between HBV, HIV, HCV?
HIV: Rna, very high mutation. 10^10 virions per day, viral genetic archiving through integration, multiple drug targets, no cure due to integrated viral DNA, current therapeutic goal is lifelong suppression
HBV: DNA, high mutation rate, 10^13 virions per day obvi most non-infectious, yes viral archiving through cccDNA, one drug target, no cure because of cccDNA, current therapeutic goal is lifelong suppression
HCV: Rna, very high mutation, 10^12 virions per day, no viral archiving, multiple drug targets, yes cure, current therapeutic goal is cure: clearance from plasma and liver
34
About HDV?
- Sub-viral agent, doesn't replicate on its own
- Depends on HBV infection for replication
- Share HBV envelope proteins
- Single stranded circular RNA virus
- Encode long and small delta antigens
- Bear ribozyme
- Undergoes RNA editing by host cytidine deaminase, phage coding when in cell
- 20 million carriers
35
Path of the nucleic acid HDV?
- genome, antigene, mRNA for viral antigens
- Ribozyme in both genomic and antigenomic RNA, catalytic cytosine, specific folds for activity => cleavage
- Start with genome, make antigene, cleave linear antigenome with ribozyme then ligated and circular again, becomes linear when making genome and it gets cleaved by ribozyme as well and become linear and clean and then recicularizes to make genome
- From the genome can get template for mRNA BUT must be cleaved through ribozyme activity to get mature mRNA for translation
