Influenza Flashcards
Influenza family?
Orthomyxoviridae
Influenza genera?
A B C D Thogovirus
Which influenza genus infects humans only?
B
Which influenza genus primarily infects birds but can infect humans and pigs?
A
Which influenza genus primarily infects both humans and pigs?
C
How many genome segments are present in influenza A?
8
Baltimore classification and genome type?
Group V
-ssRNA
Genome of influenza A?
Segmented- 8 segments
Multipartite
Each genomic segment tends to encode a single protein
Ribonucleoprotein attached to nucleocapsid protein and RNA polymerase
Virion structure?
Enveloped
2 types of surface glycoproteins: Neuraminidase and hemagglutinin
Neuraminidase structure?
Homotetramer
Hemagglutinin structure?
Homotrimer
The RNA polymerase of influenza is made up of?
PB1
PB2
PA
Heterotrimeric complex
What is neuraminidase?
An enzymatic glycoprotein
A homotetramer
It has a sialidase activity, able to cleave sialic acid-galactose linkage
Why is neuraminidase important?
Prevents aggregation of viral particles
Allows penetration of mucus
Prevents cell re-infection
Which antivirals target neuraminidase?
Tamiflu and Relenza
How do Tamiflu and Relenza work?
Molecular mimicry of sialic acid
What is the function of hemagglutinin?
Homotrimer
It binds the sialic acid receptor on the cell surface
Mediates entry and fusion
What the hemagglutinin precursor?
HA0
What is the hemagglutinin precursor cleaved into?
HA1 and HA2
What cleaves HA0?
Human airway tryptases
What is the consequence of a multibasic cleavage site in hemagglutinin?
Allows the HA0 precursor to be cleaved into HA1 and HA2 by furin which is a ubiquitously expressed protease, allows unrestricted replication of influenza in multiple parts of the body
Why is timing of HA0 cleavage essential?
Don’t want HA0 to be cleaved prematurely as it can lead to cell re-infection… want it to be cleaved once the viral particle is ready to infect and uninfected cell
Which types of avian viruses have shown multibasic cleavage sites?
H5N1
H7N9
When did H7N9 develop into a HPAI capable of dissemination?
In February 2017
The tropism of influenza can be expanded by?
Multibasic cleavage sites
What is the function of HA1 and what can it be referred to as?
HA1 is the head
It is what binds sialic acid
What is the function of HA2 and what can it be referred to as?
It is the stalk/stem
It is what mediates fusion with the endosome
HA1 is variable or conserved?
Tends to be variable
Antigenic drift
Is HA2 variable or conserved?
Conserved
Where is the fusion peptide found?
The N terminus of HA2 is the fusion peptide
Until the endosome where can the fusion peptide be located?
It is hydrophobic
Hidden within the homotrimer of hemagglutinin
What is the C terminus of HA2?
Transmembrane domain
How are HA1 and HA2 associated?
Non-covalent interactions
Associated via disulfide linkages
When is fusion triggered?
During endosome acidification
M2 ion channel function?
Acidification of the virion occurs
Allows release of the -ssRNA into the cytoplasm where it can enter the nucleus
Releases -ssRNA from M1 matrix protein
Usually -ssRNA is bound to what in the viron?
M1 matrix protein
M2 ion channel is the target of what antivirals?
Amantadine
Matrix (M1) protein immunomodulation function?
It is able to prevent the interaction of C1q with IgG Fc region, can prevent the activation of classical complement
What forms ribonucleoprotein in the virion?
The -ssRNA bound to the RNA polymerase complex (PB2, PB1 and PA) and the nucleocapsid protein
Function of PB1?
This has the RNA polymerising activity
Function of PB2?
Binding the 5’ cap of cellular mRNA
Function of PA?
It is an endonuclease
Its function is cleavage
Nucleocapsid protein is how frequent and what is its function?
Spaced every 10-20nt
It functions in protecting the RNA
What are the immunomodulation functions of NS1?
NS1 can inhibit RIG-I signalling
NS1 can prevent post-transcriptional modification of cellular mRNAs, can prevent the cellular mRNAs from having 3’ poly-A tails added which means they are restricted to the nucleus
NEP/NS2 function?
Functions in nuclear export of replicated -ssRNA genomes
Which ubiquitously expressed protease can cleave hemagglutinin with multibasic cleavage sites?
Furin
pH at which fusion with the endosome occurs is what for avian influenza viruses in comparison to human influenza viruses?
Less acidic for avian viruses, fusion occurs at higher pHs
Why is it important that fusion occurs at lower pHs for human influenza viruses?
To ensure the robustness of the viral particle outside of the cell
As the human upper respiratory tract is mildly acidic, do not want the irreversible conformational change to occur before cell entry- as it would prevent cell entry
Where does influenza replication occur?
In the nucleus
How do replicated genomes of influenza exit the nucleus?
Via NEP viral protein
Via Crm1 cellular protein
Which cellular protein aids in export of influenza replicated -ssRNA from the nucleus?
Crm1
How is it ensured that all 8 different segments are packaged into the virion without multiples of the same segment being packaged?
Each segment has a unique packaging signal
M2 is also important during budding?
It mediates scission, allowing virion release. It also determines virion stability
Spanish flu occurred in and was which subtype?
1918
H1N1
Which flu occurred in 1957?
Asian flu
What was the subtype of Asian flu?
H2N2
Which flu occurred in 1968?
H3N2
Hong Kong flu
Which flu threat occurred in 1997?
H5N1
Avian flu threat
Which flu occurred in 2009?
Swine flu
H1N1
Which flu threat occurred in 2013?
H7N9
Avian flu threat
What are all the years flu pandemics occurred in?
1918: Spanish: H1N1
1957: Asian: H2N2
1968: Hong Kong: H3N2
1997: H5N1 avian flu threat
2009: H1N1: Swine flu
2013: H7N9 avian flu threat
What is the natural host of influenza A?
Wild water fowl
How is influenza A spread between wild water fowl and where does it replicate?
Spreads in the water
Infects their guts
Why is influenza relatively apathogenic in birds?
As it co-evolved with the birds overtime, became less virulent
Why are pandemics relatively infrequent?
Due to the host-range barrier
What is the host range barrier?
The barrier that must be overcome in order to allow the virus to infect other species
The strength of the barrier determines?
The likelihood that the virus will be able to infect another species/host
What are the barriers influenza must overcome to infect humans?
- Must be able to replicate effectively in humans
- Must be able to transmit between humans
- Must be able to infect cells of humans
Which avian viruses have managed to overcome the host range barrier?
H5N1
H7N9
Why are we not too concerned by H5N1 and H7N9?
They are not (yet) capable of sustained human-to-human transmission
H5N1 avian flu threat began when?
1997
H7N9 avian flu threat began when?
2013
What is required for a pandemic?
- Sustained human-to-human transmission
- Novel antigens such that the whole population is immunologically naive
- Ability to effectively replicate in the human airway
In order for an avian virus to overcome the host range barrier what adaptations will it need?
- Needs to be able to bind SA-alpha2,6-Gal receptors in the upper respiratory tract for effective human to human transmission
- Needs a long neuraminidase stalk to allow penetration of sialic acid rich mucus
- Needs PB2 627E–>627K mutation to allow the RNA polymerase to function in human cells
- Needs to fuse with the endosome at lower pHs
As lots of mutations are needed for a pandemic to occur?
It means that pandemics occur relatively infrequently
How can these mutations be acquired?
- Through genetic reassortment
- Through selection pressures which drive selection of advantageous mutations
What is required in the cell to allow the Influenza A RNA polymerase to function?
ANP32A
What does ANP32A stand for?
Acidic nuclear phosphoprotein 32kDa
Why is the ANP32A of flighted birds longer? And how much longer?
Longer by 33aa
Thought to have occurred due to a chromosomal duplication
How do we know this change occurred after the divergence of flighted birds?
As Ostriches have the same ANP32A without the additional 33 amino acids
What mutation is required in avian influenza to allow the RNA polymerase to utilise the shorter mammalian form of ANP32A?
Mutation in pB2
PB2 627E= Glutamate
To
PB2 627K= Lysine
What is the structure of ANP32?
Has Leucine Rich Repeats: LRRs
Has LCARs on the other end Low complexity acidic region
Where are the additional 33 amino acids inserted?
Between the Leucine Rich Repeats and Low Complexity Acidic Region
LRR-33aa-LCAR
Why must avian influenza adapt to fuse with the endosome at lower pHs?
As the upper respiratory tract of humans is mildly acidic
What is wrong with fusion that occurs too late?
IFITM3 is present in the late endosome
What does IFITM3 stand for?
Interferon induced transmembrane protein
What is the role of IFITM3?
To prevent fusion of the late endosome
To prevent viral replication
Which bird flu virus has shown dual receptor binding capability?
H7N9
What is an essential prerequisite of sustained human-to-human transmission?
The ability of avian influenza to recognise the alpha 2,6 sialic acid galactose linkages of the upper respiratory tract
Why is a long neuraminidase stalk required?
For efficient penetration through the mucus of the lungs
When did the H7N9 avian flu threat emerge?
2013
When did they realise H7N9 developedinto a HPAI?
February 2017
What is the human mortality rate of H7N9?
40% currently
What is LPAI?
Low pathogenicity avian influenza
How did LPAI H7N9 turn into HPAI?
Due to multibasic cleavage sites
When did the 5th wave of H7N9 occur?
2017
Which influenza virus shows dual receptor binding capabilities?
H7N9
Chinese government response to the 5th wave?
Began vaccinating chickens against H7N9
Why was H1N1 Spanish flu so virulent?
Caused a cytokine storm
Cytokine degranulation
What are some at risk groups to influenza infection?
Obese
Pregnant
Immunocompromised e.g. HIV infection
What was the SNP identified in IFITM3 gene?
Identified an SNP that makes you more susceptible to severe infection when you encounter influenza virus
C allele
What are the genotypes?
CC
CT
TT
They noticed that the majority of individuals hospitalised during the 2009 swine flu pandemic had?
CC genotype
CC genotype is not very common in?
Caucasians
CC genotype is very common in the?
Han Chinese
Why does the C SNP make you more susceptible to developing severe infection symptoms?
Leads to the production of a truncated IFITM3 protein which is less able to prevent viral replication
The CC genotype is how much more likely to develop severe infection?
6 fold greater risk than CT and TT genotypes
Which flu vaccine is given to adults?
Inactivated flu vaccine
Which flu vaccine is given to children?
Live attenuated flu vaccine
What would the universal vaccine cause the immune system to target?
Would cause the immune system to target the stalk of hemagglutinin which is conserved and less variable than the head of hemagglutinin. Would induce antibodies to target the stalk.
How would the universal vaccine cause the immune system to produce antibodies targeting the hemagglutinin stalk rather than the head?
Via synthetic vaccinology
