L5 - Respiratory Syncytial Virus Flashcards
(110 cards)
1
Q
When and from where was the Respiratory Syncytial virus (RSV) first isolated?
A
RSV was first isolated in 1956 from a laboratory chimpanzee that was exhibiting cold-like symptoms. Within a year (1957) , a very similar virus was isolated from infants suffering from respiratory illness. This early discovery hinted at the virus’ potential to affect both animals and humans particularly the young.
2
Q
What did seroloial studies reveal about the prevalence of the respiratory syncytial virus (RSV) shortly after its discovery?
A
Serological studies quickly established that RSV was very common amongst children and infants. This indicated that most children were likely exposed to the virus at a young age, even if the severity of illness varied. Serology, which detects antibodies in the blood, provided early evidence of widespread infection in this population.
3
Q
What critical realisation emerged regarding the impact of the respiratory syncitial virus (RSV on young children?
A
It become apparent that RSV was a major cause of serious respiratory disease in young children. This understanding shifted the perception of RSV from a seemingly mild virus (given its initial isolation from a chimpanzee with cold like symptoms) to a significant threat to infant and early childhood health often requiring medical intervention.
4
Q
When do RSV cause outbreaks in temperate climates?
A
during winter. the exact timing and duration of the season can vary slightly depending on the geographic location and year, but it generally coincide with the colder months. This seasonality is an important factor in anticipating and preparing for RSV-related illnesses
5
Q
when do yearly epidemics occur and peak (in temperate climates)
A
typically being ~ October until March
Peak ~ December or January
6
Q
After infection, can an individual get re-infected
A
yes (this is a key feature of RSV) and protection only typically lasts anywhere between 3 to 12 months before it starts to wane (this underscores why RSV remains a significant cause of respiratory illness throughout life, why it affects so many people and why it poses a challenge for long term immunity strategies )
7
Q
What sort of illness does RSV cause in children vs adults
A
Children : can cause serious or even fatal disease. In those under 2 this is a common cause for hospital admissions (highlighting the burden of RSV - hospitalisation often arises from breathing difficulties, dehydration or the need for oxygen support
adults : colds
8
Q
Who are most vulnerble to severe or even fatal outcomes from respiratory syncitial virus (RSV) infection and why are they at higher risk?
A
Very young children (especially infants) and the very old are at the highest risk of serious or even fatal RSV infections. Young children have immature immune systems and smaller airways making them more susceptible to brioncholitis (inflammation of the small airways in the lungs) and pneumonia. Older adults may have weakened immune systems and underlying health conditions that increase their risk of severe complications
9
Q
What is the genetic diversity like within the respiratory synscitial virus (RSV) population? What are the major classifications?
A
There is a large number of co-circulating genotypes of RSV indicating significant genetic diversity within the viral population. These genotypes are broadly classified into two major subgroups, typically designated as RSV-A and RSV-B. Both subgroups can circulate simultaneously during an outbreak and infection with one subgroup doesn’t necessarily protect against subsequent infection with another subgroups. this genetic variability can also complicate vaccine development
10
Q
What virus has a similar case fatality vs a distinct case fatality pattern to RSV
A
similar = influenza (although influenza is less infectious, it has a higher death rate –> evens out to have similar fatality rates)
distinct = SARS CoV2 (because SARS isn’t fatal for children)
11
Q
What significant historical event occured in the 1960s related to Respiratory Syncitial virus (RSV) vaccine development? What was the tragic outcome?
A
in the 1960s, scientists tested a formalin inactivated respiratory syncitial virus (RSV) vaccine that led to a number of deaths and severe illness in vaccinated infants upon subsequent natural infection. This tragic event highlighted the complexities of developing an effective and save vaccine - It underscores understanding the virus’s pathogenesis and the immune response it elicits
12
Q
What is the overall structure of the RSV
A
an enveloped viurs (surrounded by a lipid bilayer membrane derived from the host cell during budding which has all the surface proteins) with a nuclear capsid that that surrounds the genome :non segmented negative sense ssRNA
13
Q
what are all the components of the RSV
A
- Genome: A single-stranded, negative-sense RNA molecule.
- Nucleocapsid: The RNA genome tightly associated with the nucleoprotein (N), phosphoprotein (P), and large polymerase protein (L), forming a helical structure.
- Matrix (M) protein: A layer of protein located beneath the envelope, providing structural support and playing a role in virus assembly. It also causes the F and G proteins to agglomerate together on the inside and associated with the nuclear capsid and the RNA genome and also ensures that polymerase and its cofacter phosphoprotein (P) are incorporated into the budding virus particle
- Envelope: The outer lipid bilayer embedded with viral glycoproteins.
- Surface Glycoproteins: Projections extending from the envelope, crucial for attachment to host cells and fusion. The main ones are the fusion protein (F) and the attachment glycoprotein (G).
- other surface proteins: Ion channels (SH) which are incorporated into the outer membrane and alter membrane permeability and play various roles in the viral life cycle and pathogenesis
14
Q
Where is polymerase located in RSV and how is this important
A
It is associated with the viral genome inside the particle. this is necessary because it is a negative sense RMA virus which isn’t found in the human cells (host machinery won’t work) so it requires it to be copied before ribosomes can translate it
15
Q
What are the two modes in which RSV can enter a host cell
A
- fusion with the cell membrane
- Micropinocytosis
16
Q
explain viral entry methods through 1. Fusion and 2. Micropinocytosis
A
- RSV initaites attatchent by RSV-G glycoproteins binding to candidate receptors e.g. TLR4, CXCR1 and HSPG, tethering the virus particle to the cell surface. RSV-F proteins may also be involved binding to nucleolins which triggers RSV fusion with the virus and host cell membranes. The virion fuses and enters the cell where it can successfully replicated
- It is unclear which receptors are involved in micropenocytosis however it is known that rearrangement of the actin cytoskeleton and phosphatidylinositol 3 kinase (signalling molecule) activity are required for internalisation. The virus is then enclosed in a Rab5-positive endosome. Inside this endosome, the RSV-F protein is cleaved by proteases, which then triggers the fusion of the viral envelope with the endosomal membrane, releasing the viral contents (capsid and genome) into the host cell’s cytoplasm.
17
Q
what does viral escape of the endosome require
A
Proteolytic cleavage of the RSV-F protein within the Rab5+ endosome. This cleavage activates the fusion potential of the F protein.
18
Q
What happens when the G proteins is deleted from RSV
A
It will infect with a much reduced efficiency (barley alive)
19
Q
Outline the steps of the RSV replication cycle after entry into the host cell.
A
- virus enters the cytoplasm where the viral runonucleprotein complex (consisting of -ve ssRNA genome along with polymerase complex L and P) is released
- Polymerase transcribes the genome into multiple +ve sense mRNA molecules (each one typically encodes for one or a few viral proteins)
- newly synthesised viral mRNAs are transported to the host cell ribosomes where they are translated into various structural and non-structural RSV proteins e.g. F, G, M, P and N
- Once there are sufficient levels of viral proteins (particularly N and P proteins), the viral polymerase (L and P) switches its activity from mRNA transciption to genome replication. It binds to the -ve sense genome RNA and using it as a template to make antigenomes (exact complements of the viral genome +ve sense)
- The antigenomes are used as a template for the viral polymerase to produce more copies of -ve sense RNA genomes which get incorporated into the new viral particles
- The newly synthesized progeny genomes can then serve as templates for another round of mRNA transcription further fueling the replication cycle and the production of new virions (represents a positive feedback loop that amplifies viral production)
- The newly synthesised viral proteins and the progeny genomes come together to form new virus particles : the nucleocapsid associates with the M protein at the inner surface of the host cell membrane. The envelope glycoporteins (F and G) are also embedded in these regions and often cluster due to the interaction with the M protein
- The nucleocapsid and associated proteins form an envelope / bud that protrudes from the cell surface
- the bud eventually pinches off releasing a new infectious RSV virion which can go on to infect other cells.
20
Q
Apart from preparing for budding, what is a viral benefit for coating the infected cell with F and G glycoporteins
A
It turns the host cell into a giant virus which can attach and fuse with other nearby cells. This is a highly effective way for the virus to penetrate deep into the lungs faster without immediately killing the cell
21
Q
Explain the conventional “backward” reading direction of negative/anti-sense RNA genomes during transcription.
A
Unlike typical messenger RNA (mRNA) which is read 5’ to 3’ by ribosomes, the negative/anti-sense RNA viral genome itself is not directly translated. Instead, it serves as a template for the viral polymerase to synthesize positive-sense mRNA molecules. During this transcription process, the polymerase reads the negative-sense RNA genome in the 3’ to 5’ direction to produce the 5’ to 3’ mRNA. Think of it like making a photographic negative – you need to read the negative to get the positive image.
22
Q
At which end of the negative/anti-sense RNA genome does the phosphate group typically associate?
A
the phosphate group at the end of the chain will be associated with the 3’ hydroxyl group of the terminal nucleotide. While the polymerase reads 3’ to 5’, the resulting synthesized mRNA will have a 5’ phosphate and a 3’ hydroxyl end, consistent with standard mRNA structure.
23
Q
Where is the start codon (AUG) located in relation to the viral genome of a negative-sense RNA virus like RSV?
A
The start codon (AUG) is not found directly on the negative/anti-sense viral genome itself. Instead, the AUG start codon is located on the complementary positive-sense messenger RNA (mRNA) molecules that are transcribed from the viral genome.
24
Q
Describe the function and characteristics of a gene end signal in the genome of a negative-sense RNA virus like RSV.
A
A gene end signal is a specific nucleotide sequence embedded within the RSV genome that serves as a termination signal for the viral polymerase during mRNA transcription. When the polymerase encounters this signal, it releases the newly synthesised mRNA molecule and adds a poly(A) tail to the 3’ end to stabilise it and so it can be recognised by ribosomes.
25
what is the difference between mRNA and the anti-genome?
Unlike the mRNAs transcribed from the genome, the anti-genome does not undergo polyadenylation and is also read entirely to the end to make a complete uninterrupted template for the synthesis of new progeny -ve sense RNA. Generally when synthesising the anti genome the gene's stop codons are read through
26
how many genes are encoded in the RSV genome and how many nucleotides make up this number of genes
10 genes made from ~15,000 nt
27
What is at the end of each ORF
1. a gene end signal (short nt sequence) which signals for the polymerase to stop transcribing that particular gene and triggers the release and polyadenylation of the newly synthesised mRNA
2. following a gene end signal is a gene start signal for the next gene which tells thee viral polymerase to begin transcription of the subsequent genes.
28
Describe the path of the viral polymerase as it synthesizes mRNAs along the RSV genome.
The viral polymerase initiates transcription at the 3' end of the negative-sense RSV genome. It proceeds to transcribe each gene sequentially:
1. It starts by transcribing the NS1 gene until it reaches the gene end signal for NS1, at which point the NS1 mRNA is released and polyadenylated.
2. The polymerase then continues along the genome until it encounters the gene start signal for the next gene (NS2) and begins transcribing it.
This process repeats for each gene in order along the genome: NS2, N, P, M, SH, G, and F, with each gene being transcribed, and its mRNA being released and polyadenylated upon reaching its respective gene end signal.
3. The transcription of the final two genes, M2 and L, is a bit more complex and can involve transcriptional read-through and the production of polycistronic mRNAs (mRNAs encoding multiple proteins) that are later processed.
29
Why dis there a gradient of mRNA abundance, with genes closer to the 3' end of the genome being transcribed more abundantly than those towards the 5' end?
because of the fact that polymerase synthesis is a biological process which involves mistakes. With the sequential transcription the polymerase has a higher chance of dissociating before reaching the later genes and in these cases, the polymerase can only rebind and continue synthesising if it rebinds onto the beginning start codons again. This means that the first few genes are read in higher abundance but means that the virus can have some level of control In gene expression when only having one promoter.
30
Which genes are most expressed in an infected cell?
NS1 and NS2 (left hand end)
31
which gene is the least expressed in an infected cell?
L gene (encoding the large polymerase subunit) on the right hand side.
32
Explain the unique transcriptional feature related to the L polymerase gene and the M2 gene.
The transcript for the L polymerase gene begins inside the M2 gene (the start codon is within the M2 gene). This means that the 5' end of the L mRNA overlaps with the 3' end of the M2 gene. The M2 gene itself codes for two proteins, M2-1 and M2-2, from overlapping reading frames within the same mRNA.
33
what has to happen for the polymerase to read to the L gene start signal
it needs to finish synthesising the mRNA for F, ignore the M2 start signal (as well as the end signal) and go forward to read the gene start for L ( presumably you don't need much polymerase)
34
Explain the coding capacity of the M2 gene mRNA in RSV.
The M2 gene mRNA is bicistronic, meaning it contains the coding information for two different proteins: M2-1 and M2-2. These two proteins are translated from overlapping reading frames within the same mRNA molecule, showcasing a mechanism for maximizing the coding potential of the viral genome.
35
What mechanism causes the ribosome to pause after translating the M2-1 protein from the M2 mRNA?
After translating the M2-1 protein, the ribosome encounters a specific secondary structure in the M2 RNA. This hairpin-like structure causes the ribosome to pause on the mRNA.
36
Describe the process by which the ribosome initiates translation of the M2-2 protein from the M2 mRNA.
To reach the start codon (AUG) for M2-2, the paused ribosome at the M2-1 stop codon is thought to back up on the mRNA. This repositioning shifts the ribosome into a different reading frame which is offset by a number of nucleotides that is not a multiple of 3 from the M2-1 reading from. The ribosome can then re-initiate translation at the AUG start codon for M2-2 within this alternative reading frame.
37
What determines the start point and the order in which the ribosome reads the codons (reading frame) during translation?
The position of the AUG start codon on the mRNA dictates the start point of translation and sets the reading frame. The ribosome will begin translating the mRNA at the AUG and then read subsequent nucleotides in triplets, determined by the frame established by the AUG.
38
What is the primary function attributed to the M2-2 protein in the RSV replication cycle?
M2-2 is thought to promote genomic RNA replication over transcription. This suggests that M2-2 plays a crucial role in the control process that determines whether the virus will primarily focus on making more copies of its genome or on producing more viral mRNAs and proteins.
39
Describe the technique used to measure transcript abundance in RSV-infected cells.
Transcript abundance was measured using direct RNA sequencing. This advanced technique involves sequencing the entire mRNA molecules present in a sample and then quantifying the number of reads corresponding to each specific mRNA, which reflects the combined effects of transcription rates and mRNA stability
40
What were the unexpected findings regarding transcript abundance in RSV-infected cells based on RNA sequencing, and what factors might contribute to this?
Contrary to the expectation of a strong 5' to 3' gradient based solely on sequential transcription, RNA sequencing revealed that there wasn't a significant decrease in the abundance of most transcripts towards the 3' end of the genome. The L transcript was a notable exception, being present at very low levels. This suggests that factors beyond just the order of genes on the genome play a crucial role in determining mRNA levels, potentially due to factors e.g.
Differential mRNA stability: Some transcripts might be more resistant to degradation than others.
Differences in polymerase activity: The efficiency with which the polymerase recognizes different gene start and end signals can vary.
41
Explain the phenomenon of "polycistronic transcripts" in RSV and its potential implications.
The fact that many RSV transcripts are polycistronic means that a single mRNA molecule contains the coding information for two or more adjacent genes (cistrons). This occurs when the viral polymerase frequently ignores gene end and start signals during transcription, even when it is presumably in transcription mode. This could be accidental or purposeful (as a mechanism to co-regulate the expression of functionally related genes)
42
what is a citron?
A citron is another name for a gene, defined as a segment of DNA or RNA that codes for a specific polyprotein
43
Describe the initial steps of RSV infection in cell culture, focusing on viral attachment and entry.
In cell culture, RSV attaches to host cells via the G glycoprotein. Subsequently, the F protein triggers membrane fusion, allowing the entry of the viral ribonucleoprotein complex (RNA, N, P, and L proteins) into the host cell's cytoplasm.
44
Explain how RSV promotes its spread between cells in culture and the name of structures formed
The expression of F and G glycoproteins on the surface of infected cells allowed the cells to fuse with neighbouring uninfected cells which forms large multinucleated cells aka SYNCYTIA. This cell-cell fusion aids the spread of the virus and allows it to evade extracellular immune responses.
45
What gives respiratroy syncitial virus its name
the fact that it makes lagre SYNCITIA
46
What is the typical viral yield in cell culture after RSV infection?
Approximately 100 plaque-forming units (pfu) per cell are generated after RSV infection in cell culture, typically within 24-48 hours. This indicates a relatively efficient replication cycle within susceptible cells and although it isn't that many virions, it illustrates how much virus is produced doesn't always correlate with how dangerous it is (e.g. adenovirus generates 10-20,000 pfu in 24 hours but it is rarely if ever fatal but RSV is routinely life-threatening)
47
What are the general effects of RSV infection on host cell metabolism in culture?
RSV infection in cell culture leads to a slow reduction in host cell DNA and RNA metabolism. However, host cell protein synthesis remains largely unaffected, allowing the virus to utilize the host's protein synthesis machinery for its own replication.
48
Describe the innate immune response to RSV infection nad the virus's counter strategies
The innate immune response is the body's first line of defence which recognises RSV infection. However, RSV has evolved mechanisms to subvert this response, particularly through its NS1 and NS2 proteins. These two proteins actively interfere with interferon production and signaling, which are crucial for antiviral defense.
49
How might the RSV genome itself interact with the host's innate immune system?
Similar to other RNA viruses, if the RSV genome is chemically modified by the host cell during replication, it is thought to hide the incoming virus from the innate immune response and make the virus more virulent
50
what supports the hypothesis that RSV genoe methylation increases virulence
RSV grown in cells unable to methylate RNA were purified and found to be less harmful in rat models of respiratory syncytial virus compared to those grown in cells capable of methylating RNA.
51
What is the typical incubation perioid for RSV infection and the primary mode of spread?
Symptoms of RSV infection typically appear 4-5 days after infection. The primary mode of spread is through contaminated respiratory secretions, mainly via large saliva droplets produced during coughing or sneezing, not aerosols or small droplets.
52
Where does replication of RSV occur?
In the upper respiratory tract
53
What are the main routes of experimental RSV infection? What route is less likely?
Experimental infections indicate that the nose (nasal mucosa) and the conjunctiva (lining of the eye) are the main routes of infection. The mouth is a less likely primary route of infection.
54
What is the likely mechanism of RSV transmission based on experimental infection routes?
Based on the experimental infection data, mechanical transmission is believed to be a significant mode of spread. This occurs via hands touching contaminated surfaces (with large respiratory droplets) and then making contact with the nose and eyes.
55
Describe the progression of RSV replication within the respiratory tract following initial infection.
Initial replication of RSV occurs in the upper respiratory tract. This is followed by infection of the lower respiratory tract, leading to infection of the bronchioles (small airways) and, in some cases, bronchiolitis (inflammation of the bronchioles).
56
What is the primary cause of airway damage in RSV infection?
The immune system contributes to the damage through generalised inflammation within the lungs (with the migration of inflammatory cells e.g. monocytes and T cells), which can cause necorisis of the epithelial cell wall, edema in the submucosa and increase mucous production. virus-induced cell death of the infected respiratory epithelial cells is also a key component leading to airway damage in RSV infection.
Together, the sloughed epithelial cells, mucous plugs, and accumulated immune cells cause obstruction of the lower airway.
57
Explain why RSV infection can lead to severe respiratory problems in infants, especially premature infants or those with underlying lung disorders.
Infants, particularly premature babies or those with pre-existing lung conditions, have physically smaller airways. Inflammation caused by RSV infection, the accumulation of cellular debris from dead infected cells, and the infiltration of immune cells all contribute to the bronchioles becoming blocked (already smaller to begin with) impairing airflow, leading to respiratory problems and potentially respiratory failure.
58
What factors contribute to the increased spread of RSV during the winter months in temperate climates?
- Increased time spent indoors: Closer proximity facilitates transmission of large droplets.
- Onset of school after the summer break: School-aged children can introduce the virus into households with younger siblings.
59
How does the seasonality of RSV outbreaks potentially differ in tropical climates?
In tropical climates, reports suggest that RSV outbreaks may coincide with religious festivals or the rainy season, indicating that different environmental or social factors might influence transmission patterns compared to temperate regions.
60
What impact did early data from Australia suggest regarding RSV disease burden and what was it attributed to?
Early data from Australia indicated a huge reduction in their RSV disease burden. This was attributed to increased public health measures implemented (likely in response to other respiratory viruses e.g. COVID) and increased self-awareness of the importance of personal hygiene.
61
Which age group of infants is considered most at risk for severe RSV infection?
Infants between the ages of 6 weeks to about 9 months
62
What is an additional risk factor for severe RSV infection in infants beyond their age?
is having older siblings, especially if they are of school age, as they can bring the virus home.
63
why are children under the age of 6 weeks less at risk
because they are protected by maternal antibodies
64
What is the approximate rate of hospitalization among infants at highest risk for RSV infection in modern industrialized nations?
0.5-2% (these numbers can get worse in less developed countries)
65
What is the approximate mortality rate among infants hospitalized for RSV infection in modern industrialized nations?
Of those infants hospitalized for RSV infection, approximately 0.5-2% will die from respiratory failure.
66
why are students big drivers of RSV epidemics
because each student is bringing the most prevalent strain from their region (different everywhere) and sharing it with others
67
what effect does mask wearing have with face touching
It supposedly reduces the number of times you touch your face
68
What are the main RSV antigenic proteins recognised by B cells?
G (attatchment) and F(fusion) glycoproteins (they stimulate antibody production)
69
What is the nature of the antibodies raised against the F and G proteins of RSV?
In many cases these antibodies are neutralising which are capable of protecting the host from re-infection and reduces the severity of clinical disease. However, it doesn't usually prevent reinfection entirely, contributing to the repeated nature of RSV infections throughout life.
70
Which RSV proteins elicit a T lymphocyte response?
N (nucleoprotein), SH (small hydrophobic), F (fusion), M (matrix), M2 (both M2-1 and M2-2), and NS2 (non-structural protein 2).
71
What is the primary role of the T cell response in RSV infection?
The T cell response is more important in the clearance of established RSV infection rather than providing protecting from reinfection
72
What is the significance of an "inappropriate" T cell response in the context of RSV vaccine development?
An inappropriate or skewed T cell response is thought to have been responsible for the immune pathology (enhanced disease) observed during a formalin-inactivated RSV vaccine trial in the 1960s, highlighting the importance of eliciting a balanced and protective T cell response in vaccine design.
73
what are the two major subgroups of RS virus
A and B
74
What is a notable difference in the isolation frequency of the two major RSV subgroups from hospitalized children? What might this suggest?
Subgroup A is isolated more often from hospitalised children than subgroup B, suggesting that subgroup A may be more pathogenic (more likely to cause severe disease requiring hospitalisation).
75
Where are the most notable genetic differences found between RSV subgroups A and B? What does the overall genetic divergence suggest?
Differences between subgroup A and B are apparent in the sequences of all the genes but are most notable in the F, SH, and especially G proteins. The widespread genetic differences across the entire genome suggest that the two subgroups represent diverging evolution rather than simple antigenic heterogeneity in a few surface proteins.
76
Describe the further division within each major RSV subgroup.
Within each major subgroup (A and B), further divisions can be made, and these are known as genotypes.
77
What are genotypes?
the genetic makeup of an individual organism
78
How can each RSV subgroup be further divided?
By their genotypes?
79
Example subgroup A genotypes?
GA1
GA2
GA3
GA4
GA5.....
80
What is the prevalence of RSV genotypes during outbreaks?
ultiple genotypes within both subgroups are known to co-circulate in a single outbreak and can be isolated worldwide, contributing to the genetic diversity of the circulating virus population and the fact that you can get repeated re infection throughout your life
81
How does the antigenic diversity of RSV contribute to its ability to repeatedly reinfect individuals throughout life?
The existence of two major subgroups (A and B) and multiple genotypes within each subgroup leads to significant antigenic variation. This allows the virus to evade the host's existing immunity acquired from previous infections with different subgroups or genotypes, enabling repeated reinfections throughout life.
82
Which RSV protein exhibits the most significant antigenic diversity?
Most of the antigenic diversity in RSV is found within the G protein (although there are some regions of the protein which are highly conserved between all isolates of RSV)
83
Describe the extent of amino acid variation in the G protein of RSV.
The G protein, which is 298 amino acids long, is highly divergent in its amino acid sequence both within and between the two major subgroups (A and B). This high variability contributes significantly to the antigenic differences between RSV strains.
84
what makes up the G protein
- N region inside the membrane
- Yransmembrane (TM) regions which crosses the lipid membrane stolen (has a hydrophobic transmembrane domain) from the infected cell
- outside region (extracellular domain) which is the exposed portion crucial for attachment to host cells, antigeneicty and glycosylation
- 4 Cysteine Regions which are disulphide bonded together which help maintain the correct folding of the G protein for proper receptor binding and immune recognition.
85
What is thought to be the heart of the attachment side of the G protein
The 4 cysteine region
86
what is an example of a constant region in the G protein
The transmembrane region
87
what is accurate to say about areas that the RS virus can and cannot change
certain proteins of the RSV are highly tolerant to change but still retain their function which allows them to be variable. Constant regions cannot retain their function when changed.
88
How can RS manage to reinfect people symptomatically and cause illness
Repeat re-infection is a hallmark of RSV. While the exact mechanisms allowing symptomatic re-infection are still debated, it's presumed that some form of antigenic drift, similar to influenza, might play a role, allowing the virus to evade existing immunity. However, proving the direct evolution of new dominant lineages from old ones over time has been challenging. Instead, dominant lineages often shift and get replaced by new lineages in subsequent seasons within a city. when a region gets dominated by a new lineage/ genotype they won;t have pre existing immunity allowing it to spread more rapidly amongst the immunologically naive population
89
Describe the outcome of the formalin-inactivated RSV vaccine trials in the 1960s.
Infants and children who received a formalin-inactivated RSV vaccine in the mid-1960s experienced increased frequency and severity of RSV disease during the subsequent seasonal outbreak compared to unvaccinated individuals.
90
What immunological findings were associated with the enhanced disease observed in the formalin-inactivated vaccine recipients?
: Investigations revealed that the vaccine group developed a high titer antibody response, but these antibodies were not effectively neutralizing, especially against the F protein. Consequently, their memory antibody response failed to provide protection, requiring them to mount a primary immune response upon natural infection as if they had never been vaccinated.
91
What insights from mouse models shed light on the exaggerated pathology seen with the formalin-inactivated vaccine?
Experiments in mice suggested that the inappropriate antibodies generated by the formalin-inactivated vaccine were not directly responsible for the exaggerated pathology. Further research in mice indicated that the vaccine induced an imbalanced T cell response although the mechanisms remain unclear.
92
what group was the formalin inactivated vaccine tested upon and why could this have given false results?
it was tested apon infants and children who have mature immune systems (less able to mount a balanced and protective immune response)
93
How has the experience with the formalin-inactivated RSV vaccine influenced subsequent attempts to develop an effective vaccine?
The disastrous outcome of the formalin-inactivated vaccine trial has significantly influenced and complicated all subsequent attempts to develop an effective and safe RSV vaccine, leading to heightened caution and a deeper focus on understanding the nuances of RSV immunology.
94
What are some of the primary hurdles in developing an effective RSV vaccine targeting young infants?
- Immunological immaturity: Infants have a developing immune system that may not respond effectively to vaccination.
- Maternal antibodies: High levels of circulating neutralizing antibodies passed from the mother can neutralize the vaccine antigens, hindering the infant's own immune response.
- Long term immunity might also not be effective as the virus already manages to repeatedly re-infect
95
What other population group is considered a promising target for RSV vaccination?
Elderly patients, who can also suffer serious RSV-related disease, are considered another promising target group for RSV vaccination.
96
What significant progress has been made in RSV vaccine development, particularly targeting the F protein?
Studies of the F protein structure revealed its pre-fusion and post-fusion states. The pre-fusion state contains potent antibody binding sites that are highly effective at neutralizing the virus.
97
What strategy has been employed to enhance the efficacy of F protein-based RSV vaccines?
Extensive research has focused on introducing mutations into the F protein to stabilize it in the pre-fusion state and prevent it from flipping to the less immunogenic post-fusion conformation.
98
What are the outcomes of recent clinical trials involving stabilized pre-fusion F protein vaccines? What vaccine platforms have been successful?
The latest versions of these pre-fusion stabilized F protein vaccines have shown highly effective results in clinical trials, leading to long-term, highly neutralizing antibody responses. Successful vaccine platforms include both adenovirus-based and mRNA-based vaccines. These vaccines have now been licensed for use in specific populations (e.g., older adults, maternal vaccination to protect infants).
99
What is the status of "cold-adapted" mutant RSV strains in vaccine development?
"Cold-adapted" mutants of RSV, which are attenuated (weakened) strains designed to replicate poorly at body temperature but can induce an immune response, have been assessed in infants but are currently on the back burner in terms of widespread development compared to the F protein-based vaccines.
100
what have experimental studies in mice shown
that passive antibody transfer of serum antibodies could be protective
101
What evidence suggested the importance of neutralizing antibodies in protecting against severe RSV disease in young infants?
- Maternal antibodies: Circulating maternal antibodies protected very young (<6 weeks) infants from serious RSV disease.
- Cord blood titers: A correlation was observed between high neutralizing antibody titers in cord blood and a reduced frequency of severe RSV infection in infancy.
- Passive antibody transfer in mice: Experimental studies in mice showed that transferring serum antibodies could provide protection against RSV
102
What is Synagis (Palivizumab)? What is its target and mechanism of action?
Synagis (Palivizumab) is a humanized monoclonal antibody specifically designed to bind to and neutralize RSV of both subgroups (A and B). It works by binding to the fusion (F) protein of RSV, thereby preventing virus-cell membrane fusion and inhibiting viral entry into host cells.
103
Way of remembering Synagis / Palivizumab name
Syn-: Think of "synchronizing" or "stopping" the virus.
Pali-: Connect it to "palliative" meaning protective or easing suffering.
vizu-: Connect it to the vulnerable "visage" (face) of an infant.
mab: Monoclonal antibody reminder.
104
What is the spectrum of activity of Palivizumab against different RSV strains? What was its efficacy in clinical trials?
Palivizumab neutralizes both subgroup A and subgroup B viruses and all lineages within the subgroups tested to date. Administration to pre-term infants at high risk for RSV infection in a large multicenter trial demonstrated its effectiveness in preventing severe disease.
105
What is Nirsevimab, and how does it compare to Palivizumab?
Nirsevimab is a newer and even better humanized monoclonal antibody used for RSV prevention. It exhibits superior binding to RSV (both subgroups) and more potent neutralization of the virus compared to Palivizumab. Clinical trials have shown it offers a very high (>80%) reduction in hospital admissions in pre-term or immunocompromised newborns. It has been widely deployed recently.
106
What is the current status of RSV vaccine development? What types of vaccines are now available?
Several vaccines based on the stabilized pre-fusion F protein are now available. These include:
- Two purified protein vaccines (Pfizer and GSK)
- An mRNA vaccine (Moderna)
- An adenovirus-based vaccine (J+J)
All these vaccines contain versions of the F protein stabilized in its pre-fusion conformation for both subgroup A and subgroup B of RSV.
107
What vaccination strategy is being promoted in addition to vaccinating the elderly to protect vulnerable infants?
In addition to vaccinating the elderly, vaccinating pregnant women is being promoted as a strategy to provide passive immunity to their newborns through the transfer of maternal antibodies.
108
What is Ribavirin, and what is its proposed mechanism of action against RSV? What are its limitations?
Ribavirin is the only antiviral drug indicated for use in RSV-infected patients. It is a nucleoside analogue that is thought to increase the rate at which errors are introduced into the viral genome, potentially leading to error catastrophe. However, it also generally inhibits RSV mRNA production. The text implies that Ribavirin is considered "rubbish", suggesting it has significant limitations in efficacy or tolerability, and its exact mechanism of action against RSV is not fully clear.
109
What approach has been used to identify new antiviral agents against RSV?
New antiviral compounds against RSV have been identified using a well-established approach of screening large numbers of compounds in assays that measure some aspect of viral replication. This allows researchers to identify molecules that can interfere with different stages of the RSV life cycle.
110
What is ALS8176, and what viral target does it inhibit?
ALS8176 is a promising antiviral compound that targets the viral polymerase of RSV. By inhibiting the polymerase, it would interfere with viral RNA replication and transcription, thus blocking viral propagation.
