Influenza

Question 1

Subtypes of Influenza

Answer 1

A,B,C

Question 2

Most virulent strain of Influenza

Answer 2

A

Question 3

Virus surface antigens

Answer 3

Haemagglutinin (H1-18)
Neuraminidase (N1-11)

Question 4

Antigenic Shift

Answer 4

• Found in Influenza A
• gene swapping in cells simultaneously co-infected with 2 different influenza viruses
• human-bird-animal influenza viruses
• unpredicatable - formation of new strains
• shifts appear at long intervals - cause epidemics

Question 5

Antigenic Drift

Answer 5

• found in both influenza A and B
• point mutation lead to a change in protein coat
• seasonal variation from year to year

Question 6

Avian strains with particular concern

Answer 6

H5N1
H7N9
(most recently have infected humans)

Question 7

Reproductive number of Influenza

Answer 7

1.3

Question 8

Clinical Features of Influenza

Answer 8

• abrupt onset, shivering, malaise, headache, aching limbs, temp > 39

Question 9

How is influenza virus cleared?

Answer 9

Innate and adaptive immunity

• viral RNA recognised by PRRs -> secretion of IFNs and proinflamm cytokines/chemokines

1. IFNs produced by macrophages, pDCs -> stimualtes ISG expression in neighbouring cells
2. proinflamm cytokines -> systemic and local inflamm
   - chemokines -> recruit NFs, monocytes, NK cells to airways

-> neutralising Abs on mucousal surfaces to prevent reinfection (CD4 & CD8 T cell response and memory)

Question 10

How is dsRNA Influenza detected

Answer 10

• infected cell is phagocytosed by macrophages
• recognition of dsRNA by TLR3
• induction of NFkB proinflamm cytokines, IFN, IFN-stimulated genes

Question 11

How is ssRNA Influenza virus detected

Answer 11

• contained within viron
• released via degradation of viral membrane and capsid within acidified endosomes
• ssRNA recongised by TLR7 in pDCs
• TLR7 induces NFkB
• activation of IRF7

Question 12

How is viral RNA within cell recognised

Answer 12

• within cytosol, RIG-1 receptors recognise
• activation of MAVS
• induction of proinflamm cytokines, IFN type 1
• M2 ion channel acitvation -> caspase 1 activation
• release of IL1B and IL-18

Question 13

Influenza proteins that interfere with PRR signalling and IFN production

Answer 13

NSI - expressed in cytoplasm and nucleus, competes with RIG-1 for binding dsRNA -> blocks expression of IFN inducted ISG genes in cells

PB1-F2 - destabilises MAV complex

Question 14

How to Abs interfere with stages of viral life cycle

Answer 14

Anti NA:
1. blocks release of virus from mucins
2. blocks virus release from host cells
3. trigger FcR mediated effector functions (ADCC)
4. activate complement

Anti HA:
1. blocks interaction between HA and host cell receptors -> blocks attachment of virus to host cell
2. blocks fusion of viral and endosomal membranes
3. HA needs to be cleaved into HA1, HA2 subunits to produce infectious particles -> blocks HA cleavage

Question 15

How are virally infected cells cleared

Answer 15

CD8+ T cells

Question 16

Most immuno-dominant viral proteins for T cell responses

Answer 16

Nucleoprotein and matrix protein
(highly conserved across strains)

Question 17

Humoural immune response

Answer 17

B lymphovytes differentiate into Ab-secreting plasma cells

Question 18

Cell-mediated immune response

Answer 18

Ag presentation via MHC1 and MHC2 via DCs
-> activation of CD4/8
CD4- Th cells - cytokine release
CD8 - CTL - directly kill

Question 19

Kinetics of Immune Response to a Primary Influenza Infection

Answer 19

IFN response is immediate followed by:
- NK cells
- CTLs
- Abs

Question 20

Season Influenza strains

Answer 20

H1N1/ H3N2
- strong tropism of URT, trachea, bronchi
- virus attached to ciliated epi cells
- necrosis of resp epi and infiltration of lamina propria by lymphocytes
- leads to rhinitis, paranasal sinusitis, pharyngitis, laryngitis

Question 21

HPAIV

Answer 21

• highly pathogenic avian influenza virus

HPAIV H5N1
- weak tropism for URT, trachea, bronchi
- inefficient infection in humans

Question 22

H5N1

Answer 22

• strong tropism for LRT, brinchioles, alveoli

Binds to
- clara cells lining bronchioles
- alveolar macrophages
- type II pneumocytes lining alveoli

Question 23

H5N1/N7H9 infection

Answer 23

• severe illness complicated by ARDS and MOF
• high presentation of pneumonia and lymphopenia
• large no. of macros infected with H5N1 compared to H3N2
• large production of cytokines (IL1B, IL-6, IL-8, TNFa)
• large production of chemokines (CCL2 (MCP1), IP10)

Question 24

MCP-1

Answer 24

macrophage chemotactic protein 1
(attracts macrophages to infected lung)

Question 25

IL-8

Answer 25

attracts NFs to lung

Question 26

NS1 gene mutations in H5N1

Answer 26

makes NS1 a more potent inhibitor of IFN production

Question 27

Reason for HPAIV H5N1 severity

Answer 27

high replication in alveolar macrophages induction of secreted pro-inflamm cytokines by infiltrating macrophages

Question 28

Human influenza and associated galactose receptors

Answer 28

2,6 galactose receptors **adaption to recognise this receptor is a requirement for successful infection of human resp cells

Question 29

Avian influenza virus and associated galactose receptors

Answer 29

2,3 galactose receptors in GIT

Question 30

Events required to make viruses successfully infect humans

Answer 30

- optimal temp (shift from 40 degs to 37) - site of replication from intestinal to resp tract - virus receptor specificty changing (alpha 2,3 sialic acid -> alpha 2,6 sialic acid intermediate hosts) *quails and turkeys play a role as they possess sialic acid receptors

Question 31

What strains are highly pathogenic in human and domesticated poultry

Answer 31

H5 and H7 *less pathogenic in aquatic bird reservoirs

Question 32

Influenza vaccine 22/23

Answer 32

influenza A (H1N1) influenza A (H3N2) influenza B (B/victoria lineage) influnza B (B/yamagata lineage)

Question 33

Why are influenza vaccines sometimes suboptimal

Answer 33

antigenic mismatch between vaccine strain and circulating strain

Question 34

Antigenic Sin theory

Answer 34

- flu epitopes encountered in early childhood can permanently shape Ab response to subsequent flu exposures - interferes with new response to the new virus

Question 35

Types of vaccines

Answer 35

Quadrivalent - 4 components - protect against 2nd lineage of B viruses Live, Attenuated (FluMist) - closest to real thing - viruses grown in culture (20 degs rather than 37) adapt to their new conditions and become attenuated (weakened version of virus) Recombinant (FluBlock) - 1st recombinant DNA tech trivalent influenza vaccine - produced using insect virus (baculovirus)

Question 36

Criteria for next generation (universal) influenza vaccines

Answer 36

- 75% effectiveness against symptomatic infection - protection against group 1 and 2 influenza viruses - durable protection that lasts at least a year - suitable for all age groups

Question 37

Influenza viral spike (HA) composition

Answer 37

1. **Head** - sialic acid containing GP receptor - mediates attachement to host cells 2. **Stem** - located prox to viral envelope, involved in fusion to host cell membrane

Question 38

What part of spike are neutralising Abs exposed to

Answer 38

**Head** region - they block virus attachment to cells - these ABs are strain specific - don't neutralise drifting variants due to high mutation rate of HA head - antigenic drift allows viruses to escape AB response

Question 39

Predominant Memory B cell response of influenza infection is to what part of HA

Answer 39

HA Head - STEM directed Abs less prevalent in serum

Question 40

Conserved region of HA

Answer 40

Stem - little increased AB affinity (SHM) observed

Question 41

Head vs Stem of anitgens

Answer 41

**Stem** - not accessible to immune system - restricted access of Abs - Abs with broad reactivity to various strains **Head** - epitopes most likely triggered - immunodominant Abs *universal flu vaccine needs to trigger conserved STEM region

Question 42

Influenza subunit vaccines

Answer 42

use conserved regions of HA stem - promising candidate for broadly protective vaccines - universal vaccine