Viral block

Question 1

What are viruses?

Answer 1

Obligate intracellular parasites

Question 2

What does a virus particle consist of?

Answer 2

a nucleic acid genome protected by a protein shell (capsid), which may be surrounded by a membranous envelope

Question 3

What are the members of the virus group I? Examples?

Answer 3

dsDNA viruses - HSV, adenovirus

Question 4

Group II, examples

Answer 4

ssDNA viruses - parvovirus

Question 5

Group III, examples

Answer 5

dsRNA - Reoviruses, bluetongue

Question 6

Group IV, examples

Answer 6

sense RNA viruses - HCV, polio, Yellow fever

Question 7

Group V, examples

Answer 7

Antisense RNA - Influenza, Ebola, Measles

Question 8

Group VI, examples

Answer 8

RNA reverse transcriptase virus - HIV

Question 9

Group VII, examples

Answer 9

DNA reverse transcriptase virus - HBV

Question 10

What is an example of an icosahedral virus?

Answer 10

Adenovirus

Question 11

What are the 4 steps of the virus lifecycle?

Answer 11

Enter, Replicate, Assemble, Release

Question 12

What are the 3 types of viral components synthesised in the infected cell?

Answer 12

1. the essential replication factors - non-structural proteins
2. subunits that are assembled to form new capsids & virions - structural proteins
3. copies of the viral genome

Question 13

What examples of cytopathic viruses that destroy target cell by cell lysis?

Answer 13

Almost all non-enveloped viruses (adenovirus, polio virus etc)

Question 14

How were viruses identified before the introduction of ELISA?

Answer 14

1. suspected virus-containing cultures grown in widely permissive cells (Vero, Hela, A549)
2. many viruses showdistinct patholgies in culture (e.g. polio in Hep-B cells) - e.g. distinctive plaque formation
3. imaging of infected cells on electron micrographs

Question 15

What are the ELISA based methods?

Answer 15

Identification directly on basis of their antigens or by detecting antibodies to the virus

Question 16

What are the 4 common types of viral disease?

Answer 16

1. Acute Infection e.g. rhinovirus, rotavirus, influenza virus
2. Persistent infection, smouldering e.g. lymphocytic choriomeningitis virus
3. Persistent infection, latent e.g. Herpes simplex virus
4. Persistent infection, slow e.g. Measles virus SSPE, HIV, Human T-lymphotropic virus

Question 17

What are some examples of the cytosolic PAMP sensors?

Answer 17

cGAS, NOD2, MD5, RIG-I

Question 18

What do the cytosolic PAMP sensors do?

Answer 18

trigger expression of inflammatory cytokines (TNFa, IL-1B, IL-12) and 2 classes of interferons - type I (IFN-a, IFN-b) and type III (IFN-L)

Question 19

How do the interferons work against viruses?

Answer 19

they trigger a cascade of Interferon Stimulated Genes (ISGs) which encode over 300 antiviral proteins

Question 20

What do type II interferons (IFNg) do?

Answer 20

they are a key activator of macophages and induces MHC II expression
In innate response: produced by NK cells
In adaptive response: produced by T & B cells

Question 21

What is ELISPOT?

Answer 21

Process of staining antigen stimulated cells for the presence of IFNg

Question 22

How does the adaptive immune system recognise viruses?

Answer 22

Viruses initially present antigens as endogenous protein (MHC I) –> induction of cytotoxic T cells
Once released from the infected cel, virions can present as exogenous antigens via MHC Class II –> CD4 T helper cells

Question 23

What is meant by ‘prodromal’?

Answer 23

Most common symptoms of viral infection. Du to the general effects of innate immune responses (due to interferons)

Question 24

What are the intracellular molecules used for signalling by PRRs?

Answer 24

MyD88, TRAM, TIRAP, TRIF

Question 25

How are NK cells activated in a viral infection? (general)

Answer 25

MHC I act as inhibitory signals to inactivate NK cells. Reduced levels of MHC I caused by viruses would therefore lead to a 'missing self' phenotype which activates NK cells

Question 26

What are the 3 ways in which NK cells are activated?

Answer 26

1. By releasing IFNg - potent inducer of ISGs 2. By releasing cytolytic granules --> directly target the MHC I null cell for destruction 3. By death-receptor mediated cytolysis of target cell

Question 27

What causes NK cells to move towards infected cells?

Answer 27

IL-12 gradients

Question 28

What are the cytotoxins contained within a CD8 T cell?

Answer 28

perforin, granzyme, granulysin

Question 29

How does FAS ligand help in the cytotoxic response?

Answer 29

MHC class I recognition induces CD8 cell proliferation and expression of FAS ligand (FASL). Binding of FASL to FAS on target cell induces a cascade of pro-apoptatic signals leading to target cell destruction

Question 30

What is Antibody-Directed Cell Cytotoxicity (ADCC)?

Answer 30

NK cells have Fc receptor (FcgRIII - CD16) which binds to Fc portion of IgG bound to surface of infected cells. This triggers killing of virus response

Question 31

What type of virus is the influenza virus?

Answer 31

segmented RNA virus. member of orthomyxoviruses

Question 32

Infection in which area of the respiratory tract is associated with a high mortality?

Answer 32

Lower respiratory tract

Question 33

What is antigenic drift?

Answer 33

Gradual accumulation of mutations with changes in the dominant membrane antigens Haemagglutinin (H) & Neuraminidase (N)

Question 34

What is antigenic shift?

Answer 34

A sudden change in the antigenic type, caused by reassortment of the individual segments of genome

Question 35

What group of virus is the HIV?

Answer 35

Class VI

Question 36

What is the family and the genus for HIV?

Answer 36

Retroviridae family, Lentivirus genus

Question 37

What type of virus is the HIV?

Answer 37

Enveloped, single-stranded, positive sense RNA virus

Question 38

What 3 major genes does HIV encode?

Answer 38

1. gag (capsid or core protein) 2. pol (polymerase, integrase, protease) 3. env (envelope)

Question 39

What 6 accessory genes does HIV-1 encode?

Answer 39

tat, rev, nef, vif, vpu, vpr

Question 40

Which cell does HIV infect?

Answer 40

CD4+ T cells

Question 41

How does HIV bind to the host cell?

Answer 41

Binding via the gp120 envelope protein and 2 co-receptors (CCR5, CSCR4) which subsequently bind to gp120 and cause structural changes to allow virla membrane to fuse with CD4+ T cell plasma membrane

Question 42

What changes occur during translocation to the nucleus?

Answer 42

Reverse transcriptase converts the viral ssRNA into a dsDNA copy, the viral integrase enzyme then cuts the host DNA & ligates in the viral dsDNA genome (provirus)