D1. Virus Immunity

Question 1

Describe Virus

Answer 1

protein coat + DNA or RNA genetic code.
Can use reverse transcriptase: convert RNA to DNA
lacks machinery to self-replicate -> host

Question 2

Viral particles =

Answer 2

virions

Question 3

Life cycle of virus

Answer 3

virus enter cell via endocytosis -> uncoated: nucleus -> packaging -> budding & released: virions

Question 4

obligate parasite

Answer 4

requires host to replicate (e.g. virus)

Question 5

To respond to virus immune response must

Answer 5

1. Kill virus particles
2. Clear virus infected cell
3. neutralise viral toxins

Question 6

immune response to virus uses which parts of immune system

Answer 6

innate: type1-IFN, NK, Dendrictic
adaptive: T & B cells

Question 7

which cytokine indicates viral infection

Answer 7

Type 1 IFN = early warning signal: alerts nearby cells
induces: shut down of protein making functions + increases RNA cutting enzymes
activates immunoproteasome + increases MHC expression

Question 8

define Immunoproteasomes

Answer 8

constitutively expressed in APC e.g. dendritic cells, provide specialized cleavage of protein substrates –> high‐quality peptides for MHC‐class I presentation and cytotoxic T cell activation

Question 9

IFNa & IFNB do what to combat virus

Answer 9

1. Induce resistance to viral replication in all cells
2. Increase MHC-I expression & antigen presentation in infected cells
3. Activate dendritic cells & macrophages
4. Activate NK cells to kill virus-infected cells

Question 10

Name a mechanism virus use to avoid immune response

Answer 10

switch off MHC-1 expression / inhibit processing pathway

Question 11

activated NK cells produce ___ which does….

Answer 11

produce IFNy
help activate macrophages, induce T cells –> Th1, kill using same mechs as CTL: apoptosis, carry out antibody-dependent cell mediated cytotoxicity

Question 12

Describe how NK cells

Answer 12

1. antibody binds antigen on surface of target cell
2. Fc receptor on NK recognise bound antibody
3. Cross-linking of Fc receptors signals the NK cell to kill the target cell
4. . Target cell dies by apoptosis

Question 13

virally infected cells die by which mechanism

Answer 13

apoptosis, advantageous: no inflammation

Question 14

how are NK cells activated

Answer 14

by recognition of altered self - altered surface proteins on infected cell may indicate infection (= direct killing by NK)

Question 15

How does NK cells stop evasion of virus, when cytotoxic T cells cant

Answer 15

reduced level of MHC-I might allow virus infected cell to evade cytotoxic T cells
-> NK cells recognise as doesnt express sufficient MHC-I to switch NK cell off

Question 16

Give an example of virus evasion & mechanism

Answer 16

Herpes simplex virus 1: ICP47 –>block peptides entry to endoplasmic reticulum
Mechanism: blocks peptide binding to TAP

Question 17

describe killing mechanism of Cytotoxic T lymphocytes

Answer 17

recognition virus:MHC-I activates CTL killing

release intracellular granules activates apoptosis. Moves on to next cell

Question 18

Pioneer of vaccines

Answer 18

edward Jenner
people infected w/ cow-pox rarely infected w/ small pox
immunised someone w/ cow puss then 8 days later injected virulent small pox
- cow generated memory T cells recognised small pox