Viral and Immune system

Question 1

Influenza virus

Answer 1

causes infections of URT.
RNA- enveloped virus

Inside the lipid envelope there are 8 segments of single stranded RNA

Question 2

Function of M1 and M2

Answer 2

Matrix protein 1- beneath the envelope, provides virus its shape and stability

Matrix 2 protein- ion channel protein in virus envelope. important for uncoating the virus once it enters the cell

Question 3

2 surface proteins of virus

Answer 3

Haemagluttinin
Neuraminidase

Question 4

Function of haemagluttinin

Answer 4

binds to sialic acid groups on host cells, crucial for viral entry into cell

Question 5

Function of neuraminidase

Answer 5

cleaves sialic acid from host cells so virsues don’t stick together and helps them spread efficiently

Question 6

how many types of influenza are there and which ones

Answer 6

3
A- most common, caused major pandemics
affects humans, pigs.
There are variations in HA and NA which make subtype of A virus.

B- found in humans and seals

C- causes mild illness

Question 7

During the first exposure to viruses, humoural response is activated. What does this mean?

Answer 7

Natural IgM is produced

Complement is activated

These combined neutralise the virus and cause lysis

Question 8

Which antibody is produced during first expsoure to the virus and what is its function

Answer 8

Natural IgM

1- Recognise specific markers on apoptotic cells and binds to them.
Once bound, it helps recruit phagocytes like macrophages which enhance phagocytic clearance of dead and dying cells.

2- It recognises a wide range of viral antigens. and cause neutralisation e.g. covering surface proteins which then prevents virus from entering the host cells and causing infection

3- Can activate the complement as it is the most potent activator of complement

They act as an early non-specific defense system and provides protection against pathogens not encountered

Question 9

Other than humoural response, cell mediated response is also activated when virus infects the cell for the first time. What cells are included in this

Answer 9

Non-immune cells

Cytotoxic T cells and NK cells

APCS
Dendritic for cross-presentation

Question 10

How do non-immune cells respond to a virus

Answer 10

Infected non-immune cells produce IFN (a and b) and IL-12

Interferon gamma binds to interferon gamma receptors which leads to:

1- Increased expression of specific genes
2- degradation of viral RNA - no more viruses can be made
3- inhibition of protein synthests- this prevents virus from making its own proteins and prevents replications

These two also trigger the stimulation of NK cells

Question 11

How do CD8 cells destroy viruses

Answer 11

Phagocytes engulf the infected or apoptotic cells.
These are presented on MHC-1 molecules
Cytotoxic T cells recognises the viral antigens presented and induce apoptosis via fas-dependent or fas-indeoendednt mechanims.

Question 12

NK mechanism

Answer 12

These only induce apoptosis in cells which have lower MHC-1 molecules

Killing via fast-dependent and fas-independent

Question 13

What role do antibodies play in responding to viral infections

Answer 13

-prevent binding of viruses to host cell receptors
- even if viruses bind to receptors, Ab can block fusion steps, stopping viruses from entering the cell membrane/endosome.
-Prevent viruses from budding out of infected cells, stopping its spread to new cells
- induce ADCC

Question 14

How do antibodies and complement together help with eliminating viruses

Answer 14

causes agglutination- helping with clearance from lymphoid organs
opsonisayion
Lysis via classical pathway (only enveloped virus)

Question 15

Which PRR recognises ssRNA

Answer 15

TLR7

Question 16

Which PRR recognises viral DNA

Answer 16

TLR9

Question 17

Once these TLR receptors are activated, what happens?

Answer 17

signalling cacade leading to alteration of gene expressions
this leads to the release of pro-inflammatory cytokines. The expression of the interferon receptor is upregulated

Question 18

How does virus evade phagocytosis

Answer 18

herpes virus express surface proteins which inhibit macrophage activation

Question 19

hoe does virus evade complement

Answer 19

some viruses cause host cells to produce CD5s proteins which block complement attack

some viruses like hiv use complement receptors like CR1 to enter into the host cell

Question 20

how does virus block cytokines release

Answer 20

block interferon gamma a and b, which helps activate protein kinsase (helping shut down viral replication)

no protein kinase- virus keeps replicating

Question 21

How do viruses evade cell mediated cytotocicity

Answer 21

downregulate MHC1 expression
Some may make fake MH1 proteins

Some downregulate MHC2 - no antigen presentation - no apcs

some viruses blockantigen presentation processing - e,g, blocking tap

Question 22

how do viruses evade antibody response

Answer 22

bind to Fc region, preventing binding of other cells like NK, macrophages