Immune Response and Evasion of Immune Response

Question 1

What are the two most important innate immune responses to virus?

Answer 1

Type 1 Interferons and Natural Killer cells.

Question 2

What do Type 1 interferons do?

Answer 2

Antiviral cytokines that make cells more resistant to virus. Upregulate MHC I presentation.

Question 3

What do Natural Killer cells do?

Answer 3

Recognise decreased MHC expression as a symptom of viral infection.

Question 4

What does virus neutralising antibody do?

Answer 4

Production of antibody against surface antigens interferes with attachment and prevents infection.

Question 5

What do CD8+ T cells do?

Answer 5

Seek out and destroy virus infected cells by detecting MHC I.

Question 6

Give 2 viruses that evade immune system by avoiding innate immunity. How do they do this?

Answer 6

Inhibit interferon response. Pestiviruses (e.g. BVDV) produce proteins that stop production of IFN. Poxviruses stop signalling through IFN r, so no response to cytokine.

Question 7

What viruses use immune priveledged sites to avoid immune system? Which immune system does it evade?

Answer 7

Rabies can gain access to CNS, so evades immune detection. It avoids adaptive immune system.

Question 8

How can a virus avoid VN antibody? (3)

Answer 8

Avoid extracellular transmission, Antigen decoys, Antigenic variation

Question 9

What two viruses avoid extracellular transmission? How do they do this?

Answer 9

Parainfluenza make syncitium. Retroviruses integrate their DNA and cause malignant transformation. (One reason to not use Xenotransplantation)

Question 10

How do antigen decoys help avoid immune system?

Answer 10

Structural protein and soluble version made. Large amounts of soluble are released to saturate antibody, so structural protein is not neutralised. e.g. Ebola.

Question 11

How does Antigenic variation help to avoid immune system?

Answer 11

Affects virulence and vaccines. Antigenic drift and antigenic shift.

Question 12

How do some viruses block antigen presentations to CD8? What will this do to their succeptibility to NK cells?

Answer 12

Immunoevasins can interfere with MHC pathway. Some block peptide entry into ER, others prevent MHC transport. More succeptible to NK cells.

Question 13

How can a virus avoid cell mediated immunity? (4)

Answer 13

Block antigen presentation to CD8+, Avoid NK cells using MHC decoys, Produce superantigens, resistance to apoptosis

Question 14

How do some viruses avoid NK cells?

Answer 14

Some viruses express fake MHC, often accompanied by MHC pathway blocking.

Question 15

How does a superantigen help to evade the immune system?

Answer 15

Superantigens cross link MHC and TCR non specifically. Non-specific activation which dilutes antigen specific response.

Question 16

What virus uses direct immune suppression to evade immune system? How does it do this?

Answer 16

Feline immunodeficiency virus. It kills CD4+ T cells, and cells of macrophage lineage. TH cells decline, depression of cell and AB mediated immunity.

Question 17

How is FIV transmitted?

Answer 17

Transmitted by blood, saliva and other bodily secretions. Esp biting.

Question 18

How does FeLV avoid the immune system? What is it?

Answer 18

Immune suppression. It is an oncogenic retrovirus. 60% of cats recover, 40% are persistently infected. Eventually cancer of lymph nodes. Spread by grooming.

Question 19

What virus evades the immune system by indirect immune suppression? How does it do this?

Answer 19

Herpesvirus produces IL-10, which is the natural immune system immunosuppressive cytokine.

Question 20

How does BVDV cause immune tolerance?

Answer 20

BVDV infection during pregnancy, foetus survives, but is persistently infected as it recognises viral antigens as self. Calf then sheds large amount of BVDV.

Question 21

What are the two types of BVDV? Which is most important?

Answer 21

Non-cytopathic BVDV causes persistent infection of calves. It can mutate to cytopathic disease = muscosal disease.

Question 22

How would you control BVDV in a herd?

Answer 22

Aim to keep BVDV free herd, test and remove PI calves. Vaccinate to avoid infection during pregnancy.

Question 23

What virus uses latency to avoid the immune system? How does it do this?

Answer 23

Herpesvirus uses latency. e.g. FHV, EQV (1&4). Causes disease in one cell type, then becomes latent in another. Does not integrate DNA and does not replicate. Re-emerges under certain conditions and replicates.

Question 24

Why is Equine Herpes virus significant? What does it cause? Two types?

Answer 24

It is initially resp disease, but viraemia transports virus to pregnant uterus and CNS. 1&4 cause abortion, 1 causes neurological signs in adult.

Question 25

How would you control EHV in pregnant mares?

Answer 25

Early diagnosis, minimise stress in pregnancy, keep pregnant mares isolated from eachother.