Pathogenic Evasion

Question 1

Do pathogens or the immune system have a better advantage?

Answer 1

Pathogens
* Replicate so much that they can evolve very rapidly
* Adaptive immunity can adapt to some extent

Question 2

Methods of passive evasion

Answer 2

Virokines/viroceptors
Bacterial capsules
Infect immunopriviledged tissues
Antigenic drift
Antigenic Shift

Question 3

Virokines/viroceptors

Answer 3

○ Proteins that viruses make that mimic cytokines or cell receptors
* Act as ‘decoys’

Question 4

Bacterial capsules

Answer 4

Slimy outer layer
Covers up proteins on bacteria which tigger and immune reponse

Question 5

Viral latency

Answer 5

○ Shut off replication and lay dormant in cells
○ Evades detection
○ Reactivated at times of stress when immune system is ‘distracted’
○ E.g. herpesviruses

Question 6

Infection of immunopriviledged tissues

Answer 6

○ Hide and replicate in tissues
E.g. testes

Question 7

Antigenic Drift

Answer 7

Basically lots of mutations leading to changes in surface proteins

○ Viruses in particular
○ Undergo lots of replication cycles
○ No correction mechanism of RNA so lost of mistakes accumulate
○ Can code for different surface proteins which will no longer be recognised by antibodies from previous vaccination or infection
Leads to different variants

Question 8

Antigenic shift

Answer 8

Basically gene reassortment leading to new surface proteins

○ Influenza viruses are good at large scale changes in antigenicity
Look distinctly different according to surface proteins
○ If two distinct viruses infect the same cell at the same time
Different proteins of the virus encoded in segments of genes can get reassorted
○ Results in virus with proteins encoded by both parent viruses

Question 9

Methods of active evasion

Answer 9

Infect and kill immune cells
Inhibition of immune effector molecules
Inhibition of cell signalling pathways leading to apoptosis
Stimulation of cell signalling pathways leading to apoptosis

Question 10

Inhibition of immune effector molecules

Answer 10

○ Switching of production of cytokines
○ Interfering with cell signalling pathways

Question 11

Inhibition of cell signalling pathways leading to apoptosis

Answer 11

○ Prevents apoptosis of cells so they continue to replicate virus

Question 12

Stimulation of cell signalling pathways leading to apoptosis

Answer 12

Helps to spread virus by releasing viral proteins