Chapter 6

Question 1

How can a pathogen interfere with the complement pathway to avoid the innate immune response?

Answer 1

Using a capsule to prevent C activation or access to fixed C3b
Have bacterial membrane resistant to MAC complex formation
Use a decoy protein to divert C components away from the bacterial surface

Question 2

What are some antiphagocytic strategies?

Answer 2

Toxins
Prevention of opsonisation by covering constant chain
Prevention of contact using a capsule
Inhibition of phagolysosome
Escape in the cytoplasm
Resistance to killing by production of antioxidants

Question 3

What uses iron binding molecules to avoid the innate immune response?

Answer 3

Neisseria produces its own iron-binding proteins to circumvent a shortage created by transferrin.

Question 4

How can the blockage of interferons (INF) be used to avoid the innate immune response?

Answer 4

Some viruses are poor inducers of INF (hepatitis B)

Some produce molecules that block the action of INF in cells (HIV)

Question 5

Why is the adaptive immune response more difficult to evade?

Answer 5

Due to lymphocytes.
B cells can recognize any shape (capsule and coat surface) to opsonize
T cells can recognize any amino acid sequence (even peptides from organisms presented with the MHC)

Question 6

How can viruses avoid immune defenses?

Answer 6

They are intracellular and have no receptors.
They get into the genetic information of the host and replicates with it, can stay latent.
No damage=no signal to immune system

Question 7

What is the hit and run evasion strategy?

Answer 7

When the microbe invades, multiplies and sheds within a few days.
Too quick for adaptive immune system activation

Question 8

What viruses use the hit and run strategy?

Answer 8

Rhinovirus and rotavirus

Question 9

What are some sites where pathogens can hide from circulating lymphocytes?

Answer 9

Skin, intestinal lumen and various secretions, CNS, joints, testes, placenta

Question 10

What happens when pathogens hide in sites from circulating lymphocytes?

Answer 10

IgA can bind to the pathogen and reduce infectious potential, but not kill or control replication

Question 11

What happens in sites with less circulating lymphocytes when the inflammatory process is induced?

Answer 11

Lymphocytes, antibodies and complement will rapidly appear on site.

Question 12

What do retroviruses do?

Answer 12

Their retroviral RNA is reverse transcribed to DNA which becomes integrated into the host DNA
As long as viral products aren’t expressed they aren’t detected

Question 13

What is the most privileged location in the body for pathogens?

Answer 13

The host DNA, occupied by retroviruses like HIV

Question 14

How does molecular mimicry work?

Answer 14

Microbial antigens look like that of the host cell.

Doesn’t prevent the host from making an antimicrobial or autoimmune response, may start attacking itself.

Question 15

What pathogen uses molecular mimicry where?

Answer 15

Streptococcal M-protein in the human heart tissue to cause rheumatic heart disease

Question 16

What happens when the microbial surface is covered with host molecules?

Answer 16

Immunoglobulin molecules of all specificities are bound in an upside down position so the variable chain is not available for detection.
Protein A on streptococcus aureus

Question 17

What is antigenic variation?

Answer 17

The changing of cell surface antigens to escape the immune system so previous antibodies don’t recognize it.

Question 18

When can antigens change?

Answer 18

During infection in the host or when moving between hosts throughout a population

Question 19

How does mutation in the influenza virus work?

Answer 19

Genes encoding hemagglutinin and neuraminidase undergo mutation which leads to antigen change that makes them unrecognizable by B and T memory cells from last flu infection

Question 20

What is antigenic drift? In what does it occur?

Answer 20

Small changes in the antigenic structure (nucleotide bases) due to mutation
Occurs in influenza virus, rhinovirus, enteroviruses

Question 21

What is genetic shift?

Answer 21

Large changes in the antigenic structure due to recombination that can create a completely new virus
Pandemic possibility

Question 22

How does the African trypanosome use gene switching?

Answer 22

It has genes for 1000 different surface molecules.
It can switch 1 gene for the next so that the surface antigens can change weekly. Fever disappears and reappears with each new antigen
Immune system is always playing catch up

Question 23

What is the best example of recombination?

Answer 23

Influenza A virus, when human and avian strains combine after infecting the same host.

Question 24

How does neisseria gonorrhoeae use gene switching?

Answer 24

It changes it’s bacterial surface properties as the infection proceeds.
Initially it will express pili and outer membrane proteins that allow for attachment to the urethral epithelial cells. Once it is established, it may switch off so it’s not sticky for phagocytes
Allows people to be reinfected multiple times, can be different between hosts.

Question 25

What immune cells does HIV infect?

Answer 25

T Cells, Macrophages and Dendritic cells

Stops function

Question 26

How does the measles virus do immunosuppression?

Answer 26

Stops function of T cells

Question 27

How does EBV do immunosuppression?

Answer 27

Stops function of B cells

Question 28

How is the immune response interfered with?

Answer 28

Adenoviruses reduce MHC-1 expression

N. gonorrheoeae and S. pneumoniae are IgA protease

Question 29

How can microbes persist?

Answer 29

Lower infectivity (adenovirus in tonsils)
Stay in a continuously infectious form (hepatitis B virus in blood)
Go into a non-infectious form (latent virus, HSV)

Question 30

What can latent infections do?

Answer 30

Reactivate
Associate with chronic infections (HIV with AIDS)
Associate with cancer (HBV with liver cancer)
Persistance in the community

Question 31

When does reactivation usually occur?

Answer 31

Typically during periods of immunocompromise (disease, cancer, tissue transplant, elderly, pregnancy)

Question 32

What are the 2 stages of reactivation?

Answer 32

Stage A: Stimulus

Stage B: Spread and replication

Question 33

How does HSV reactivate?

Answer 33

Stage A: Stimulated by sunlight or hormonal shift
Stage B: Travels via sensory axon to skin/mucosal surface where it infects epithelial tissues and form virus rich vesicles (cold sore)