Microbial Immune Evasion

Question 1

What are virulence factors?

Answer 1

➝ components that drive pathogenic processes

Question 2

What is virulence?

Answer 2

➝ the degree to which a pathogen causes disease

Question 3

What 3 things do virulence factors mainly do?

Answer 3

➝ promote adherence or receptor binding
➝ allow bacteria to colonise
➝ promote tissue damage - toxins

Question 4

What are the 5 roles of the complement?

Answer 4

➝ Activate, promote and regulate the inflammatory process
➝ increase phagocytosis by opsonization
➝ increasing vascular permeability 
➝ mast cell degranulation
➝ lysis of cell membranes

Question 5

How does the complement activate, promote and regulate the inflammatory process?

Answer 5

➝ Releasing factors that chemo attract effector cells like macrophages and neutrophils

Question 6

How does the complement increase phagocytosis by opsonization?

Answer 6

➝ binding to the surface of bacteria and viruses allowing them to be phagocytosed by macrophages

Question 7

Why is complement sometimes unable to bind to bacteria?

Answer 7

➝ They have polysaccharide capsuled on their surface and endotoxins
➝ they don’t allow the early stages of the complement cascade to bind to their surfaces

Question 8

What happens if bacteria can bind to factor H?

Answer 8

➝ it can stop the complement activating on the surface

Question 9

How do some bacteria stop C3B binding?

Answer 9

➝ they coat themselves in non-fixing IgA

Question 10

What is C3B ?

Answer 10

➝ a powerful opsonin which allows opsonisation into macrophages

Question 11

When is C5A released?

Answer 11

➝ after the complement is activated

Question 12

What is C5A?

Answer 12

➝ a chemoattractant

Question 13

What are 3 intracellular pathogens?

Answer 13

➝ mycobacterium tuberculosis
➝ listeria
➝ salmonella

Question 14

What is used by bacteria to avoid phagocytosis?

Answer 14

➝ capsules

Question 15

What is protein A?

Answer 15

➝ binds antibodies the wrong way round

➝ they have Fc receptors that bind the antibody by the Fc region not the epitope

Question 16

How does staph damage immune cells?

Answer 16

➝ they produce extracellular toxins that damage the membrane of white cells
➝they prevent opsonization by complement

Question 17

How does M.tuberculosis prevent phagocytosis?

Answer 17

➝ blocks the phago-lysosome formation and stops acidification of the endosome

Question 18

How does Listeria prevent phagocytosis?

Answer 18

➝ escapes the phago-lysosome into the cytoplasm

Question 19

How do some bacteria neutralise the ROS made in the phago-lysosome?

Answer 19

➝ some bacteria produce catalases and peroxidases

Question 20

How do microbes make Fc receptors?

Answer 20

➝ they have proteins on their surface that encode mimics of the Fc receptors

Question 21

Why are microbe Fc receptors effective?

Answer 21

➝ Even if the immune system generates antigen specific antibodies the Fc receptors will bind the antibodies the wrong way round
➝ they can no longer be phagocytosed and killed

Question 22

What are the 4 ways pathogens conceal antigens?

Answer 22

➝ hide inside cells
➝ privileged sites
➝ block MHC antigen presentation
➝ Surface uptake of host molecules - CMV

Question 23

What virus blocks MHC antigen presentation?

Answer 23

➝ Herpes

Question 24

What are 4 ways that pathogens cause immunosuppression?

Answer 24

➝ Decreased MHC
➝ downregulate receptors like interferon gamma, apoptosis, cytokine switch, IgA proteases
➝ Antigenic variation
➝ Persistence/latency/reactivation

Question 25

What pathogen is the common cause of lobar pneumonia?

Answer 25

➝ Streptococcus pneumoniae

Question 26

How is streptococcus pneumoniae breathed in?

Answer 26

➝ through the nasopharynx

Question 27

How does streptococcus pneumoniae prevent antibody degradation?

Answer 27

➝ by secreting IgA proteases

Question 28

What disease does streptococcus pneumoniae often follow and why?

Answer 28

➝ A viral infection because it will have damaged the structure of the defense mechanisms in the respiratory tract

Question 29

What are the main defense mechanisms against streptococcus pneumoniae?

Answer 29

➝ Surfactant and mucus in the lungs

Question 30

How does streptococcus pneumoniae invade the lungs?

Answer 30

➝produces IgA proteases which cleave antibodies ➝ Induces and switches on the genes for pneumolysin which is a toxin that lyses the membranes and causes pores in pneumocytes of the lungs

Question 31

How many serotypes of streptococcus pneumoniae are there?

Answer 31

➝ 80-90

Question 32

How can streptococcus pneumoniae escape phagocytosis?

Answer 32

➝ they have capsules

Question 33

What are 4 ways that pathogens can evade the immune system?

Answer 33

1) Latency 2) decreased antigen presentation 3) decreased MHC expression 4) mutation of epitopes

Question 34

What 2 pathogens can become latent and why?

Answer 34

➝ VZV, HSV | ➝ if the virus were to infect everybody at the same time then the virus would die out

Question 35

Where do latent viruses usually affect and why?

Answer 35

➝ Nerve cells | ➝ they have very little immune surveillance so they can exist undisturbed

Question 36

Which virus decreases antigen presentation and how?

Answer 36

➝ HPV | ➝ binds to the TAP protein and blocks antigen transfer to MHC molecules

Question 37

Which virus decreases MHC expression?

Answer 37

➝ CMV

Question 38

Why do viruses mutate epitopes?

Answer 38

➝ so the B cell antibodies can't work | ➝ they evade the immune cells

Question 39

What is antigenic diversity?

Answer 39

➝ Genetically stable and alternative forms of antigens in a population of microbes

Question 40

What is antigenic variation?

Answer 40

➝ Successive expression of alternative forms of an antigen in a specific clone or its progeny

Question 41

How is antigenic variation done?

Answer 41

➝ Pathogens can switch antigens on or off at low frequency

Question 42

What kind of an infection is gonorrhoea?

Answer 42

➝ Inflammatory and pyogenic infection of the anterior urethra

Question 43

Where does gonorrhoea infect?

Answer 43

➝ mucosal surfaces with a columnar epithelium | ➝ urethra, cervix, rectum , pharynx, conjunctiva

Question 44

What are the 4 symptoms of gonorrhoea?

Answer 44

➝ Dysuria ➝ Redness ➝ swelling ➝ pain on urination

Question 45

What are the 9 pathologies that can occur as a result of gonorrhoea?

Answer 45

``` ➝ Destruction of mucosa ➝ prostatitis ➝ orchitis ➝ strictures ➝ ovaritis ➝ fistulas ➝ PID ➝ proctitis ➝ sterility ```

Question 46

What are three disseminated infections that can occur as a result of gonorrhoea?

Answer 46

➝ Arthritis ➝ Endocarditis ➝ Meningitis

Question 47

Which structures of gonorrhoea can undergo phase variation?

Answer 47

``` ➝ Capsule ➝ pilus ➝ outer membrane ➝ Opa ➝ Inner membrane ```

Question 48

What are the two components of the influenza virus?

Answer 48

➝ Haemagglutinin | ➝ Neuraminidase

Question 49

How many haemagglutinin types are there?

Answer 49

➝ 15

Question 50

How many neuraminidase types are there?

Answer 50

➝ 9 types

Question 51

What kind of genome does the influenza virus have?

Answer 51

➝ segmented negative ssRNA genome | ➝ 8 segments, 10 genes

Question 52

What causes epidemics?

Answer 52

➝ Antigenic drift

Question 53

What is antigenic drift?

Answer 53

➝ as the virus replicates itself it has errors | ➝ if there is a mutation then antibodies do not recognise it

Question 54

What causes pandemics?

Answer 54

➝ Antigenic shift

Question 55

What is antigenic shift?

Answer 55

➝ Two viruses infecting a single cells ➝ they undergo recombination of the genome ➝ There are combinations that are new and the population has not seen before

Question 56

What are the 6 ways that viruses avoid the adaptive immune system?

Answer 56

➝ MHC mimics - block killing by NK cells ➝ downregulate MHC ➝ Block antigen processing by TAP ➝ induce immune suppression by decreasing cell mediated immunity and CD4+ cells ➝ host mimicry ➝ cytokine binding mimics and binding proteins

Question 57

What are the 2 ways that viruses avoid innate immunity?

Answer 57

➝ Latency reactivation | ➝ Rapid growth and transmission prior to adaptive immunity

Question 58

What are the 3 ways that bacteria avoid the adaptive immune system?

Answer 58

➝ Inhibition of antigen presentation ➝ superantigens and inappropriate immune activation ➝ induction/inhibition of apoptosis

Question 59

What are the 4 ways that bacteria avoid the innate immune system?

Answer 59

➝ Prevent opsonin binding ➝ C3a and C5A proteases, anti-inflammatory and anti chemoattractant ➝ inhibits opsonisation ➝ inhibits complement activation