Immune Evasion

Question 1

what constitutes our immune response?

Answer 1

neutrophils
eosinophils
basophils
dendritic cells
macrophages

Question 2

function of neutrophils?

Answer 2

perform effector functions –> kill microbes
most abundant leukocyte in blood

Question 3

why must neutrophil responses be balanced?

Answer 3

to prevent infection, but also prevent damage to host

Question 4

steps of how neutrophils work?

Answer 4

1) microbes enter body and become opsonised with antibodies and complement
2) results in production of gradient of C3a and C5a as well as bacterial proteins and peptides
3) C3a and C5a bind to their receptors on endothelial cells which causes endothelial cells to express ICAM at their surface
4) when neutrophils contact endothelial cells they detect this increase in ICAM, roll along surface and then transmigrate across endothelial layer
5) they become primed by gradient of c3a and c5a
6) migrate towards complement components and bacterial proteins via chemotaxis
7) become activated and perform effector functions -> can be phagocytosis or degranulation
8) neutrophils also recruit other immune cells

Question 5

what is staph. aureus?

Answer 5

gram positive bacteria which is commensal and lives harmlessly in some humans
OPPORTUNISTIC so has the ability to cause minor-severe infections in some people

Question 6

s.pygogenes?

Answer 6

gram-positive
can live harmlessly in the throat of humans
also opportunistic, can cause a range of disease e.g. skin infections

Question 7

antibody opsonisation?

Answer 7

antibodies bind to bacterial antigens which allows:
deposition of complement
neutrophils and other phagocytes the ability to detect invading microbes

Question 8

capsule polysaccharide?

Answer 8

one of the ways how bacteria evade antibody opsonisation
bacteria express capsule on their surface
this capsule hides antigenic structures that would be detected by antibodies

Question 9

surface proteins

Answer 9

Spa (protein A) and M surface proteins bind antibodies via Fc region but not Fab region
this prevents normal opsonisation
neutrophils cannot detect S.aureus or S.pyogenes

Question 10

proteases?

Answer 10

another method to evade antibody opsonisation
proteases cleave or modify antibodies
this prevents normal opsonisation and therefore neutrophils cannot detect s.pyogenes

Question 11

what are the 3 mechanisms via which the bacteria can evade antibodies?

Answer 11

capsule expression
inhibit antibody opsonisation
degrade antibodies via proteases

Question 12

antigenic variation?

Answer 12

switching up the antigens expressed at surface

Question 13

complement opsonisation?

Answer 13

made up of a large number of proteins that react with one another to opsonise pathogens or directly kill them via MAC formation

Question 14

steps of complement cascade?

Answer 14

1) initiation
2) formation of C3 convertase
3) formation of C5 convertase
4) MAC formation

Question 15

degradation of C3?

Answer 15

a method of evading complement opsonisation
proteases degrade C3
prevents cascade
C3b not deposited
C3a not formed
C5a not formed

Question 16

inhibition of C3/C5 convertases?

Answer 16

SCIN protein binds C3bBb and inhibits formation of C3 convertase and C5 convertase
This again, prevents:
C3b deposition
C3a formation
C5a formation

Question 17

recruitment of negative regulators?

Answer 17

e.g. factor H
these inactivate C3b

Question 18

three strategies of bacteria complement evasion?

Answer 18

degrade C3
inhibit complement convertases
recruit negative regulators

Question 19

how do neutrophils sense and respond to their environment?

Answer 19

express hundreds of different immune receptors at their surface, secretory vesicles and granules

these receptors enable them to sense and respond to their environment

Question 20

how do immune receptors detect bacteria?

Answer 20

directly detect microbes or microbial products e.g.
conserved microbial structures (via TLR receptors)

microbial carbohydrates (via CLEC receptors)

formylated peptides (via FPR receptors)

Question 21

indirect detection of bacteria

Answer 21

microbes can become opsonised by antibodies or complement

neutrophils detect opsonised microbes through Fc receptors or complement receptors