Bacterial infection 3

Question 1

Innate immune response

Answer 1

Rapid, general, always on

Non-specific
Physical and chemical barriers
Can target infected host cells

Question 2

Adaptive immune response

Answer 2

Slower, specific, memory

React to antigens
Generates antibodies
Forms immune memory ice pathogen encountered
Can target infected host cells

Question 3

MAMPs

Answer 3

Microbe-associated molecular patterns

Question 4

PRRs

Answer 4

Pattern recognition receptors

Question 5

TLRs

• means?
• e.g?

Answer 5

Toll-like receptors

e.g. TLR4 binds LPS

Question 6

Innate immune cells

Answer 6

Macrophages

PMNs
= Polymorphonuclear lymphocytes
e.g. neutrophils

Dendritic cells

Mast cells

Monocytes

Question 7

Macrophages

Answer 7

Resident in tissues

1st to encounter pathogen

Secrete cytokines

• can make blood vessels more leaky
• > let neutrophils out
• conc grad
• > directs neutrophils

Communicate w/ adaptive IS
-> present antigens (APC)

Question 8

Oxygen-independent killing

Answer 8

Lysozyme

AMPs
-antimicrobial peptides

Question 9

Oxygen-dependent killing

Answer 9

Activated by TLRs

Free radical production

Oxidative burst
(great increase in O2 consumption)

Question 10

Phagocyte

Answer 10

Cell capable of phagocytosis

e.g. macrophage, neutrophil

Question 11

Phagolysosome

Answer 11

Lysosome deposits enzymes into phagosome

-> cleaves macromolecules + generates ROS

= destroys pathogen

Question 12

NETs

Answer 12

= Neutrophil Extracellular Traps

• release their DNA saturated w/ antimicrobials into surroundings
• > traps + kills bacteria

-> Easier for macrophages to engulf

Question 13

Immune evasion strategies

Answer 13

Stealth
= avoids triggering immune response

Subversion
= manipulate, divert, dampen responses

Resistance
= Vary targets to avoid recognition
- could directly destroy immune effectors

Question 14

Extracellular pathogens must survive…:

Answer 14

Phagocytosis
Antimicrobial peptides
Lysozyme
Mucus shedding

Question 15

Attachment mechanisms can contribute to avoidance…

• when?
• eg?

Answer 15

In pathogens that remain on mucus membrane

e. g. EPEC pedestal formation
- prevents phagocytosis

Question 16

Antimicrobial peptides

Answer 16

e. g. Defensins
- kill bacteria entering crypts to protect stem cells + avoid infection

Bind to bacterial membranes
> form pores + rupture membrane
OR
> enter cell + inhibit functions

Question 17

Antimicrobial protein resistance

Answer 17

EPEC produce OmpT protease
= Outer Membrane Protease

degrade antimicrobial proteins

Question 18

Biofilms

Answer 18

Surface-associated multicellular communities

Cells embedded in exopolymeric matrix

Question 19

Biofilms

-protection

Answer 19

Protect from AMPs, lysozyme + mechanical clearance

Question 20

Stealth

- 3 strategies

Answer 20

> Avoid triggering response
Hide from IS
Mask antigens +/or mimic host ‘self’ antigens

Question 21

Stealth

- masking antigens

Answer 21

Salmonella LPS
- detected by immune cells

S.typhi

• no IS response
• SP17 (PAI) encodes a capsule
• > masks LPS

Question 22

Capsules

- roles

Answer 22

Contains sialic acid residues
- mimic host cells
= prevents phagocytosis

Binds to antimicrobial peptides + complement proteins
- keeps them way from target site

Opsonisation
- Abs bind to capsules to help phagocytosis

Shields antigens/LPS from immune receptors
-> prevents activation of ROS killing + reduces cytokine production

Question 23

Phase variation

Answer 23

Phenotypic variation in a population
- heritable but reversible

Normally affects surface-exposed antigens

ON/OFF switch by promoter inversion

Question 24

Antigenic variation

Answer 24

Not ON/OFF
- range of possible variants

Cell has genetic info to express range on antigenically distinct proteins
-> BUT only expresses 1 at a time

Changes arise via recombination between variable gene regions

Question 25

Antigenic variation

- gene conversion example

Answer 25

N. meningitidis varies pili protein it expresses

Circulates between human hosts
-> requires avoidance of pre-existing Abs
OR avoiding Abs induced upon colonisation