Infection and innate immunity

Question 1

What is innate immunity

Answer 1

First line or immediate response to pathogen invasion.

Question 2

What are 3 highly developed and interlinked processes that provide you with innate immunity

Answer 2

1. complement C
2. myeloid cells and phagocytosis (neutrophils and macrophages)
3. pattern recognition receptors (PRR)

Question 3

What is the defence strategy for viruses

Answer 3

Defence relies on antibodies and cellular immunity. It needs to be able to distinguish infected from normal cells

Question 4

What is the defence strategy for bacteria

Answer 4

Defence primarily mediated by innate mechanisms and phagocytosis

Question 5

What is the defence strategy for protozoa and parasites

Answer 5

Complex multi-cellular organisms require direct killing by chemical mediators released by specialist myeloid cells.

Question 6

What do granules contain in relation to degranulation

Answer 6

Granules are filled with cytotoxic chemicals. Degranulation releases these toxic inflammatory chemicals such as histamine.

Question 7

What is gram positive bacteria

Answer 7

They have a thick peptidoglycan cell wall as a defence mechanism.

Question 8

How are gram positive bacteria killed (and not killed by)

Answer 8

Requires phagocytosis but not killed directly by complement.

Question 9

What are gram negative bacteria

Answer 9

Have a think peptidoglcan layer surrounded by an outer membrane. These bacteria can often be lysed directly complement membrane atttack complex.

Question 10

What is neutrophil extravastion

Answer 10

Where neutrophils first sense an infection on other side of cappilary. They slow down and bind to cappilary walls. The cells here would be actuvated to find neutrophils about infection on other side of the cappilary.

Question 11

What are the five steps of neutrophil extravastion

Answer 11

1. Activation
2. Tethering
3. Adhesion
4. Diapadesis
5. Chemotaxins

Question 12

What is activation of neutrophil extravasation

Answer 12

Chemokines from tissue injury or inflammation activate the local endothelial cells lining an adjacent cappilary wall.

Question 13

What is tethering in neutrophil extravasation

Answer 13

Neutroophils tethers to the inside cappilary wall. It is mediatd by selectins which are upregulated on endothelial cells and sialyl Lewis X - carbohydrate antigen on neutrophils.

Question 14

What is adhesion in neutrophil extravasation

Answer 14

Strong binding between neutrophil integrens and ICAM-1 on the endothelium. Neutrophil immobilises and flattens.

Question 15

What is diapadesis in neutrophil extravasation

Answer 15

The neutrophil squeezes between the endothelial cells into the interstitial space.

Question 16

What is chemotaxis in neutrophil extravasation

Answer 16

Neutrophil migrates along a chemical gradient to the site of infection.

Question 17

How do neutrophils phagacytosises

Answer 17

• Chemoattractants such as C5a are being released that radiate away from the bacteria and are sensed by the leading edge of the neutrophil
• Neutrophils migrate up the chemoattractatn gradient, polymerising actin filaments at their leading edge and de-polymerising those filaments at their trailing edge
• Neutrophils have receptors thta bind deposited complement proteins, mainly C3b on the surface.

Question 18

where are complement receptors found

Answer 18

On the surface of all myeloid cells.

Question 19

What are complement receptors

Answer 19

Myeloid cell receptors that bind activated complement components deposited on bacteria.

Question 20

What initiates phagocytosis

Answer 20

Cross-linking of the surface CR’s

Question 21

What is the main neutrophil receptor that binds to C3b

Answer 21

Cr1

Question 22

How does FcR (antibody) mediated phagocytosis work

Answer 22

• Antibody (IgM) and IgG) bind to bacterial antigens.
• This exposes the antibody Fc region which the nuetrophil binds to.
• Activates phagoctyosis
• Membrane invaginates forming a phagosome
• fuses with lysosome to form phagolysosome, which acidifies and superoxides kill bacteria.

Question 23

What is molecular pattern recognition

Answer 23

• Pattern recognition receptors (PRR) bind complex molecules that are unique to microbes
• Activation stimulates a srong innate response through an importatn inflammation pathway.

Question 24

What is the best known pattern recognition receptor (PRR)

Answer 24

Toll-like receptors, they are leucine rich receptors (LRR) that look like a slinky.

Question 25

strucutre,

What are pathogen associated molecular patterns (PAMP’s)

Answer 25

• Molecules unique to microbes recognised by PRR’s.
• They are structurally very complex, which enables antibodies and TLR to recognise its unique features.
• stable

Question 26

What are PAMP’s relationship with adaptive response

Answer 26

PAMP’s stimulate the ‘power’ switch for the adaptive response.

Question 27

What is LPS

Answer 27

A membrane component of all gram negative bacteria which tiny amounts of it can induce a powerful innate response.

Question 28

What can release of LPS by gram negative bacterial infections do

Answer 28

Lead to life threatning septic shock.

Question 29

What does it mean when LPS is described as a pyrogen?

Answer 29

It can cause fever when injected into the bloodstream.