Lec 8: Granulocytes and Secretion Pathways

Question 1

What is a granule

Answer 1

It depends, but generally, it is a vesicle within a granulocyte

contains immune mediators

Question 2

Purpose of FcR

Answer 2

binds Antibodies can activate granulocytes

Question 3

What are the 4 types of granulocytes

Answer 3

Mast cells
Neutrophils
Eosinophils
Basophils

Question 4

Which activators cause granulocytes to release their granules

Answer 4

FcR
Cytokines
Inflammation
PRR activation

Question 5

How are granules formed

Answer 5

Granules are formed by vesicles budded from the Golgi complex during cell differentiation

Secretory granules are different for they are formed during the course of development, and have a different set of immune mediators from regular granules

Question 6

How are granules classified

Answer 6

Classification is based on:

Production during granulopoiesis
Distinct protein markers

Question 7

What are the three types of graules in NEUTROPHILS, and their mediators

Answer 7

Primary/ azurophilic
Secondary/ specific
Tertiary/ gelatinase

These are in order of production, and release from th= cell is coordinatinated and the reverse of synthesis

Question 8

Markers of Primary/ azurophilic granules and their mediator

Answer 8

myleoperoxidase/ CD63

Myleoperoxidase = Production of HOCl

Question 9

Markers of Secondary/ specific granules and their mediator

Answer 9

Lipocalin–2/ CD66b

Lactoferrin = Up-regulation of neutrophil adhesion molecules and deayed apoptosis

Question 10

Markers of tertiary/ gelatinase granuels and their mediator

Answer 10

Gelatinase/ CD11b

Gelantianse = degradation of the cartilage matrix

Question 11

Neutrophil produced Secratory vessicles

Answer 11

Markers = albumin, CD45, Cd16b and CD13

formed by endocytosis and can secreted extracellular vesicles “exosomes”

Secratory granules can contain newly-synthesized mediators like cytokines and chemokines

Question 12

Classical secratory pathways (w/ granules)

Answer 12

regulated exocytosis
Piecemeal degranulation
consitutive exocytosis

Question 13

Nonclassical secratory pathways (w/ granules)

Answer 13

membrane transporter
exosome release
microvesicle shedding
cell lysis

Question 14

Piecemeal degranulation

Answer 14

small vesicles shuttling large granule contents

Question 15

Regulated granule secreation

Answer 15

Engagement of PRRs or Fc receptors can initiate granule discharge

note PRR and FcRs are DIFFERENT triggers

During activation, not all granules are released simultaneously -> first formed, last released
-> controller release of granules by type based on initiating stimuli

Granules can also be released upon death

Question 16

Snare System (brief overview)

Answer 16

Vsnares and Tsnares allow specificity of granule secreation to target a specific plasma membrane

Snare proteins make SNAREpin structures with lipid membranes

Question 17

V-Snares

Answer 17

V for Vesicle

found on the synaptic vesicle membrane

also called (synaptobrevin/ VAMP)

Question 18

T-Snares

Answer 18

T for Target

found on the plasma membrane

SNAP-23 and Syntaxin-4

Question 19

Purpose of SNARE proteins// mechanism

Answer 19

bindng of snare proteins triggers a conformational change and brings plasma membranes close together and releases contents of the granule

Note, this process is reversible, and thus the granul;e membrane may be recycled and refilled after release from the target membrane

Question 20

Regulated Exocytosis

Answer 20

see diagram

Question 21

Constitutive Exocytosis

Answer 21

see diagram

Question 22

Regulated death of granulocytes

(4 types) and are they pro or non-inflammatory

Answer 22

Apoptosis (less inflammatory)

NETosis, Necroptosis and pyrotosis (deez are inflammatory)

Question 23

Neutrophil death

Answer 23

once a neutrophil is activated it will die (by PAMPS, DAMPS and immune complexes)

phagocytosis -> apoptotic blebbing -> and or autophagy to kill an intracelluar pathogen if present

cellular content released which is highly inflammatory ie/ cellar explosion

Disruption of neutrophil function is associated with tissue injury, chronic inflammation dn autoimmunity

Question 24

NADPH oxidase complex

Answer 24

generates high levels of Reative Oxygen Species,

important in phagosome in which a microbe may be transported into. ROS busts open the micobe cell membrane nd then granules with pre-stored mediators may fuse with the phagosome

Question 25

Neutrophil Extracellular Traps (NETs)

Answer 25

Netosis is the process of secreting NETs -> basically just barfed out DNA Traps for pathogens - > localization of antigens - > increased effectiveness of granulocytes - > Increased concentration of cytokines slows diffusion and allows for better enzymatic antimirobial activity

Question 26

NETosis and Neutrophil Activation

Answer 26

leads to: Activity of phagosome NADPH oxidase generation of ROS Breakdown of intracellular membranes ``` Neutrophil elastase (NE) and myeloperozidase (MPO) enter the nucleus and modify histones, thus chromatin dencondenses ``` Plasma membrane ruptrues and releases cell contents Cell dies form NETosis

Question 27

Problems associated with NETosis

Answer 27

XS antigen presentation from self DNA which leads to antibodies generated against self DNA =clinical conditions like lupus, and other autoimmune dieases

Question 28

What are in NETs

Answer 28

Granule proteins Elastase and cathepsin -> proteinases with broad substrate specificty MPO -> myeloperoxidase has antimicrobial activity DNA and Histones -> Promotion of Thrombosis

Question 29

NETs as drivers of adaptive immunity

Answer 29

Traps pathogena nd keeps it in one area ``` Easier to bind antigen in a closed area -> concentrated area Drives inflammation -> more APCs -> more activaton ```

Question 30

How can microbes evates NETs

Answer 30

directly inhibiting NET formation Coating themselves in a capsule// slime layer secreting endonucleases that degrade NETs Pathogens can also secrete enzymes that convert NET compounds into toxic molecules that kill immune cells -> production of deosyadenosine (dAdo) triggers apoptosis in nearly macrophages

Question 31

What is a granule? What types of mediators are found in granules

Answer 31

?

Question 32

How are granules produced aand secreated

Answer 32

?

Question 33

Name a functiohnof a secreted mediator from neutrophiles

Answer 33

elastase

Question 34

Name a functiohnof a secreted mediator from Basophils

Answer 34

Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.

Question 35

Name a functiohnof a secreted mediator from Eosionophils

Answer 35

eosinophil peroxidase, ribonuclease (RNase), deoxyribonucleases (DNase) and lipase

Question 36

Name a functiohnof a secreted mediator from Mast cells

Answer 36

Histamine

Question 37

Explain how FcRs can facilitate granule secreation. Give an example

Answer 37

? Antibodies -> bind -> activate

Question 38

What is the function of a neutrophil NET, and explain the risk/ benefit ratio

Answer 38

?