Lec 8: Granulocytes and Secretion Pathways Flashcards
What is a granule
It depends, but generally, it is a vesicle within a granulocyte
contains immune mediators
Purpose of FcR
binds Antibodies can activate granulocytes
What are the 4 types of granulocytes
Mast cells
Neutrophils
Eosinophils
Basophils
Which activators cause granulocytes to release their granules
FcR
Cytokines
Inflammation
PRR activation
How are granules formed
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
How are granules classified
Classification is based on:
Production during granulopoiesis
Distinct protein markers
What are the three types of graules in NEUTROPHILS, and their mediators
Primary/ azurophilic
Secondary/ specific
Tertiary/ gelatinase
These are in order of production, and release from th= cell is coordinatinated and the reverse of synthesis
Markers of Primary/ azurophilic granules and their mediator
myleoperoxidase/ CD63
Myleoperoxidase = Production of HOCl
Markers of Secondary/ specific granules and their mediator
Lipocalin–2/ CD66b
Lactoferrin = Up-regulation of neutrophil adhesion molecules and deayed apoptosis
Markers of tertiary/ gelatinase granuels and their mediator
Gelatinase/ CD11b
Gelantianse = degradation of the cartilage matrix
Neutrophil produced Secratory vessicles
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
Classical secratory pathways (w/ granules)
regulated exocytosis
Piecemeal degranulation
consitutive exocytosis
Nonclassical secratory pathways (w/ granules)
membrane transporter
exosome release
microvesicle shedding
cell lysis
Piecemeal degranulation
small vesicles shuttling large granule contents
Regulated granule secreation
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
Snare System (brief overview)
Vsnares and Tsnares allow specificity of granule secreation to target a specific plasma membrane
Snare proteins make SNAREpin structures with lipid membranes
V-Snares
V for Vesicle
found on the synaptic vesicle membrane
also called (synaptobrevin/ VAMP)
T-Snares
T for Target
found on the plasma membrane
SNAP-23 and Syntaxin-4
Purpose of SNARE proteins// mechanism
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
Regulated Exocytosis
see diagram
Constitutive Exocytosis
see diagram
Regulated death of granulocytes
(4 types) and are they pro or non-inflammatory
Apoptosis (less inflammatory)
NETosis, Necroptosis and pyrotosis (deez are inflammatory)
Neutrophil death
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
NADPH oxidase complex
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
Neutrophil Extracellular Traps (NETs)
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
NETosis and Neutrophil Activation
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
Problems associated with NETosis
XS antigen presentation from self DNA which leads to antibodies generated against self DNA
=clinical conditions like lupus, and other autoimmune dieases
What are in NETs
Granule proteins
Elastase and cathepsin -> proteinases with broad substrate specificty
MPO -> myeloperoxidase has antimicrobial activity
DNA and Histones -> Promotion of Thrombosis
NETs as drivers of adaptive immunity
Traps pathogena nd keeps it in one area
Easier to bind antigen in a closed area -> concentrated area Drives inflammation -> more APCs -> more activaton
How can microbes evates NETs
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
What is a granule? What types of mediators are found in granules
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How are granules produced aand secreated
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Name a functiohnof a secreted mediator from neutrophiles
elastase
Name a functiohnof a secreted mediator from Basophils
Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.
Name a functiohnof a secreted mediator from Eosionophils
eosinophil peroxidase, ribonuclease (RNase), deoxyribonucleases (DNase) and lipase
Name a functiohnof a secreted mediator from Mast cells
Histamine
Explain how FcRs can facilitate granule secreation. Give an example
?
Antibodies -> bind -> activate
What is the function of a neutrophil NET, and explain the risk/ benefit ratio
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