Neutrophils Flashcards
What is another name for Ns?
Polymorphonuclear (PMN) cells
True or false - Neutrophils are the last to reach the site of trauma
FALSE - they’re the first
What are N called in birds?
heterophils
N are potent effectors. What are their 3 effector functions?
phagocytosis, degranulation and formation of extracellular traps
What does it mean by N are temporally limited?
This means that they don’t last very long
What is the regulatory function of N?
recruitment of M0 to the tissues
True or false - N contribute to extensive host tissue damage
TRUE
How do N minimize host tissue damage?
rapid granulocyte recruitment, short lifespan, replacement by Mo derived M0s
What molecules are required for granulocyte differentiation?
IL3, IL6, GM-CSF, G-CSF, and specifically IL8 (CXCL8) for N
N do 3 things rapidly. What are these?
rapidly produced to maintain numbers in circulation, rapidly mobilized from circulation to damaged tissue, rapidly replaced during granulopoises
How were N initially subdivided?
By the presence of MPO. MPO+ = auzurophil granules. MPO- = specific granules
What are the 5 enzymes present in auzurophil granules?
elastase, cathespin G, proteinase 3, MPO, lysozyme
What is the function of elastase?
N endothelial cell adhesion
What are the functions of cathespin G?
bacteriocidal, tissue remodelling, DC and Mo trafficking
What is the function of proteinase 3?
activate cells in close proximity to secrete Mo cytokines
What is the function of MPO?
generation of Ras
What are the functions of lysozyme?
destroys peptidoglycans of Gran 1’ve bacteria, innate opsonin
What are the 2 cationic proteins present in auzurophil granules?
defensins and azurocidin
What is the function of defensins?
interaction with bacteria to kill them!
What are the functions of azurocidin?
antimicrobial, increase endothelial cell adhesion for Mo and DC & Mo trafficking
What do specific granules contain?
aghesion molecules, TNF receptors, collagenase, lactoferrin & haptoglobin (iron binding molecules)
What do gelatinase granules contain?
adhesion molecules, matrix metalloproteins, TNF receptors, lysozyme and arginase
What are teh functions of matrix metalloproteins?
remodel ECM to increase ease of cell migration into tissues and cleave cytokines to increase or decrease bioactivity
During entry into tissues, N release secretory vesicles containing what that are deposited in the cell membrane to bind ligands?
adhesion molecules, PRRs, cytokine receptors, chemokine receptors, Fc receptors
What is the order of release of granule types?
gelatinase, auzurophil then specific
Once in the tissue, N release another vesicle what creates?
a chemokine gradient for infiltration of M0
What are the 4 stages of N extravasion?
tethering, rolling & adhesion, increase adhesion and N activation, trans-endothelial cell migration
How does Stage 1 of N extravasion work?
P-selectin on endothelial cells in up regulated by detection of PAMPs which will attach to the N L-selectin so N now transiently attaches
What is the expression of L-selectin regulated by?
ADAM17
How does Stage 2 of N extravasion work?
endothelial cells secrete platelet-activating factor (PAF) which triggers rolling of the N. N adhesion is facilitated by up-regulation of ICAM 1&2 by the endothelial cell and release of elastase by N which cleaves leukosialin (anti-adhesion) from endothelial cells
Expression of adhesion molecules ICAM 1&2 is regulated by?
ADAM17
How does Stage 3 of N extravasion work?
N releases P-selectin and endothelial cells E-selectin to increase adhesion. N requires a dual signal to activate. Signal causes release of some granules therefore loosening tissue matrix allowing for migration
What is the dual signal N requires for Stage 3 of N extravasion?
1 - ICAM/integrin interaction
2 - TNFalpha, CSCL8 or C5a
How does Stage 4 of N extravasion work?
attachment of N to adhesion molecules in endothelial cell tight junctions and subsequent protease digestion of the basement membrane of endothelial cells
What are the 4 stages of N phagocytosis?
Chemotaxis, adherence and opsinization, Ingestion, destruction
How does stage 1 of N phagocytosis work?
receptors called lamellipodia on N detect chemotactic agents in tissues to direct N movement
How does stage 2 of N phagocytosis work?
opsonins are posatively charged while cell membranes (host and microbe) are negatively charged so they bind and facilitate phagocytosis
true or false - opsonins are not species and age specific
false
Neonates rely heavily on _______ opsonins but receive _______ opsonins through passive immunity
innate, acquired
Fish and chickens’ maternal acquired opsonins are deposited where?
in the yolk sac during egg development
What are the 5 innate opsonins?
MBL, lysozyme, serum amyloid A, C-reactive protein, C3 breakdown products
What are the 2 acquired opsonins?
Igs via Fc receptros, IgM + Cl via C1Q receptor
What two molecules can perform opsonin-independent phagocytosis?
mannose receptors and some integrins
How does stage 3 of N phagocytosis work?
N pseudopodia surround the particle forming a phagosome which combines with lysosome to form phagolysosome.
What happens when the particle is too big to phagocytise?
The N will release some granular content to break down the particle but this will also damage host tissue
How does stage 4 of N phagocytosis work?
Kills the particle via two mechanisms
What are the two mechanisms N uses to kill the particle?
(1) Oxygen dependent and (2) oxygen independent
Draw and describe the oxygen dependent pathway
do it
How are N protected from exposure to ROS toxicity?
hydrogen peroxide splits H2O2 into O and H2O
glutathione (GSH) reduces oxidants
iron-binding proteins reduce iron bioavailability
The oxygen independent pathway is critical for what kind of species?
those lacking MPO (ex. chicken)
How does the oxygen independent pathway work?
microbial oxidation occurs which decreases pH and therefore increases activity of lytic enzymes
What are the 5 lytic enzymes?
elastase, cathespin G, lysozyme, proteases, acid hydrolases
What are the 2 cationic microbial peptides and what do they do?
defensins and cathelicidins. Function is interacting electrostatically with the negative membrane components therefore disrupting integrity of the microbial membrane
What is the function of keratinocytes and muscosal epithelial cells?
express defensin genes, induced during auzurophil granule formation
In what species is the gene for alpha defensin missing?
chickens, fish and livestock species
What species has more cathelicidin genes than primates and chickens?
pigs
What are the 6 functions of defensins?
disrupting microbial surfaces, chemoattractant for N, Ma, DC, Mo and fibroblasts, induce apoptosis of infeected host cells, anti-inflammatory by sequestering LPS and LTA, induce Ma cell degranulation, antiviral
N extracellular traps (ETs) are released by?
dying N
What are ETs composed of?
nuclear chromatin, histones, antimicrobial granule cargo
Compare netosis and apoptosis
netosis involves NADPH-oxidase-mediated superoxide production and apoptosis involves caspases and DNA becomes fragmented
How are N regulated during inflammation?
Secrete chemokines to attract Mo and chemotactic signals to attract Mo and DCs
How do N directly activate DCs?
cell-cell contact through N CD11b ligation with DC-SIGN
How do N direct immune response?
by producing IFNgamma therefore driving T-cell differentiation and M0 activation
What doe N produce that promotes B cell survival?
BlgammaS
How are N regulated during resolution?
By secreting pro-resolution molecules to terminate the influx of N and promote the influx of Mo
What are the 3 pro-resolution molecules?
lipoxins, resolvins, protectins
How are lipoxins generated?
from arachidonic acid using LOX
How are resolvins and protectins generated?
from n-3 FAs by enzyme cascades: COX2, cytochrome P450 and LOX
What do N produce to help against tissue damage?
IL-10
What is the hallmark of inflammatory tissue resolution?
clearance of apoptitic neutrophils by M0 or mucosal surfaces
N apoptosis is coordinated by what transcription factors?
hypoxia-inducible factor and FOXO3A
What are N apoptosis “find me signals”?
Thrombospondin 1 which attracts M0s
What are N apoptosis “eat me signals”?
lysophosphatidylcholine and phosphatidyserines which trigger scavenger-receptor mediated apoptosis
Draw the N phagocytosis cascade
draw it
