Neutrophils Flashcards
What happens to neutrophils
If do not encounter neutrophils then degrade around 6 hours
If encounter pathogen become active/apoptosis and taken up into tissues where last a couple of days
Neutropenia can?
Lead to severe conditions Kostman’s disease
Can be induced (by chemotherapy) as targets rapidly dividing cells
Including neutrophils
Acute myeloid leukaemia (AML) is
Neutrophilia
Immunocompromised state
Produce to many neutrophilia but not matured and hence non functional
What do neutrophils do
Migrate from blood to site of infection
Detect pathogens and inflammatory mediators from tissue macrophages and and mast cells.
Cause destruction of pathogens and also collateral tissue damage
Actively downregulate inflammation, undergo apoptosis and removed by macrophages
Neutrophils detect pathogens by PRRs
What is inflammation
General term for accumulation of fluid, plasma, proteins and leukocyte initiated by physical trauma,infection or immune response
Stages of inflammation
Activation, cellular migration and extravasation
Microbial detection and killing(mainly neutrophils, then macrophages)
Resolution, switching off and removal
OF cells
Unresolved inflammation which is chronic(>6 weeks) and mainly caused by macrophages and T-cells and leads to Fibrosis and granulomas formation
What is the time course if acute inflammation
Swelling occurs due to influx of tissue fluid
Vascular leakage from blood allows soluble molecules from blood to enter tissues
- occurs rapidly
Next stage involves neutrophils activity
Monocytes/macrophages then clear up site(clear up debris from neutrophilllic apoptosis
What does lipid mediator Thromboxanes do?
Vasoconstriction
Platlet aggregation
Lipid mediator Prostaglandins do?
Increase vascular permeability
Vascular dilation
Neutrophils chemotaxis
How does inflammation intiate?
Damaged cells, Bacterial uptake by macrophages and mast cell degranilation lead to increase in vessel permeability
This causes increase in soluble components from blood such as antibodies and complement
How are cells(what kind) recruited during inflammation
Neutrophils brought from blood to tissues via Chemoattractants
Adhesion molecules on endothelial cells and neutrophils upregulated
Heavily regulated as don’t want inflammation all the time
Examples of chemoattractants
IL-8 secreted by macrophages (also IL-1 and IL-6)
PAF platelet activating factor
How do chemoattractants work
Attract particular molecules toward cells
Peptides from bacteria bind to Receptors on neutrophil surface
Chemoattractants move towards these bound peptides as have formulated methionine
What are the main stages of leukocyte adhesion cascade?
Capture and rolling
Activation and arrest
Crawling and extravasation
Capture and rolling need?
Selectins—
Have high on/off binding rates
Binding is transient to allow leukocyte release
Facilitate rolling
Bind sialylation sugars
Signal PIKy to cause slow rolling
Activation and arrest
Integrity mediate leukocyte arrest via outside in and inside out signalling
Chemokins, TNF and chemoattractants activate integrins
Increase ICAM-1 binding on endothelial cells which is inside out signal
Increases by clustering and conformational change
Outside in via src kinases
Leukocyte adhesion deficiency is?
Due to migration defects in neutrophils
Patients often die from recurrent infection
LAD1- lack cd18 crucial integrity
LAD2- lack fuckayktransferase that generates selectin ligand
LAD3- integrity activation defect
Neutrophil killing steps
Once at site of inflammation neutrophils activated by PAMPS (LPS, b-glucans) and pro-inflammatory cytokines (TNF-a)
Neutrophils poses PRR and opsonic Receptors for recognition and uptake
Antimicrobial molecule delivered by neutrophils?
Oxidative burst - NADPH used to create hydrogen peroxide leading oxygen free radicals which are highly antimicrobial
Nitric oxide synthetase- Reactive nitrogen species produced by this enzyme
Myeloperoxidase- formation of bleach (hypochlorous acid) Pus around wounds produced by dissolution of tissue by this strong acid
What can evade neutrophil killing via disruption of NADPH oxidase complex formation?
Anaplasma phagocytophilum
Primary antimicrobial granules produced by neutrophils?
Also known as Azurophilic
BPI, Neutrophil elastase Cathespin G Protease 3 MPO CAP38 Defensins
Secondary antimicrobial granules produced by neutrophils?
Lactoferrin - binds to iron ions and sequesters nutrients from environment to prevent bacteria growing
Lipocalins - bind to Bacterial proteins binding onto ions
MMP8 MMP9 MMP25
Tertiary antimicrobial granules produced by neutrophils?
Cathepsins and gelatinase
What do neutrophils produce as antimicrobials in cytoplasm and host tissue damage
Calprotectin (divalent cation chelator)
Hypochlorous acid causes liquefaction and pus formation
Antimicrobial peptides like defensins and LL37 which punch little holes into membrane of gram negative bacteria
What are NETs?
Why is it antimicrobial?
Neutrophil extracellular traps
I’m dying moments of neutrophils, genetic component comes out and DNA works to physically tap bacteria
Histone modification is essential for NET formation
His tones are antimicrobial and DNA binds to granular products
How are NETs regulated?
IL-8 signalling and ROS production regulates NETs
Inhibited by effective phagocytosis
Induced by frustrated phagocytosis of larger pathogens/aggregates
What is PADi4 in relation to neutrophils?
Gene encodes enzyme that converts arginine to citrulline.
These arginine normally interacts with negatively charged backbone of DNA.
Histone hypercitrullation is catalysed by PADI4
(Histone modification necessary for NET formation)
Detail non-suicidal mitochondrial DNA catapults?
mtDNA with GM-CSF followed by TLR /C5a stimulation triggers mtDNA but not nuclear DNA
Priming is common mechanism of control for immune cells
Cells do not die - have delayed apoptosis
How does Anaplasma phagocytophilum evade neutrophils?
Resides in intracellular vacuoles
Preventing cytochrome b558 delivery to NADPH oxidase complex– delaying apoptosis
How does Staph aureus evade neutrophils?
MprF gene adds L-lysinse to lipids to repulse cationic defensins
Some bacteria express DNases, resistant to NET-mediated killing
How do pseudomonas aeruginosa evade NET
Absorb sialoglycoproteins which bind to inhibitory Receptors thereby reducing NET generation
Inflammation resolution
Not passive for active inflammation
Needs to be active apoptosis and generation of anti-inflammatory cytokines and anti-inflammatory mediators.
How can you identify apoptosis cells
Observing their membranes.
Will be lipids on outside membrane.
ACAMP (apoptotic cell associated molecular patterns)
Will be bound to macrophages
