WEEK 2 NEUTROPHILS Flashcards
What is the main immune cell that eliminates bacterial pathogens?
- Neutrophils
Who are people with insufficient numbers of neutrophils and what does this mean for infection?
- Chemotherapy patients or immunocompromised people
- Means that they are at high risk of severe bacterial infection
What are two conditions that occur as a result of dysfunctional neutrophils?
- chronic granuloma disease
- Leukocyte adhesion deficiency
What occurs in CGD and what are the long term effects of this?
- Failure to produce reactive oxygen species required for microbial killing
- Repeated infections and reduced lifespan
What occurs in Leukocyte Adhesion deficiency (LAD) I, II, III and what are the long term effects of this?
- Failure to recruit neutrophils to sites of infection
- Results in repeated infections and reduced lifespan
What are the 3 main roles of the neutrophil?
- Detect and eliminate invading bacteria and fungal pathogens
- Detect and eliminate dead and dying cells
- Aid in tissue repair
Where are neutrophils generated?
- in the bone marrow
What is the neut. half life in the circulation?
- 8 hrs but longer if inflammation occurs
In humans, what % of circulating leukocytes are neutrophils?
- 50-70%
Are neutrophils released as immature or mature cells under normal conditions?
- Mature cells
What are the 4 main nautrophil granules and their types of proteins?
- Azurophililic –> primary: MPO
- Specific (seocndary): Lactoferrin
- Gelatinase (Tertiary) : Gelatinase
- Secretory vesicles: CD11b formyl peptide receptor (cell surface molecules)
What are the three main types of neutrophil granule contents?
- Anti-microbial proteins/peptides e.g. Defensins
- Matrix-degrading enzymes e.g. Collagenase
- Neutrophil membrane proteins e.g. CD11b
Are all the neutrophil granule contents released at the same time?
- NO
What is the neutrophil granule release controlled by and what is the order of release?
- A chemokine gradient
- Released upon increasing strength of the stimulus
- First the Secretory granules are released e.g.g CD11b
- Then the secondary and tertiary granules are released )FPR1, gelatinase B
- Lastly, the primary granules are released: MPO, eastase etc. where the immune complex is
What cytokines, chemokines, ans growth factors are involved in tissue injury and repair?
- cytokines: IL-1beta, TNF
- Chemokines: CXCL8, CCL3, CCL19
- Growth Factors: VEGF, G-CSF
What are the three mechanisms by which neutrophils can kill bacteria?-
- Phagocytosis, degranulation, NETs
In neutrophil phagocytosis, what is bacteria uptake assisted by?
- Fc receptors for antibody coated bacteria
- Complement receptors for complement opsonised bacteria
What are the general events in neutrophil engulfement?
- Bacteria are in a phagosome
- ROS generated within phagosome
- Anti bacterial proteins (cathepsins, defensins, lactoferrin, lyzozyme) released into phagosome and bacteria killed
How is the phagosome in neutrophil engulfement generated?
- Fusion of specific granules with cell membrane
In neutrophil engulfment, what does the NADPH oxidase complex do?
- Generates O2- and converts to H2O2
In the neutrophil phagocytosis, what does MPO do?
- It is discharged into the phagosome and uses H2O2 to catalyse the formation of oxidants –> HOCl (potent antibacterial)
What can people with Chromic Granulomatis disease not generate?
- O2-
- because they have mutations in NADPH oxidase
How are bacteria killed by degranulation?
- Extracellular bacteria killed via the release of anti-bacterial proteins –> capthesisn, defensins, lactoferrin, lyzozyme
What occurs in the NETs?
- DNA web released (highly activated neut)
- Hsitones, MPO and elastase attached -
- These are capable of trapping and destroying bacteria
How has neutrophil bacterial killing resulted in evasion of NETs?
- DNase dissolves the NETs so bacteria can escape
- S.aureus has evolved to express DNase as virulence factor
What are some examples of conditions/fatals events that neutrophils are involved in?
- When blood flow to area is blocked off then returns–> neuts will be HIGHLY activated and flood area causing ischemia reperfusion (could be myocardial, kidney etc)
- Arthritis
- Sepsis
- Acute long injury
How are neutrophil mediated resposnes detected?
- Sentinel cells such as mast cells, DCs, tissue macrophages detect signs of infection or damage and then initiate the response
How are neutrophil mediated resposnes initiated?
- the inflammation increases interactions of circulating neuts in vascular endo. –> rolling, adhesion, migration
Why do we have rolling, adhesion and transmigration with neuts?
- To have neutrophils recruited to the site of infection so they can perform their effector functions
What is neutrophil tethering and rolling mediated by?
- Selectins and their ligands
e. g. E-selectin and P-selectin interact with PSGL-1 and L-selectin
What is neut activation and arrest mediated by?
- Chemoattractants and their receptors
What are the transmembrane GPCRs that neutrophils express involved in activation and arrest?
- CXCR1 and CXCR2 (bind to CXC chemokines e.g. IL-8/CXCL8)
- C5aR, CR3, CR4 (complement components)
- Platelet activating factor receptor (-PAF)
- FPR1 and FPR2 (formylated peptides)
- BLT1 (Leukotreine B4)
What is neutrophil adhesion and intravascular crawling mediated by and what are the specific molecules?
- Integrins and ligands
- aLb2 (LFA-1, CD11a/CD18)
- aMb2 (Mac-1, CD11b/CD18)
When are the neutrophil adhesion molecules affected (in which disease?)
- IN LAD ( leukocyte adhesion defficiency)
Do neuts express multiple chemoattractant receptors?
- YES
e. g. CXCR1, CXCR2 (IL-8 receptor), FPR1, FPR2 (fMLP receptors)
How does the neutrophil decide on which gradient to follow when it comes to chemoattractants?
- It follows a hierarchy
In terms of the chemotaxis and hierarchy of chemoattractants, what are the intermediate chemoattractants and what do they do?
- CXCL8 (IL-8)
- Leukotrine B4
- They label the blood vessels at sites of inflammation (marker)
In terms of the chemotaxis and hierarchy of chemoattractants, what are the end-target chemoattractants and what do they do?
- fMLP,
- C5a (product of opsonisation)
- They define the EXACT position of a microbe
Do the neutrophils favour the intermediate or end target chemoattractants?
- end-target (move to fMLP)
What is sterile inflammation?
- Inflammation that occurs in response to cell injury or death in the ABSENCE of infection
e. g. burns, traumatic injury, ischemia/reperfusion (myocardial infarction, stroke) - Neuts and macros recruited to site bc. the aim is to restore homeostasis
How do neuts detect sterile inflammation?
DAMPs –> released from dead or dying cells
What are examples of intracellular DAMPs?
- ATP
- mtDNA
- HSPs
- Uric acid
What are examples of EC DAMPs?
- Byglycan
- HA
- Heparin Sulfate
what does inhibition of FPR1 result in?
- Reduction of neut. migration to sterile injury site
