15 - ETosis Flashcards
What happens in vivo?
- pathogen –> NET –> chemotaxis –> catching and immobilisation of microbes (possibly directly killing them –> phagocytosis of microbes
- suggested that survival of neutrophils after chromatin extrusion is possible
- capture and mobilise in traps and maintain enough functionality and they can phagocytose
NET formation in vitro
Long time period (min. 4 h) – would potentially allow pathogens to evade traps
Infection induced NETosis in vivo (Yipp et al. 2012)
- sterile inflammation
- DNA increases up to 60 minutes indicating it happens faster in vivo than in vitro (extensive NET formation at 60 minutes)
Do NETs keep in the area they’re injected?
Mice treated with DNAse or saline
- concentrated bacteria in the skin, the DNAse has not allows the traps to form at 4 hr meaning the bacteria has not been trapped and allowed to disseminate into the blood and travel around the body
Anuclear cells can sill produce traps
Types of NETosis
Suicidal and vital NETosis
Suicidal vs Vital NETosis
Suicidal:
- PMA or IL-8 stimulate trap formation
- ROS generation
- breaking down of membrane and plasma membrane
- production of long traps
Vital:
- allows PMNs to maintain conventional host defensive functions
- cell is still carrying out function
- budding off extracellular trap - membrane doesn’t completely disintegrate
- leaves a functional cell rather than dead one
Conventional host defence
Conventional neutrophil host response incudes the recruitment cascade, emigration, chemotaxis, phagocytosis, and microbial killing
- vascular recruitment - rolling, adhesion crawling, transmigration
- crawling, chemotaxis
- phagocytosis, degranulation
Tissue NETosis
Vital NETosis aids in containing local infection, such as Gram-positive cellulitis, by allowing PMNs to rapidly release NETs, yet continue chemotaxis and phagocytosis
- vascular recruitment - rolling, adhesion crawling, transmigration
- crawling, chemotaxis, non-lytic NETosis
- phagocytosis, degranulation, non-lytic NETosis
- intact nuclear PMN, imprisoned microbes
Phagocytosis of live bacteria continues, membrane integrity maintained, bacteria captured
Intravascular NETosis
Intravascular NET release optimises the capture the both of bacteria and viruses within the blood steam
- intravascular NETosis may also contribute to thrombosis
- vascular recruitment - rolling, adhesion, transmigration
Is it only neutrophils? (with studies)
- ETosis reported in macrophages
-Statins reported to stimulate ETs in neutrophils and macrophage cell line RAW267 (Chow et al., 2010. Cell Host & Microbe 8, 445–454 - Bovine macrophages generated ETs in response to pathogens (Aulik et al., 2012. Infection and Immunity, 80, 1923–1933
Bovine macrophages and ETs
- Macrophages from cows produced extracellular traps when stimulated with the bovine lung pathogen Mannheimia haemolytica or its leukotoxin
- Decoration and need for ROS in cow macrophage ET production similar to that demonstrated by human neutrophils
- Bovine alveolar macrophages produced extracellular traps, but not peripheral blood monocytes
Is it only phagocytes?
- Extracellular traps produced from human eosinophils – named EETosis (Ueki et al., 2013, Blood, 121(11):2074-2083)
- Some granules released by ‘budding’ from the cell as plasma membrane– enveloped clusters
- Plasma membrane lysis liberates DNA, forming extracellular DNA nets and releases free intact granules
- EETosis-released eosinophil granules, still retaining their proteins, activated to secrete when stimulated with cytokine CC chemokine ligand 11 (eotaxin-1)
- EETosis occurred in response to similar stimuli to neutrophils, within 120 minutes, and in an NADPH oxidase- dependent manner
What did the Ueki et al study show?
- EM showing intact eosinophil granules associated with ET
- Eosinophil extracellular traps found to be thicker and more stable than
neutrophil ETs, possibly due to less protease activity
What did the vonKockritz-Blickwede study show?
- Extracellular traps produced from human mast cells – named MCETosis
-MCs release less trap material in comparison to neutrophils - > 90% of neutrophils undergo ETosis (3 h post-PMA stimulation), compared with 40% mast cells (after 6 h stimulation)
- Elastase and MPO involved in NET formation and perform an antimicrobial role.
- Elastase and MPO not expressed in mast cells, but MC-specific tryptase is a trap component of mast cells
What does the expulsion of chromatin do?
- Expulsion of chromatin from neutrophils (NETosis) and other cells (ETosis) forms antibacterial mesh traps which kill pathogens
- Evidence suggests possible survival of neutrophils following chromatin expulsion - suicidal versus vital Etosis
