Lecture 2 leukocyte-endothelial cell interactions Flashcards
Topics involved with Leukocyte trans-endothelial migration?
- immune surveillance
- inflammation
- cancer metastasis
- immune diseases
- Stem cell homing (after transplantation)
- atherosclerosis
Transendothelial migration: what happens?
Expression of adhesion molecules of endothelial cells: then leukocytes start rolling, arrest, adhesion, crawling, paracellular or transmigration. Only upon stimulation.
(rolling, crawling, diapedesis: passage of cells through cell wall)
How are actin dynamics essential for transendothelial migration?
Actin dynamics are essential for transendothelial migration. Neutrophils bind to small structures that stick out of inflamed endothelial cells (filopodia). The more of these structures, the more neutrophils will go exactly there = hotspot. All regulated by a particular group of proteins.
(can be made visible by LifeAct-GFP/mCherry)
What kind of migration takes place by what types of cells?
Paracellular = through the junctions (mostly monocytes/neutrophils) Trans = through endothelial cell body (Mostly T-cells)
F-actin-rich endothelial pores during diapedesis: TightEC-Leukocyte contact. Why? And what is the max. size?
Gap = never bigger than nucleus size. F-actin-rich ring restrict endothelial gap size. All transmigration events are accompanied by strong actin rings during diapedesis (when passing through with filapodia) = to prevent leakage.
Properties of actin?
Actin is a globular, roughly 42-kDa protein found in all eukaryotic cells
-> One of the most highly-conserved proteins
Actin polymerization results into cell migration/spreading or uptake/release vesicles, mitosis
What does the listeria bacteria do?
Listeria bacteria: manipulates our actin pol. System. Actin pol. Is induced behind the bacteria, they move around in the cell, infect other cells.
What protein family regulates the actin cytoskeleton? What are the most important ones?
Small GTPases regulate actin cytoskeleton.
Remember: most studied: RhoA, Rac1, Cdc42 (EXAM)
What types of actin structures exist and what do they do?
1) stress fibers: make sure that the ‘butt’ is coming along. (RhoA)
2) Lamellipodia: looks like a wave, e.g. to follow bacteria (Rac1)
3) filapodia: very tiny ‘fingers’ sticking out to sense the environment/bacteria (Cdc42)
What are chemokines? What do they do?
Chemokines: proteins that can trigger the leukocytes (‘road map), bound on surface of endothelial cells (chemokine receptor) huge family: makes the specificity.
- Small glycoproteins (8-10kD) that are immobilized on the surface of the endothelium
How is movement possible with small GTPases/chemokines?
Small GTPases are locally activated where they are needed.
Chemokines act as a roadmap and induce directional migration.
What is CXCL12?
chemokine is present on the bonemarrow endothelial only. With receptor, cells are going to the chemokines.
Bone marrow: highly vascular.
HOW DO IMMUNE CELLS BREACH THE VESSEL WALL?
Vessel walls are kept together by VE-cadherin. Endothelial cells glued together. Leukocyte has to breach the VE-cadherin barrier: opens up and then closes again
The vascular bone marrow niche: why research this part?
Issues related to stem celltransplantation:
•Only small grafts available → “every
stemcell counts”
•BM reconstitution is ‘slow’ → immune-compromised ➔ Understanding stem cell homing allows more efficient strategies in the future
What happens upon blockage of VE-cadh? (Ve cadh does not work properly)
blockage of VE-cadh: more stemcells can leave but also more leakage (in vivo and vitro) for stemcell transplantation
