Leukocyte migration + Chemotaxis Flashcards
General: what controls leukocyte migration?
What is its purpose?
Leukocytes move from blood to sites of inflammation + immune activation:
Directional control of migration is co-ordinated by tissue expression of adhesion molecules and chemotactic stimuli.
In order to participate in host defence, inflammation + initiate repair.
General: what are the stages of leukocyte diapedesis?
Circulation in blood vessel.
Tethering and rolling.
Firm adhesion to endothelial cells
Transmigraiton between endothelial cells.
General: what guides tethering and rolling?
Selectins - specific homing receptors + their ligands.
L, P and E selectins.
What are selectins?
Specific homing receptors and their ligands which initiatie tethering and rolling of leukocytes.
Lectin-like adhesion molecules.
Weakly bind to CHO structures
L-selectins = expressed by leukocytes.
P-selectins = expressed by platelets/endothelium.
E-selectins = endothelium
P+L selectins for tethering and rolling, with E selectin next.
What is L selectin?
Constitutively active expression on leukocytes.
Lectin like adhesion molecule to initiate tethering to vascular cells.
Transient increase in avidity as start to cluster on surface after Leukocyte activation.
But are rapidly shed by proteolytic cleavage by Shedase…
= enables rolling after initial tethering with L selectin…
What is P selectin?
Constitutively active in platelets and endothelium, but stored in granules.
Can be rapidly translocated to surface after cell activation by thrombin, histamine…
What is E selectin?
Endothelial expression needs to be INDUCED by cytokines or LPS.
Requires de novo synthesis, so quite slow response.
Expression inhibited by glucocorticoids
General: what causes firm adhesion of leukocytes?
Rolling along endothelial surface activates integrins.
Integrins are activaed by chemokines on endothelial surface.
Heterodimeric proteins expressed on leukocyte surface..
= Ligand on endothelial cell = ICAM!!!!
= FIRM ADHESION!
What are the different integrins?
Different cells express different beta-integrins.
BUT
Beta-2 chain/CD18 is common to all Beta-integrins.
Variable alpha chains - AL, AX, AM.
= forms 3 different types of heterodimers…
AL/B2.
AX/B2
AM/B2…
Also expressed on eosinophils, monocytes, T cells etc.
A4/b1.
- binds VCAMs… VMAC-1 induced by cytokines..
How are integrins expressed?
Integrins are basally expresed on leukocyte cell surface but when leukocytes are activated.
Activation induces conformational changes to increase affinity + cause clustering of integrins.
What are the ligands of Integrins?
ICAMs
= ICAM-2 on endothelium.
= ICAM-1 induced on endothelium during inflammation by IL-1, TNF…
How do integrins allow firm adhesion to site of inflammation?
Also expressed on eosinophils, monocytes, T cells etc.
A4/b1.
AL/B2.
AX/B2
AM/B2…
expressed on surface of leukocytes.
ICAM-1 expression is induced in endothelial cells by inflammatory cytokines IL-1 and TNF.
VCAM-1 expression induced by inflammation too.
= Activation by cytokines of leukocytes themselves causes conf. change + clustering of Integrins to increase affinity.
Aswell as Integrins binding both ICAM-1 and VCAM-1 simulatenously to form CAM pairs!!!!
What is the process of transmigration?
CAMS, chemotaxins.
What are LADs?
Leukocyte adhesion deficiencies
A defect in an adhesion molecule:
Type II = rolling deficiency… = Selectins..
Type III = activation…
What is Natalizumab?
Monoclonal antibody against a4 integrin - part of heteromeric integrin complex expressed on T cells.
In Multiple Sclerosis = autoreactive T cells circumvent the BBB, migrating to the brain and attacking myelin.
Natailuzumab inhibits T lymphocyte interactions with brain endothelium.
Despite exciting preliminary results, there was a significant incididence of progression brain viral infection.
Now used to treat MS when combined with IFN-B to avoid brain viral infection.
Licensed also for Crohn’s disease.
= MS and Crohn’s treatment = prevent autoreactive T lymphocyte firm adhesion with endothelium.
What are chemotaxins?
Chemoattractants for attracting and activating leukocytes.
- inducing increased integrin affinity (conf. change) and avidity (clustering).
-directional movement to site of inflammation/immune activation.
Mostly secreted from site of inflammation but some are immobilised and present to leukocytes through endothelial surface expression/ECM.
What are chemokines?
Structurally defined subset of chemotaxins.
- all chemokines are chemotaxins, but not all chemotaxins are chemokines.
Chemotaxins vary in cell types they attract…
Whilst chemokines mainly attract neutrophils and T cells (some monocyte and eosinophils)
Produced in response to IL-1, TNF and LPS.
Act on GPCR’s, unlike most cytokines, with specific cell targets.
What are non-selective and selective chemotaxins?
Non-selective chemotaxins include LTB4, C3a, C5a etc.
LTB4 induces neutrophil dependent venulodilation…
Selective chemotaxins - chemokines.
- large family of proteins - but small, around 70-80 AAs…
Chemotaxins vary in cell types they attract…
Whilst chemokines mainly attract neutrophils and T cells (some monocyte and eosinophils)
What are IL-8 and SDF-1
IL-8 is a neutrophil-targeted chemokine acting on CXCR1, CXCR2 receptors…
SDF-1 acts on CXCR4 receptors on T lymphocytes.
CXC = Cysteine, X, Cysteinesequence in receptor…
What are the non-neutrophil/T cell chemokines?
MCP-1 acts on CCR2 receptors on moncytes.
Eotaxin acts on CCR3 on eosinophils…
Cysteine, Cytseine sequence
What are the different chemokine receptors?
CXC, CC etc.
4 families of receptors.
7 TM structure couples to G-protein for signal transduction.
What is Maraviroc?
A CCR5 antagonist used to treat HIV-1
first in class of ENTRY inhibitors.
Blocks attachment of HIV GP120 to CCR5 receptor to halt HIV replication.
BUT only effective for CCR5, not any other chemokine receptors…
- HIV using CXCR4 receptors will be unaffected, allowing their replication to continue…
= ONLY FOR HIV-1 using CCR5 receptor for entry.
What cells are associated with acute and chronic inflammation?
Neutrophils - acute
Monocytes, lymphocytes for chronic
Tissues express distinct selectins and CAMs and leukocytes with Integrins.
