Lymphocyte Migration
31
description
Transcript of Lymphocyte Migration
Homingto
lymphnode
L-se
lect
in
VLA
-4
Homingto inflamed
vascularendothelium
CD
45R
A
CD
45R
O
Differentialsplicing of
CD45 mRNAin naïve & armed
T cells
CD
2
LFA
-1
CD
44
Adhesion molecules
Naïve
Activated
Differences between armed, effector T cellsand naïve T cells - Naïve CD4 cells
+
-
+ + -+ + -
++ ++ ++ +++-
Associates with TcR and CD4 - phosphatase activity reduces threshold of T cell
signalling
Patterns of lymphocyte traffickingNaïve T cells
Thymus
Naïve T cellBone Marrow
Lymph nodeHEV
Post capillary venules in 2º lymphoid tissue
HIGH ENDOTHELIAL VENULES.
Specialised to allow lymphocytes and nothing else into the lymph node
HEV
High endothelial venules
Post capillary venules in other tissues are lined by
simple squamous epithelium
Role of endothelial cells in trafficking and recirculation
Endothelial are involved in:Vasomotor tone, vascular permeability, regulation of coagulation, immune
modulation and lymphocyte extravasation
High endothelial venules
Constitutively present insecondary lymphoid tissue
Need to allow egress ofnaïve cells from the circulation
Post-capillary venules
Present in non-lymphoid tissues
Molecules expressed by endothelial cells regulate traffickingand recirculation through lymphoid and non-lymphoid tissues
The multi-step paradigm of leukocyte migration: Step 1: Tethering & rolling
Cells normally roll past resting endothelial cells
Cytokine activated endothelial cells express adhesion moleculesLeukcocytes ‘marginate’ from the peripheral pool to the marginal pool
Tethering and rolling are mediated by SELECTINS and ADDRESSINS
Tethering4000 microns/sec
Rolling40 microns/sec
SELECTINSLeucocytes inc. Naive T cells: L SELECTINEndothelial cells: P SELECTIN & E SELECTINP selectin: Weibel-Palade bodies. E selectin: TNF & IL-1 induced
A common core with different extracellular C type lectin domains that bind carbohydrates in a Ca2+ dependent manner.Each selectin binds to specific carbohydrates and is able to transduces signals into the cell
Selectins & addressins
VASCULAR ADDRESSINSOn high endothelial venules in lymphoid tissue:
Carbohydrates that “decorate” CD34 and GlyCAM-1Sialyl LewisX molecules
Peripheral Node addressins (PNAd)
Mucosal endothelium:MAdCAM-1
Guides lymphocyte entry into lymphoid tissues
Rolling
Neutrophilis activated
bychemokines
Selectin is shed
Cytokines from epithelium activate expression of Intracellular adhesion molecules (ICAMs)
INTEGRIN (adhesion molecule) has low affinity for
ICAM
Cell activation changes
integrin to high affinity
format
Steps 2 & 3: Activation & arrest
Activation
G-protein-linkedseven transmembrane
spanning receptors
For granulocyte activation:Chemokines
Platelet activating factorC5a
In T cells: ??
1-3 seconds
Activation
Rolling phenotype only - no stable adhesion
Ligand of lymphocyte toxin-sensitive receptor not yet identified
Inhibit G protein with pertussis toxin Occupancy oflarge numbers
of surfacereceptors
Rolling
Neutrophilis activated
bychemokines
Selectin is shed
Cytokines from epithelium activate expression of Intracellular adhesion molecules (ICAMs)
INTEGRIN (adhesion molecule) has low affinity for
ICAM
Cell activation changes
integrin to high affinity
format
Steps 2 & 3: Activation & arrest
Integrin
Arrest
IntegrinsTwo chain molecules - that bind to Ig superfamilymolecules and extracellular matrix components
INTEGRIN Ig FAMILY LIGANDL2 (LFA-1) ICAM-1
Ig family ligand
Activation of lymphocyte
increases affinity of integrin(Mn2+ in vitro)
“Inside out” signalling
Activation of lymphocyte
Remove cytoplasmic tailof integrin -chain
Activation of lymphocyte
Activation of the extracellular high affinity integrin binding site is dependentupon activation of the lymphocyte, & the cytoplasmic domain of the integrin
i.e. signals from “inside” the cell have an effect “outside”
“Outside in” signalling
High affinity interaction of integrins with their ligands mayalter the behaviour of the cell
i.e. signals from “outside” the cell have an effect “inside”
Ligation of lymphocyteintegrin by ligand
Activation oflymphocyte
Step 4:Migration and diapedesis
Firm adhesion causes the leukocyte to flatten and migrate between the endothelial cells
Leukocyte migrates towards site of infection by detecting and following a gradient of chemokine.
Leukocytes migrate readily to the chemokine RANTES made by epithelilal cells that have encountered microorganisms
Arrest is reversible ifdiapeisis does not occur
~10 Minutes
Diapedesis
Metalloproteasesdigest the
basement membranePECAM expressed
at intercellularjunctions of
endothelial cellsand on the lymphocyte
Chemotactic gradient
Simultaneousoccupancy oflarge numbersof surface receptors -the cell will stay still.
Migration
Signals similar to those important in step 2 are involved i.e. chemokines
Differential receptor occupancy between the trailing
and leading edges of the cells.Operates at low levels of receptor expression
Extracellularmatrix provides
traction formoving cells
Non-lymphoid cells
Pass through the blood vessels in the lymph node and continue arterio-
venous circulation
Recirculation
HEV
HEV
Naïve lymphoid cells
Adhere to and squeeze between High Endothelial Venules (HEV), then
percolate through the lymph node and exit via the efferent lymphatic vessel
Inflammation
Normal oesophagus Normal palatine tonsils Normal skin
Candida infection Streptococcal infection Staphylococcalinfection
Role of endothelial cells in trafficking and recirculation
High endothelial venules
Constitutively present insecondary lymphoid tissue
Need to allow egress ofnaïve cells from the circulation
Post-capillary venules
Present in non-lymphoid tissues
Injury and inflammation alters morphology to resemble HEV
Need to allow egress of memorycells to sites of infection
Inflammation or injury induces changesin endothelial cells
Weibel-Paladebodies with
pre-formed adhesionmolecules
Injury or irritationgenerates thrombin
histamine, Leukotrienes etc
t = seconds
Adhesion molecule expression
TNF & IL-1 releaseddue to inflammation
in tissue
IB phosphorylated & degraded.NF-B translocates
to nucleus
t = hours
Adhesion molecule expression
Memory and naïve T cells
Naïve
Activated
+
-
L-se
lect
in
+ + -+ + -
VLA
-4CD
45R
A
CD
45R
O
CD
2
LFA
-1
CD
44
++ ++ ++ +++-
Associates with TcR and CD4 - phosphatase activity reduces threshold of T cell
signalling
Naïve cells need to access lymphoid tissue to become stimulated Memory cells need to access sites of inflammation
ICAM-1 VCAM-1
Integrins facilitate the access of leukocytes to sites of inflammation
TNF-
Activated vascular endotheliumINFLAMMATION
Peripheralvascular
endothelium
Activated effector memory cell withL selectin shed from surface
L2 (LFA-1) 41(VLA-4)
Trafficking, homing and adhesion
Trafficking: Non-random movement of cells from tissues, blood or lymph.
Includes migration to and from sites of lymphocyte maturation as well as
homing.
Adhesion: Binding of cells to other cells or extracellular matrix
Homing: Tendency of lymphocytes activated in aparticular region of the body to
preferentially return to the same region
Includes localisation of cells in distinct regions of lymphoid tissue.
Section through A
Evidence that lymphocytes exhibit specialised trafficking patterns
3H-labelled lymphocytes frommesenteric lymph nodes
3H-labelled lymphocytes fromskin
Remove tissues, sectionand autoradiograph
A
Discovery of the T cell gut-homing mechanism
MurineLymphomaTK-1
Lymph nodeHEV
Peyer’s patchHEV
Inhibition of binding using a panel of monoclonal antibodies identified the lymphocyte molecule that mediated binding to Peyer’s Patch HEV:
the integrin 47.
A similar approach was used to identify the endothelial ligand of 47:the mucosal addressin: MAdCAM-1
Skin-homing T cells
Cutaneous T cell lymphomasExtensive infiltration of epidermis with T cells
Cells home to the skin and express the cutaneous lymphocyte associated antigen (CLA)
Applycontact sensitiser
Induce delayed-typehypersensitivity
Sample T cells by raising a suction blister
Cells in the suction blister express CLA - the skin homing receptorE-selectin is the ligand of CLA
Why is lymphocyte homing necessary?
Tendency of lymphocytes activated in a particular region of the body to preferentially return to the same region.
Gut
Gut pathogene.g. rotavirus
Anti-rotavirusT cells activated
Response resolves, lymphocytes non-
randomly redistributed
Anti-rotavirusT cells will neverbe needed in the skin
Anti-rotavirusT cells willbe neededin the gut
Quantitative aspects of lymphocyte migration
Traffic between lymphoid/non-lymphoid tissues involves~ 5 x 1011 cells per day
Only ~2% (1 x 1010) of these cells are in the blood at any one time
Lymphocytes only stay in the blood for ~30 minutes
Circulating blood pool of lymphocytes is exchanged 48 times a day
However……
Less than 10% of blood lymphocytes migrate into lymph nodes, tonsils & Peyer’s patches.
~90% of lymphocytes leave the blood to enter organs such as the liver, lung spleen and bone marrow.
Traffic is 5 times faster than traffic through lymphoid tissue
Summary
L-selectin PNAd (CD34, Gly-CAM)
L2 (LFA-1) ICAM-1
Contact - Rolling - Arrest - DiapedesisT cells Endothelial cells
Naïve cells entering Peripheral Lymph Nodes
L-selectin MAdCAM carbohydrate47 MAdCAM-1L2 (LFA-1) ICAM-1
Contact - Rolling - Arrest - DiapedesisT cells Endothelial cells
Naïve cells entering Peyer’s Patches
47 MAdCAM-1L2 (LFA-1) ICAM-1
T cells Endothelial cellsContact - Rolling - Arrest - Diapedesis
Memory cells homing to Peyer’s Patches
CLA E-selectin41 (VLA-4) VCAM-1L2 (LFA-1) ICAM-1
T cells Endothelial cellsContact - Rolling - Arrest - Diapedesis
Memory cells homing to Skin
41 (VLA-4) VCAM-1L2 (LFA-1) ICAM-1
T cells Endothelial cellsContact - Rolling - Arrest - Diapedesis
Memory cells entering Inflamed tissue
