Cellular Adhesion Molecule

 Cell adhesion molecules (CAMs) - important molecules
to selective recruitment of circulating leukocytes to sites
of inflammation by promoting cell–cell and cell–matrix
interactions
Middleton 7th edition

CAMs subdivided 3 main families
1. Selectins
2. Integrins
3. Immunoglobulin gene super family (IgSF) members
4. Other; gelectin, cadherin and CD44
Middleton 7th edition

Selectin
 Selectins are a family of CAMs which bind to specific
sugar determinants on the surface of adjacent cells
 Selectin family
 leukocyte-expressed L-selectin (CD62L)
 endothelial-expressed E-selectin (CD62E)
 P-selectin (CD62P) which is expressed by both platelets and
endothelial cells
Middleton 7th edition

Klaus Ley and Kansas GS. Nat Rev Immunol 2004 (4):1-11

critical 120-amino acid N-terminal Ca2+-
dependent (C-type) lectin
2-9 consensus repeats similar to those found in
complement regulatory proteins, a
transmembrane region
17–35 amino acid cytoplasmic tail
epidermal growth
factor-like region
Middleton 7th edition

L-selectin
 L-selectin was originally identified as a peripheral lymph
node homing receptor responsible for lymphocyte
adhesion to high endothelial venules in lymph nodes
 Expressed on the tips of the microvilli of most leukocytes,
neutrophils, eosinophils, monocytes, naïve T and B cells as
well as on the surface of some activated T cells and
memory T cells
Middleton 7th edition

L-selectin
 L-selectin mediates leukocyte margination and tethering
to endothelium under conditions of shear stress
associated with blood flow
 L-selectin is irreversibly and rapidly shed from the
leukocyte cell surface by endogenous membrane-bound
proteases
Middleton 7th edition

E-selectin
 E-selectin is not expressed on the surface of unstimulated
endothelium but is induced within several hours following
exposure to either IL-1, TNF-α, or bacterial endotoxin
 Surface expression of E-selectin in vitro is relatively
transient, with endothelial expression levels peaking at 4–
6h and approaching baseline levels by 24 h
Middleton 7th edition

P-selectin
 P-selectin functions as a vascular ligand for most myeloid
and lymphoid cells
 Expressed by activated platelets
 P-selectin is stored in intracellular granules (Weibel-
Palade bodies and in α granules of platelets)and can be
rapidly translocated to the cell surface when endothelial
cells are stimulated with agents such as C5a, histamine,
thrombin, phorbol esters or leukotriene C4
Middleton 7th edition

 Leukocyte interaction with endothelial P-selectin has
been shown to alter leukocyte cellular functions, including
superoxide production, integrin-mediated phagocytosis,
and production of cytokines and chemokines
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Selectin ligands
 All 3 selectins can recognize glycoproteins and/or
glycolipids containing the tetrasaccharide sialyl-LewisX
(sialyl-CD15, sLeX) and in some cases its isomer sialyl-
Lewis
Middleton 7th edition

Selectin Ligands Distribution
E-selectin Sialylated Lewis X and Endothelium
related glycans activated by
(eg. CLA1) cytokines (IL1, TNF)
P-selectin Sialylated Lewis X and Storage granules &
related glycans on PSGL-1 surface of
(P-selectin glycoprotein endothelium and
ligand-1) platelets
L-selectin GlyCAM-1(HEV) Lymphocytes (high
MadCAM-1(GALT) expression on Naive
CD 34 T cell)

Integrin
 Structurally related non-covalently linked α and β
heterodimeric cell adhesion receptors
 α and β subunits are type I transmembrane proteins
containing large extracellular domains (700–1100 amino
acids) and relatively small cytoplasmic domains (30–50
amino acids)
 In vertebrates there are 18 α subunits and 8 β subunits
combining to form 24 integrins
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 4 of the β subunits are expressed on leukocytes (ie, β1,
β2, β3, and β7)
 β2 and β7 expression limited to leukocytes, and β1
expression occurring on most of the body’s cell types.
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 Globular heads contain divalent cation-binding
domains
 Divalent cation: integrin receptor function, interact
with integrin ligands
 Stalks: Extend from globular heads to plasma
membrane  transmembrane segment and
cytoplasmic tails
 Extracellular domains bind: extracellular matrix
glycoproteins, activated complement component and
proteins on surface of other cells
 Cytoplasmic domains bind cytoskeletal
component (vinculin, talin, actin
Middleton 7th edition

Structure of β2 integrin. Schematic representation of the structure of the β2
integrin heterodimer. The I domain and divalent cation-binding domains on the α
subunit that contribute to adhesive function are shown, as is the cysteine-rich
repeat region of the β2 subunit that is conserved among integrin β subunits.

β1 Integrin
 VLA molecules (very late activation)
 a1b1 and a2b1: express on T cell 2-4 wks after
repetitive stimulation
 CD49a-fCD29
 Most express on leukocytes
 VLA4 (a4b1): constitutively express on some T cell
or rapidly induced
 homing lymphocytes to endothelium at peripheral site of
inflammation
 binds to VCAM-1
Middleton 7th edition

Subunit (CD, name) Ligands Lymph Mon Neutr Eosino Baso Mast
o o o
α1β1 (49a/29,VLA-1) Laminin, collagen + − − − − −
α2β1 (49b/29,VLA-2) Collagen, laminin + + − − − −
α3β1 (49c/29,VLA-3) Collagen, laminin, fibronectin + − − − − +
α4β1 (49d/29, VLA-4) VCAM-1, fibronectin CS-1 + + − + + +
domain
α5β1 (49e/29,VLA-5) Fibronectin + + + − + +
α6β1 (49f/29,VLA-6) Laminin + + + + − −
αLβ2 (11a/18, LFA-1) ICAM-1,-2,-3,-4, and -5 + + + + + −
αMβ2 (11b/18, Mac-1) ICAM-1 and -2, C3bi, − + + + + −
fibrinogen, heparin
αXβ2 (11c/18, p150,95) C3bi, fibrinogen + + + + + +
αdβ2 (αd/18) ICAM-3,VCAM-1 + + + + + −
αvβ3 (51/61) Vitronectin, PECAM-1, other − + − − − +
RGD peptides
α4β7 (49d/β7, ACT-1) MAdCAM-1,VCAM-1, + + − + + −
fibronectin CS-1 domain
αEβ7 (103/β7, HML-1) E-cadherin + − − − − −

β2 Integrin
 CD11a-cCD18
 Expression restricted to leukocytes
 CD11aCD18 = LFA-1(leukocyte function-associated
antigen-1) Important role in
adhesion of lymphocytes with other cell ex. APCs,
vascular endothelium
Middleton 7th edition

 Mac-1 (CR3) & CR4 mediate leukocyte attachment to
endothelial cell & subsequent extravasation
 For all leukocytes : processes dependent on β2
integrins
 Firm adhesion
 Locomotion
 Transendothelial migration
Middleton 7th edition

Integrin signaling
 Inside-out signaling
 activation of the cytoplasmic tail of the integrin sends a signal
to the extracellular domain of the integrin to change its
conformation
 important in a key step of the adhesion of leukocytes to
endothelium
 Outside-in signaling
 transduce the extracellular signal from the cell surface to the
interior of the cell
 influence cell proliferation, differentiation, migration, gene
transcription, and apoptosis
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Inside-out signaling

Chemokine and Integrin
 Activation by chemokines can enhance or inhibit integrin
avidity
 CCR3: enhance LFA-1 function but inhibiting VLA-4
function
 Chemokines, such as eotaxin and IL-8, are potential in situ
regulators of integrin activity on leukocytes (i.e.
eosinophils and neutrophils, respectively) interacting with
vessel walls or migrating across the extracellular matrix
Middleton 7th edition

IMMUNOGLOBULIN GENE SUPERFAMILY
 consists of more than 25 molecules
 Have a series of globular Ig-like domains, formed by
disulfide bonds

leukocyte endothelial cell adhesion,
as well as in endothelial cell-
endothelial cell, and leukocyte-
leukocyte adhesion
Structure of immunoglobulin gene superfamily. Schematic representation of several
immunoglobulin gene superfamily molecules expressed on endothelial cells and leukocytes. The
counterligands, most of which are integrins, are also shown.

Intercellular adhesion molecule (ICAM)
 ICAM-1 (CD54)
 increase following stimulation by cytokines (IL-1, TNF-α, IFN-γ),
or bacterial endotoxin
 IFN-γ selectively induces ICAM-1 expression without affecting
expression of other adhesion molecules
 Ligands for the most N-terminal domain of ICAM-1 include
LFA-1, fibrinogen, and most serotypes of rhinovirus, whereas
the third domain is recognized by Mac-1
Middleton 7th edition

 ICAM-2 (CD102)
 2 Ig-like extracellular domains that possess 34% homology to
the first two domains of ICAM-1
 ligand binding site for LFA-1
 ICAM-2 is constitutively expressed on mononuclear cells,
basophils, mast cells, and platelets, and expression appears to
be unaffected by cytokines
Middleton 7th edition

 ICAM-3 (CD50)
 functions as an LFA-1 ligand , αdβ2 integrin
 expressed on all leukocytes and on mast cells
 ICAM-3 cross-linking results in calcium mobilization, tyrosine
phosphorylation, enhanced adhesion, chemokine secretion, and
modulation of basophil mediator release
Middleton 7th edition

Vascular cell adhesion molecule
 VCAM-1 (CD106) is a cytokine-inducible endothelial cell
adhesion molecule
 Expressed on macrophage, DC, astrocytes, & BM stromal
cells and respiratory epithelium cell line
 Expression on umbilical vein endothelial cells induced by
IL-1, TNF-α, or LPS
 Expression on endothelial cells induced by IL-4, IL-13

Platelet-endothelial cell adhesion
molecule
 PECAM-1 (CD31) is a cell adhesion molecule expressed
on endothelial cells and circulating leukocyte
 plays an important role in mediating neutrophil and
monocyte transendothelial migration
Middleton 7th edition

Other adhesion molecules
 Galectins
 family of β-galactose-recognizing proteins that exhibit a
conserved ≈130 amino acid carbohydrate-recognition domain
(CRD)

 Cadherins
 transmembrane proteins that mediate intercellular adhesion in
epithelial and endothelial cells
 found on structural cells, including endothelium and epithelium
and are potentially involved in maintaining tissue integrity, cell–
cell recognition, signaling, communication, growth, and
angiogenesis
Middleton 7th edition

 CD44
 found in high levels on most leukocytes, endothelial cells,
epithelial cells, and other cells
 has been implicated in a variety of biological processes
including lymphopoiesis, angiogenesis, wound healing, leukocyte
extravasation at inflammatory sites, and tumor metastasis
 IL3, IL5, GM-CSF  increase CD44 levels on eosinophil
Middleton 7th edition

DISEASE ASSOCIATED WITH ADHESION MOLECULE DEFICIENCY
Human syndrome Adhesion molecule Clinical phenotype
defect
LAD-I β2 integrin structure Absent or near-absent expression of all β2 integrins;
blood neutrophilia with tissue neutropenia, delayed
(mutation CD18) umbilical cord separation, recurrent soft tissue
infections (e.g., skin, periodontal), impaired pus
formation and wound healing; reduced or absent
neutrophil adhesion, transendothelial migration, and
chemotactic responses; normal rolling adhesion
LAD-I variants β2 integrin function β2 integrins expressed but dysfunctional; biologic
consequences identical to those of LAD-I
LAD-II GFTP gene Defect in fucosylation of many structures, including
sialyl-Lewis-X (sLeX); developmental abnormalities (e.g.,
(guanosine severe mental retardation, short stature, distinctive facial
diphosphate-fucose appearance). (hh) blood phenotype, impaired pus
formation, pneumonia, periodontitis, and otitis;
transporter gene) neutrophil studies, reduced or absent sLeX expression,
and sLeX reduced rolling adhesion, normal firm adhesion
LAD-III Integrin signaling LAD-III is a very rare disorder characterized by severe
recurrent infections, a bleeding tendency and marked
(failed inside-out leukocytosis. Leukocytes and platelets have normal
signaling) expression of CD18 (defective in LAD-I), normal
expression of CD15a (defective in LAD-II), but defective
integrin signaling
E-selectin E-selectin Case report of child with clinical presentation similar to
LAD disease but whose neutrophils expressed normal
levels of β1 integrins, L-selectin, and sLeX; staining of
inflamed tissue revealed no E-selectin
Middleton 7th edition