Integrins and Cell Adhesion Molecules

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Integrins
Cell adhesion molecule key markers
Non-integrin cell adhesion molecules
Cell adhesion molecule key marker

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Integrins

Integrins are transmembrane proteins that function in cellular adhesion to extracellular matrix (ECM) components such as collagens, fibronectin and laminin or endothelial expressed proteins. Table 1 lists key integrins and their ligands. Each integrin is a heterodimer of one of several alpha subunits and one of several beta subunits that combine to confer specificity to the extracellular binding domain. Binding of the ligand results in modification of the interaction of the cytoplasmic tails of the molecule, both directly and indirectly, with several intracellular proteins, including protein kinases and cytoskeletal proteins. The resulting signal cascade may influence pathways as diverse as the cell cycle to cell migration.

Table 1. Integrins and their ligands.

Integrin	CD Nomenclature	Ligand
Integrin alpha L	CD11a	Binds ICAM-1, 2 and 3 as part of LFA-1
Integrin alpha M	CD11b	Binds ICAM-1, fibrinogen, and iC3b as part of Mac-1
Integrin alpha X	CD11c	Binds ICAM-1, fibrinogen, iC3b
Integrin beta 2	CD18	Binds ICAM-1, 2 and 3 as part of LFA-1
Integrin beta 1	CD29	Binds multiple diverse targets as part of VLA-1 to 6 by dimerizing with CD49 or CD51
Integrin alpha 2b	CD41	Binds fibrinogen, fibronectin, thrombin and von Willebrand factor by dimerizing with CD61
Integrin alpha 1	CD49a	Binds collagen IV by dimerizing with CD29 to form VLA-1
Integrin alpha 2	CD49b	Binds collagen and laminin by dimerizing with CD29 to form VLA-2
Integrin alpha 3	CD49c	Binds collagen, laminin and fibronectin by dimerizing with CD29 to form VLA-3
Integrin alpha 4	CD49d	Binds fibronectin, VCAM and MadCAM by dimerizing with CD29 to form LPAM-1
Integrin alpha 5	CD49e	Binds fibronectin by dimerizing with CD29 to form VLA-5
Integrin alpha 6	CD49f	Binds laminin by dimerizing with CD29 to form VLA-6 or with CD104
Integrin alpha v	CD51	Binds fibronectin, vitronectin, fibrinogen, von Willebrand factor, thrombospondin and CD31 by dimerizing with a number of beta integrins
Integrin beta 3	CD61	Binds fibrinogen, fibronectin, thrombin and von Willebrand factor by dimerizing with CD41
Integrin alpha e	CD103	Binds E-Cadherin by dimerizing with integrin beta 7
Integrin beta 4	CD104	Binds laminin by dimerizing with CD49f
Alpha 7 integrin		Binds laminin by dimerizing with CD29
Alpha 9 beta 1 integrin		Binds to VCAM-1 and osteopontin
Alpha v beta 5 integrin		Binds to vitronectin

Table 2 shows a number of the different markers available to detect the various cell adhesion molecules.

Table 2. Human, mouse and rat cell adhesion molecule markers and antibodies.

Integrin	Human	Mouse	Rat
CD11a	MCA1848	MCA1368
CD11b	MCA551, VMA00481	MCA74, MCA711	MCA275, MCA618, MCA619
CD11c	AHP1226, MCA2087, MCA2786	MCA1369	MCA1441
CD18	MCA2086, MCA2510, MCA503		MCA775
CD29	MCA1189, MCA1949, MCA2028, VMA00063	MCA2298	MCA2298
CD41	MCA467	MCA2245
CD49a	MCA1133, VPA00569
CD49b	MCA2025, MCA2027, MCA743	MCA2125
CD49c	MCA1948, MCA5694
CD49d	AHP1225, MCA2503, MCA697, MCA923	MCA1230, MCA2082, MCA2294, MCA6063	MCA2872
CD49e	MCA1187	MCA2296
CD49f	MCA1457	MCA699	MCA2034
CD51		MCA2461
CD61	MCA2588, VPA00632	MCA2299	MCA2299, MCA1773
CD103	MCA1416, MCA708	MCA4705
CD104	MCA1456, VMA00285
Integrin alpha 7	MCA5238, VPA00525
Integrin alpha 9 beta 1	OBT1715, MCA1585
Integrin alpha v beta 5	5355-2657

Featured Cell Adhesion Molecule Key Markers

Hamster Anti-Mouse CD11c Antibody, clone N418 recognizes the murine homolog of human CD11c also known as integrin alpha X, a 150/90 kDa member of the beta 2 integrin family. Integrin alpha X binds ICAM-1, fibrinogen and iC3b and in mice, CD11c is primarily expressed by dendritic cells (DCs). Rat Anti-Mouse CD11b Antibody, clone M1/70.15 recognizes the murine CD11b cell surface antigen also known as the alpha M integrin chain or MAC-1, a differentiation antigen expressed by granulocytes, monocytes, NK cells, DCs and tissue macrophages. Integrin alpha M binds ICAM-1, fibrinogen, and iC3b as part of Mac-1. These mouse CD11b and CD11c specific antibodies have been used together in flow cytometry (Figure 1), to differentiate between myeloid lineage DCs that express both markers and lymphoid lineage DCs that lack CD11b.

Fig. 1. Flow cytometry analysis of Mouse Integrin Markers CD11b and CD11c.

Fig. 1. Flow cytometry analysis of Mouse Integrin Markers CD11b and CD11c. A, Alexa Fluor 647 conjugated Rat Anti-Mouse CD11b (MCA74A647) and FITC conjugated Hamster IgG Isotype Control (MCA2356F). B, Alexa Fluor 647 conjugated Rat Anti-mouse CD11b (MCA74A647) and FITC conjugated Hamster Anti-Mouse CD11c (MCA1369F). All experiments performed on murine bone marrow in the presence of Murine Seroblock FcR (BUF041A).

Non-Integrin Cell Adhesion Molecules

In addition to their ECM ligands, integrins can also bind to a range of cellular adhesion molecules expressed for example on endothelial cells, many of which can themselves undergo homophilic interaction. This kind of interaction is seen when leukocytes interact with the endothelium during inflammation. Table 3 lists key cell adhesion molecules and their ligands.

Table 3. Cell adhesion molecules and their ligands.

Cell Adhesion Molecules	CD Nomenclature	Ligand
PECAM-1	CD31	Homophilic interaction in endothelial junctions is disrupted by homophilic interaction with leukocyte CD31 during transmigration
CD34		Binds to L-Selectin on leukocytes
ICAM-1	CD54	Endothelial CD54 binds to LFA-1 or Mac-1 on leukocytes
E-Selectin	CD62E	Binds to the carbohydrate component of leukocyte glycoproteins such as ESL-1 and PSGL-1
L-Selectin	CD62L	Binds to GlyCAM-1, MadCAM-1 and CD34 on endothelium, facilitating leukocyte homing
P-Selectin	CD62P	Binds to PSGL-1 on lymphocytes
CD99		Homophilic interaction between CD99 expressed on leukocytes and endothelium plays a similar role in transmigration as CD31
ICAM-2	CD102	Plays a similar role to ICAM-1 in the binding of LFA-1 on leukocytes
VCAM	CD106	Binds to LPAM-1 on leukocytes
Basigin	CD147	Expressed on leukocytes and endothelium, interacts with several integrins
JAM-1	CD321	Usually exhibits homophilic binding on endothelial borders but can bind to LFA-1 on leukocytes during inflammation
JAM-2	CD322	An interaction with JAM-C, JAM-2 is able to bind VLA-4 on leukocytes
JAM-C	CD323	Usually exhibits homophilic binding on endothelial borders but can bind to Mac-1 on leukocytes during inflammation
MadCAM-1		Can bind to LPAM-1, VLA-4 and L-Selectin on leukocytes
LAMP-2 (MAC-3)	CD107b	Lysosomal associated membrane protein, binds galaptin (galectin) in the extracellular matrix

Adhesion molecules on the activated endothelium are able to bind their counter receptors on leukocytes, resulting in rolling, tethering and eventual adhesion to the endothelium. The leukocyte can then migrate over the endothelial surface and eventually transmigrate by a paracellular or transcellular route. Figure 2 illustrates the leukocyte adhesion cascade leading to transendothelial migration from the blood vessel to the surround tissue, involved in inflammatory cell recruitment.

Fig 2. Leukocyte endothelium interaction during inflammation.

Fig 2. Leukocyte endothelium interaction during inflammation.

Table 4 shows a number of the different markers available to detect the various cell adhesion molecules.

Table 4. Human, mouse and rat cell adhesion molecule markers and antibodies.

Cell Adhesion Molecule	Human	Mouse	Rat
CD31	MCA1738, MCA1812, MCA4105, VMA00321	MCA1370, MCA2388	MCA1334
CD34	MCA1578, MCA547	MCA1825
CD54	AHP2183, MCA1615, MCA532, VPA00014	MCA1371	MCA773
CD62E	MCA1969, MCA5671		MCA6053
CD62L	MCA1076, VPA00599	MCA1259
CD62P	MCA2418, MCA2419, MCA2420, MCA796	MCA2419	MCA2419, MCA2420
CD99	MCA1850, MCA1919
CD102	MCA1140, MCA2290	MCA2295
CD106	VMA00461, MCA2237, MCA907	MCA2297	MCA4633
CD147	VMA00021, MCA1876, MCA2882	MCA2283	MCA729
CD321	MCA2269, MCA2270, MCA3827	MCA2346
CD322	AHP2452
JAM-C	MCA5934, MCA5935	MCA5934, MCA5935
MadCAM-1	MCA2096, MCA2320, MCA2321

Fig.3. Immunohistochemistry analysis of Human Cell Adhesion Marker CD31. Mouse Anti-Rat CD31 (MCA1334) staining of blood vessels and lymphatics, shown in red. Experiments performed on frozen rat lymph node.

Featured Cell Adhesion Molecule Key Marker

Mouse Anti-Human CD31 Monoclonal Antibody, clone WM59 recognizes the human CD31 antigen, a ~130 kDa single pass type I transmembrane glycoprotein. Also known as PECAM-1, CD31 is a cell adhesion molecule, where homophilic interaction in endothelial junctions is disrupted by homophilic interaction with leukocyte CD31 during transmigration.

CD31 is expressed by all continuous endothelia including arteries, veins, lymphatic vessels and non-sinusoidal capillaries, platelets, granulocytes and some lymphocytes. Human CD31 Antibody has been used in immunohistochemistry (Figure 3) to show blood vessels, lymphatics and some leukocytes.