CD11b ITGAM (integrin αM), α-chain of C3biR, CR3, Mac-1, Mo1
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
NK Cell
Granulocyte
Monocyte
B Cell
T Cell
165 / 165
170 / 170

Expression
CD11b is expressed on granulocytes, monocytes, NK cells, and subsets of T and  B cells.


Structure
MOLECULAR FAMILY NAME: Belongs to the integrin a chain family.

CD11b is a single-pass type-1 α chain 1136 aa glycoprotein.  It contains an 1092 aa extracellular domain which contains 7 tandem repeats domains that have been modeled to resemble a b propeller fold, an I-domain and 19 potential N-glycosylation sites, a 26 aa transmembrane domain and a 19 aa cytoplasmic domain.  A major ligand binding site has been mapped to a von Willebrand A domain, I domain, which is inserted between repeats 2 and 3.  The structure of the CD11b I domain is shown to resemble a classic a-b dinucleotide binding fold.   It is expressed as a non-covalently linked heterodimer with CD18.

MOLECULAR MASS
Cell Type Unreduced Reduced
Leukocytes 165 kDa 170 kDa

POST-TRANSCRIPTIONAL MODIFICATION

An extra codon CAG between bp 1580 and 1581 is found in some CD11b cDNAs.  Genomic sequencing revealed that this codon forms the last 3 bases of the intronic acceptor located between exons 13 and 14 of CD11b, suggesting an alternative splicing.  Receptors with or without the extra codon are functionally indistinguishable.

POST-TRANSLATIONAL MODIFICATION

There are 19 potential N-glycosylation sites.

Ligands
Ligands of CD11b/CD18 (Mac-1, CR3) are 1C3b, CD54 (ICAM-1), fibrinogen, Kininogen, haptoglobin, Factor X, CD23, CD102, (ICAM-2), heparin, β-glucan, LPS complexed with LPS binding protein (LPS/LPB), neutrophil inhibitory factor of Ancylostoma caninum, filamentous hemagglutinin from Bordetella pertussis, gp63 of Leishmenia donovani and WI-1 antigen of Blastomyces dermatitidis.

LIGANDS AND MOLECULES ASSOCIATED WITH CD11b
Molecule Comment
iC3b -
Fibrinogen
Factor X
FcR II Cis interactions
FcR III  Cis interactions
uPAR  Cis interactions
CD14  Cis interactions
ICAM-1 (intercellular adhesion molecule 1) (CD54)
ICAM-2 (intercellular adhesion molecule 2) (CD102)
ICAM-4 (intercellular adhesion molecule 4) (CD244)
Heparin
Haptoglobin
Kininogen
CD23
LPS/LPB (complex of LPS and LPS binding protein)
Neutrophil inhibitory factor from Ancylostoma C Microbial protein
Filamentous hemagglutinin form Bordetella P Microbial protein
gp63 from Leishemia D. Microbial protein
WI-1 antigen from Blastomyces D. Microbial protein

The binding site for some ligands such as iC3b, CD54 (ICAM-1), CD102 (ICAM-2), and fibrinogen is in the A I-domain.  The structural basis for many of the reported CD11b/CD18 ligands is presently unclear.  There is increasing evidence that CD11b/CD18 is associated with many other membrane proteins at the cell surface including CD14, CD87, and the Fcg receptors CD16 and CD32.




Function
CD11b/CD18 Mac-1 is also known as the complement receptor type 3 (CR3) because of its binding to the iC3b complement fragment on opsonized targets.  It also mediates the subsequent ingestion process.  CD11b/CD18 is also important in the transendothelial migration of monocytes and neutrophils whose interactions occur with stimulated endothelium.  There is adherence of the polymorphonuclear neutrophils and monocytes to fibrinogen and the CD54 endothelium.  Its association with other membrane proteins may account for the many signaling functions of CD11b/CD18.  Most binding activities  involve the I-domain of CD11b.  Neutrophil respiratory burst or degranulation is stimulated by other receptors such as FcR or C5a and channeled through CD11b/CD18: spreading, chemotaxis and apoptosis.  CD11b is important in the phagocytosis of iC3b or IgG complement coated particles. 

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD11b IN INTACT ANIMAL

CD11b is absent in leukocyte adhesion deficiency (LAD-1) patients who have major problems with bacterial infections and is the target of anti-inflammatory drug therapeutics.

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD11b
Molecule Comment
PU.1
Sp1
MS-2

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD11b: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 3684P11215
MouseS00551P05555X07640
Antibodies
198   View Reactivity
BAQ147A   View Reactivity
BEAR1   View Reactivity
CA16.3E10   View Reactivity
CAM13A   View Reactivity
CC126   View Reactivity
ICRF44   View Reactivity
LND51A   View Reactivity
LND77A   View Reactivity
LND88A   View Reactivity
MM10A   View Reactivity
MM12A   View Reactivity
MM13A   View Reactivity
RT18A   View Reactivity

Revised June 25, 2008


Contact us: Webmaster |  509-335-9515 | Accessibility | Copyright | Policies
College of Veterinary Medicine Washington State University, Pullman, WA, 99164-7010 USA
Copyright 1995-2003 Washington State University