CD68 Macrosialin (mouse), gp110
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Eosinophil
Liver
Neutrophil
Serum
Basophil
Lymphocyte
Nonhematopoietic Cell
Mast Cell
Dendritic Cell
Myeloid Cell
Progenitor Cell
Bone Marrow
T Cell
B Lymphocyte
Peripheral blood
Monocyte
Macrophage
110 / 110

Expression
CD68 is expressed intracellularly on cytoplasmic granules but can be detected in smaller amounts on the surface of cells.  CD68 is expressed on monocytes, macrophages, dendritic cells, neutrophils, basophils, eosinophils, mast cells, myeloid progenitor cells, a subset of CD34+ hematopoietic bone marrow progenitor cells and activated T cells.  CD68 is expressed on approximately 40% of peripheral blood B-lymphocytes and 50% of all B-ALL which stains weakly for CD68.  CD68 is found on the cytoplasm of non-hematopoietic tissues, especially in the liver, glomeruli and renal tubules.  Soluble forms have also been found in serum and urine.



Structure
MOLECULAR FAMILY NAME:  Belongs to the LAMP family and scavenger family

CD68 is a single-pass type-1 354 aa  glycoprotein.  It contains a 298 aa extracellular domain which is highly glycosylated and contains 2 distinct domains connected by a rich proline-rich hinge, a distal mucin-like domain and a proximal domain with a significant sequence homology with the family of lysosomal/endosomal plasma membrane shuttling proteins (LGP) which include lamp 1 and lamp 2.  CD68 belongs to a family of acidic, highly glycosylated lysosomal-associated membrane proteins (lamps) that include lamp-1 CD107a and lamp-2 CD107b.  The extracellular domains of lamps are partitioned into 2 related subdomains by a short linker rich in proline, threonine and serine residues which may bear O-linked glycan chains.  In CD68, there is only 1 domain that is related to the lamps, and this is adjacent to the membrane.  The N-terminal region shares no homology with the lamps and is likely to be heavily O-glycosylated on the basis of comparison with the CD43 antigen.  The N-terminal region represents a mucin-like domain comprised of short peptide repeats.

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
Unspecified 110 kDa

POST-TRANSCRIPTIONAL MODIFICATION

Alternative splicing yields 2 different isoforms.

POST-TRANSLATIONAL MODIFICATION

CD68 has 9 potential N-linked glycosylation sites which are highly glyocosylated.


Ligands
Macrosialin from lysates of mouse peritoneal macrophages and a macrophage cell line has been shown to bind oxidized low density lipoprotein.  Whether macrosialin participates in the uptake of oxidized-LDL or binds following its internalization remains to be determined.

LIGANDS AND MOLECULES ASSOCIATED WITH CD68
Molecule Comment
Oxidatively modified low density lipoprotein Bound by murine macrosialin





Function
CD68 binds to tissue- and organ-specific lectins or selectins, is a scavenger receptor which binds and internalizes oxidized low density lipoprotein (LDL) and functions to clear cellular debris, promote phagocytpsis and mediates the recruitment and activation of macrophages.  LAMPs are the major component of lysosomal membranes and may protect the membranes from attack by acid hydrolases. It is not clear whether the surface expression of CD68 is functionally significant or due to leakage from the lysosomes, as could be the case for the lamps. Inflammatory agents upregulate macrosialin expression and this is accomplished by changes in the pattern of its glycosylation.

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD68 IN INTACT ANIMAL

CD68 is one of several scavenger receptors of macrophages that contribute to foam cell formation in atherosclerosis and may be the best macrophage marker in imunohistochemistry.
  

Comments
Expression cloning has identified macrosialin as the mouse orthologue of CD68.  Macrosialin is known to be O-glycosylated and its expression is restricted to macrophages and, at lower levels to dendritic cells.

MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD68: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD68: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 968P34810
MouseS28587P31996X68273
Antibodies
EBM11   View Reactivity
Ki-M6   View Reactivity

Revised June 25, 2008


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