CD48 BLAST-1, Hulym3, BCM1(mouse), OX-45
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
GPI anchor
Leukocyte
Hematopoietic Cell
T Cell
B Cell
Lymphocyte
Erythrocyte
Endothelium
45 / 45

Expression
CD48 is widely expressed on hematopoietic cells with the exception of granulocytes and some eosinophils, platelets and erythrocytes.  CD48 is expressed on pan leukocytes but not on neutrophils.  Expression is upregulated on activated lymphocytes and on T and B cells.  Rat CD48 OX-45 is more widely expressed being present on erythrocytes, endothelium and some connective tissue. 

Structure
MOLECULAR FAMILY NAME: Belongs to the immunoglobulin supergene family.

CD48 is a single-pass GPI-anchored 194 aa glycoprotein.  It contains an extracellular domain which contains 1 Ig-like C2-type and 1 Ig-like-V-type domain but no transmembrane domain or cytoplasmic domain.  CD48 contains a GPI-anchor after the removal of the GPI signal sequence and the addition of the GPI-anchor.  CD48 is a member of the CD2 family of molecules within the Ig gene superfamily which includes CD58, CD229 (Ly-9), CD244 (2B4) and CD150.  Within this group CD48 is most similar to CD58, which is a ligand for human CD2.  Like 1 splice variant of CD58, CD48 possesses a glycosylphosphatidylinositol membrane GPI-anchor. The site of GPI attachment is considered to be at Ser194 on the basis of homology with the rat sequence.  The CD48 gene lies close to the Ly-9 and 2B4 genes in the mouse and within 410 kb of the putative human Ly-9 gene.  These genes are likely to have arisen in a series of gene duplication events, and duplication of this entire chromosomal region is likely to have given rise to the region encoding CD2 and CD58.

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
Leukocytes 45 kDa 45 kDa

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION

The GPI-anchor is to the cell surface.  Treatment of CD48 with N-glycosidase F reduces the size to 26 kDa, indicating a high degree of N-linked glycosylation.

Ligands
CD48 displays high affinity binding to CD244 (2B4) and  human CD48 has been reported to bind CD2 but with an affinity considerably  >100-fold lower than CD58, the major CD2 ligand.  In mice and rats CD48 appears to be the major CD2 ligand.  Rat CD48 binds CD2 with an affinity of kDa 60-90 mM  and dissociates with a very fast dissociation rate constant to K off >6s-1.  The CD2 binding site lies on the GFCC'C'' b sheet of the V-set domain and CD2 binds CD48 in a head-to-head orientation.  Immunoprecipitation studies suggest associations with the cytoplasmic tyrosine kinases Lck and Fyn.

LIGANDS AND MOLECULES ASSOCIATED WITH CD48
Molecule Comment
CD2 CD48 is the low affinity ligand for CD2 in humans. However in rodents, it is the only identified ligand for CD2
lck CD48 antibodies co-precipitate the tyrosine kinases lck and fyn
fyn CD48 antibodies co-precipitate the tyrosine kinases lck and fyn

 

Function
CD48 has recently been identified as a ligand of the NK cell inhibitory receptor CD244 (2B4).  In the mouse and the rat CD48 is the major CD2 ligand and but in the human system this interaction has a very low affinity and may promote IL-2 and IFN-γ production by T cells and may contribute to T cell antigen recognition.  CD48 antibodies suppress the immune response in mice but the precise role of the CD48-CD2 interaction is unclear since no abnormalities have been detected in CD2-deficient mice.  CD48 adhesion occurs through its receptor, CD2. CD48 has a role in gd T cell recognition, adhesion and costimulation and as an accessory molecule as predicted for ab T cell antigen recognition.  CD48/CD244 interaction between homotypic cells augments the immune response, otherwise, this interaction inhibits NK effector functions.

BIOCHEMICAL ACTIVITY OF CD48

CD48 is reported to bind human CD2 with a very low affinity of kDa > 0.5 mM .

DISEASE RELEVANCE AND FUNCTION OF CD48 IN INTACT ANIMAL

The frequency of CD48-positive lymphocytes is decreased in patients with paroxysmal nocturnal hemoglobinuria (PNH).  CD48 is a mast cell receptor for the fimbrial adhesion molecule Fim H of E. coli and a critical mediator of mast cell activation following exposure to mycobacterium.

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD48: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD48: No information.

ADDITIONAL INSIGHTS

Unlike its murine counterpart, CD48 has a very low affinity for CD2 in humans of kDa > 0.5 mM.  It has been suggested that CD48 may form a receptor-ligand pair with a recently identified member of the CD2 subfamily.

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 962P09326
MouseJL0143P18181X17501
RatS01299P10252X13016
Antibodies
MEM-102   View Reactivity
TU145   View Reactivity

Revised June 25, 2008


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