CD23

Fc fragment of IgE, low affinity II, receptor for (CD23)
PDB rendering based on 1t8c.
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 1HLI, 1KJE, 1T8C, 1T8D, 2H2R, 2H2T, 4EZM, 4G96, 4G9A, 4GI0, 4GJ0, 4GJX, 4GK1, 4GKO, 4J6J, 4J6K, 4J6L, 4J6M, 4J6N, 4J6P, 4J6Q, 4KI1
Identifiers
Symbols	FCER2 ; BLAST-2; CD23; CD23A; CLEC4J; FCE2; IGEBF
External IDs	OMIM: 151445 MGI: 95497 HomoloGene: 1517 ChEMBL: 2940 GeneCards: FCER2 Gene
Gene ontology Molecular function • integrin binding • protein binding • IgE binding • carbohydrate binding • metal ion binding Cellular component • plasma membrane • integral component of plasma membrane • external side of plasma membrane • extracellular exosome Biological process • positive regulation of humoral immune response mediated by circulating immunoglobulin • Notch signaling pathway • positive regulation of nitric-oxide synthase activity • positive regulation of killing of cells of other organism • positive regulation of nitric-oxide synthase biosynthetic process Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	2208	14128
Ensembl	ENSG00000104921	ENSMUSG00000005540
UniProt	P06734	P20693
RefSeq (mRNA)	NM_001207019	NM_001253737
RefSeq (protein)	NP_001193948	NP_001240666
Location (UCSC)	Chr 19: 7.69 – 7.7 Mb	Chr 8: 3.68 – 3.69 Mb
PubMed search	[1]	[2]

CD23, also known as Fc epsilon RII, or FcεRII, is the "low-affinity" receptor for IgE, an antibody isotype involved in allergy and resistance to parasites, and is important in regulation of IgE levels. Unlike many of the antibody receptors, CD23 is a C-type lectin. It is found on mature B cells, activated macrophages, eosinophils, follicular dendritic cells, and platelets.

There are two forms of CD23: CD23a and CD23b. CD23a is present on follicular B cells, whereas CD23b requires IL-4 to be expressed on T-cells, monocytes, Langerhans cells, eosinophils, and macrophages.

Function

CD23 is known to have a role of transportation in antibody feedback regulation. Antigens which enter the blood stream can be captured by antigen specific IgE antibodies. The IgE immune complexes that are formed bind to CD23 molecules on B cells, and are transported to the B cell follicles of the spleen. The antigen is then transferred from CD23+ B cells to CD11c+ antigen presenting cells. The CD11c+ cells in turn present the antigen to CD4+ T cells, which can lead to an enhanced antibody response.

Clinical significance

The allergen responsible in dust mite allergy Der p 1 is known to cleave CD23 from a cells surface. As CD23 is soluble, it can move freely and interact with cells in plasma. Recent studies have shown that increased levels of soluble CD23 cause the recruitment of non-sensitised B-cells in the presentation of antigen peptides to allergen-specific B-cells, therefore increasing the production of allergen specific IgE. IgE, in turn, is known to upregulate the cellular expression of CD23 and Fc epsilon RI (high-affinity IgE receptor).

In flow cytometry, CD23 is helpful in the differentiation of chronic lymphocytic leukemia (CD23-positive) from mantle cell leukemia (CD23-negative). CD23 can also be demonstrated in germinal centre B-cells using immunohistochemistry, but it is not present in the resting cells of the surrounding mantle zone. Lymphomas arising from the mantle zone are generally negative for CD23, but most B-cell chronic lymphomocytic leukaemias and low-grade B-cell lymphomas are positive, allowing immunohistochemistry to distinguish these conditions, which otherwise have a similar appearance. Reed–Sternberg cells are usually positive for CD23.

See also

• Cluster of differentiation, a list of all the CD-numbered proteins