FcεRII
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CD23, also known as Fc epsilon RII, or FcεRII, is the "low-affinity"
receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
for
IgE Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig) " isotype") that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the ε c ...
, an
antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
isotype involved in
allergy Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...
and resistance to
parasites Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
, 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 B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted o ...
, activated
macrophages Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
,
eosinophils Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. A ...
,
follicular dendritic cells Follicular dendritic cells (FDC) are cells of the immune system found in primary and secondary lymph follicles (lymph nodes) of the B cell areas of the lymphoid tissue. Unlike dendritic cells (DC), FDCs are not derived from the bone-marrow hema ...
, 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 A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...
, monocytes,
Langerhans cells A Langerhans cell (LC) is a tissue-resident macrophage of the skin. These cells contain organelles called Birbeck granules. They are present in all layers of the epidermis and are most prominent in the stratum spinosum. They also occur in t ...
, 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 Dust mite allergy, also known as house dust allergy, is a sensitization and allergic reaction to the droppings of house dust mites. The allergy is common and can trigger allergic reactions such as asthma, eczema or itching. It is the manifestat ...
Der p 1 is known to cleave CD23 from a cell’s 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 lymphoma (CD23-negative). CD23 can also be demonstrated in
germinal centre Germinal centers or germinal centres (GCs) are transiently formed structures within B cell zone (follicles) in secondary lymphoid organs – lymph nodes, ileal Peyer's patches, and the spleen – where mature B cells are activated, prolifera ...
follicular dendritic cells using immunohistochemistry but is minimally expressed by benign germinal center B cells. In contrast to neoplastic mantle cells (which are negative for CD23), the resting cells of physiologic mantle zone express CD23. Paradoxically,
Lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). In current usage the name usually refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enla ...
s arising from the mantle zone are generally negative for CD23, while most B-cell chronic lymphomocytic leukaemias are positive, allowing immunohistochemistry to distinguish these conditions, which otherwise have a similar appearance.
Reed–Sternberg cell Reed–Sternberg cells (also known as lacunar histiocytes for certain types) are distinctive, giant cells found with light microscopy in biopsies from individuals with Hodgkin lymphoma. They are usually derived from B lymphocytes, classically con ...
s are usually positive for CD23.


See also

*
Cluster of differentiation The cluster of differentiation (also known as cluster of designation or classification determinant and often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules providing targets for immunophen ...
, a list of all the CD-numbered proteins


References


Further reading

* * * * * * * * * * * * * * * * * * * *


External links

*
PDBe-KB
provides an overview of all the structure information available in the PDB for Human Low affinity immunoglobulin epsilon Fc receptor {{Immune receptors Fc receptors Clusters of differentiation