CD23

CD23, also known as Fc epsilon RII, or FcεRII, is the "low-affinity" receptor for is_associated_with::IgE, an is_associated_with::antibody isotype involved in is_associated_with::allergy and resistance to parasites, and is important in regulation of IgE levels. Unlike many of the antibody receptors, CD23 is a C-type is_associated_with::lectin. It is found on mature is_associated_with::B cells, activated is_associated_with::macrophages, is_associated_with::eosinophils, follicular dendritic cells, and is_associated_with::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 is_associated_with::T-cells, is_associated_with::monocytes, is_associated_with::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 is_associated_with::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 is_associated_with::germinal centre B-cells using is_associated_with::immunohistochemistry, but it is not present in the resting cells of the surrounding mantle zone. is_associated_with::Lymphomas arising from the mantle zone are generally negative for CD23, but most is_associated_with::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. is_associated_with::Reed-Sternberg cells are usually positive for CD23.