CD23

CD23, also known as Fc epsilon receptor II (FcER2) and cluster of differentiation 23, is a low-affinity receptor for immunoglobulin E (IgE) expressed on several immune cell types. In humans it is encoded by the FCER2 gene and corresponds to a 45–50 kDa type II transmembrane glycoprotein. CD23 is found mainly on mature B cells, including those in germinal centers, as well as on basophils, monocytes, and certain dendritic and follicular dendritic cells. The receptor can be released from the cell surface as a soluble form (sCD23) through proteolytic cleavage.

CD23 exists in membrane-bound and soluble forms. The extracellular domain shed from the cell surface generates sCD23, a regulator of IgE synthesis and B cell function. Proteolytic enzymes of the ADAM family (such as ADAM10/17) contribute to this shedding. Membrane CD23 participates in ligand binding and, when crosslinked, can influence B cell activation, antigen presentation, and immunoglobulin class switching. Soluble CD23 has immunomodulatory effects that can either promote or inhibit IgE production depending on context and concentration.

Clinical relevance of CD23 includes its role as a marker for certain B cell subsets and its diagnostic value in hematologic neoplasms. In chronic lymphocytic leukemia (CLL), CD23 is commonly expressed (CD5+CD23+), helping distinguish CLL from other B cell malignancies such as mantle cell lymphoma, which typically lacks CD23. Polymorphisms in FCER2 can be associated with variations in IgE levels and atopic risk. CD23 and its soluble form are also investigated as potential targets or biomarkers in allergic diseases, with therapies aiming to modulate IgE production.

Therapeutically, anti-CD23 antibodies have been explored to reduce IgE synthesis and allergic responses, though such approaches are not widely established in routine care.