Fc epsilon RII/CD23

Fc epsilon receptor (FcεR) is the Fc receptor that binding immunoglobulin E (IgE). There are two types of FcεRs, called Fc epsilon RI (FcεRI) and Fc epsilon receptor II (FcεRII/CD23). FcεRII/CD23 is the low-affinity receptor for immunoglobulin (Ig)E and plays important roles in the regulation of IgE responses. FcεRII/CD23 can be cleaved from cell surfaces to yield a range of soluble CD23 (sCD23) proteins that have pleiotropic cytokine-like activities. As a membrane protein, FcεRII/CD23 is a type II transmembrane glycoprotein of approximately 45 kDa molecular weight comprising a large C-terminal globular extracellular domain that is strikingly similar to C-type lectins, followed by a stalk region bearing several repeats that serve as a putative leucine zipper that are important in CD23 oligomerization; the stalk region is followed by a short extracellular sequence (in human CD23), a single hydrophobic membrane-spanning region and a short N-terminal cytoplasmic domain. FcεRII/CD23 is expressed in T and B lymphocytes, polymorphonuclear leucocytes, monocytes, follicular dendritic cells, intestinal epithelial cells and bone marrow stromal cells, and its expression to subject to regulation by a number of stimuli.