Low-affinity receptor for immunoglobulin E (IgE) and CR2/CD21. Has essential roles in the regulation of IgE production and in the differentiation of B-cells (it is a B-cell-specific antigen). Homotrimer. Also exists as a soluble excreted form, sCD23. N- and O-glycosylated. The secreted form sCD23 is produced by ADAM10-mediated ectodomain shedding. There are two kinds of Fc receptors for IgE, which differ in both structure and function: high affinity receptors on basophils and mast cells and low affinity receptors on lymphocytes and monocytes. CD23