CD23, also known as the low-affinity IgE receptor (Fc蔚RII), is a 45 kDa type II integral membrane glycoprotein that plays a crucial role in regulating IgE production and B-cell differentiation. It is expressed on various immune cells, including mature B cells, monocytes, eosinophils, follicular dendritic cells, and platelets. CD23 exists in two isoforms, CD23a and CD23b, which differ in their amino acid sequences and functions. The molecule can also be cleaved into a soluble form (sCD23) that retains IgE-binding capabilities.