CD23, also known as Fc epsilon RII, or FcεRII, is the "low affinty" receptor for IgE, an antibody isotype involved in allergy and (arguably) resistance to parasites and is important in regulation of IgE levels. Unlike many of the antibody receptors, CD23 is a C-type lectin. It is found on mature B cells, activated macrophages, eosinophils, follicular dendritic cells and platelets.

There are two forms of CD23: CD23a and CD23b. CD23a is unconditionally present on B cells, while CD23b requires IL-4 to be expressed on T-cells, monocytes, Langerhans cells, eosinophils and macrophages.Abbas, A.K. and Andrew Licktman, 2003, Cellular and Molecular Immunology, pp.324-325. ISBN 0721600085.

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