CD23 antigen is a 45-60 kDa membrane glycoprotein identified as a low affinity receptor for IgE production as well as a receptor for lymphocyte growth factor. CD23 is found in some mature B-cell lymphomas and in Reed-Sternberg cells in Hodgkin disease.¹  Follicular dendritic cells and some activated B-cells within germinal centers express CD23 in high density and mantle zone B-cells are stained weakly.² The majority of chronic lymphocytic leukemias/small lymphocytic lymphomas are CD23 positive, whereas mantle cell lymphomas are generally negative, so this marker is useful when applied with other markers to separate the small cell lymphomas.²  Precursor B and T lymphomas, myeloid neoplasms, and mature T-cell lymphomas are CD23 negative and other small cell lymphomas are occasionally positive.³  CD23 is also positive on activated mature B-cells expressing IgM or IgD, monocytes/macrophages, follicular dendritic cells, T-cell subsets, eosinophils, Langerhans cells and small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL).