Low affinity immunoglobulin epsilon Fc receptor(CD23) is a secreted and single-pass type II membrane protein which is also exists as a soluble excreted form. There are two forms of CD23: CD23a and CD23b. CD23a is present on follicular B cells, whereas CD23b requires IL-4 to be expressed on T-cells, monocytes, Langerhans cells, eosinophils, and macrophages. Unlike many of the antibody receptors, CD23/FCER2 is a C-type lectin. It is found on mature B cells, activated macrophages, eosinophils, follicular dendritic cells, and platelets. In flow cytometry, CD23/FCER2 is helpful in the differentiation of chronic lymphocytic leukemia (CD23-positive) from mantle cell leukemia (CD23-negative). CD23/FCER2 can also be demonstrated in germinal centre B-cells using immunohistochemistry, but it is not present in the resting cells of the surrounding mantle zone. CD23/FCER2 has essential roles in the regulation of IgE production and in the differentiation of B-cells (it is a B-cell-specificantigen).