CD23 is a 45 kDa type II cell membrane glycoprotein belonging to the C-type lectin family and is identical to the low affinity IgE receptor (FceRII) found on B cells (Pallesen; Aubry). CD23 takes part in the regulation of B-cells maturation, and is primarily expressed on B cells and monocytes, and shows a strong expression on EBV-transformed B lymphoblasts. Together with a panel of antibodies, CD23 is an important diagnostic marker of B-cell chronic lymphocytic leukaemia/small B cell lymphoma (B-CLL), and is generally negative in mantle cell lymphomas (MCLs) (Lampert, et al.) Together with CD21, CD23 is also used to detect structural alterations of follicular dendritic cells and as a marker of rare follicular dendritic tumours.