CD23 is the low‑affinity IgE receptor found on mature B cells. In chronic lymphocytic leukemia (CLL) CD23 is commonly and strongly expressed; coupled with CD5 positivity this immunophenotype helps distinguish CLL from other B‑cell neoplasms (for example, mantle cell lymphoma is usually CD23‑negative). CD23 is assessed by flow cytometry and contributes to diagnosis and disease classification.

CD23 (FcεRII) is a low‑affinity IgE receptor expressed mainly on mature and activated B cells, some follicular dendritic cells and monocytes. It serves as a marker of B‑cell activation and differentiation in immunophenotyping. Clinically, CD23 helps distinguish chronic lymphocytic leukemia (typically CD23‑positive) from mantle cell lymphoma (usually CD23‑negative) and is involved in allergic responses.

CLL cells characteristically express B‑cell markers CD19 and CD20 (usually dim) with aberrant T‑cell marker CD5 and CD23 positivity. They typically show weak surface immunoglobulin and CD79b, and are CD43 and CD200 positive; CD22 is often expressed. CD45 is present. Prognostic markers include CD38 and ZAP‑70, which may be positive in subsets.

CD23 is characteristically positive on tumor B cells in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), helping distinguish CLL (CD5+, CD23+) from mantle cell lymphoma (usually CD5+, CD23–). CD23 is also expressed by follicular dendritic cell tumors and can be variably present in some other B‑cell lymphomas. Its pattern aids immunophenotypic diagnosis in hematopathology.

CD23‑negative means a cell lacks surface expression of CD23 (the low‑affinity IgE receptor, FcεRII). In clinical immunophenotyping it indicates absence of this marker on B cells, aiding diagnosis—for example distinguishing mantle cell lymphoma (often CD23‑negative) from chronic lymphocytic leukemia (usually CD23‑positive). It may also reflect altered IgE regulation and B‑cell function.

CD33 is a myeloid-lineage transmembrane receptor typically expressed on monocytes, granulocytes and myeloid progenitors and is generally absent on normal lymphocytes (B, T, NK). Occasional low or aberrant CD33 expression may be detected on lymphoid blasts in certain leukemias or after activation, but routine immunophenotyping treats lymphocytes as CD33-negative; CD33 positivity usually indicates myeloid lineage.