CD33 (Myeloid Cell Marker)

Yes. CD33 (Siglec-3) is a myeloid-lineage surface marker expressed on mature myeloid cells—monocytes, granulocytes—and on myeloid progenitors and many acute myeloid leukemia blasts, but typically absent on lymphoid cells. It’s routinely used in flow cytometry to identify myeloid differentiation and as a therapeutic target in myeloid malignancies. It guides diagnosis, prognosis, and targeted therapy selection.

CD33 positivity means cells express the CD33 myeloid surface antigen, indicating myeloid lineage. It’s found on normal myeloid progenitors, monocytes, and in many cases of acute myeloid leukemia and other myeloid disorders. CD33 positivity helps with diagnosis, classification, and can guide targeted therapy, but must be interpreted with morphology, other markers, and clinical context — it isn’t diagnostic by itself.

Yes. CD13 (aminopeptidase N) is commonly used as a myeloid-lineage marker, present on neutrophils, monocytes and many myeloid blasts (including AML). It is not entirely specific: CD13 is also found on some nonhematopoietic tissues (intestinal epithelium, kidney, endothelium) and certain tumor or lymphoid cells, so results should be interpreted with additional markers and clinical context.

Approximately 85–90% of acute myeloid leukemia (AML) cases express the myeloid surface antigen CD33 on leukemic blasts. Expression levels vary by AML subtype and between patients, influencing suitability for CD33‑directed therapies (for example, antibody–drug conjugates). Proportion estimates depend on detection thresholds and laboratory methods, so testing by flow cytometry guides clinical decisions.

A myeloid marker is a protein or antigen expressed on cells of the myeloid lineage (granulocytes, monocytes, macrophages and dendritic cells). These markers—detected by flow cytometry or immunohistochemistry—help identify, classify and track normal myeloid cells and myeloid malignancies such as acute myeloid leukemia. Common examples include CD13, CD33, CD14 and myeloperoxidase, guiding diagnosis and treatment decisions.

CD33 (Siglec‑3) is a myeloid-lineage surface receptor predominantly expressed on monocytes, granulocytes, and myeloid progenitors, and is not expressed on normal mature T lymphocytes. Rare or low-level CD33 signals have been reported in certain disease states, activated or aberrant T‑cell populations, or experimental settings, but CD33 is generally absent on healthy peripheral T cells.