CD13 (aminopeptidase N) is a myeloid-lineage marker primarily expressed on neutrophils, monocytes, macrophages and myeloid progenitors. It is also found on some dendritic cells and certain endothelial, epithelial and stromal cells. In clinical labs it helps identify and classify myeloid leukemias and distinguish myeloid from lymphoid cells by flow cytometry.

CD13 positive means a cell expresses the CD13 protein (aminopeptidase N) on its surface. It’s commonly present on myeloid-lineage cells (granulocytes, monocytes) and some epithelial cells. Detecting CD13 by flow cytometry or immunostaining helps classify cell types and is useful in diagnosing and monitoring blood disorders, notably acute myeloid leukemia.

Myeloid lineage commonly expresses CD13, CD33, CD117 (c‑Kit) and myeloperoxidase (MPO). Mature granulocytes show CD15, CD16 and CD11b; monocytes characteristically express CD14, CD64 and CD11c. Early progenitors may be CD34+ with variable HLA‑DR. Clinical immunophenotyping uses panels of these CD antigens to classify myeloid disorders and monitor treatment.

CD33 is a transmembrane sialic‑acid–binding immunoglobulin‑like lectin (Siglec‑3) expressed on myeloid‑lineage cells — monocytes, macrophages, neutrophils and early myeloid progenitors. It mediates inhibitory signaling to regulate innate immune activation and cell adhesion. Clinically, CD33 is a diagnostic marker and therapeutic target in myeloid malignancies such as acute myeloid leukemia; it is low or absent on mature lymphocytes.

CD13 (aminopeptidase N) is a membrane metalloprotease broadly expressed on myeloid-lineage cells — monocytes, macrophages and neutrophils — and on certain dendritic cells. It’s also found on vascular endothelial cells, stromal fibroblasts and various epithelial cells, notably renal proximal tubule and intestinal brush‑border epithelium, as well as other tissues (e.g., lung, placenta).

Myeloid leukemia is identified by myeloid-lineage markers, most notably myeloperoxidase (MPO) positivity and surface antigens CD13, CD33 and CD117 (c‑KIT). Additional markers include CD15 and monocytic markers in subtypes. Diagnosis and prognosis also rely on cytogenetic and molecular abnormalities—examples include PML‑RARA in acute promyelocytic leukemia and mutations such as FLT3 and NPM1 in acute myeloid leukemia.