CD123 (Monocytic Macrophage Marker)

CD123 is the alpha chain of the interleukin‑3 receptor and serves as a cell‑surface marker for plasmacytoid dendritic cells. It is also highly expressed on malignant cells in hematologic cancers—notably acute myeloid leukemia blasts, leukemic stem cells, and blastic plasmacytoid dendritic cell neoplasm—making it useful diagnostically and as a therapeutic target.

Monocytes are generally CD123 negative; they characteristically express CD14, CD16, CD11b and HLA‑DR. CD123 (the IL‑3 receptor α chain) is typically found on plasmacytoid dendritic cells, basophils and certain hematologic malignancies. Rarely, activated or atypical monocyte subsets may show low-level CD123 expression in specific pathological contexts, but CD123 is not a conventional monocyte marker.

No. Mature macrophages generally do not express CD123 (IL‑3Rα) at appreciable levels. CD123 is classically a marker of plasmacytoid dendritic cells, basophils and certain hematopoietic progenitors. Inflammatory signals can induce transient IL‑3Rα expression on monocytes or precursors, but constitutive CD123 on differentiated tissue macrophages is minimal. Therefore CD123 is not a reliable macrophage marker for diagnostics or flow cytometry.

CD123 is the alpha chain of the interleukin‑3 receptor. It is normally expressed on plasmacytoid dendritic cells, basophils and some myeloid blasts; healthy peripheral T cells usually have little or no CD123. Detectable CD123 on T cells often indicates activation or aberrant/leukemic expression and can be used diagnostically or as a therapeutic target in certain blood cancers.

Common CD markers used to identify leukemia subtypes: B‑cell ALL—CD19, CD10, CD22, CD20; T‑cell ALL—CD2, CD3, CD5, CD7 (±CD1a, CD4/CD8); AML—myeloid markers CD13, CD33, CD117 and stem/progenitor CD34 (MPO/HLA‑DR patterns help); CLL—coexpression of CD19, CD5 and CD23 (dim CD20); hairy cell leukemia—CD11c, CD25, CD103. Immunophenotyping by flow cytometry determines diagnosis and guides treatment decisions.

Yes. Human eosinophils express CD123 (the IL‑3 receptor α chain), typically at low-to-moderate levels compared with plasmacytoid dendritic cells or basophils. CD123 on eosinophils is functional—eosinophils respond to IL‑3 alongside IL‑5 and GM‑CSF via shared signaling, but IL‑5 receptor α (CD125) is the more characteristic, highly expressed eosinophil marker. Levels vary with activation state.