CD25 (Hairy Cell / NHL Marker)

Hairy cell lymphoma shows a classic B‑cell immunophenotype: strong CD19, CD20 and CD22 expression, with characteristic co‑expression of CD11c, CD25, CD103 and CD123. CD200 is often positive. It is usually negative for CD5 and CD10. This panel is used in flow cytometry and immunohistochemistry to distinguish HCL from other B‑cell leukemias.

A CD25 test measures the soluble interleukin‑2 receptor alpha (sIL‑2R or CD25) in blood, a marker of T‑cell activation. It’s used to detect or monitor immune activation in conditions such as autoimmune diseases, certain lymphomas, sarcoidosis and hemophagocytic lymphohistiocytosis, and can be elevated with infections or inflammation. Results are interpreted alongside clinical findings and other laboratory tests.

Hairy cell leukemia diagnosis relies on morphology and immunophenotype: circulating “hairy” B cells positive for CD19, CD20, CD22 and characteristic markers CD11c, CD25, CD103 and CD123, with tartrate‑resistant acid phosphatase (TRAP) and annexin A1 positivity. Molecular testing for BRAF V600E mutation is a key biomarker for classic HCL; variant HCL often lacks CD25 and BRAF V600E. Detected by flow cytometry and molecular assays; clonal IGH rearrangement supports diagnosis.

The confirmatory test for hairy cell leukemia is a bone marrow biopsy with immunophenotyping (flow cytometry) demonstrating the characteristic B‑cell markers (CD19, CD20, CD11c, CD25, CD103, CD123) and, when possible, molecular testing for the BRAF V600E mutation. TRAP staining historically supported diagnosis, but flow cytometry plus BRAF testing is now the diagnostic standard.

Common CD markers used to identify lymphomas: B‑cell markers—CD19, CD20, CD79a, PAX5; patterns such as CD5+ with CD23+ suggest CLL/SLL, while CD5+ CD23− favors mantle cell. Germinal‑center B‑cell lymphomas often express CD10. T‑cell markers include CD3, CD4, CD8, CD2, CD7. Hodgkin Reed–Sternberg cells are typically CD30+ and CD15+, usually CD45−; NK/T lymphomas may express CD56.

Hairy cell leukemia (HCL) is a rare chronic B‑cell malignancy usually classified as a form of chronic leukemia rather than a conventional non‑Hodgkin lymphoma (NHL). Both HCL and many NHLs arise from mature B lymphocytes and are related, but HCL’s typical blood and bone marrow predominance and clinical course lead clinicians to treat it as a distinct leukemic entity.