HLA-DR

Summary

HLA-DR is considered a pan-B lineage marker in leukaemia and in cases where lineage is ambiguous the expression of HLA-DR may contribute to (but not prove) the assignment of B cell lineage. The molecule is also expressed by myeloid blasts, but rarely by promyelocytes so has value in identification of acute promyelocytic leukaemia (APL).

Background

HLA-DR presents antigen to T-helper cells and is typically expressed by cells involved in antigen processing and recognition - including macrophages, B-cells and dendritic cells. HLA-DR is also expressed by early myeloid progenitor cells but expression is lost as they mature to promyelocytes.

Diagnostic Use

• Acute myeloid leukaemias generally express HLA-DR, but expression is expected to be absent from mature myeloid leukaemias such a APL and erythroid leukaemia
• B-lineage leukaemias and lymphomas each will usually express HLA-DR, although expression is generally lost as they mature to plasma cells
• T-lineage ALL is generally HLA-DR negative, although rarely mature T-cell neoplasms may express HLA-DR

---