Extra

HLA-DR

HLA-DR is considered a pan-B lineage marker in leukaemia, although its widespread expression limits its value.

Where lineage is ambiguous the expression of HLA-DR may contribute to the assignment of B cell lineage

In myeloid leukaemias the absence of HLA-DR can have value in identification of acute promyelocytic leukaemia (APL)

details HLA-DR is typically expressed by macrophages b-cells and dendritic cells. HLA-DR presents antigen to t-helper cells serving to suppress t-helper cell responses and prevent the production of antibodies against self-antigens. HLA-DR is also expressed by early myeloid progenitor cells but expression is lost as they mature to promyelocytes.

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