Flow cytometric analysis of CD123 is useful for immunophenotyping classical Hodgkin lymphoma

Although the diagnosis of classical Hodgkin lymphoma (CHL) is traditionally made morphologically in tissue sections, it is now possible to diagnose CHL by flow cytometry (FC). In an effort to identify additional antigens on Hodgkin and Reed-Sternberg (HRS) cells that might be useful for immunophenotyping this lymphoma by FC, we examined the expression of CD123 (α chain of the IL-3R) on HRS cells and compared this with the expression of CD123 in other lymph node samples (372 tissue specimens, including 98 reactive and 274 neoplastic cases), using a nine-color FC reagent combination including anti-CD123. CD123 was found to be expressed on the majority of HRS cell populations (59% of 59 CHL lymph nodes examined), rarely on B-cell non-Hodgkin lymphomas (NHLs) (3 of 3 hairy cell leukemia cases, 3 of 29 chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) cases, 1 of 55 large B-cell lymphoma cases, but not on 95 other B-cell NHL examined), and in none of the 16 T-cell NHL cases examined. In reactive lymph nodes, CD123 expression was largely limited to plasmacytoid dendritic cells and rare histiocyte populations that can readily be distinguished from HRS populations. As the expression of this antigen is shown to be relatively limited in B- and T-NHL and in reactive lymph node populations, assessment of CD123 expression is useful for supporting the FC diagnosis of CHL.