Differential expression of CD24-related epitopes in mycosis fungoides/Sezary syndrome: A potential marker for circulating Sezary cells

In the hematopoietic system, the B-cell associated antigen CD24 is expressed at high density on B cells, B-cell precursors, and B-cell malignancies as well as at low density on peripheral blood polymorphonuclear leukocytes. The 42-Kd sialoglycoprotein has not been previously demonstrated to be expressed on T cells, thymocytes, or T-cell malignancies. We identified three patients with mycosis fungoides/Sezary syndrome that showed low density expression of the CD24-related epitope recognized by antibody BA-1 on circulating T cells. All three patients had Sezary cells by morphologic assessment and clonal T-cell populations in the peripheral blood by gene rearrangement studies. In two of these patients, indirect immunofluorescence with a panel of six anti-CD24 monoclonal antibodies demonstrated reactivity for two of six antibodies in one case and only one of six antibodies in the other. The biologic significance of CD24-related epitope expression on circulating T cells in mycosis fungoides/Sezary syndrome is unclear. However, these findings suggest that differential, low density expression of CD24-related epitopes (BA-1⁺, OKB2^-) may be a useful phenotypic marker for identifying circulating Sezary cells.