Phenotypic heterogeneity of leukemic Sézary cells.

Leukemic blood cells from eight patients with Sézary's syndrome were analyzed for enzyme cytochemical features, Fc receptors, and surface phenotype. Enzyme cytochemically the cases were heterogeneous in their activity of acid esterase, acid phosphatase and dipeptidylaminopeptidase IV (DAP IV). Only one case showed positive staining for DAP IV. The expression of Fc receptors for IgG and IgM also varied. The DAP IV-positive case exhibited Fc mu receptors. In contrast, four other cases showed only Fc gamma receptors. Analysis of the surface antigen pattern of Sézary cells with monoclonal antibodies revealed the phenotype of helper T lymphocytes (Leu-3 a/OKT4+) in all but one case. The Leu-3 a/OKT4-negative case showed a phenotypic feature of natural killer cells (Leu-7+). The results obtained with the antibodies TU14 and Anti-human Lyt-1 were more heterogeneous. The heterogeneity of Sézary cells may be interpreted as a sign of differences in functional differentiation or of proliferation of different T-cell subclones.