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Occurrence of particular isoenzymes in fresh and cultured leukemia‐lymphoma cells. III. Esterase isoenzyme in monocytes

The expression of a particular α‐naphthyl acetate esterase isoenzyme which is specific for monocytes was examined in a panel of cultured leukemia‐lymphoma cell lines (n = 88), freshly obtained leukemia‐lymphoma cells (n = 527), and in fresh (n = 10) and cultured (n = 22) leukemia cells treated with the phorbol ester 12‐O‐tetradecanoylphorbol 13‐acetate (TPA). The sodium fluoride‐sensitive isoenzyme was separated by isoelectric focusing on horizontal thin‐layer polyacrylamide gels. The esterase isoenzyme was not detected in untreated or TPA‐treated lymphoid, erythroid, or Hodgkin's disease‐derived cell lines, but was seen in leukemia cell lines of monocytic origin. TPA induced the new expression of this marker isoenzyme in two leukemia cell lines of promyelocytic and erythroid origin that are known to differentiate along the monocytic‐macrophage cell lineage; TPA stimulation increased the staining intensity of the band in monocytoid cell lines. This esterase isoenzyme was found in 92% of the cases classified morphologically as acute myelomonocytic or monocytic leukemia, but only in 3% of the non‐monocytic acute myeloid leukemias. All lymphoid or erythroid leukemias or lymphomas were negative. Treatment with TPA of AML and CML cells, which commonly differentiate to monocyte/macrophage‐like cells, showed de novo the monocyte‐specific isoenzyme. It is concluded that this isoenzyme is a characteristic marker for monocytic leukemia cells and will be a useful tool for the discriminatory identification of the monocytic element in normal and leukemic cells. Cancer 59:77–82, 1987.