Esterase Isoenzyme Profiles in Acute and Chronic Leukemias

Using isoelectric focusing (IEF) a number of carboxylic esterase isoenzymes (EC 3.1.1.1) with isoelectric points between pH 4.5-8.0 can be separated. One particular isoenzyme with an isoelectric point at about pH 6.0, the Mono-band, can be selectively and completely inhibited by sodium fluoride; this isoenzyme comprises a number of closely related subcomponents and may appear in more than one band on the gel. We analyzed the expression of typical esterase isoenzyme patterns in cells from a large panel of leukemias which were tested under identical conditions by IEF on horizontal thin-layer polyacrylamide gels with an ampholyte of pH 2-11. The 442 cases of acute and chronic myeloid and lymphoid leukemia (AML/AMMoL, CML/CMML, ALL, CLL) were classified according to clinical, morpho-cytochemical and immunophenotyping criteria. While bands between pH 4.5-5.5 appeared not to be specific for lineage or stage of differentiation, isoenzymes between pH 6.6-7.7 provided information on the type of leukemia involved. Seven typical isoenzyme patterns termed Mono1/Mono2 (fo monocyte-associated), My1/My2 (myeloid), Lym1/Lym2 (lymphoid) and Und (undifferentiated) could be discerned. Lym and Und patterns are characterized by fewer bands with a weaker staining intensity than Mono and My patterns. Nearly all cases of lymphoid leukemias (acute and chronic) expressed only Lym or Und esterase isoenzyme patterns, but no Mono or My patterns. Cases of acute or chronic myeloid and (myelo)monocytic leukemia showed strong isoenzyme staining displaying predominantly Mono or My isoenzyme patterns. The isoenzyme patterns found in CML in lymphoid or myeloid blast crisis corresponded to those seen in the respective acute leukemias, ALL or AML. The Mono-band was found in most cases of leukemias with monocytic elements (AMMoL 80%, CML 44%, CMML 100%), in the occasional case of CML-myeloid blast crisis or AML, but in none of the cases of ALL or CLL. This isoenzyme is a distinctive, specific marker for leukemias of monocytic origin and is of discriminatory value for the differentiation of monocytic from non-monocytic leukemia variants. Esterase isoenzyme profiles can give additional evidence on the origin and stage of differentiation of leukemic cells.