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Serum concentrations of lactate dehydrogenase (LDH), alpha-hydroxybutyrate dehydrogenase (HBD), phosphohexose isomerase (PHI), leucine aminopeptidase (LAP), beta-glucuronidase (beta-gluc) and angiotensin-converting enzyme (ACE), were measured in 107 cases of untreated acute myeloid leukaemia which were classified by morphological, immunological and cytochemical criteria. The results show that serum LDH was increased in most cases, irrespective of leukaemic subtype, serum PHI and LAP were significantly higher in monocytic variants and serum beta-gluc and ACE levels were generally within normal limits. In addition, significant (p less than 0.05) relationships were found between serum LDH, PHI, LAP and beta-gluc concentrations and the numbers of circulating leucocytes.

The expression of membrane CD11c by leukaemic blast cells was examined (indirect immunorosetting) in 75 cases of acute leukaemia (myeloid, n = 60; lymphoid, n = 15) and evaluated as a potential marker for the diagnostic discrimination between monocytic (AMML-M4 and AMoL-M5) and non-monocytic (M1, M2 and M3) AML subtypes. Preliminary studies of normal bone marrow cells indicated that CD11c expression was not restricted to cells of monocytic lineage but was also present, with apparent lower density, on significant proportions of mature and immature granulocytes. Examination of acute myeloid leukaemia (AML) subtypes revealed that the non-monocytic leukaemias (n = 33) were CD11c-, defined as less than 30% positive cells, whereas all but one of the AMML-M4 (n = 13) and AMoL-M5 (n = 14) cases were CD11c+. All 15 cases of lymphoblastic leukaemia (ALL) showed less than 5% CD11c+ blasts. Membrane CD11c expression was also compared to the more widely used markers of monocytic differentiation; cytoplasmic alpha-naphthyl acetate esterase (ANAE) and membrane CD14 expression. This analysis showed that all 13 AMML-M4 leukaemias studied, including seven cases that were CD14- and eight that were ANAE-, were CD11c+. In addition, the AMoL-M5 cases (all of which were ANAE+) could be phenotypically subdivided into CD11c+ CD14+ (n = 9), CD11c+ CD14- (n = 4) and CD11c- CD14- (n = 1) subgroups. The study also confirmed that the discriminitive ability and sensitivity of the immunorosetting procedure for the detection of membrane CD11c compared favourably to immunofluorescent staining intensities as measured by flow cytometry.

A total of 412 cases of acute leukaemia were examined for the presence of nuclear terminal deoxynucleotidyl transferase (TdT) by indirect immunofluorescence. Of the 129 cases of acute myeloblastic leukaemia (AML FAB groups M1/M2) examined, 18% (n = 23) had significant proportions (greater than 10%) of TdT-positive blasts. Although most of these AML cases (n = 18) were of poorly differentiated (M1) type; 5 cases of AML showing features of granulocytic differentiation (M2) were also found to be TdT-positive. Even though TdT was generally more strongly expressed in the M1 group and associated with other markers of myeloid immaturity (Ia positive and lack of chloroacetate esterase), there was no inverse relationship with Sudan black or myeloperoxidase activity. In addition, although the proportion of AML-M1 cases with increased TdT-positive cells was slightly higher (18/95, 19%) than for the AML-M2 group (5/34, 15%) the results suggest that the presence of nuclear TdT in leukaemic myeloblasts may not only reflect cellular immaturity but may also be due to maturational asynchrony in otherwise well-differentiated blasts.

The alpha naphthyl acetate esterase (ANAE) cytochemical staining patterns were examined in 40 cases of acute myeloblastic leukaemia (AML: FAB groups M1 and M2) classified by morphological and immunological criteria. The blast cells in most cases (62%) were ANAE-negative with the remainder showing diffuse, granular or focal reactions of varying intensity. The nature of cytoplasmic ANAE enzymes was further characterised in 20 cases by isoelectrophoretic analysis of ANAE isoenzymes. The results suggest that the presence of significant cytoplasmic ANAE reactivity in leukaemic myeloblasts is not due to the presence of monocyte-associated isoenzymes, in otherwise well-defined myeloblasts, but may reflect abnormally increased synthesis or atypical localisation of normally-occurring ANAE isoenzymes. In particular, the results of this study indicate the lack of discriminatory value of ANAE cytochemistry in the differentiation of AML from other acute leukaemias of non-monocytic type.