Patterns of Membrane Antigen Expression by AML Blasts: Quantitation and Histogram Analysis

Leukaemic myeloid blasts from non-monocytic (M1-M3, n = 36) and monocytic (M4 and M5, n = 21) AML cases were examined for the expression of 12 different membrane determinants by flow cytometry. Data analyses for each antigen included the determination of (a) the mean fluorescence intensity for the whole blast cell population, (b) the relative levels of membrane fluorescence for individual events (cells), and (c) a conventional assessment of the proportion of cells staining positively (i.e. exceeding a pre-defined level of fluorescence). Three main types of staining histogram were observed and, of these, the most commonly seen (348/432 and 176/252 of non-monocytic and monocytic AML histograms respectively) was characterised by an homogenous distribution of staining intensities which did not exceed two log decades of fluorescence (S-type). The second staining pattern was characterised by a continuous spectrum of fluorescence which exceeded two log decades of fluorescence (SE-type), and the third pattern showed evidence of two leukaemic populations with different levels of fluorescent staining (BI-type). With the exception of occasional AML cases which expressed CD7 or CD19 with low staining intensity, the expression of lymphoid-associated membrane CD3, CD10, and CD22 by AML blasts was insignificant. For comparison, analysing the histogram patterns of expression for the myeloid and non-lineage associated membrane determinants revealed that CD11c, CD13, CD14, and CD38 were mainly of S- or SE-type for the non-monocytic AML variants, with a minor but significant proportion of such cases expressing CD33 (7/36), CD34 (6/36) and HLA-Dr (6/36) with a BI-type staining pattern. Similarly, histogram patterns for CD13, CD33, CD34 and CD38 expression by the monocytic AML variants were predominantly of S- or SE- type, with minor proportions of cases expressing CD11c (7/21), CD14 (10/21), and HLA-Dr with BI-type staining. Comparisons between the mean fluorescence staining intensities for the whole blast cell population and conventional positive versus negative delineations for each antigen studied further suggested that semi-quantitative measurements of fluorescent staining were more informative and potentially of greater relevance to the study and diagnostic assessment of acute myeloid leukaemia subtypes.