Diagnostic features (cytochemistry, immunophenotyping and serum biochemistry) were examined in 51 cases of acute monocytic leukaemia (AMoL). Peroxidase, Sudan black B and alpha naphthyl acetate esterase (ANAE) cytochemical reactions were unrelated to morphological (FAB groups M5a and M5b) or immunological subtype. ANAE cytochemistry, however, indicated that AMoL cases could be subdivided into those with typical (M-type) reactions and those with insignificant staining or monocytic ANAE isoenzymes (defined by IEF). All cases were phenotypically CD13/CD33 positive and, with one exception, had greater than 30% HLA-DR positive cells. Membrane CD14 expression was insignificant or variable in 33% of M5a cases in contrast to 23/24 M5b cases which showed high proportions of CD14-staining cells with at least two monoclonal antibodies. Serum lysozyme, LDH and beta-2 microglobulin (beta 2m) were increased in 88%, 68% and 81% of cases respectively but, with the exception of statistically higher lysozyme levels in CD14+ cases, were unrelated to the morphological, cytochemical or immunological diagnostic subgroups. Clinical and diagnostic features were also examined as possible prognostic indicators. The morphological, cytochemical and immunological subgroups of AMoL were not found to be of prognostic relevance but age (P = 0.004), renal failure (P = 0.005) and serum beta 2m levels (P = 0.002) were related to patient survival. Moreover, renal failure and serum beta 2m remained significant (P = 0.012 respectively) when age was taken into account and were shown to be independent prognostic variables.

Blast cells from 26 cases of acute myeloid leukaemia (AML) were examined, by single and “two‐colour” flow cytometry, for relationships between membrane CD11b (monoclonal antibody OKM1), CD11c (KB90) and CD14 (Leu‐M3). Increased expression of all three determinants was associated with myelomonocytic leukaemias, with their relative diagnostic value in discriminating monocytic (M4 and M5) from non‐monocytic (M1, M2 and M3) subtypes being CD14 > CD11c > CD11b. However, the results also indicated, because of the heterogenous expression of CD11c in particular, and to a lesser extent CD11b, that the patterns or histograms of fluorescent staining were potentially more informative than an empirical subdivision of blasts into positive and negative sub‐populations. In addition, analysis of phenotypic correlations by simultaneous two‐colour fluorescence showed that the expression of CD11b and CD11c determinants by leukaemic myeloid blasts was highly correlated, in contrast to the expression of CD14 and CD11c which were relatively independent. Consequently, CD11c + myeloid blasts almost always co‐expressed CD11b whereas CD14 + cases of AML often comprised CD14 + CD11c + and CD14 + CD11c‐ subpopulations. It is concluded from these observations that CD11c immunophenotyping is a useful supplementary investigation, particularly in CD14‐ cases of myelomonocytic leukaemia. However, it is also apparent that the presence of membrane CD11c per se is not lineage‐specific and that the level of expression is perhaps a more discriminatory factor.

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.

Absolute numbers and distributions of peripheral blood T-cells and NK cells were immunophenotypically determined in 21 patients with B-CLL and compared with those obtained from a series of 13 elderly normal controls with an age range of 60-87 years. For absolute CD3+, CD4+ and CD8+ T-cell, and CD16+ NK subpopulation numbers, there were no consistent differences between the normal and B-CLL groups although some individual patient variation was seen. Immunophenotypic analyses did however reveal that CD3+ T-cells in almost half (10/21) of the B-CLL patients were Ia+ (defined as > 20% positive cells), compared to 0/13 of the elderly control group (p < 0.001), and that the proportions of CD4+ and CD8+ cells expressing membrane CD45RO were significantly increased compared to the control group. Subdivision of the B-CLL cases into those with low (< 20%) and high (> 20%) proportions of CD3+ T-cells co-expressing Ia further showed that CD45RO expression by CD4+ fractions was particularly prominent in the Ia+ subgroup, and that the relative increase of CD4+CD45RO+ cells was primarily a consequence of decreased absolute numbers of CD4+CD45RA+ lymphocytes. This study also examined extracted DNA from enriched CD3+ T-cell fractions (obtained by immunomagnetic bead selection in 9 of the B-CLL cases) by PCR analysis with two primers for the T-cell gamma gene locus. With the V gamma C (consensus) primer, 8/9 cases were polyclonal and the remaining case was oligoclonal. For comparison, 7/9 CD3+ fractions were oligoclonal with the V gamma 9 primer with the other two cases being polyclonal. No monoclonal CD3+ components were found. It is suggested that the observed increased Ia expression by CD3+ cells and the predominance of CD4+ cells expressing membrane CD45RO in patients with B-CLL may be of potential relevance to understanding the pathogenesis and patterns of disease progression.

The expression of membrane CD1c, as defined by monoclonal antibody L161, was examined on malignant lymphoid cells from 191 cases of chronic lymphoproliferative disease and on eight 'normal' enriched tonsil B-cell extracts. Of 79 cases of chronic lymphocytic leukaemia (CLL) studied, 77 showed low (less than 20% positive cells) CD1c expression whereas 63/71 (89%) cases of B-PLL, HCL and B-NHL showed increased CD1c+ (but not CD1a or CD1b) components. In contrast, malignancies corresponding to terminal stages of B-cell differentiation (immunocytoma and myeloma) generally showed low CD1c expression as did lymphoid cells from 10 cases of post-thymic malignancy. Although there was some correlation between the expression of membrane CD1c and immunoglobulin (SIg) light chain densities (P less than 0.001), it is relevant in diagnostic terms that seven cases of B-NHL with low SIg staining intensities more typically associated with CLL were CD1c+. CD1c expression was not, however, correlated with the presence of CD23 or FMC7 determinants but did show a similar pattern of expression to that previously reported for beta-2 microglobulin. Determination of cellular CD1c by APAAP immunocytochemistry confirmed the presence of higher antigen densities in malignant B-cells at intermediate/late stages of differentiation and this interpretation was further supported by the finding that the majority of phenotypically mature tonsil B-cells were also CD1c+. The determination of CD1c expression by malignant B-cells may therefore be of particular value in the diagnostic differentiation of chronic lymphoproliferative disorders.