Utility of flow cytometric analysis of mast cells in the diagnosis and classification of adult mastocytosis.

The diagnosis of bone marrow (BM) involvement in mastocytosis has mainly been based on conventional histology. Nevertheless, in recent years, three major methodological advances have been made: the measurement of serum tryptase levels, the immunohistochemical assessment of mast cell (MC) tryptase, and the immunophenotypical characterization of BMMC using flow cytometry (FCM). The most characteristic immunophenotypic feature in mastocytosis is the coexpression of CD2 and CD25 antigens, which are never present in normal BMMC and constitute a phenotypic hallmark of BMMC in adult mastocytosis. Such observations would support the need to include the immunophenotypic analysis of MC in the diagnosis of mastocytosis.

Immunophenotypic characterization of human bone marrow mast cells. A flow cytometric study of normal and pathological bone marrow samples.

The goal of the present paper was to define the immunophenotype of bone marrow mast cells (BMMC) from healthy controls and patients with hematologic malignancies (HM) based on the use of multiple stainings with monoclonal antibodies analyzed by flow cytometry. Our results show that BMMC from both groups of individuals display a similar but heterogeneous immunophenotype. The overall numbers of BMMC are higher in the HM group of individuals (p = 0.08). Three patterns of antigen expression were detected: (1) markers constantly positive in all cases analyzed (CD9, CD29, CD33, CD43, CD44, CD49d, CD49e, CD51, CD71, CD117, and Fc(epsilon)RI), (2) antigens that were constantly negative (CD1a, CD2, CD3, CD5, CD6, CD11a, CD14, CD15, CD16, CD19, CD20, CD21, CD23, CD25, CD30, CD34, CD38, CD41a, CD42b, CD65, CD66b, HLA-DR, and CD138), and (3) markers that were positive in a variable proportion of cases--CD11b (50%), CD11c (77%), CD13 (40%), CD18 (20%), CD22 (68%), CD35 (27%), CD40 (67%), CD54 (88%) and CD61 (40%). In addition, BMMC from all cases explored were CD45+, and this antigen was expressed at an intensity similar to that of mature granulocytes. In summary, our results show that BMMC from both healthy controls and HM patients display a relatively heterogeneous immunophenotype. Interestingly, we have observed clear differences between the immunophenotype of BMMC and MC from other tissues. This could be due either to the heterogeneity of human MC according to their tissue localization or to the sensitivity of the method used for antigen detection.

Expression of Bcl-2 by human bone marrow mast cells and its overexpression in mast cell leukemia.

Bcl-2 protein plays a major role in the prevention of programmed cell death of differentiating cells. In the present study, the expression of cytoplasmic bcl-2 by human Bone Marrow Mast Cells (BMMC) from both normal and pathological bone marrow samples was examined. A total of 35 subjects corresponding to 9 healthy volunteers, 8 cases of adult indolent systemic mast cell disease (SMCD), 4 cases of pediatric mastocytosis (PM), 11 cases of hematological malignancies (HM), 2 cases of reactive bone marrow, and 1 case of mast cell leukemia (MCL) were analyzed. The expression of bcl-2 was studied using quantitative three-color flow cytometry. We also studied the molecular configuration of the bcl-2 gene and other relatives by Southern blot and polymerase chain reaction (PCR) in the MCL case. Bcl-2 expression was detected in BMMC from all samples analyzed. No significant differences on the expression of bcl-2 were detected between BMMC from healthy subjects and patients with SMCD, PM, HM, and reactive bone marrow. By contrast, bcl-2 protein was overexpressed in BMMC from MCL patient without gene rearrangement. Our results show that bcl-2 protein was constitutively expressed by BMMC. BMMC from MCL display overexpression of bcl-2, which could not be related to molecular rearrangements involving the bcl-2 gene. The expression of this protein by mature MC may play a role in the prevention of MC apoptosis and thus help to explain the long survival of these cells. The overexpression of bcl-2 by BMMC in MCL may help to explain their resistance to chemotherapy-induced apoptosis.

Comparative analysis of the morphological, cytochemical, immunophenotypical, and functional characteristics of normal human peripheral blood lineage(-)/CD16(+)/HLA-DR(+)/CD14(-/lo) cells, CD14(+) monocytes, and CD16(-) dendritic cells.

Human peripheral blood (PB) CD14(lo)/HLA-DR(+) cells were initially described as a subset of mature monocytes. Recently, it has been suggested that these represent a part of a new subset of dendritic cells (DC), characterized by the coexpression of MDC-8/HLA-DR/CD16. The aim of the present paper was to analyze the morphological, cytochemical, phenotypical, and functional characteristics of PB CD16(+)/HLA-DR(+) cells compared to both PB CD14(+) monocytes and CD16(-) DC. In contrast to CD14(+) monocytes, purified CD16(+)/HLA-DR(+) cells displayed cytoplasmic veils and lacked cytoplasmic myeloperoxidase and alpha-naphthyl acetate esterase. Normal human PB CD16(+)/HLA-DR(+) cells also displayed phenotypic characteristics different from those of CD14(+) monocytes: they lacked the CD64 Fcgamma receptor, showed lower levels of CD32, and expressed higher amounts of CD16 compared to CD14(+) monocytes. They also displayed a different pattern of expression of other antigens, including CD14, HLA-DR, CD45RA, CD45RO, complement receptors and complement regulatory surface proteins, adhesion and costimulatory molecules, and cytokine receptors, among others. When compared to CD16(-) DC, CD16(+)/HLA-DR(+) cells showed reactivity for CD16, dim positivity for CD14, higher expression of both Ig- and complement-receptors and lower reactivity for HLA-DR, adhesion, and costimulatory molecules (with the exception of CD86). The CD16(+)/HLA-DR(+) cell subset displayed a higher Ig/complement-mediated phagocytic/oxidative activity than CD16(-) DC, although this activity was significantly lower than that of mature monocytes. Regarding cytokine production at the single cell level, LPS plus IFN-gamma-stimulated PB CD16(+)/HLA-DR(+) cells produced significant amounts of IL1beta, IL6, IL12, TNFalpha, and IL8; however, the percentage of cytokine-producing cells and the amount of cytokine/cell were lower in CD16(+)/HLA-DR(+) cells than in CD14(+) monocytes. In addition, upon comparing CD16(+)/HLA-DR(+) cells with CD33(+++)/CD16(-) DC, we found that the percentage of cytokine-producing cells and the amount of cytokine/cell were significantly different in both cell subsets. In summary, our results show that CD16(+)/HLA-DR(+) cells clearly display different morphologic, cytochemical, immunophenotypical, and functional characteristics compared to both mature monocytes and CD16(-) DC. Interestingly, these cells are more frequent than other DC in normal human adult PB and cord blood samples, while they are less represented in normal bone marrow.

Indolent systemic mast cell disease in adults: immunophenotypic characterization of bone marrow mast cells and its diagnostic implications.

The aim of the present study was to explore the diagnostic value of the immunophenotypic analysis of bone marrow mast cells (BMMC) in indolent systemic mast cell disease (SMCD) patients. For that purpose, a total of 10 SMCD patients and 19 healthy controls were analyzed. Our results show that BMMC from SMCD are different from normal BMMC with regard to both their light scatter and immunophenotypic characteristics. Accordingly, forward light scatter (FSC), side (90 degrees) light scatter (SSC), and baseline autofluorescence levels were higher in BMMC from indolent SMCD patients than they were in control subjects. From the immunophenotypic point of view, the most striking findings were the constant expression of CD2 (P = .0001), CD25 (P = .0001), and CD35 (P = .06) molecules by BMMC from SMCD patients, markers that were absent from all normal controls. In contrast, CD71, absent in BMMC from indolent SMCD, was positive in BMMC from normal subjects. Although, slight differences between BMMC from SMCD patients and normal controls were found in several other markers, they did not reach statistical significance. In conclusion, our results show that simultaneous assessment of FSC/SSC and reactivity for the CD117, CD2, CD25, CD33, and CD35 forms the basis for the immunophenotypic characterization of BMMC from SMCD in adults and should be integrated with clinical and morphologic studies for the diagnosis of the disease.

The CD69 early activation molecule is overexpressed in human bone marrow mast cells from adults with indolent systemic mast cell disease.

We have analysed the quantitative expression of surface CD69 antigen on human mast cells (MC), from both normal and pathological bone marrow (BM) samples, using flow cytometry. Our major aim was to analyse whether CD69 is constitutively expressed by normal BMMC and to explore the possible differences between CD69 expression by BMMC from normal controls and patients suffering from different pathological conditions. The constitutive expression of surface CD69 was clearly demonstrated in BMMC; however, systemic mast cell disease (SMCD) patients showed significantly higher levels of surface CD69 expression than healthy controls (P < 0.001), chronic lymphocytic leukaemia (P = 0.001), monoclonal gammopathy of unknown significance (P < 0.001), multiple myeloma (P < 0.001) patients, and myelodysplastic syndromes (P = 0.002). Furthermore, almost no overlap between the levels of CD69 expression on BMMC was observed between SMCD cases and the remaining groups of individuals except for the paediatric mastocytosis group (P > 0.05). From the other groups of patients, monoclonal gammopathy of unknown significance (P = 0.04), myelodysplastic syndromes (P = 0.03) and paediatric mastocytosis (P = 0.003) cases showed a significantly higher expression of surface CD69 as compared to normal subjects. In summary, our findings show that the CD69 antigen is overexpressed in SMCD patients.

Immunophenotypic analysis of human mast cells by flow cytometry.

The immunophenotypic identification and enumeration of human bone marrow mast cells represents a clear demonstration of the utility of flow cytometry for rare-event analysis. The basic approach can be applied to a variety of specimens, including bone marrow, peripheral blood, ascitic fluid, and lymphoid tissue such as adenoids. Special emphasis is placed on markers with potential utility for distinguishing between normal, reactive, and pathological mast cells. From the clinical aspect, immunophenotypic analysis of mast cells may have great utility in supporting the diagnosis of tissue involvement in mastocytosis.

Human bone marrow mast cells from indolent systemic mast cell disease constitutively express increased amounts of the CD63 protein on their surface.

The quantitative measurement of the expression of both cytoplasmic and surface CD63 antigen by human mast cells from both normal and pathological bone marrow samples was studied by use of flow cytometry. Our major goal was to analyze whether in vivo CD63 expression by human bone marrow mast cells could be useful to discriminate bone marrow mast cells from patients with mastocytosis from other conditions. For that purpose, a total of 65 subjects corresponding to 12 healthy volunteers, 25 B-cell chronic lymphoproliferative disorders, 5 reactive bone marrow samples, 4 myelodysplastic syndromes, and 19 mastocytosis were analyzed. The expression of both surface and cytoplasmic CD63 by human bone marrow mast cells is clearly demonstrated. Our results show that high amounts of CD63 are present in human bone marrow mast cells most of it corresponding to an intracellular localization. No significant differences in CD63 expression were observed as regards both total and cytoplasmic CD63, except for higher CD63 levels in adult patients with mastocytosis (P = 0.05). By contrast, the mean level of surface CD63 significantly varied between the different groups of individuals. Accordingly, patients with monoclonal gammopathies displayed a slight decrease (P = 0.1) in surface CD63 expression, whereas bone marrow mast cells from adults with indolent systemic mast cell disease showed significantly (P = 0.0005) higher levels of surface CD63 as compared to healthy controls.